Problem 6 - Biology Today and Tomorrow Without 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

The child has a 50 percent chance of being heterozygous.

Step 1: Understanding Genetic Terms

The term 'heterozygous' refers to having two different alleles for a particular gene. In this case, it means one allele is dominant and the other is recessive. A dominant autosomal allele means it is located on a non-sex chromosome and will express the dominant trait if present.

Step 2: Determine Parent Genotypes

The problem states one parent is heterozygous, meaning their genotype is 'Aa', where 'A' is the dominant allele and 'a' is the recessive allele. The other parent does not carry the allele, meaning their genotype is 'aa'.

Step 3: Setting Up the Punnett Square

Create a Punnett square to determine the genetic combinations of the offspring. With one parent having genotype 'Aa' and the other 'aa', we write 'A' and 'a' at the top for the first parent, and 'a' and 'a' on the side for the second parent.

Step 4: Filling the Punnett Square

Fill in the Punnett square by crossing the alleles: 'A' from the heterozygous parent with each 'a' of the homozygous recessive parent gives 'Aa'. Similarly, crossing 'a' from the heterozygous parent with each 'a' from the recessive parent gives 'aa'. The results are two 'Aa' and two 'aa' out of possible four combinations.

Step 5: Calculating the Probability

Count the number of heterozygous outcomes, which are 'Aa'. Out of four possible combinations (two 'Aa' and two 'aa'), two combinations are 'Aa'.

Key Concepts

Genetics

Genetics is the study of heredity and variation in organisms. It's how traits, such as eye color and height, are passed down from parents to their offspring. This field involves understanding how genes, which are sequences of DNA, control these inherited traits. A gene can exist in different forms called alleles. For example, the gene responsible for hair texture may have one allele for curly hair and another one for straight hair. Genetic research uses tools like the Punnett square, a handy tool that predicts how alleles from each parent combine to affect the offspring. The principles of genetics help us explore not only physical traits but also the potential for inheriting certain genetic disorders. Genetics is crucial for predicting the likelihood of an organism expressing a trait, and it encompasses the concepts of heterozygosity, autosomal alleles, and how different alleles interact.

Heterozygous

The term heterozygous describes a specific kind of genetic makeup. It means that an individual has two different alleles for a given gene. To illustrate, for a gene represented by the alleles 'A' and 'a', a heterozygous genotype would be 'Aa'. This means the organism inherited one version (allele 'A') from one parent and another version (allele 'a') from the other. Heterozygosity is essential for genetic diversity. It can sometimes mean one allele is dominant over the other (recessive). This dominant allele dictates the organism's trait, even though the recessive allele is still present. In our exercise, a heterozygous parent has one dominant allele and one recessive allele for an autosomal gene, providing a good blend of genetic traits that may be passed on to offspring.

Autosomal Allele

Autosomal alleles refer to gene variants located on autosomes, which are chromosomes not involved in determining the sex of an organism. Humans have 22 pairs of autosomes, and they carry most of the genetic information. Each person inherits one set of autosomes from each parent. These alleles play an essential role in defining traits that are not related to sex, such as blood type or hair color. Autosomal alleles can be either dominant or recessive. They are inherited through generations following Mendelian inheritance patterns, which can be demonstrated using a Punnett square. In genetics, understanding autosomal alleles helps us predict patterns of inheritance for many traits, and they frequently form the basis of genetic studies.

Dominant and Recessive Alleles

Dominant and recessive alleles are a fundamental concept in genetics explaining how traits are expressed. A dominant allele, symbolized often by a capital letter, is powerful enough to express its trait even if only one copy is present. For instance, if 'A' is a dominant allele for brown eyes, having just one 'A' in the genotype (like 'Aa') will result in brown eyes. On the other hand, a recessive allele, represented by a lowercase letter, will only express its trait when two copies are present, such as 'aa'. If 'a' is a recessive allele for blue eyes, an individual must have 'aa' genotype to have blue eyes. These alleles work together to determine physical traits in offspring. The combination of dominant and recessive alleles in each parent's genotype helps predict the likelihood of traits using tools like the Punnett square to visualize potential genetic outcomes.