The data set attached summarizes F2 numbers from an F1 cross arising from two, true-breeding Drosophila strains (P generation), which differ with respect to two mutant traits. Here are the hypothesis: Leg length - The wild-type and mutant alleles for leg length are incomplete dominant relative to each other. Justification: The data set includes three phenotypic categories for leg length: wild type (long leg), medium leg, and truncated wings. The presence of three distinct phenotypes suggests an incomplete dominance pattern, where the heterozygous individuals exhibit an intermediate leg length phenotype (medium leg). The absence of purebred short-legged individuals supports the idea that the long leg allele is dominant over the short leg allele. This shows that mode of inheritance is incomplete dominance of the alleles relative to each other. Since the data does
The data set attached summarizes F2 numbers from an F1 cross arising from two, true-breeding Drosophila strains (P generation), which differ with respect to two mutant traits.
Here are the hypothesis:
Leg length - The wild-type and mutant alleles for leg length are incomplete dominant relative to each other.
- Justification: The data set includes three phenotypic categories for leg length: wild type (long leg), medium leg, and truncated wings. The presence of three distinct
phenotypes suggests an incomplete dominance pattern, where the heterozygous individuals exhibit an intermediate leg length phenotype (medium leg). The absence of purebred short-legged individuals supports the idea that the long leg allele is dominant over the short leg allele. This shows that mode of inheritance is incomplete dominance of the alleles relative to each other. Since the data does not mention any specific differences between males and females, we can assume that the mode of inheritance for the trait is autosomal specific to each allele (as well as the trait).
Wing shape - There are two alleles for wing type, one dominant and one recessive. Truncated wings allele is recessive, and the gene is X-linked. This means the inheritance pattern is X-linked recessive.
- Justification: The data set includes two phenotypic categories for wing shape: wild type (long leg) and truncated wings since there’s a clear disparity in phenotype based on sex. The presence of truncated wings only in males suggests an X-linked inheritance pattern. Since males have only one X chromosome, the presence of a single truncated wing allele would result in the observed phenotype. Since the data set does not show truncated females as a category, this suggests the mode of inheritance is X-linked recessive. For example, let's denote the allele as X^T (truncated) and the wild-type allele as X^t. then the male truncated phenotypes are obviously (X^T)Y, so the female parent has to have an X^T. but then when the female X^T is fertilized by a male X (doesn't matter if X^T or X^t), the X^T will express itself because we assumed it's dominant (or codominant/incomplete). but every single female was wild-type wings with no hint of X^T, so it's exceedingly unlikely this is true, so the data supports the idea that it's X-linked recessive.
a) Explain/describe how the data set seems to support your genetic hypothesis for each trait. For example, explain why you think a trait is recessive vs dominant or X-linked vs autosomal. To do this, you could comment on the observed ratios and/or differences or similarities in male and female numbers and explain how these provide support for your hypotheses. Example: For wing shape, if you want to know how many truncated males there are, you just do 337 + 165 + 168 = 670 and since there are no truncated females, the total number of truncated individuals is 670. Basically calculating how many truncated individuals there are and the numbers are just me adding up all the truncated categories and you would also compute how many wild-type individuals there are by adding all the other slots (since everything is either wild-type or turncated) then you have a number for truncated and a number for wildtype and you can figure out what the ratios are by looking at those numbers (3:1, 1:2:1, etc). Ratios correspond to a pattern of inheritance
b) Assign genetic symbols to the four alleles involved. Be sure your allele notations are informative. For example, use upper case to indicated dominance and lowercase to indicate recessive. If you use the superscript “+” it only tells the reader the allele is wildtype and not its dominance status. Be sure to review the posted video on LEARN to review how to assign meaningful alleles. For the incomplete dominance leg lenght alleles, use L and supercript the categorie (i.e. LM for medium lenght).
c) Illustrate how each of your genetic hypotheses is supported by the data. Show this using Punnett squares for each F1 cross and resulting F2 generation. Be sure all genotypes and phenotypes are clearly indicated directly within the Punnett or branching diagram. Separately analyze each gene and each gender. There should be separate ratios for females and males in each trait. An example of this is shown in the file attached.
d) Indicate the expected (predicted) phenotypic numbers for the F2 generation from your Punnett square constructed in d) above.
Make sure the answer is fully typed, well organized, correct spelling, grammar, and notations used throughout.
Tips:
- When the date set says "long legs", it actually means "long legs and wild-type wings". It is assumed that it's wild-type if it doesn't specify.
- There are categories for truncated males but there are notably no categories for truncated females which means the number is 0 but that suggests an X-linked inheritance pattern. Elaborate on this for c).
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