Mitosis: Cell Division
‘’Dance of Chromosomes’’
Chromosome
The Key Roles of Cell Division
• The ability to reproduce is one of the key features that
separates life from non-life.
• All cells have the ability to reproduce, by making exact
copies of themselves.
• In unicellular organisms, division of one cell reproduces
the entire organism
• In multicellular organisms, cell division is needed for:
• Development of an embryo from a sperm/egg
• Growth
• Repair
Asexual Reproduction
• Asexual reproduction is reproduction that
involves a single parent producing an
offspring.
• The offspring produced are, in most cases,
genetically identical to the single cell that
produced them.
• Prokaryotic organisms (like bacteria)
reproduce asexually, as do some eukaryotes
(like sponges). Also termed Binary fission.
Prokaryotic Chromosomes
• Prokaryotic cells lack nuclei. Instead, their DNA molecules are found in the
cytoplasm.
• Most prokaryotes contain a single, circular DNA molecule, or chromosome,
that contains most of the cell’s genetic information.
Eukaryotic Chromosomes
• In eukaryotic cells, chromosomes are located in the nucleus, and are made up
of chromatin.
• Chromatin is composed of DNA and histone proteins.
• DNA coils around histone proteins to form nucleosomes.
• The nucleosomes interact with one another to form coils and supercoils that
make up chromosomes.
Sexual Reproduction
• In sexual reproduction, offspring are produced by the fusion of two sex cells
– one from each of two parents. These fuse into a single cell before the
offspring can grow.
• The offspring produced inherit some genetic information from both parents.
• Most animals and plants, and many single-celled organisms, reproduce sexually.
Contrasting Reproduction types
Cell Division
• Cells duplicate their genetic material before
they divide, ensuring that each daughter cell
receives an exact copy of the genetic
material, DNA.
• A dividing cell duplicates its DNA, allocates
the two copies to opposite ends of the cell,
and only then splits into daughter cells.
• A cell’s endowment of DNA (its genetic
information) is called its genome.
• DNA molecules in a cell are packaged into
chromosomes.
Terminologies
• DNA: is the hereditary material in humans and almost
all other organisms. Most DNA is located in the cell
nucleus (where it is called nuclear DNA.
• GENE: A gene is a locus (or region) of DNA that
encodes a functional RNA or protein product, and is the
molecular unit of heredity.
• CHROMOSOME: In the nucleus of each cell, the
DNA molecule is packaged into thread-like structures
called chromosomes. Each chromosome is made up of
DNA tightly coiled many times around proteins called
histones that support its structure.
•.
Terminologies
• CHROMATID: A chromatid is one copy of
a newly replicated chromosome, which
typically is joined to the other copy by a
single centromere. Before replication, one
chromosome is composed of one DNA
(double-helix) molecule.
• CHROMATIN: is a complex of DNA and
proteins that forms chromosomes within the
nucleus of eukaryotic cells.
• NUCLEOSOME: The nucleosome is the
fundamental subunit of chromatin.
Each nucleosome is composed of a little less
than two turns of DNA wrapped around a
set of eight proteins called histones, which
are known as a histone octamer.
Terminologies
• CENTROMERE: The centromere is the part of a
chromosome that links sister chromatids. During mitosis,
spindle fibers attach to the centromere via the
kinetochore.
• KINETOCHORE:A kinetochore is a protein structure
that forms on a chromatid during cell division and
allows it to attach to a spindle fiber on a chromosome.
• HISTONES: are highly alkaline proteins found in
eukaryotic cell nuclei that package and order the DNA
into structural units called nucleosomes. They are the
chief protein components of chromatin, acting as spools
around which DNA winds, and playing a role in gene
regulation.
Chromosome
Terminologies
• TELOMERASE: is a ribonucleoprotein that adds
the polynucleotide "TTAGGG" to the 3' end
of telomeres, which are found at the ends
of eukaryotic chromosomes.
• TELOMERE: is a region of repetitive nucleotide
sequences at each end of a chromatid, which
protects the end of the chromosome from
deterioration or from fusion with neighboring
chromosomes.
• SEPARASE: also known as separin, is a cysteine
protease responsible for triggering anaphase by
hydrolyzing cohesin, which is the protein
responsible for binding sister chromatids during
the early stage of anaphase.
Terminologies
• COHESIN: Protein complexes that glues sister
chromatids at the centromere.
• CONDENSIN: is an elongated complex of several
proteins that binds and encircles DNA. In contrast to
cohesin, which binds two sister chromatids together,
condensin binds a single chromatid at multiple spots,
twisting the chromatin into a variety of coils and loops.
• SEPARASE: also known as separin, is a cysteine
protease responsible for triggering anaphase by
hydrolyzing cohesin, which is the protein responsible for
binding sister chromatids during the early stage of
anaphase.
Chromosomes
• The genetic information that is passed on from one generation of cells to the
next is carried by chromosomes.
• Every cell must copy its genetic information before cell division begins.
• Each daughter cell gets its own copy of that genetic information.
• Cells of every organism have a specific number of chromosomes.
Chromosome
Chromosomes During Cell Division
• In preparation for cell division, DNA is replicated and the chromosomes condense
• Each duplicated chromosome has two sister chromatids, which separate during cell division
• The centromere is the narrow “waist” of the duplicated chromosome, where the two
chromatids are most closely attached
Phases of the Cell Cycle
• The cell cycle consists of
• Interphase (cell growth and copying of chromosomes in preparation for
cell division)
• Mitotic (M) phase (mitosis and cytokinesis)
• Interphase (about 90% of the cell cycle) can be divided into sub
phases:
• G1 phase (“first gap”)
• S phase (“synthesis”)
• G2 phase (“second gap”)
G1 Phase: Cell Growth
• In the G1 phase, cells increase in size
and synthesize new proteins and
organelles.
S Phase: DNA Replication
• In the S (or synthesis) phase, new DNA is
synthesized when the chromosomes are
replicated.
G2 Phase: Preparing for Cell Division
• In the G2 phase, many of the organelles
and molecules required for cell division
are produced.
M Phase: Cell Division
• In eukaryotes, cell division occurs in two
stages: mitosis and cytokinesis.
• Mitosis is the division of the cell nucleus.
• Cytokinesis is the division of the cytoplasm.
Prophase/Prometaphase
• During prophase, the first phase of mitosis, the
duplicated chromosome condenses and becomes
visible.
• The centrioles move to opposite sides of nucleus
and help organize the spindle.
• The spindle forms and DNA strands attach at a
point called their centromere.
• The spindle forms and DNA strands attach at a point
called their centromere.
• The nucleolus disappears and nuclear envelope
breaks down.
Prophase
Prometaphase
Metaphase
• During metaphase, the second phase
of mitosis, the centromeres of the
duplicated chromosomes line up across
the center of the cell. The spindle
fibers connect the centromere of each
chromosome to the two poles of the
spindle.
• The spindle fibers connect the
centromere of each chromosome to the
two poles of the spindle.
Anaphase
• During anaphase, the third phase of
mitosis, the centromeres are pulled
apart and the chromatids separate to
become individual chromosomes.
• The chromosomes separate into two
groups near the poles of the spindle.
Telophase
• During telophase, the fourth and final
phase of mitosis, the chromosomes
spread out into a tangle of chromatin.
• A nuclear envelope re-forms around each
cluster of chromosomes.
• The spindle breaks apart, and a
nucleolus becomes visible in each
daughter nucleus.
Cytokinesis
• Cytokinesis is the division of the cytoplasm.
• The process of cytokinesis is different in
animal and plant cells.
• The cell membrane is drawn in until the
cytoplasm is pinched into two equal parts.
• Each part contains its own nucleus and
organelles.
The Cell Cycle Control System
• The sequential events of the cell cycle are directed by
a distinct cell cycle control system, which is similar to a
clock
• The clock has specific checkpoints where the cell cycle
stops until a go-ahead signal is received. For many
cells, the G1 checkpoint seems to be the most
important one
• If a cell receives a go-ahead signal at the G1
checkpoint, it will usually complete the S, G2, and M
phases and divide
• If the cell does not receive the go-ahead signal, it will
exit the cycle, switching into a non dividing state
called the G0 phase
Loss of Cell Cycle Controls in Cancer Cells
• Cancer cells do not respond normally to the body’s control mechanisms
• Cancer cells form tumors, masses of abnormal cells within otherwise
normal tissue
• If abnormal cells remain at the original site, the lump is called a benign
tumor
• Malignant tumors invade surrounding tissues and can metastasize,
exporting cancer cells to other parts of the body, where they may form
secondary tumors
Phase
Interphase
Prophase
Chromosome Appearance &
Location
DNA copies itself; chromatin
Chromosomes coil up
Important Events
DNA replication, cell grows and
replicates organelles
Nuclear envelope disappears, spindle
fibers form
Chromosomes line up in the middle
Spindle fibers connect to
chromosomes
Anaphase
Chromosome copies divide and move
apart
Spindle fibers pull chromosome
copies apart to opposite poles
Telophase
Chromosomes uncoil back into
chromatin
Nuclear envelopes reform, 2 new
nuclei are formed, spindle fibers
disappear
Metaphase
Cytokinesis
Chromatin
Division of the rest of the cell:
cytoplasm and organelles
I.P.M.A.T
INTERPHASE
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
Apoptosis: Programmed Cell Death
Apoptosis or programmed cell death, is
carefully coordinated collapse of cell,
protein degradation , DNA fragmentation
followed by rapid engulfment of corpses
by neighboring cells.
EXAMPLES
The formation of the fingers and toes of thefetus
The sloughing off of the inner lining of the uterus
The formation of the proper connections between
neurons in the brain .
Apoptosis is needed to destroy cells
Examples:
Cells infected with viruses
Cells of the immune system
Cells with DNA damage
Cancer cells
• THE END
Meiosis
SEXUAL REPRODUCTION
Sets of Chromosomes in Human Cells
• Human somatic cells (any cell other than a
gamete) have 23 pairs of chromosomes.
• A karyotype is an ordered display of the
pairs of chromosomes from a cell.
• The two chromosomes in each pair are
called homologous chromosomes, or
homologs.
• Chromosomes in a homologous pair are
the same length and carry genes
controlling the same inherited characters.
APPLICATION
TECHNIQUE
Pair of homologous
replicated chromosomes
Centromere
Sister
chromatids
Organisms that reproduce Sexually are made up
of two different types of cells.
1.
2.
Somatic Cells are “body” cells and contain the
normal number of chromosomes ….called the
“Diploid” number (the symbol is 2n). Examples
would be … skin cells, brain cells, etc.
Gametes are the “sex” cells and contain only ½
the normal number of chromosomes…. called the
“Haploid” number (the symbol is n)….. Sperm
cells and ova are gametes.
3. n = number of chromosomes in the set…
so….2n means 2 chromosomes in the set….
Polyploid cells have more than two
chromosomes per set… example: 3n (3
chromosomes per set)
Gametes
• The Male Gamete is the Sperm and is
produced in the male gonad the Testes.
• The Female Gamete is the Ovum (ova =
pl.) and is produced in the female gonad
the Ovaries.
• During Ovulation the ovum is released from
the ovary and transported to an area where
fertilization, the joining of the sperm and
ovum, can occur…… fertilization, in Humans,
occurs in the Fallopian tube. Fertilization
results in the formation of the Zygote.
(fertilized egg)
Sperm + Ovum (egg)
Zygote
Chromosomes
• If an organism has the Diploid number
(2n) it has two matching homologues
per set. One of the homologues
comes from the mother (and has the
mother’s DNA).…
the other
homologue comes from the father (and
has the father’s DNA).
• Most organisms are diploid. Humans have
23 sets of chromosomes… therefore
humans have 46 total
chromosomes….. The diploid number
for humans is 46 (46 chromosomes per
cell).
Homologous Chromosomes
Pair of chromosomes (maternal and
paternal) that are similar in shape and size.
Homologous pairs (tetrads) carry genes
controlling the same inherited traits.
Each locus (position of a gene) is in the
same position on homologues.
Humans have 23 pairs of homologous
chromosomes.
22 pairs of autosomes
1 pair of sex chromosomes
Autosomes
(The Autosomes code for most of the offspring’s traits)
In Humans the
“Autosomes” are sets
1 - 22
Sex Chromosomes
The Sex Chromosomes code for the sex of the offspring.
** If the offspring has two “X” chromosomes it will be a female.
** If the offspring has one “X” chromosome and one “Y” chromosome it will be a male.
In Humans the “Sex
Chromosomes” are the 23rd set
XX chromosome - female
XY chromosome - male
Meiosis
is the process by which ”gametes” (sex cells) , with half the number of chromosomes, are
produced.
During Meiosis diploid cells are reduced to
haploid cells
Diploid (2n)
Haploid (n)
If Meiosis did not occur the chromosome number
in each new generation would double…. The
offspring would die.
Meiosis in males is called spermatogenesis and produces
sperm.
Meiosis in females is called oogenesis and produces ova.
Meiosis
• Prior to meiosis I, there are 46
chromosomes, each with two chromatids
(total of 92 chromatids). At the end of
meiosis I (the reduction division), there
will be 23 chromosomes (each having two
chromatids, for a total of 46 chromatids)
in each cell. In meiosis II, the 23
chromosomes split at the centromeres and
the chromatids from each respective
chromosome migrate to opposite poles. So,
at the end of meiosis I, you have 23
chromosomes, each with two chromatids
and at the end of meiosis II, you also have
23 chromosomes, however each has a
single chromatid.
Interphase I
Similar to mitosis interphase.
Chromosomes replicate (S
phase).
Each duplicated chromosome
consist of two identical sister
chromatids attached at their
centromeres.
Centriole pairs also replicate.
Nucleus and nucleolus visible.
Meiosis I (four phases)
Cell division that reduces
the chromosome number by
one-half.
Four phases:
a. prophase I
b. metaphase I
c. anaphase I
d. telophase I
Prophase I
• Longest and most complex phase. 90% of the meiotic process is
spent in Prophase
• Chromosomes condense.
• Synapsis occurs: homologous chromosomes come together to form
a tetrad.
• Tetrad is two chromosomes or four chromatids (sister and nonsister
chromatids).
During Prophase I “Crossing Over”
occurs
Crossing Over is one of the major occurrences of Meiosis
During Crossing over segments of nonsister chromatids break and reattach to the other chromatid. The
Chiasmata (chiasma) are the sites of crossing over.
Crossing Over:
During Crossing over segments of nonsister chromatids break and reattach to the other chromatid. The Chiasmata
(chiasma) are the sites of crossing over.
nonsister chromatids creates variation (diversity) in the offspring’s traits.
chiasmata: site of crossing
over
Tetrad
variation
Metaphase I
Shortest phase
Tetrads align on the
metaphase plate.
INDEPENDENT
ASSORTMENT OCCURS:
1. Orientation of
homologous pair to poles is
random.
2. Variation
3. Formula: 2n
Anaphase I
Homologous chromosomes separate and move towards the poles.
Sister chromatids remain attached at their centromeres.
Telophase I
Each pole now has haploid set
of chromosomes.
Cytokinesis occurs and two
haploid daughter cells are
formed.
Meiosis II…….Reduction Division
• No interphase II
• (or very short - no more DNA replication)
• Remember: Meiosis II is similar to mitosis
• Prophase II
• Metaphase II
• Anaphase II
• Telophase II : four haploid daughter cells
produced.
• gametes = sperm or egg
Telophase II: Nuclei splits into two, followed by cytokinesis.
Oogenesis
Spermatogenesis
Question:
A cell containing 20 chromosomes (diploid) at the beginning of
meiosis would, at its completion, produce cells containing how many
chromosomes?
Answer:
10 chromosomes (haploid)
Question:
A cell containing 40 chromatids at the beginning of meiosis would, at its
completion, produce cells containing how many chromosomes?
Answer:
10 chromosomes
Non-disjunction
Non-disjunction is one of the anomalies in meiosis
• Non-disjunction is the failure of homologous chromosomes, or sister chromatids,
to separate during meiosis.
• Non-disjunction results with the production of zygotes with abnormal
chromosome numbers……
• …. An abnormal chromosome number (abnormal amount of DNA) is damaging to
the offspring.
Non-disjunctions usually occur in one of
two fashions.
• The first is called Monosomy, the second is
called Trisomy.
• If an organism has Trisomy 18 it has three
chromosomes in the 18th set
• Trisomy 21…. Three chromosomes in the 21st
set.
• If an organism has Monosomy 23 it has only
one chromosome in the 23rd set.
Common Non-disjunction Disorders
•
•
•
•
Down’s Syndrome – Trisomy 21
Turner’s Syndrome – Monosomy 23 (X)
Kleinfelter’s Syndrome – Trisomy 23 (XXY)
Edward’s Syndrome – Trisomy 18
Amniocentesis
• An Amniocentesis is a procedure a pregnant
woman can have in order to detect some
genetics disorders…..such as non-disjunction.
Amniocentesis
Amniotic fluid withdrawn
Karyotype
(picture of an individual’s chromosomes)
One of the ways to analyze the
amniocentesis is to make a
Karyotype
What genetic disorder does this
karyotype show?
Trisomy 21….Down’s Syndrome
• THE END
Mendelian Patterns of
Inheritance
Fundamentals of Genetics
• Genetics is the branch of science that
studies how the characteristics of
living organisms are inherited.
• An allele is a specific version of a
gene.
• Examples: eye color, hair color, earlobe
type
• The two different alleles are on the
same part of a chromosome.
Fundamentals of Genetics
• Gene: A hereditary unit consisting of a
sequence of DNA that occupies a specific
location
on
a
chromosome
and
determines a particular characteristic in
an organism.
• An allele is an alternative form of a gene
(one member of a pair) that is located at
a specific position on a specific
chromosome.
• Locus:
(plural loci) is the specific
location of a gene or DNA sequence or
position on a chromosome.
Fundamentals of Genetics
• The interaction of alleles determines the
appearance of the organism.
– The genotype of an organism is the
combination of alleles that are present in
an organism’s cells
• Ex. BB, Bb, bb
• Homozygous – two identical alleles
• Heterozygous – two different alleles
– The phenotype of an organism is how it
appears outwardly and is a result of an
organism’s genotype
• Blue eyes, brown eyes
Fundamentals of Genetics
• A dominant allele masks the recessive allele in the phenotype of
an organism
– Dominant allele is usually shown by a capital letter
– Recessive alleles are usually shown by a lower-case letter.
• B – brown-eyes, b – blue-eyes
• BB, Bb, bb.
Fundamentals of Genetics
• Genetic cross is a planned mating between two organisms
• Punnett square shows the possible offspring of a particular genetic cross
• AS * SS
A
S
S
AS
SS
S
AS
SS
Punnett Square
• Height: T=tall, t=short
• Question
The genotype of plant’s parent is below. Identify all the Genotypes and
Phenotypes of the offspring using the Punnet square table.
TT x tt
Tt x Tt
TT x Tt
Mendel’s Laws of Genetics
• Mendel recognized genetic principles
• Organisms have two pieces of genetic information for each trait (later called
alleles)
• Law of Dominance states that some alleles interact with each other in a dominant
and recessive manner, where the dominant allele masks the recessive trait.
• Ex: PP = purple
pp = white
•
Pp = purple
• Law of Segregation says when a diploid organisms forms gametes, the two alleles
for a characteristic separate from one another.
One-Trait Inheritance
• Mendel performed cross-breeding experiments
• Used “true-breeding” (homozygous) plants
• Chose varieties that differed in only one trait (monohybrid cross)
• Performed reciprocal crosses
• Parental generation = P
• First filial generation offspring = F1
• Second filial generation offspring = F2
• Formulated the Law of Segregation
Mendel’s Monohybrid Crosses:
An Example
Dihybrid crosses
• Matings that involve parents that differ in two genes (two
independent traits).
For example, flower color:
P = purple (dominant)
p = white (recessive)
and stem length:
T = tall
t = short
Dihybrid cross: flower color and
stem length (shortcut)
TT PP tt pp
(tall, purple)
Possible Gametes for parents
(short, white)
T P
TP
tp
t p
F1 Generation: All tall, purple flowers (Tt Pp)
Tt Pp
Dihybrid cross F2
If F1 generation is allowed to self pollinate, Mendel observed 4 phenotypes:
Tt Pp Tt Pp
(tall, purple)
(tall, purple)
TP
Possible gametes:
TP Tp tP tp
Tp
tP
tp
Tp
TTPP TTPp TtPP
TTPp TTpp TtPp
TtPp
Ttpp
tP
TtPP
TtPp
ttPP
ttPp
TtPp
Ttpp
ttPp
ttpp
TP
tp
Four phenotypes observed
Tall, purple (9); Tall, white (3); Short, purple (3); Short white (1)
Dihybrid cross
9 Tall
purple
TP
TP
3 Tall
white
Tp
tP
tp
3 Short
purple
1 Short
white
Tp
tP
tp
TTPP TTPp TtPP
TTPp TTpp TtPp
TtPp
Ttpp
TtPP
TtPp
ttPP
ttPp
TtPp
Ttpp
ttPp
ttpp
Phenotype Ratio = 9:3:3:1
Law of Segregation
• Each individual has a pair of factors (alleles) for each trait.
• The factors (alleles) segregate (separate) during gamete (sperm & egg)
formation.
• Each gamete contains only one factor (allele) from each pair. Fertilization
gives the offspring two factors for each trait.
Sample Problems
1. A coined is flipped four times and comes up with a head each time. What is the probability
that the next coin flip will come up with a head?
2. Classify the following as heterozygous or homozygous: RR, Rr, yy
3. What is the Phenotype of the following of the following: Yy, Rr, yy
4. What is the probability of Rr x Rr producing wrinkled seeds?
5. What is the probability of Yy x yy producing green seeds?
Investigating Mendelian conditions in human
A member of a family who first comes to the attention of a geneticist is called the proband. Usually the
phenotype of the proband is exceptional in some way (for example, the proband might be a dwarf).
Males are hemizygous for loci on the X and Y chromosomes,
where they have only a single copy of each gene, so the
question of dominance or recessiveness does not arise in
males for X- or Y-linked characters.
The five basic Mendelian pedigree patterns
•
Mendelian characters may be determined by loci on an autosome or on the X or Y sex chromosomes.
Autosomal characters in both sexes and X-linked characters in females can be dominant or recessive.
Thus there are five archetypal Mendelian pedigree patterns:
1.
2.
3.
4.
5.
Autosomal dominant
Autosomal recessive
X-linked recessive
X-linked dominant
Y-linked
•
Only one important gene has been located on the human Y chromosome, the TDF gene, which codes for
a testis-determining factor and plays a primary role in maleness.
•
Therefore, in practice the important mendelian pedigree patterns are autosomal dominant,
autosomal recessive and X-linked.
Autosomal Dominant Disorders
• Autosomal dominant inheritance means that the gene carrying
a mutation is located on one of the autosomes (chromosome
pairs 1 through 22). This means that males and females are
equally likely to inherit the mutation. "Dominant" means that
having a mutation in just one of the two copies of a particular
gene is all it takes for a person to have a trait, such as an
increased risk of developing cancer
A pedigree showing autosomal dominant
inheritance
Autosomal dominant pedigree pattern
• In pedigree analysis, the main clues for identifying a dominant disorder are that the
phenotype tends to appear in every generation of the pedigree and that affected fathers
and mothers transmit the phenotype to both sons and daughters.
• Examples of autosomal dominant disorders include Huntington's disease and
neurofibromatosis-1.
Pedigree of a dominant phenotype
Autosomal Recessive Disorders
• Autosomal recessive inheritance means that the gene is located on one of the autosomes (chromosome
pairs 1 through 22). This means that males and females are equally affected.
• "Recessive" means that two copies of the gene are necessary to have the trait, one inherited from the
mother, and one from the father.
• A person who has only one recessive gene is said to be a "carrier" for the trait or disease, but they
do not have any health problems from "carrying" one copy of the gene.
• Once parents have had a child with a recessive trait or disease, there is a one out of four, or 25
percent chance, with each subsequent pregnancy, for another child to be born with the same trait or
disorder.
Autosomal Recessive Pedigree for Sickle Cell disease
Examples of autosomal recessive disorders include cystic fibrosis, sickle cell
anemia.
X-Linked Recessive Pedigree
X-linked
recessive
inheritance
is
a
mode
of inheritance in which a mutation in a gene on the X
chromosome causes the phenotype to be expressed (1)
in males (who are necessarily hemizygous for the gene
mutation because they have only one X chromosome)
and (2) in females who are homozygous for the gene
mutation (i.e., they have a copy of the gene mutation
on each of their two X chromosomes).
red-green color blindness.
X-Linked Dominant Pedigree
X-linked dominant traits do not necessarily affect
males more than females (unlike X-linked
recessive traits). The exact pattern of inheritance
varies, depending on whether the father or the
mother has the trait of interest. All daughters of an
affected father will also be affected but none of his
sons will be affected (unless the mother is also
affected). In addition, the mother of an affected
son is also affected (but not necessarily the other
way round)e.g. Rett Syndrome.
Complete Dominance
• In the genes that Mendel examined, one allele
demonstrated complete dominance.
• In heterozygotes, the dominant allele was
expressed in the phenotype and the alternative
allele (recessive) was repressed.
• An individual with a dominant phenotype could
have either a homozygous dominant genotype
(PP) or a heterozygous genotype (Pp).
Incomplete Dominance
• Incomplete Dominance is a type of
inheritance in which one allele for a
specific trait is not completely dominant
over the other allele. This results in a
combined phenotype (expressed physical
trait).
• For example, if you cross pollinate
red and white snapdragon plants, the
dominant allele that produces the red
color is not completely dominant over
the recessive allele that produces the
white color. The resulting offspring
are pink
Codominance
• In codominance the effects of both alleles are visible as
distinct effects on the phenotype.
• A good example of codominance is expression of the A
and B blood type alleles in humans.
• Multiple Alleles refers to situations in which there are
more than 2 possible alleles that control a particular trait
• For blood type there are three different alleles
• IA – blood has type A antigen on rbc surface
• IB – Blood has type B antigen on rbc surface
• i – Blood type O has neither type A nor type B antigens
on rbc surface
• Interactions Among Alleles
• For blood type there are three
different alleles
• IA – blood has type A antigen on rbc
surface
• IB – Blood has type B antigen on rbc
surface
• i – Blood type O has neither type A
nor type B antigens on rbc surface
• Type A blood has anti-B antibodies.
• Type B blood has anti-A antibodies
• Type O blood has no antibodies for A or B
Codominance
• Type O individuals (ii) are universal donors and type AB are universal recipients
Polygenic Inheritance
• Polygenic inheritance refers to the kind of inheritance in which the trait is produced
from the cumulative effects of many genes in contrast to monogenic inheritance wherein
the trait results from the expression of one gene (or one gene pair). In humans,
height, weight, and skin color are examples of polygenic inheritance, which does not
follow a Mendelian pattern of inheritance.
Pleiotropy: Pleiotropy occurs when the alleles from a single gene have multiple
phenotypic effects.
THE END
PROKARYOTES, BACTERIA & FUNGI
What are Bacteria
Single-celled microorganisms that can exist either as
independent (free-living) organisms or as parasites
(dependent on another organism for life).
Bacteria are prokaryotes. The entire organism consists
of a single cell with a simple internal structure. Unlike
eukaryotic DNA, which is neatly packed into a cellular
compartment called the nucleus, bacterial DNA floats
free, in a twisted thread-like mass called the nucleoid.
Bacteria
inhabit
soil,
water,
acidic
hot
springs, radioactive waste, and the deep portions
of
Earth's
crust.
Bacteria
also
live
in symbiotic and parasitic relationships with plants and
animals.
Escherichia Coli Bacteria
BACTERIA CLASSIFICATION
There are two major classification of Bacteria. These
are the EUBACTERIA and the ARCHAEBACTERIA (or
the Archaea ).
The members of these two kingdoms appear similar in
shape and appearance, even under the extreme
magnification of the electron microscope .
However, they are very different from each other in a
number of molecular and biochemical aspects.
It is these differences that have resulted in the
microorganisms being grouped into separate kingdoms
ARCHAEBACTERIA
Methanogens: Anaerobic bacteria which
produce energy by converting H2 & CO2 into
methane gas. E.g. Methanococcus deltae,
Methanosaeta thermophila.
Extreme Halophiles: “Salt-loving" bacteria
that use salt to generate ATP for energy.e.g.
Halobacterium.
Thermoacidophiles: Live in extremely acidic
environments (pH less than 2) that have
extremely high temperatures (up to 110o C).
e.g. geothermal springs at Yellowstone
National Park.
Morning Glory Pool Yellowstone
National Park
EUBACTERIA
Contains the bacteria commonly referred
to as germs.
This kingdom contains most of the world's
bacteria
Eubacteria are classified by:
Shape
Clustering
Respiration
E.coli
S.aureus
S.pneumoneae
EUBACTERIA SHAPE
Coccus – round shaped bacterium
Bacillus - rod-shaped bacterium
• Coccus
Spirillum - spiral-shaped bacterium
• Baccilus
• Spirillum
EUBACTERIA CLUSTERING
Diplo - a prefix used with the shape name to indicate pairing of cells.
Strepto - a prefix used with the shape name to indicate chains.
Staphylo - a prefix used with the shape name to indicate clusters
Diplo
Strepto
Staphylo
PARTS OF A BACTERIA CELL
Cell wall - some rigid and others flexible.
Cell membrane - same as other cells.
Cytoplasm - same as other cells.
DNA - a single, circular chromosome (Plasmid) located in
the cytoplasm. Bacteria do not have a nucleus.
Capsule - a thick, gel-like, protective coating on some
bacteria cells.
Pili - short, hairlike protein structures on the surface of
some bacteria that help them stick to host cells.
Flagella - long protein structures that turn to propel some
bacteria cells.
Reproduction
Asexual, by binary fission - the DNA replicates and then the cell pinches
inward and splits in two.
Conjugation - two cells exchange a portion of their DNA across a bridge
formed between the cells. New material replaces old material in the cell.
While this increases the genetic variability in the organisms, it is not true
sexual reproduction.
Endospores - during adverse conditions, the DNA is encased in a protective
envelope. This endospore can lie dormant for years or until favorable
conditions return.
Toxins
Substances that disrupts the metabolism of other organisms.
Endotoxin - made up of lipids and carbohydrates associated with the outer
membrane of gram-negative bacteria. These toxins are some of the strongest
poisons known to man and cause violent reactions in host organisms.
Exotoxin - proteins produced inside gram-positive bacteria cells and secreted
into the environment. These toxins usually produce fever, weakness, and
capillary damage.
Susceptibility & Resistance
'The "susceptible" category implies that isolates are
inhibited by the usually achievable concentrations of
antimicrobial agent when the recommended dosage is
used for the site of infection.
'The "resistant" category implies that isolates are not
inhibited by the usually achievable concentrations of
the agent with normal dosage schedules, and/or that
demonstrate zone diameters that fall in the range
where specific microbial resistance mechanisms (e.g.
beta-lactamases) are likely, and clinical efficacy of the
agent against the isolate has not been reliably shown in
treatment studies.'
Gram Staining
GRAM POSITIVE BACTERIUM: Gram-positive bacteria
retain the color of the crystal violet stain in the Gram stain.
This is characteristic of bacteria that have a cell wall
composed of a thick layer of a particular substance (called
peptidoglycan). The Gram-positive bacteria include
staphylococci ("staph"), streptococci ("strep"), pneumococci,
and the anthrax (Bacillus anthracis).
GRAM NEGATIVE : do not retain the crystal
violet stain used in the Gram staining method of
bacterial differentiation, making positive identification
possible.
The thin peptidoglycan layer of their cell wall is sandwiched
between an inner cytoplasmic cell membrane and a bacterial
outer membrane. After staining with crystal violet, an alcohol
wash is applied which decolorizes the bacteria showing that
their peptidoglycan layer is too thin to retain the stain and
enabling identification.
Antibiotics
Drugs that fight bacteria by interfering with their cellular functions.
PENICILLIN interferes with cell wall synthesis.
TETRACYCLINE interferes with protein synthesis.
Many antibiotics are derived from chemicals that bacteria or fungi produce.
Many Antibiotics are able to affect a wide variety of organisms; they are called
BROAD SPECTRUM ANTIBIOTICS.
USEFUL BACTERIA
Used in Sewage Treatment, and as Decomposers, breaking down the remains
of organic matter in dead plant and animal waste. Recyclers, returning
nutrients back to the environment.
Food production. Bacteria help us make buttermilk, sour cream, yogurt,
cottage cheese, sauerkraut and pickles.
Used in industrial chemical production. They produce organic chemicals and
fuels. They’re used in the mining of minerals and their products are used as
insecticides.
Used to help clean up environmental disasters caused by humans, such as
chemical and oil spills.
PROTISTS-UNICELLULAR EUKARYOTES
They are eukaryotes because they all have a nucleus.
Most have mitochondria. Many have chloroplasts with which
they carry on photosynthesis
Many are unicellular and all groups (with one exception)
contain some unicellular members.
Trypanosoma brucei, the cause of African sleeping sickness in
humans, is a member of the group.
Female Anopheles
Mosquito-Malaria
Ciliates
Move by the rhythmic beating of their cilia.
Examples: Paramecium, thermophila.
Tse-Tse Fly-Trypanosomiasis
Kingdom Fungi
The Characteristics of Fungi
Cell wall present, composed of cellulose and/or chitin.
Food storage - generally in the form of lipids and glycogen.
Eukaryotes - true nucleus and other organelles present.
All fungi require water and oxygen (no obligate anaerobes).
Fungi grow in almost every habitat imaginable, as long as there is some type of organic
matter present and the environment is not too extreme.
Diverse group, number of described species is somewhere between 69,000 to 100,000
(estimated 1.5 million species total).
Yeasts
Single celled fungi
Adapted to liquids
Plant saps
Water films
Moist animal tissues
Saccharomyces
Candida
Molds
Rapidly growth
Asexual spores
Many human importances
Food spoilage
Food products
Antibiotics, etc.
Noble Rot - Botrytis
Fig 31.21 Antibiotic activity
The Characteristics of Fungi
Heterotrophy - 'other food'
Saprophytes or saprobes - feed on dead tissues or
organic waste (decomposers)
Symbionts - mutually beneficial relationship
between a fungus and another organism
Parasites - feeding on living tissue of a host.
Parasites that cause disease are called
pathogens.
Mycorrhizae
“Fungus roots”
Mutualism between:
Fungus (nutrient & water uptake for plant)
Plant (carbohydrate for fungus)
Lichens
“Mutualism” between
Fungus – structure
Alga or cyanobacterium – provides food
Reproduce by spores
Spores are reproductive cells
Sexual (meiotic in origin)
Asexual (mitotic in origin)
Formed:
Directly on hyphae
Inside sporangia
Fruiting bodies
Pilobolus sporangia
Amanita fruiting body
Penicillium hyphae
with conidia
HUMAN-FUNGUS INTERACTIONS
Beneficial Effects of Fungi
Decomposition - nutrient and carbon recycling.
Biosynthetic factories. Can be used to produce drugs, antibiotics,
alcohol, acids, food (e.g., fermented products, mushrooms).
Model organisms for biochemical and genetic studies.
Harmful Effects of Fungi
Destruction of food, lumber, paper, and cloth.
Animal and human diseases, including allergies.
Toxins produced by poisonous mushrooms and within food (e.g.,
grain, cheese, etc.).
Plant diseases.
THE END
VIRUSES &
BIOTECHNOLOGY
A virus is an infectious agent made up of nucleic
acid (DNA or RNA) wrapped in a protein coat
called a capsid.
Viruses have no nucleus, no organelles, no cytoplasm or cell
membrane—Non-cellular
This is why it does NOT belong to any kingdom.
vs
Viruses have either DNA or RNA but NOT both.
Viruses with RNA that transcribe into DNA
are called retroviruses.
Viruses are parasites—an organism
that depends entirely upon another
living organism (a host) for its
existence in such a way that it harms
that organism.
1. Bacteriophage—viruses that infect bacteria
Capsid (protein coat)
– inside contains either
RNA or DNA
2. Flu (influenza), HIV
DNA or RNA
Surface
Marker
Capsid (protein coat)
C. Nonviral particle
Has protein only, no DNA or RNA (cause of mad cow
disease and Creutfeldt-Jacob disease in humans)—Prions
(affects the brain and is always fatal)
No DNA or RNA!
D. Replication is how a virus spreads.
A virus CANNOT reproduce by itself—it must invade a host cell and take
over the cell activities, eventually causing destruction of the cell and
killing it. (The virus enters a cell, makes copies of itself and causes the
cell to burst releasing more viruses.)
Virus attaches to
cell.
Step 3
Step 2
Step 1
Virus copies itself.
Step 4
DNA/RNA is copied.
DNA/RNA injected into
cell.
Cell bursts (lyses) and
releases new viruses.
Step 5
Certain viruses can only attack certain cell
types. They are said to be specific.
Example: The rabies virus only attacks brain or nervous cells.
Surface Markers
Virus
Receptor Sites
Cell
Lytic and Lysogenic Viral Life Cycles
A virus recognizes cells it can infect by matching its surface marker
with a receptor site on a cell.
Virus
Surface Markers
Cell
Receptor Sites
Importance:
*Harmful
Causes disease—pathogenic
Disease producing agent—pathogen
Human Diseases: Warts, common cold, Influenza
(flu), Smallpox, Ebola, Herpes, AIDS, Chicken pox,
Rabies
Viruses disrupt the body’s normal
equilibrium/balance
Viruses can be prevented with vaccines, but
NOT treated with antibiotics.
(antibiotics treat bacteria)
Beneficial:
Genetic Engineering—harmless virus carries
good genes into cells.
Importance of Viruses
- Since viruses can transport DNA and RNA
scientists are exploring Gene Therapy
into cells,
- In Gene Therapy, viral genetic material is
with new DNA
replaced
- In time, this could be used to cure genetic diseases.
Currently we have no cure for these types of illnesses
Biotechnology and
Recombinant DNA
What is Biotechnology
Biotechnology
Use of microorganisms, cells or cell components to
make a product
Recombinant DNA technology (rDNA)
Genetic engineering
Insertion of genes into cells that makes the cells into
“factories” to make products
Recombinant DNA
Putting a gene from one organism into another
Examples:
Human insulin gene into a bacteria to make insulin
Hepatitis B gene into a yeast to make the hepatitis B
vaccine
How to make rDNA
Gene of interest is inserted into a VECTOR
Vector is usually a plasmid that must be self-replicating
Cells containing the vector with the gene of interest then
divide to from a CLONE of identical cells
These clones can then be used to harvest the gene or
produce a product
Restriction enzymes
DNA cutting enzymes that are a key to the
development of rDNA technology
Restriction enzymes cut DNA at specific sites
and allow for DNA to be “inserted” into a
cloning vector
“Sticky ends” are generated?
Restriction Enzymes
Vectors
DNA molecules that can be used as transfer
vehicles to insert DNA into cells
Must be self-replicating and small enough to work
with outside the cell
Plasmids are common vectors
Often contain antibiotic resistance gene
Viral DNA is also used as a vector
Retroviruses, Adenoviruses, Herpesviruses
Larger amounts of DNA can be inserted
Products of genetic engineering
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