Both Tim and Jan have a widow's peak (see Module 9.8), but Mike has a straight hairline. What are their genotypes? What is the probability that Tim and Jan's next child will have freckles and a straight hairline?

Verified step by step guidance

1. Determine the inheritance pattern of the widow's peak trait. Widow's peak is a dominant trait (W), while a straight hairline is recessive (w). Since both Tim and Jan have a widow's peak, their genotypes could be either WW (homozygous dominant) or Ww (heterozygous). Mike, who has a straight hairline, must have the genotype ww (homozygous recessive).
2. Analyze the genotypes of Tim and Jan based on their child Mike. Since Mike has a straight hairline (ww), both Tim and Jan must carry at least one recessive allele (w). Therefore, their genotypes are Ww (heterozygous).
3. Determine the inheritance pattern of freckles. Freckles are also a dominant trait (F), while the absence of freckles is recessive (f). If the problem does not specify whether Tim and Jan have freckles, assume they are heterozygous (Ff) for this trait to account for all possibilities.
4. Set up a Punnett square for each trait. For the widow's peak/straight hairline trait, cross Ww (Tim) with Ww (Jan). For the freckles trait, cross Ff (Tim) with Ff (Jan). This will allow you to calculate the probabilities of each genotype and phenotype for their offspring.
5. Combine the probabilities of the two traits. To find the probability that Tim and Jan's next child will have freckles (F_) and a straight hairline (ww), multiply the probability of having freckles (F_) from the freckles Punnett square by the probability of having a straight hairline (ww) from the widow's peak Punnett square.

Key Concepts

Genotype and Phenotype

Genotype refers to the genetic makeup of an organism, specifically the alleles it possesses for a particular trait. Phenotype, on the other hand, is the observable expression of those genes, influenced by both genotype and environmental factors. In this context, Tim and Jan's widow's peak is a phenotypic trait resulting from their genotypes.

Inheritance Patterns

Inheritance patterns describe how traits are passed from parents to offspring, often explained through Mendelian genetics. Traits can be dominant or recessive, with dominant traits expressed in the phenotype even if only one allele is present. Understanding these patterns is crucial for predicting the likelihood of traits, such as freckles and hairline shape, in their children.

Punnett Squares

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two organisms. By mapping the possible gametes from each parent, it allows for the calculation of probabilities for various genotypes and phenotypes in the offspring. This tool is essential for determining the likelihood of Tim and Jan's child inheriting specific traits like freckles and hairline shape.