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Ch. 14 - Mendel and the Gene Idea
Campbell - Campbell Biology 11th Edition
Urry11th EditionCampbell BiologyISBN: 9789357423311Not the one you use?Change textbook
All textbooksUrry 11th EditionCh. 14 - Mendel and the Gene IdeaProblem 13
Chapter 14, Problem 13

The pedigree below traces the inheritance of alkaptonuria, a biochemical disorder. Affected individuals, indicated here by the colored circles and squares, are unable to metabolize a substance called alkapton, which colors the urine and stains body tissues. Does alkaptonuria appear to be caused by a dominant allele or by a recessive allele? Fill in the genotypes of the individuals whose genotypes can be deduced. What genotypes are possible for each of the other individuals?

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Examine the pedigree chart to identify the pattern of inheritance. Look for whether the disorder appears in every generation or skips generations, which can indicate whether the allele is dominant or recessive.
Identify the affected individuals in the pedigree. If alkaptonuria is caused by a recessive allele, affected individuals will have two copies of the recessive allele (homozygous recessive). If it is caused by a dominant allele, affected individuals will have at least one copy of the dominant allele.
Determine the genotypes of the parents of affected individuals. If both parents are unaffected but have affected children, the disorder is likely recessive, and both parents are carriers (heterozygous).
Fill in the genotypes of individuals whose genotypes can be deduced based on their phenotype and the genotypes of their parents. Use symbols such as 'AA', 'Aa', or 'aa' to represent homozygous dominant, heterozygous, and homozygous recessive genotypes, respectively.
Consider the possible genotypes for individuals whose genotypes cannot be directly deduced. For unaffected individuals, they could be homozygous dominant or heterozygous if the disorder is recessive. If the disorder is dominant, unaffected individuals are homozygous recessive.

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Key Concepts

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

Pedigree Analysis

Pedigree analysis involves examining family trees to understand the inheritance patterns of specific traits or disorders. It helps determine whether a trait is dominant or recessive by observing how it appears across generations. Key symbols include circles for females, squares for males, and shading to indicate affected individuals.
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Pedigrees

Dominant vs. Recessive Alleles

Dominant alleles express their traits even if only one copy is present, while recessive alleles require two copies to manifest. In genetic disorders, understanding whether a condition is caused by a dominant or recessive allele is crucial for predicting inheritance patterns and deducing genotypes from pedigrees.
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Dominant vs. Recessive Alleles

Genotype Deduction

Genotype deduction involves determining the genetic makeup of individuals based on observable traits and inheritance patterns. In pedigrees, this requires analyzing the presence or absence of a disorder and using known inheritance rules to infer possible allele combinations for each individual, especially those with known phenotypes.
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Genotype & Phenotype
Related Practice
Textbook Question

In 1981, a stray black cat with unusual rounded, curled-back ears was adopted by a family in California. Hundreds of descendants of the cat have since been born, and cat fanciers hope to develop the curl cat into a show breed. Suppose you owned the first curl cat and wanted to develop a true-breeding variety. How would you determine whether the curl allele is dominant or recessive? How would you obtain true-breeding curl cats? How could you be sure they are true-breeding?

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Textbook Question

In tigers, a recessive allele of a particular gene causes both an absence of fur pigmentation (a white tiger) and a cross-eyed condition. If two phenotypically normal tigers that are heterozygous at this locus are mated, what percentage of their offspring will be cross-eyed? What percentage of cross-eyed tigers will be white?

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Textbook Question

In maize (corn) plants, a dominant allele I inhibits kernel color, while the recessive allele i permits color when homozygous. At a different locus, the dominant allele P causes purple kernel color, while the homozygous recessive genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the offspring?

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Textbook Question

Imagine that you are a genetic counselor, and a couple planning to start a family comes to you for information. Charles was married once before, and he and his first wife had a child with cystic fibrosis. The brother of his current wife, Elaine, died of cystic fibrosis. What is the probability that Charles and Elaine will have a baby with cystic fibrosis? (Neither Charles, Elaine, nor their parents have cystic fibrosis.)

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