Genetic Diagram of Drosophila Wing Traits: F1 & F2 Generations

Subject : Biology

Question:

Show a genetic diagram of the result of crossing between pure long-winged and pure short-winged Drosophila up to the second filial generation. Here, long-wing is a dominant character over short-wing.

Expert Verified Solution:

To understand the genetic outcome of crossing pure long-winged and pure short-winged Drosophila, we need to illustrate the inheritance pattern using a Punnett square. Here’s a detailed breakdown:

1. Parent Generation (P):

• Long-winged Drosophila (Purebred): Genotype = LL (where ‘L’ represents the dominant long-wing allele).
• Short-winged Drosophila (Purebred): Genotype = ll (where ‘l’ represents the recessive short-wing allele).

2. First Filial Generation (F1):

• When LL (long-winged) is crossed with ll (short-winged), all offspring in the F1 generation will inherit one dominant allele (L) from the long-winged parent and one recessive allele (l) from the short-winged parent.
• Genotype of F1 Generation: Ll (heterozygous, showing the long-wing trait due to the dominance of L).
• Phenotype of F1 Generation: All will have long wings.

3. Second Filial Generation (F2):

• To get the F2 generation, we cross two F1 individuals (Ll x Ll).
• Punnett Square for F2 Generation:
• L (from 1st parent) l (from 1st parent)
  L (from 2nd parent) LL Ll
  l (from 2nd parent) Ll ll
• Genotypic Ratio in F2 Generation: 1 LL : 2 Ll : 1 ll
• Phenotypic Ratio in F2 Generation: 3 Long-winged (LL and Ll) : 1 Short-winged (ll)

Summary:

• P Generation: LL (long-winged) x ll (short-winged)
• F1 Generation: All Ll (long-winged)
• F2 Generation:
• Genotypes: 1 LL, 2 Ll, 1 ll
• Phenotypes: 3 Long-winged, 1 Short-winged

This Punnett square illustrates the inheritance of the long-winged trait as dominant over the short-winged trait in Drosophila.