Chapter 4 - Section 4.4 - Study Guide - Assess Your Learning Outcomes - Page 137: 6

A recessive trait can appear to skip a generation when individuals carrying the recessive allele do not express the trait themselves but can pass it on to their offspring. This phenomenon occurs due to the inheritance of specific combinations of alleles in a family's genetic makeup. Here's an explanation with examples: **1. Recessive Trait Skipping a Generation:** For a recessive trait to appear to skip a generation, you need a specific genetic scenario: - **Generation 1 (Grandparents):** Suppose both grandparents (Generation 1) are carriers of a recessive allele for a particular trait but do not express that trait themselves. They are, in this case, heterozygous (Aa), meaning they have one dominant allele (A) and one recessive allele (a) for the trait. - **Generation 2 (Parents):** The grandparents (Generation 1) pass on their alleles to their children (Generation 2). Since each parent has one dominant allele (A) and one recessive allele (a), they are also carriers of the recessive trait but do not express it because the dominant allele masks the recessive allele. - **Generation 3 (Grandchildren):** If both parents from Generation 2 pass on their recessive alleles (a) to their offspring (Generation 3), and their offspring also inherits a recessive allele (a) from the other parent, then the grandchildren will be homozygous for the recessive trait (aa). In this case, the recessive trait will be expressed in Generation 3, even though it was not apparent in Generations 1 and 2. **Examples:** - **Example 1 (Albinism):** Albinism is a recessive genetic condition that causes a lack of pigment in the skin, hair, and eyes. If both parents are carriers of the albino allele (Aa), they may not exhibit albinism themselves but can have albino children (aa). - **Example 2 (Cystic Fibrosis):** Cystic fibrosis is another recessive genetic disorder. If both parents carry the cystic fibrosis allele (Aa), they may not have the condition but can have a child with cystic fibrosis (aa). **2. What is Meant by a Carrier:** A carrier is an individual who possesses one copy of a recessive allele for a particular trait or genetic disorder but does not express the trait themselves. Carriers are typically heterozygous for the gene in question, meaning they have one dominant allele and one recessive allele. They carry the recessive allele "in silence" because the presence of the dominant allele masks the effects of the recessive one. In the context of genetic disorders, carriers are often referred to as "heterozygous carriers." They can pass the recessive allele on to their offspring, potentially leading to the expression of the trait or disorder in the next generation if both parents are carriers or if the offspring inherits two recessive alleles. Being a carrier is important in the context of genetic counseling and family planning, as carriers of certain genetic disorders may want to assess the risk of passing the condition to their children.

A recessive trait can appear to skip a generation when individuals carrying the recessive allele do not express the trait themselves but can pass it on to their offspring. This phenomenon occurs due to the inheritance of specific combinations of alleles in a family's genetic makeup. Here's an explanation with examples: **1. Recessive Trait Skipping a Generation:** For a recessive trait to appear to skip a generation, you need a specific genetic scenario: - **Generation 1 (Grandparents):** Suppose both grandparents (Generation 1) are carriers of a recessive allele for a particular trait but do not express that trait themselves. They are, in this case, heterozygous (Aa), meaning they have one dominant allele (A) and one recessive allele (a) for the trait. - **Generation 2 (Parents):** The grandparents (Generation 1) pass on their alleles to their children (Generation 2). Since each parent has one dominant allele (A) and one recessive allele (a), they are also carriers of the recessive trait but do not express it because the dominant allele masks the recessive allele. - **Generation 3 (Grandchildren):** If both parents from Generation 2 pass on their recessive alleles (a) to their offspring (Generation 3), and their offspring also inherits a recessive allele (a) from the other parent, then the grandchildren will be homozygous for the recessive trait (aa). In this case, the recessive trait will be expressed in Generation 3, even though it was not apparent in Generations 1 and 2. **Examples:** - **Example 1 (Albinism):** Albinism is a recessive genetic condition that causes a lack of pigment in the skin, hair, and eyes. If both parents are carriers of the albino allele (Aa), they may not exhibit albinism themselves but can have albino children (aa). - **Example 2 (Cystic Fibrosis):** Cystic fibrosis is another recessive genetic disorder. If both parents carry the cystic fibrosis allele (Aa), they may not have the condition but can have a child with cystic fibrosis (aa). **2. What is Meant by a Carrier:** A carrier is an individual who possesses one copy of a recessive allele for a particular trait or genetic disorder but does not express the trait themselves. Carriers are typically heterozygous for the gene in question, meaning they have one dominant allele and one recessive allele. They carry the recessive allele "in silence" because the presence of the dominant allele masks the effects of the recessive one. In the context of genetic disorders, carriers are often referred to as "heterozygous carriers." They can pass the recessive allele on to their offspring, potentially leading to the expression of the trait or disorder in the next generation if both parents are carriers or if the offspring inherits two recessive alleles. Being a carrier is important in the context of genetic counseling and family planning, as carriers of certain genetic disorders may want to assess the risk of passing the condition to their children.