Genetics and Inheritance: TEAS Practice Question with Answer & Explanation

Understanding Inheritance Patterns and Generation Skipping

In the study of genetics for the TEAS 7, understanding how traits travel through generations is essential. When a disease or trait does not appear in every generation—often referred to as 'skipping a generation'—it usually points to a specific type of genetic mechanism.

Why Autosomal Recessive is the Correct Answer

In autosomal recessive inheritance, an individual must inherit two copies of the mutated gene (one from each parent) to express the disease. If an individual has only one copy, they are a 'carrier' but do not show symptoms.

• The 'Skip' Mechanism: Two carriers (who appear healthy) can pass the recessive gene to their child. If the child receives the recessive allele from both parents, they will manifest the disease. This explains why the disease can vanish for one or two generations (carried silently by heterozygotes) and suddenly reappear.

Analysis of Incorrect Options

• Autosomal Dominant: In this pattern, you only need one copy of the gene to express the disease. Therefore, if a child has the condition, at least one parent must also have the condition. Dominant traits generally appear in every generation and do not 'hide' or skip.
• Y-linked Inheritance: These traits are passed strictly from father to son via the Y chromosome. If a father has the trait, all his sons will have it; if he doesn't, none will. It does not skip generations in a way that would reappear in a grandson without the father having it.
• Mitochondrial Inheritance: This is passed exclusively from the mother to all her children. Since mitochondrial DNA is inherited directly from the egg, it typically shows a very consistent maternal line of expression rather than skipping generations through carriers.

TEAS Concept: Genotypes and Phenotypes

The TEAS exam expects you to distinguish between a genotype (the genetic makeup, like Aa) and a phenotype (the physical expression, like 'brown eyes'). In recessive disorders, the phenotype 'healthy' can mask the genotype 'carrier,' which is why the condition can reappear after being hidden.

Memory Tip for the Exam

Think 'Recessive = Retiring.' Recessive traits are shy; they hide in the background (carriers) and only come out when they meet another shy (recessive) partner. Dominant traits are 'Demanding'—if they are present at all, you will see them in every generation!