Ch. 2 - Transmission Genetics

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

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Sanders 3rd Edition

Ch. 2 - Transmission Genetics

문제 21b

2장, 문제 21b

The accompanying pedigree shows the transmission of a phenotypic character. Using B to represent a dominant allele and b to represent a recessive allele,

Give the genotype(s) possible for each member of the family, assuming the trait is autosomal recessive.

검증된 단계별 안내

Examine the pedigree and identify individuals who express the autosomal recessive trait. These individuals must have the genotype

b b

, as they need two copies of the recessive allele to express the trait.

Determine the genotypes of the parents of individuals with the

b b

genotype. Since the trait is autosomal recessive, each parent must have at least one recessive allele (

b

) to pass it on. Their genotypes could be either

B b

b b

For individuals who do not express the trait, analyze their relationship to affected individuals. If they are offspring of parents with

B b

genotypes, their genotype could be

B B

B b

, or

b b

. However, if they do not express the trait, they cannot be

b b

Use the inheritance pattern to deduce the genotypes of siblings and other relatives. For example, siblings of affected individuals who do not express the trait are likely heterozygous (

B b

) if both parents are carriers.

Assign possible genotypes to each family member based on the above deductions, ensuring consistency with the autosomal recessive inheritance pattern. Double-check that individuals expressing the trait have

b b

genotypes and unaffected individuals have either

B B

B b

genotypes.

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주요 개념

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

Autosomal Recessive Inheritance

Autosomal recessive inheritance occurs when a trait is expressed only when an individual has two copies of the recessive allele (bb). If an individual has one dominant allele (B), the dominant trait will be expressed, masking the recessive trait. This means that carriers (Bb) do not show the phenotype but can pass the recessive allele to their offspring.

Genotype vs. Phenotype

Genotype refers to the genetic makeup of an individual, specifically the alleles they possess (e.g., BB, Bb, or bb), while phenotype is the observable expression of that genotype (e.g., the physical trait). Understanding the distinction is crucial for determining the possible genotypes of family members based on their phenotypic traits in the pedigree.

Pedigree Analysis

Pedigree analysis is a diagrammatic method used to trace the inheritance of traits through generations in a family. It helps identify patterns of inheritance, such as whether a trait is dominant or recessive, by analyzing the phenotypes of family members. This analysis is essential for deducing the possible genotypes of individuals based on their relationships and expressed traits.

The accompanying pedigree shows the transmission of a phenotypic character. Using B to represent a dominant allele and b to represent a recessive allele,Give the genotype(s) possible for each member of the family, assuming the trait is autosomal recessive.