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Ch. 2 - Transmission Genetics
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 2 - Transmission GeneticsProblem 31a
Chapter 2, Problem 31a

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?

Verified step by step guidance
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).
Step 2: Recognize that during meiosis, the alleles segregate equally into gametes. This means there is a 50% chance that the dominant allele (D) will be passed to her offspring.
Step 3: Consider the offspring of the woman. If the offspring inherits the dominant allele (D), they will also be heterozygous (Dd). If they inherit the recessive allele (d), they will be homozygous recessive (dd).
Step 4: For the grandchild to inherit the dominant allele (D), the offspring of the woman must pass it on. Since the offspring is heterozygous (Dd), there is again a 50% chance that the dominant allele (D) will be passed to the grandchild.
Step 5: Combine the probabilities. The probability of the dominant allele being passed from the woman to her offspring is 50%, and the probability of the offspring passing the dominant allele to the grandchild is also 50%. Multiply these probabilities to determine the overall likelihood of the dominant allele being inherited by the grandchild.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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. Therefore, an individual with at least one dominant allele will express the dominant phenotype, while the recessive phenotype only appears in individuals with two recessive alleles.
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Variations on Dominance

Heterozygosity

Heterozygosity refers to having two different alleles for a particular gene, such as Dd. In this case, the individual carries one dominant allele (D) and one recessive allele (d). This genetic makeup is crucial for understanding inheritance patterns, as it influences the probability of passing on alleles to offspring.
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Inversions

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two individuals. By organizing the possible gametes from each parent, it allows for the calculation of probabilities for different genotypes and phenotypes in the offspring. This tool is essential for determining the likelihood of inheriting specific alleles, such as the dominant allele in this scenario.
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Chi Square Analysis
Related Practice
Textbook Question

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 have either PKU or CF but not both?

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Textbook Question

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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Textbook Question

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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Textbook Question

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?

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Textbook Question

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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Textbook Question

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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