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Ch. 2 - Transmission Genetics
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoSanders 3rd EditionCh. 2 - Transmission GeneticsProblema 31b
Capitolo 2, Problema 31b

A woman expressing a dominant phenotype is heterozygous (Dd) for the gene.


What is the probability that two grandchildren of the woman who are first cousins to one another will each inherit the dominant allele?

Guida verificata passo dopo passo
1
Step 1: Understand the genetic makeup of the woman. She is heterozygous (Dd), meaning she has one dominant allele (D) and one recessive allele (d). Each of her children has a 50% chance of inheriting the dominant allele (D) and a 50% chance of inheriting the recessive allele (d).
Step 2: Determine the genetic makeup of the grandchildren. Since the grandchildren are first cousins, they inherit their alleles from different parents (the woman's children). Each parent has a 50% chance of passing on the dominant allele (D) to their child.
Step 3: Calculate the probability of one grandchild inheriting the dominant allele (D). This is a simple probability problem where the chance of inheriting the dominant allele from a heterozygous parent is 50%.
Step 4: Calculate the probability of the second grandchild (first cousin to the first grandchild) inheriting the dominant allele (D). Similarly, this is also a 50% chance since the second grandchild's parent is heterozygous.
Step 5: Combine the probabilities for both grandchildren inheriting the dominant allele. Since the events are independent (inheritance from one parent does not affect the other), multiply the probabilities: P(grandchild 1 inherits D) × P(grandchild 2 inherits D).

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Dominant and Recessive Alleles

In genetics, alleles are different forms of a gene. A dominant allele, represented by a capital letter (e.g., D), masks the effect of a recessive allele (e.g., d) when both are present. An individual with at least one dominant allele will express the dominant phenotype, while a recessive phenotype is only expressed when an individual has two recessive alleles.
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Variations on Dominance

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two individuals. It allows for the visualization of how alleles from each parent combine to produce offspring genotypes. By filling in the square with the possible gametes from each parent, one can easily determine the probabilities of inheriting specific alleles.
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Chi Square Analysis

Inheritance Patterns in Family Trees

Understanding inheritance patterns is crucial for predicting the likelihood of traits being passed down through generations. In this scenario, the woman (Dd) can pass either the dominant (D) or recessive (d) allele to her children. The probability of her grandchildren inheriting the dominant allele depends on the genotypes of their parents, who are the children of the woman, and their own genetic contributions.
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Phylogenetic Trees
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Domanda del libro di testo

A woman expressing a dominant phenotype is heterozygous (Dd) for the gene.


Draw a pedigree that illustrates the transmission of the dominant trait from the grandmother to two of her grandchildren who are first cousins.

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Domanda del libro di testo

A woman expressing a dominant phenotype is heterozygous (Dd) for the gene.


What is the probability that the dominant allele carried by the woman will be inherited by a grandchild?

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A male and a female are each heterozygous for both cystic fibrosis (CF) and phenylketonuria (PKU). Both conditions are autosomal recessive, and they assort independently.

What proportion of the children will be carriers of one or both conditions?

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An organism having the genotype AaBbCcDdEe is self-fertilized. Assuming the five genes assort independently, determine the following proportions:


Gametes that are expected to carry only dominant alleles.

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Dr. Ara B. Dopsis and Dr. C. Ellie Gans are performing genetic crosses on daisy plants. They self-fertilize a blue-flowered daisy and grow 100 progeny plants that consist of 55 blue-flowered plants, 22 purple-flowered plants, and 23 white-flowered plants. Dr. Dopsis believes this is the result of segregation of two alleles at one locus and that the progeny ratio is 1:2:1. Dr. Gans thinks the progeny phenotypes are the result of two epistatic genes and that the ratio is 9:3:4.

The two scientists ask you to resolve their conflict by performing chi-square analysis on the data for both proposed genetic mechanisms. For each proposed mechanism, fill in the values requested on the form the researchers have provided for your analysis.


Using any of the 100 progeny plants, propose a cross that will verify the conclusion you proposed in part (c). Plants may be self-fertilized, or one plant can be crossed to another. What result will be consistent with the 1:2:1 hypothesis? What result will be consistent with the 9:3:4 hypothesis?

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Two parents who are each known to be carriers of an autosomal recessive allele have four children. None of the children has the recessive condition. What is the probability that one or more of the children is a carrier of the recessive allele?

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