Problem 6 - Biology Today and Tomorrow with Physiology

Question

If one parent is heterozygous for a dominant autosomal allele and the other parent does not carry the allele, a child of theirs has \(a\)________ chance of being heterozygous. a. 25 percent b. 50 percent c. 75 percent d. no chance; it will die

Step-by-Step Solution

Answer

b. 50 percent

Step 1: Identify Parent Genotypes

One parent is heterozygous for the dominant autosomal allele. Let's denote their alleles as Aa, where A is the dominant allele and a is the recessive allele. The other parent does not carry the dominant allele and is homozygous recessive, denoted as aa.

Step 2: Determine Possible Child Genotypes

To determine the genetic makeup of the child, we perform a genetic cross between Aa (heterozygous parent) and aa (homozygous recessive parent).

Step 3: Use a Punnett Square

Construct a Punnett square with one parent's alleles on the top (Aa) and the other parent's alleles on the side (aa). This will help us visualize the possible genotype combinations for the child. The Punnett square should look like this: | | A | a | | -|---|---| | a| Aa | aa | | a| Aa | aa |.

Step 4: Analyze the Punnett Square

From the Punnett square, we see that the possible genotypes for the children are Aa and aa. There are two possible Aa (heterozygous) outcomes and two possible aa (homozygous recessive) outcomes. This gives us a 2:2 ratio, or simplified, a 1:1 ratio.

Step 5: Calculate Probability of Heterozygous Offspring

The probability that a child will be heterozygous (Aa) is calculated by taking the number of Aa outcomes (2) over the total possible outcomes (4). So, the probability is 2/4, which simplifies to 1/2 or 50%.

Key Concepts

Understanding Punnett Squares

A Punnett Square is a useful tool in genetics for predicting the possible genotypes of offspring based on the genetic makeup of the parents. It is essentially a grid that allows you to visualize how alleles from each parent can combine. You place the alleles from one parent along the top of the square and the alleles from the other parent along the side. By filling out the grid, you can see all possible combinations of alleles for their offspring.

This method is especially useful for assessing genetic crosses, such as when predicting whether an offspring will inherit a certain trait.

• Helps visualize allele combinations
• Determines probability of certain genotypes
• Useful for Mendelian inheritance patterns

Using a Punnett Square, we can better grasp the genetic outcomes because it organizes the information into a clear visual format.

Defining Heterozygous

In genetics, a heterozygous individual carries two different alleles for a specific gene. This means one allele is inherited from each parent, leading to a mixed genotype like Aa.

Individuals who are heterozygous can exhibit the trait associated with the dominant allele because it only takes one copy of this allele to express the trait. Understanding this concept is important as it forms the basis for examining genetic variations in offspring.

• Heterozygous: Two different alleles (e.g., Aa)
• Often display the phenotype of the dominant allele
• Plays a key role in genetic diversity and evolution

Thus, when examining genetic crosses in exercises, recognizing which parent is heterozygous can provide insights into the likelihood of an offspring displaying a particular trait.

What is an Autosomal Dominant Allele?

An autosomal dominant allele is a type of allele that is located on one of the autosomes (non-sex chromosomes) and can express its trait even if only one copy is present. Simply put, if you have the allele, the trait it corresponds to is likely to be displayed. This is in contrast to recessive alleles, which require two copies (one from each parent) to be expressed.

Traits encoded by autosomal dominant alleles can be passed on to offspring more easily and have a 50% chance of being passed from a heterozygous parent to their child in each pregnancy. This is important for calculating probabilities in genetic problems.

• Autosomal: Not linked to sex chromosomes
• Dominant: Trait expressed with one allele
• Examples include certain genetic disorders and characteristics

In genetics problems involving a dominant allele, predicting the traits of the offspring largely depends on understanding these principles.

The Basics of Probability Calculation in Genetics

Probability calculation is key in genetics for determining the likelihood of certain traits appearing in offspring. It involves interpreting the results of a Punnett Square or other genetic models. The basic idea is to find the ratio of desired outcomes to the total number of outcomes.

In our example, where one parent is heterozygous (Aa) and the other is homozygous recessive (aa), the Punnett Square predicts that there is a 50% probability of the offspring being heterozygous (Aa). This type of calculation is essential for understanding genetic inheritance patterns.

• Uses ratio of specific outcomes to total outcomes
• Involves simple math to find probability percentages
• Crucial for predicting inheritance in genetics

Thus, being able to perform probability calculations allows students to more accurately predict genetic traits and understand the principles of inheritance.