. The normal eye color of Drosophila is red, but strains inwhich all flies have brown eyes are available. Similarly,wings are normally long, but there are strains with shortwings. A female from a pure line with brown eyes andshort wings is crossed with a male from a normal pureline. The F1 consists of normal females and short-wingedmales. An F2 is then produced by intercrossing the F1.Both sexes of F2 flies show phenotypes as follows:38 red eyes, long wings38 red eyes, short wings18 brown eyes, long wings18 brown eyes, short wingsDeduce the inheritance of these phenotypes; useclearly defined genetic symbols of your own invention.State the genotypes of all three generations and thegenotypic proportions of the F1 and F2.Unpacking Problem 31Before attempting a solution to this problem, try answering thefollowing questions:1. What does the word normal mean in this problem?2. The words line and strain are used in this problem.What do they mean, and are they interchangeable?3. Draw a simple sketch of the two parental flies showingtheir eyes, wings, and sexual differences.4. How many different characters are there in thisproblem?5. How many phenotypes are there in this problem, andwhich phenotypes go with which characters?6. What is the full phenotype of the F1 females called“normal”?7. What is the full phenotype of the F1 males called “shortwinged”?8. List the F2 phenotypic ratios for each character that youcame up with in answer to question 4.9. What do the F2 phenotypic ratios tell you?10. What major inheritance pattern distinguishes sexlinked inheritance from autosomal inheritance?11. Do the F2 data show such a distinguishing criterion?12. Do the F1 data show such a distinguishing criterion?13. What can you learn about dominance in the F1? The F2?14. What rules about wild-type symbolism can you usein deciding which allelic symbols to invent for thesecrosses?15. What does “deduce the inheritance of these phenotypes” mean?
. The normal eye color of Drosophila is red, but strains in
which all flies have brown eyes are available. Similarly,
wings are normally long, but there are strains with short
wings. A female from a pure line with brown eyes and
short wings is crossed with a male from a normal pure
line. The F1 consists of normal females and short-winged
males. An F2 is then produced by intercrossing the F1.
Both sexes of F2 flies show
3
8 red eyes, long wings
3
8 red eyes, short wings
1
8 brown eyes, long wings
1
8 brown eyes, short wings
Deduce the inheritance of these phenotypes; use
clearly defined genetic symbols of your own invention.
State the genotypes of all three generations and the
genotypic proportions of the F1 and F2.
Unpacking Problem 31
Before attempting a solution to this problem, try answering the
following questions:
1. What does the word normal mean in this problem?
2. The words line and strain are used in this problem.
What do they mean, and are they interchangeable?
3. Draw a simple sketch of the two parental flies showing
their eyes, wings, and sexual differences.
4. How many different characters are there in this
problem?
5. How many phenotypes are there in this problem, and
which phenotypes go with which characters?
6. What is the full phenotype of the F1 females called
“normal”?
7. What is the full phenotype of the F1 males called “short
winged”?
8. List the F2 phenotypic ratios for each character that you
came up with in answer to question 4.
9. What do the F2 phenotypic ratios tell you?
10. What major inheritance pattern distinguishes sexlinked inheritance from autosomal inheritance?
11. Do the F2 data show such a distinguishing criterion?
12. Do the F1 data show such a distinguishing criterion?
13. What can you learn about dominance in the F1? The F2?
14. What rules about wild-type symbolism can you use
in deciding which allelic symbols to invent for these
crosses?
15. What does “deduce the inheritance of these phenotypes” mean?
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