- distinguish sex:
sex comb:
Sex combs are a fringe of about ten stout black bristles on the distal surface of the basal or uppermost tarsal joint of the first pair of legs.
Most reliable for distinguish male-present in all mature stages.
- two individual traits in Drosophila melanogaster.
1. wing type- controlled by an autosomal or non-sex-linked gene. Flies having the dominant gene for normal wings (V) would have either a VV or a Vv genotype. Flies with normal wings have fully developed wings and are able to fly. Those having no dominant (V) gene would have vestigial wings and would have a vv genotype. Flies with vestigial wings have nothing more than vestiges or degenerated elements of wings and are unable to fly. However, they can still jump and run quite well. The inheritance of these traits follows the simple rules for alleles having a dominant - recessive relationship with the sex of the fly having no influence.
2. eye color- controlled by a sex-linked gene. More specifically, this gene is X-linked in Drosophila melanogaster. Male flies with red eyes having the dominant gene for red eyes will have an XWY genotype. Female flies with red eyes having the dominant gene will either have an XWXW or XWXw genotype. Male flies with white eyes (the recessive trait) will have an X wY genotype. Female flies with white eyes will have an XwXw genotype. Remember that in Drosophila melanogaster males are heterogametic and females are homogametic. Eye color in Drosophila melanogaster is actually controlled by multiple alleles,
however, we are only examining the most dominant (red) and most recessive (white) alleles in
the allele dominance heirarchy. Because the genes for eye color are X - linked, the sex of the fly
has a definite bearing on the frequency of the red and white phenotypes in males and females.
Remember to use the W (red) and w (white) symbols as superscripts on your X symbols in order
to account for this fact.
The reciprocal cross is the means by which you can differentiate between autosomal and sex- linked traits. When you perform a reciprocal cross, you switch the phenotype of the parent in relationship to its sex in the P-generation. This has no effect on the F1 and F2results for an autosomal trait like wing-type, but it does for a sex-linked trait like eye color. P-generation flies having normal wings will also have white eyes, however, normal wings may be found in red and white-eyed flies in both the F1 and F2 generations depending on the P generation cross performed. Reciprocal crosses 1 and 2 should be reviewed in your workbook (page 160) to understand these relationships.
The reciprocal cross is the means by which you can differentiate between autosomal and sex- linked traits. When you perform a reciprocal cross, you switch the phenotype of the parent in relationship to its sex in the P-generation. This has no effect on the F1 and F2results for an autosomal trait like wing-type, but it does for a sex-linked trait like eye color. P-generation flies having normal wings will also have white eyes, however, normal wings may be found in red and white-eyed flies in both the F1 and F2 generations depending on the P generation cross performed. Reciprocal crosses 1 and 2 should be reviewed in your workbook (page 160) to understand these relationships.
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