BIOL1006 Lecture 17: Lecture 17

1. Which statement about Punnett Squares is true?

2. Which of the following statements is true of sex-linked traits on the X chromosome?

1. Question: Whatphenotypes and ratios did you observe in the F₁generation?

2. Question: Based onwhat you know about Mendelian genetics, did the F₂generation demonstrate the phenotypic ratio that you expected? Ifnot, what phenotypic ratio was obtained with this cross, andwhy?

3. Question:Describe the phenotypes obtained in theF₂ generation. Examine the phenotypes and sexes of eachfly. Is there a sex and phenotype combination that is absent orunderrepresented? If so, which one? What does this result tell youabout the sex chromosome location of the white eye allele?(HINT: When analyzing the crossresults, remember that Y-linked traits are passed down only fromaffected males to their sons. Females are unaffected by Y-linkedtraits since they do not have Y chromosomes. On the other hand, both males and females can inheritX-linked traits since they both have X chromosomes.)

In birds, females are the heterogametic sex (ZW) and males are homogametic (ZZ). The feather color gene in pigeons is on the Z chromosome with dominance expressed as red > blue > brown. A female from a true breeding red line is crossed with a male from a true breeding brown line to yield an F1 male. In another cross, a female from a true breeding blue line is crossed with a male from a true breeding brown line to yield an F1 female. The F1 male and F1 female are crossed. What are the genotypes of these two F1 individuals and what are the expected proportions of genotypes and phenotypes (including sex) from the resultant F2 progeny ?