Organisms with the genotypes AABbCcDd and AaBbCcDd are crossed. What are the expected proportions of the following progeny?


A–B–C–D–

Verified step by step guidance

1. Step 1: Understand the problem. The genotypes AABbCcDd and AaBbCcDd represent the parental organisms. The goal is to determine the proportion of progeny with the genotype A–B–C–D–, where each dash (–) indicates that either the dominant or recessive allele is acceptable for that gene.
2. Step 2: Break down the problem into individual loci (A, B, C, and D). For each locus, calculate the probability of obtaining at least one dominant allele (A–, B–, C–, D–) in the progeny. Use the rules of Mendelian inheritance to determine the probabilities for each locus.
3. Step 3: For the A locus, the parental genotypes are AA (homozygous dominant) and Aa (heterozygous). The offspring will always inherit at least one dominant allele (A–), so the probability for A– is 1.
4. Step 4: For the B locus, the parental genotypes are Bb (heterozygous) and Bb (heterozygous). Use a Punnett square to determine the probability of obtaining at least one dominant allele (B–). The probabilities are: BB = 1/4, Bb = 1/2, and bb = 1/4. Add the probabilities for BB and Bb to get the probability of B–.
5. Step 5: Repeat the same process for the C and D loci. For the C locus, both parents are Cc (heterozygous), so use a Punnett square to calculate the probability of C–. For the D locus, the parental genotypes are Dd (heterozygous) and Dd (heterozygous). Multiply the probabilities for A–, B–, C–, and D– to find the overall proportion of progeny with the genotype A–B–C–D–.

Key Concepts

Genotype

A genotype refers to the genetic constitution of an organism, specifically the alleles it possesses for a particular gene. In the given question, the genotypes AABbCcDd and AaBbCcDd indicate the combinations of dominant and recessive alleles for four different genes. Understanding how these alleles interact is crucial for predicting the offspring's traits.

Punnett Square

A Punnett square is a diagram used to predict the genotypes of offspring from a genetic cross. It allows for the visualization of how alleles from each parent combine, helping to determine the expected proportions of different genotypes and phenotypes in the progeny. This tool is essential for solving the question regarding the expected proportions of the progeny.

Independent Assortment

Independent assortment is a principle of genetics stating that alleles for different genes segregate independently of one another during gamete formation. This means that the inheritance of one trait generally does not influence the inheritance of another. This concept is vital for calculating the expected proportions of progeny with specific combinations of traits in the cross described.