Question

Sample Random Mating Lab Drosophilla

P generation was 2 males and 2 females of dumpy, vesitgal, Black Body, Sepia eyed, Irregular facets, and white eyed.

1) In the F1 generation, the most common phenotype is usually wild type for all traits. Based on allele frequencies, why, even though no true breeding wild type flies were present in the P generation does the F1 generation usually have a majority of wild type?

Answer 1

• Experiment is conducted to distinguish between male and female drosophila flies, with specific heritable traits, their mode of inheritance, genotype and phenotype ratio of each P, F1and F2 generation.
• Common mutant phenotypes like eye color, body color, shapes are also analyzed by conducting genetic crosses and data used to establish ratio of trait in male and female flies.
• During recombination process (like meiotic recombination, where recombination occurs between non-sister chromatids), the further the genes are the more is their tendency to cross over or higher is the recombination frequency (as indicated by Morgan).
• While, genes that are close together are linked, and the recombination frequency is less. Usually if recombination frequency is less than 50%, it indicates that the genes are linked.

Linkage may occur in two phases-

1. In coupling phase:

• Dominant alleles of the gene are located in one chromosome, while the recessive alleles in the other. Thus, the alleles from the same parent goes to the same gamete.
• The dominant alleles generated by same parent or are linked or in cis-configuration.

2. In repulsion phase:

• Dominant allele linked to a recessive allele or in trans-configuration.
• Thus, one parent contributes to dominant allele of one gene, while the other parent contributes to dominant allele of the other gene. Or, the alleles from one parent may go to different gametes.

Thus, depending upon the phases, there will be more of wildtype in F1 or a recombinant type.

If linked genes are in coupling phase, more of parental types will be generated. While in repulsio phase, more recombinant types may be obtained.