
a.
To determine:
The
Introduction:
Test cross is the genetic cross between an individual that has dominant phenotype in specific trait to homozygous recessive for these specific traits. Test cross is used to identify the genotype of individual carrying dominant phenotype, and also used to check the linkage between the genes. In drosophila melanogaster, ebony eyes (e), and rough eyes (ro) are encoded by autosomal recessive gene that is present on chromosome they are separated by 20 map units. The gene that code for fork bristle (f) is X-linked recessive and assort independently of (e), and (ro).
a.

Explanation of Solution
Pictorial representation: The cross between
Fig.1: The cross between
Two autosomal genes in drosophila melanogaster, for body type and eyes are located 20 map unit apart from each other on chromosome 3.
Therefore, total percentage of recombinant would be 20 and non recombinant would be 80.
In females eight gametes are possible which will have four parental and four recombinants. Total percentage of recombinants is 20% so for each recombinant 5%. Similarly total percentage of non recombinant is 80% so each non recombinant will have 20%.
Given information is that, when drosophila is heterozygous for autosomal genes that are present in cis configuration with X-linked gene for heterozygous bristle. This female is crossed with homozygous recessive male for two autosomal genes and hemizygous for the X-linked gene.
The female are able to produce eight types of different gametes and these gametes are:
The result of the cross is:
The following table represents the expected proportion from the cross:
Genotype | Body color | Eyes | Bristles | Proportion |
Normal | Normal | Normal | 20% | |
Normal | Normal | Forked | 20% | |
Ebony | Rough | Normal | 20% | |
Ebony | Rough | Forked | 20% | |
Normal | Rough | Ebony | 5% | |
Ebony | Normal | Normal | 5% | |
Normal | Rough | Forked | 5% | |
Ebony | Normal | Forked | 5% |
Table 1: The expected proportion from the cross.
b.
To determine:
The phenotype of progeny and their expected proportion when a female of each genotype is test crossed with the male
Introduction:
Test cross is the genetic cross between an individual that has dominant phenotype in specific trait to homozygous recessive for these specific traits. Test cross is used to identify the genotype of individual carrying dominant phenotype, and also used to check the linkage between the genes. In drosophila melanogaster, ebony eyes (e), and rough eyes (ro) are encoded by autosomal recessive gene that is present on chromosome they are separated by 20 map units. The gene that code for fork bristle (f) is X-linked recessive and assort independently of (e), and (ro).
b.

Explanation of Solution
Pictorial representation: The cross between
Fig. 2: The cross between
Given information is that, when drosophila is heterozygous for autosomal genes that are present in Tran’s configuration with X-linked gene for heterozygous bristle. This female is crossed with homozygous recessive male for two autosomal genes and hemizygous for the X-linked gene.
The female are able to produce eight types of different gametes and these gametes are:
The result of the cross is:
The following table represents the expected proportion from the cross:
Genotype | Body color | Eyes | Bristles | Proportion |
Normal | Rough | Normal | 20% | |
Ebony | Normal | Normal | 20% | |
Normal | Rough | Forked | 20% | |
Ebony | Normal | Forked | 20% | |
Normal | Normal | Normal | 5% | |
Normal | Normal | Forked | 5% | |
Ebony | Rough | Normal | 5% | |
Ebony | Rough | Forked | 5% |
Table 2: The expected proportion from the cross.
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Chapter 7 Solutions
Genetics: A Conceptual Approach
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