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Ch. 14 - Mendel and the Gene
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263당신이 사용하는 게 아니라요?교과서 변경
14장, 문제 7

In flies, small wings are recessive to normal wings. If a cross between two flies produces 8 small-wing offspring and 28 normal-wing offspring, what are the most likely genotypes of the parents? (Use S to represent the normal-wing allele and s to represent the short-wing allele.)

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Step 1: Understand the inheritance pattern. The problem states that small wings are recessive to normal wings. This means that the allele for normal wings (S) is dominant, and the allele for small wings (s) is recessive. For a fly to have small wings, it must inherit two recessive alleles (ss).
Step 2: Analyze the offspring ratio. The cross produces 8 small-wing offspring and 28 normal-wing offspring. Calculate the ratio of small-wing to normal-wing offspring: 8 small-wing : 28 normal-wing. Simplify this ratio to determine the proportion of phenotypes.
Step 3: Use the phenotypic ratio to infer the genotypes of the parents. A 3:1 ratio of dominant to recessive phenotypes is typical for a monohybrid cross where both parents are heterozygous (Ss). This is because heterozygous parents produce offspring with the following genotypic ratios: 1 SS (normal wings), 2 Ss (normal wings), and 1 ss (small wings).
Step 4: Confirm the genotypes of the parents. If both parents are heterozygous (Ss), their offspring would include 75% normal-wing flies (SS and Ss) and 25% small-wing flies (ss), which matches the observed ratio of 28 normal-wing to 8 small-wing offspring.
Step 5: Conclude that the most likely genotypes of the parents are Ss (heterozygous for normal wings), as this explains the observed phenotypic ratio in the offspring.

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주요 개념

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Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through generations based on the principles established by Gregor Mendel. It involves understanding dominant and recessive alleles, where dominant alleles mask the expression of recessive ones. In this case, the normal-wing allele (S) is dominant over the small-wing allele (s), influencing the phenotypic ratios observed in offspring.
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가이드 코스
04:26
Mendelian and Population Genetics

Genotype and Phenotype

The genotype refers to the genetic makeup of an organism, while the phenotype is the observable physical or biochemical characteristics resulting from the genotype. In this scenario, the phenotypes of the offspring (small and normal wings) provide clues about the genotypes of the parent flies, allowing us to deduce their genetic combinations based on the observed ratios.
추천 영상:
06:36
Genotype & Phenotype

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two organisms. It helps visualize the possible combinations of alleles from each parent, allowing for the calculation of expected phenotypic ratios. By applying a Punnett square to the given offspring ratios, we can infer the most likely genotypes of the parent flies involved in the cross.
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01:37
Punnett Squares
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