A man has six fingers on each hand and six toes on each foot. His wife and their daughter have the normal number of digits. Remember that extra digits is a dominant trait. What fraction of this couple's children would be expected to have extra digits?

검증된 단계별 안내

Understand that having extra digits is a dominant trait, meaning that only one copy of the dominant allele is needed for the trait to be expressed.

Determine the genotype of the man with extra digits. Since he has the trait, he could be either homozygous dominant (AA) or heterozygous (Aa). However, since his wife has the normal number of digits, she must be homozygous recessive (aa).

Consider the possible genotypes of the children. If the man is homozygous dominant (AA), all children will inherit at least one dominant allele (A) and thus have extra digits. If he is heterozygous (Aa), there is a 50% chance for each child to inherit the dominant allele (A) and have extra digits.

Use a Punnett square to visualize the possible genetic combinations. If the man is heterozygous (Aa), the Punnett square will show a 1:1 ratio of Aa to aa offspring, meaning 50% of the children will have extra digits.

Conclude that if the man is homozygous dominant (AA), all children will have extra digits. If he is heterozygous (Aa), half of the children are expected to have extra digits.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Dominant Trait

A dominant trait is one that is expressed in the phenotype even when only one copy of the gene is present. In genetics, dominant alleles mask the effects of recessive alleles, meaning that if a person inherits a dominant allele from one parent, the trait will be expressed. In this scenario, having extra digits is a dominant trait.

Genotype

Genotype refers to the genetic makeup of an individual, specifically the alleles they possess. For a dominant trait like extra digits, the genotype could be homozygous dominant (two dominant alleles) or heterozygous (one dominant and one recessive allele). The man with extra digits could be either, but his wife, with normal digits, is likely homozygous recessive.

Punnett Square

A Punnett Square is a tool used in genetics to predict the probability of offspring inheriting particular traits. By mapping the alleles of the parents, it helps visualize how traits are passed down. In this case, it can be used to determine the likelihood of the couple's children inheriting the dominant trait for extra digits, given the genotypes of the parents.