What is the expected phenotypic ratio of a test cross involving a heterozygous i
Practice Questions
Q1
What is the expected phenotypic ratio of a test cross involving a heterozygous individual?
1:1
3:1
9:3:3:1
1:2:1
Questions & Step-by-Step Solutions
What is the expected phenotypic ratio of a test cross involving a heterozygous individual?
Step 1: Understand what a test cross is. A test cross is when you cross an individual with an unknown genotype with a homozygous recessive individual.
Step 2: Identify the genotype of the heterozygous individual. A heterozygous individual has one dominant allele (let's say 'A') and one recessive allele (let's say 'a'), so its genotype is 'Aa'.
Step 3: Identify the genotype of the homozygous recessive individual. A homozygous recessive individual has two recessive alleles, so its genotype is 'aa'.
Step 4: Set up the cross. You will cross 'Aa' (heterozygous) with 'aa' (homozygous recessive).
Step 5: Use a Punnett square to determine the offspring. The Punnett square will show the possible combinations of alleles from the parents.
Step 6: Fill in the Punnett square. The combinations will be: 'A' from 'Aa' and 'a' from 'aa' gives 'Aa' (dominant phenotype), and 'a' from 'Aa' and 'a' from 'aa' gives 'aa' (recessive phenotype).
Step 7: Count the phenotypes. You will have 1 'Aa' (dominant phenotype) and 1 'aa' (recessive phenotype).
Step 8: Determine the phenotypic ratio. The ratio of dominant to recessive phenotypes is 1:1.
