Week 4 Discussion Questions (2)

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Biology

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Apr 3, 2024

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BIOL 2140 Week 4 Questions Discussion 1. Shudderer is an X-linked dominant mutation (X Sh ) of Drosophila melanogaster . The mutant is characterized by sporadically occurring leg jerks which cause the fly to lurch and shudder. Parent and offspring phenotypes from four different crosses are given in the table. From the information provided, fill in the genotypes for each parent in crosses 2-5, using the same format shown for Cross 1 . Designate the X chromosome with the normal (wild type) allele as X + . Cross Male Parent Phenotype Female Parent Phenotyp e Male Offspring Phenotype Female Offspring Phenotype Male Parent Genotype Female Parent Genotype 1 normal shudderer all shudderer all shudderer X + Y X Sh X Sh 2 normal shudderer ½ normal; ½ shudderer ½ normal; ½ shudderer X + Y X Sh X + 3 shudderer shudderer ½ normal; ½ shudderer all shudderer X Sh Y X Sh X + 4 shudderer shudderer all shudderer all shudderer X Sh Y X Sh X Sh 5 shudderer normal all normal all shudderer X Sh Y X + X + How does the inheritance pattern and frequency of offspring with a X-linked dominant mutant trait differ from an X-linked recessive trait (such as minature wings, X m , from the Achieve homework)? The females have to be homozygous for the x-linked recessive for it be shown while for the dominant x-linked the females can be heterzygous. 2. Suppose researchers identified two Drosophila melanogaster mutant phenotypes. One phenotype is called maniac and the other is called shiny. To determine the mode of inheritance of the mutant allele responsible for each phenotype, males that have both mutant phenotypes are mated with wild-type (wt) females to produce F1 progeny. Then, the F1 progeny are mated together. The F2 progeny are scored for their sex and if they have the maniac or shiny phenotype (if only maniac or shiny is observed, it means the fly is wild-type for the other characteristic). Interpret the phenotypes of the F1 and F2 progeny to infer the mode of inheritance of maniac and shiny . The modes of inheritance to consider are autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. The two traits do not have the same mode of inheritance.

BIOL 2140 Week 4 Questions Discussion What is the genotype of the original male parent with the maniac, shiny phenotype? Keep in mind that for X-linked traits males are hemizygous. X s YMM 3. A black female cat is mated with an orange male cat. They produce two tortoiseshell females, two black males, one orange female, and one tortoiseshell male, for a total of six kittens. Orange and black fur color are encoded by different alleles ( of the same X-linked fur color gene. a. Based on the phenotypes of the parents, what sex chromosomes do the orange female and the tortie male offspring have? Female: X B X B Male: X o Y b. How did these sex chromosome genotypes come about? Diagram the events in meiosis that would give gametes that are aneuploid for the sex chromosomes. Meiotic nondisjunction of sex chromosomes can lead to the formation of aneuploid gametes. When these gametes fuse with a normal gamete during fertilization, it can give rise to aneuploid offspring. 4. Suppose a species of tulip has three alleles for the gene that codes for flower color. The 𝐶 𝑅 allele produces red tulips, the 𝐶 𝑝 allele produces purple tulips, and the 𝐶 w allele produces white tulips. 𝐶 𝑅 is dominant over 𝐶 p and 𝐶 w , and 𝐶 𝑝 is dominant over 𝐶 𝑤 . For each cross, give the phenotypes of the parents and determine the expected phenotype ratio of offspring flower color. Parent 1 Phenotype Parent 2 Phenotype Offspring Phenotype Ratio Cross 1: C r C p x C r C w red red 3:1 red to purple Cross 2: C r C p x C p C w red purple 1:1 red to purple Cross 3: C r C p x C w C w red white 1:1 red to purple Cross 4: C r C w x C p C w red purple 2:1:1 red to purple to white 5. Suppose two independently assorting genes are involved in the pathway that determines fruit color in squash. At the first locus, the W allele codes for a dominant white phenotype, whereas the w allele codes for a colored squash. At the second locus, the allele Y codes for a dominant yellow phenotype, and the allele y codes for a recessive green phenotype. Plants with a W allele will always have white fruit no matter what alleles they have for the other gene. a. Using a branch diagram, determine the ratio of color phenotypes from self-fertilization of a Ww Yy dihybrid.

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