Problem 5 - Biology Concepts and Applications

Question

One parent is heterozygous for an allele inherited in an autosomal dominant pattern; the other parent does not carry the allele. Any child of these two parents has a _________ chance of having the trait associated with the allele. a. 25 percent b. 50 percent c. 75 percent d. 100 percent

Step-by-Step Solution

Answer

50% chance of having the trait.

Step 1: Understand Autosomal Dominant Inheritance

In autosomal dominant inheritance, only one copy of the dominant allele is needed for the trait to be expressed. This means if an individual carries the dominant allele, they will exhibit the trait.

Step 2: Define Parent Genotypes

One parent is heterozygous, carrying one dominant allele (A) and one recessive allele (a), so their genotype is Aa. The other parent does not carry the allele, so their genotype is aa.

Step 3: Set Up a Punnett Square

Draw a Punnett square with four squares: one parent's alleles on the top (A, a) and the other parent's alleles on the side (a, a).

Step 4: Fill in the Punnett Square

Complete the Punnett square by filling in the squares: Aa, Aa, aa, aa. This shows the possible alleles for their offspring.

Step 5: Calculate the Probability

From the Punnett square, there are two squares with Aa, which carry the dominant trait, and two squares with aa, which do not. Therefore, the probability of any child having the trait is 2 out of 4, or 50%.

Key Concepts

Punnett Square

A Punnett Square is a grid system used to predict the possible genetic outcomes of a cross between two organisms. It helps visualize how alleles from the parent organisms can combine in their offspring.

• Each parent contributes one allele per gene to their offspring. These alleles can be a combination of dominant and recessive forms.
• For our exercise, we place the alleles of one parent along the top of the square and the alleles of the other parent along the side.
• The four boxes inside the square represent the potential allele combinations for their children.

By using a Punnett Square, it's easier to see how traits are passed on and to calculate the probability of different genetic outcomes.

Heterozygous Genotype

A heterozygous genotype means that an organism has two different alleles for a particular gene.

• In our example, the heterozygous parent has one dominant allele (A) and one recessive allele (a).
• This is written as 'Aa'. Here, 'A' is expressed, making it the visible trait in the organism.
• Heterozygous individuals show the dominant trait, even if they have one copy of the recessive allele.

Understanding heterozygosity is crucial in predicting how traits are inherited and expressed in offspring. In autosomal dominant inheritance, carrying just one copy of the dominant allele is enough to express the associated trait.

Allele Inheritance Probability

Allele inheritance probability refers to the likelihood of an offspring inheriting a specific allele combination from its parents. By using a Punnett Square, we calculate these probabilities in a straightforward manner.

• In our scenario, the parent with genotype 'Aa' can pass on either the 'A' allele (dominant) or the 'a' allele (recessive) to their offspring.
• The other parent with genotype 'aa' can only pass on the 'a' allele (recessive).
• From the four possible combinations in the Punnett Square, two result in the 'Aa' genotype, and two result in 'aa'.
• This means there is a 50% chance of the child inheriting the 'Aa' genotype and showing the dominant trait.

This calculation helps us understand the likelihood of different genetic traits appearing in the offspring and assists in predicting genetic outcomes in families.