ps3answers - Chromosome Theory of Inheritance; Linkage...

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Problem Set #3 Answers: 1. Because 1/4 of the progeny (both males and females) from an F1 cross of heterozygotes for the vestigial gene manifest the recessive vestigial-wing phenotype, this phenotype appears to be inherited in an autosomal recessive fashion. However, 1/2 of the males from a cross of the F1’s manifest the recessive yellow-body phenotype, whereas none of the females manifest this phenotype. This result is consistent with recessive sex-linked transmission of the yellow- body trait. 2. (a). Pedigree 1: autosomal recessive; Pedigree 2: X-linked recessive; Pedigree 3: autosomal dominant; Pedigree 4: X-linked dominant. (b). Pedigree 1: 25%; Pedigree 2: daughter 0% chance, son 25% chance; Pedigree 3: 50%; Pedigree 4: 0% chance. 3. (a). recessive. (b). autosomal. (c). Individual I-1: a,a Individual I-8 : A,a Individual I-9: A,a Individual II-6: A,a Individual II-8: A,a Individual III-4: A,a 4. Transmission of the colorblindness trait is consistent with a sex-linked recessive pattern of inheritance. The genotypes are as follows: I-1: X C ,X c I-2: X C ,Y II-1: X C ,X ? II-2: X c, ,Y II-3: X C ,X c II-4: X C ,Y III-1: X C ,X c III-2: X C ,X ? III-3: X c, ,Y III-4: X C ,Y 5. (a). Alleged father 1: Xg(a) type inconsistent; Alleged father 2: Rh type inconsistent, Alleged father 4: Rh type inconsistent. Father 3 is consistent. (b). If the daughter had Turner syndrome (XO) a non-disjunction event during meiosis in the mother or the father would result an O egg being fertilized by an X sperm, or an X egg being fertilized by an O sperm. Thus, the daughter’s X-chromosome genotype might derive exclusively from the mother. In this case, father 1 could not be excluded. 6 (a). Two possible combinations could have resulted in an XXY hemophiliac son. X h normal egg with X h Y abnormal sperm X h X h abnormal egg with normal Y sperm (b). In order to insure that 50% of the offspring will be hemophiliac, regardless of sex, the mother must be X H X h and the father must be X h Y. (c).
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7 (a). Since the gene is rare, the chances of someone outside the family contributing the defective gene are extremely small. The gene is therefore autosomal, since individual II-4, a mate outside the family, is not likely to have a defective gene. Thus her son (III-6) could not have contracted the cancer. The gene responsible for the cancer is also dominant. The females do not display the trait because it is sex-limited; females cannot get testicular cancer.
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(b). If it was common, then people outside the family could contribute the defective trait, raising the possibility that it is sex linked. Individuals I-1, II-2 and III-6 would therefore be carriers. However, from this pedigree, we cannot tell whether the sex linked trait is dominant or recessive. 8. (a).
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ps3answers - Chromosome Theory of Inheritance; Linkage...

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