Biology 160 genetic work sheet

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Genetics Worksheet BIOL 160 Mendelian Monohybrid Cross 1. Two heterozygous purple-flowered pea plants are bred together. Purple coloring is dominant over white coloring. a. What is the pea plants’ genotype? ____Pp____ b. What is the pea plants’ phenotype? ___Purple flowers__ c. Complete the Punnet Square P p P PP Pp p Pp pp d. What is the genotype ratio? _1 PP_ : _2 Pp_ : _1 pp_ e. What is the phenotype ratio? _3 purple : 1 white_ f. What is the probability one of their offspring will have white flowers? _25_% 2. Huntington’s disease is a progressive, fatal neurological disease caused by a buildup of protein ‘plaque’ within brain cells. Huntington’s is an autosomal dominant disorder. A woman who is heterozygous for Huntington’s has children with a man who is homozygous recessive for Huntington’s. Her genotype is Hh, his genotype is hh. a. What is the woman’s phenotype? _________________________ b. What is the man’s phenotype? ___________________________ Complete the Punnet Square c. What is the genotype ratio? ______Hh : ______hh d. What is the phenotype ratio? ______Huntington’s : ______ disease-free e. What is the probability one of their children will have Huntington’s? ______% 3. Achondroplastic dwarfism is a disorder characterized by shortened limbs, but normally proportioned torso and head. It is caused by a premature hardening of the growth plate that normally allows long bones in the arms and legs to grow lengthwise. Achondroplastic dwarfism is an autosomal dominant disorder. A man who is heterozygous for achondroplastic dwarfism has children with a woman who is homozygous recessive. (Remember to choose your letter based on the dominant phenotype – in this case, D for dwarf) a. What is the man’s genotype? _______ b. What is the woman’s genotype? ______ c. What is the man’s phenotype? _______________________ d. What is the woman’s phenotype? _______________________ e. Complete the Punnet Square f. What is the genotype ratio? _________________________________ g. What is the phenotype ratio? ____________________________________________ h. What is the probability one of their children will be an achondroplastic dwarf? ______% Mendelian Dihybrid Cross 4. A pea plant that is homozygous dominant for purple flowers and heterozygous for long stems is crossed with a pea plant that is homozygous recessive for purple flowers and homozygous dominant for long stems. Purple flowers and long stems are dominant traits, while white flowers and short stems are recessive traits. a. What is the genotype of the first pea plant? ________________________ b. What is the phenotype of the first pea plant? _______________________ c. What is the genotype of the second pea plant? _______________ d. What is the phenotype of the second pea plant? ______________ e. Complete the Punnet Square. f. What is the genotype ratio? _________________________________ g. What is the phenotype ratio? ____________________________________________ h. What is the probability one of their offspring will be a tall, purple-flowered plant? ______% Incomplete dominance 5. Sickle-cell anemia is often considered an incompletely autosomal dominant disorder. The disease is characterized by misfolded hemoglobin protein, which distorts the blood cells into a crescent moon shape. These misshapen blood cells cause poor circulation, fatigue, bone and muscle pain, and vision problems. Dominant homozygotes do not have any form of the disease. Heterozygotes have an intermediate, mild form of the disease. Recessive homozygotes have a severe form of the disease. A man with a mild form of sickle cell anemia has children with a woman who also has a mild form of sickle cell anemia. a. What is the man’s genotype? _________ b. What is the woman’s genotype? ________ c. What is the man’s phenotype? _______________________ d. What is the woman’s phenotype? _______________________ e. Complete the Punnet Square f. What is the genotype ratio? ____________________________________________ g. What is the phenotype ratio? ____________________________________________ h. What is the probability one of their children will have a severe form of sickle cell anemia? ______% Codominance Note: The alleles for blood types are written in a rather unique fashion. We write the allele for blood type A as IA, blood type B as IB, and blood type O as i. 6. In humans, blood type is expressed in a codominant fashion. The possible human phenotypes for blood group are type A, type B, type AB, and type O. Type A and B blood are codominant, and if inherited together both will be expressed. On the other hand, type O blood is completely recessive to both. Type A and B individuals can be either homozygous (IAIA or IBIB, respectively), or heterozygous (IAi or IBi, respectively), whereas type O blood can only be homozygous recessive (ii). Someone who is a heterozygote for type A is crossed with someone who is a heterozygote for type B blood. a. What is the genotype of the type A person? _______________________ b. What is the genotype of the type B person? _______________________ c. Complete the Punnet Square d. What is the genotype ratio? _______________________________________________ e. What is the phenotype ratio? ______________________________________________ f. What is the probability one of their children will have type O blood? ______% Epistasis 7. In Labrador retriever dogs, coat color is determined via epistatic interaction between two genes. The first gene, designated the B gene, controls whether black or brown pigment is deposited. The second gene, the E gene, controls the expression of the first gene. The B gene acts in a Mendelian dominant fashion. The dominant homozygote (BB) and the heterozygote (Bb) will have black fur. The recessive homozygote (bb) will have brown fur. The E gene also acts in a Mendelian dominant fashion. The dominant homozygote (EE) and the heterozygote (Ee) allows for the expression of the B gene. The recessive homozygote (ee) will not allow for expression of the B gene, and will result in a dog with blonde fur. A female dog that is heterozygous for both the B and the E genes is bred with a male dog that is also heterozygous for both the B and the E genes. a. What is the genotype of the female dog? ________________________ b. What is the phenotype of the female dog? _______________________ c. What is the genotype of the male dog? __________________________ d. What is the phenotype of the male dog? _________________________ e. Complete the Punnet Square. f. What is the genotype ratio? ______________________________________________ g. What is the phenotype ratio? ______________________________________________ h. What is the probability one of their offspring will be blonde? ________% Sex-linked genes 8. The most common type of red-green colorblindness is caused by defective versions of the color receptor genes, found on the X chromosome. Approximately 8% of males of European descent are estimated to have sex-linked red-green colorblindness. A woman without red-green colorblindness BUT with a strong history of colorblindness in her family has children with a man without red-green colorblindness. Use the correct XY notation below for the genotypes. a. What is the man’s genotype? _________ b. What is the woman’s genotype? ________ c. Complete the Punnet Square. d. What is the genotype ratio? _________________________________________________ e. What is the phenotype ratio? ________________________________________________ f. What is the probability one of their children will be female? ______% g. What is the probability one of their children will be colorblind? ______% Challenge: codominance plus a dihybrid cross 9. Rh is another way to measure blood type. Originally discovered in Rhesus macaque monkeys, the Rh factor is a transmembrane ion channel. Rh has a simple dominant/recessive inheritance pattern. Someone who is blood type AB and a heterozygote for Rh has children with someone who also has type AB blood, but is Rh-. a. What is the genotype of the first person? ___IAIBRr_____ b. What is the genotype of the second person? _____________ c. Complete the Punnet Square. d. Genotype ratios: ________________________________________________________________ e. Phenotype ratios: _______________________________________________________________ f. What is the probability one of their children has the blood type A+? _______%
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