If a trait is controlled by a single gene with two alleles, where A is dominant
Practice Questions
Q1
If a trait is controlled by a single gene with two alleles, where A is dominant over a, what is the expected phenotypic ratio in the offspring of a cross between Aa and aa?
1:1
3:1
2:1
1:2
Questions & Step-by-Step Solutions
If a trait is controlled by a single gene with two alleles, where A is dominant over a, what is the expected phenotypic ratio in the offspring of a cross between Aa and aa?
Step 1: Identify the genotypes of the parents. One parent is Aa (heterozygous) and the other is aa (homozygous recessive).
Step 2: List the possible gametes (sperm or egg cells) each parent can produce. The Aa parent can produce gametes A and a, while the aa parent can only produce gametes a.
Step 3: Set up a Punnett square to visualize the cross. Place the gametes from one parent on the top and the gametes from the other parent on the side.
Step 4: Fill in the Punnett square by combining the gametes. The combinations will be Aa (from A and a) and aa (from a and a).
Step 5: Determine the phenotypes from the genotypes. Aa will show the dominant trait (A), and aa will show the recessive trait (a).
Step 6: Count the phenotypes. You will have 1 Aa (dominant) and 1 aa (recessive), giving a total of 2 offspring.
Step 7: Calculate the phenotypic ratio. There is 1 dominant phenotype (A) and 1 recessive phenotype (a), resulting in a 1:1 ratio.
Mendelian Genetics – Understanding the inheritance patterns of traits controlled by single genes and the concept of dominant and recessive alleles.
Punnett Square – Using a Punnett square to predict the genotypic and phenotypic ratios of offspring from genetic crosses.
