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Ch. 3 - Cell Division and Chromosome Heredity
All textbooksSanders 3rd EditionCh. 3 - Cell Division and Chromosome HeredityProblem 7
Chapter 3, Problem 7

Explain how the behavior of homologous chromosomes in meiosis parallels Mendel's law of segregation for autosomal alleles D and d. During which stage of M phase do these two alleles segregate from one another?

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1
span>Understand Mendel's law of segregation: It states that alleles segregate from each other during the formation of gametes, ensuring that each gamete carries only one allele for each gene.</span
span>Recognize that homologous chromosomes are pairs of chromosomes containing the same genes but possibly different alleles, one inherited from each parent.</span
span>During meiosis, homologous chromosomes undergo a process called synapsis in prophase I, where they pair up closely along their lengths.</span
span>In anaphase I of meiosis, homologous chromosomes are pulled apart to opposite poles of the cell, effectively segregating the alleles they carry (e.g., D and d) into different daughter cells.</span
span>This segregation of homologous chromosomes during anaphase I parallels Mendel's law of segregation, as it ensures that each gamete receives only one allele of each gene.</span

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Key Concepts

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

Homologous Chromosomes

Homologous chromosomes are pairs of chromosomes in a diploid organism, one inherited from each parent. They carry the same genes at the same loci but may have different alleles. During meiosis, these chromosomes undergo pairing and recombination, which is crucial for genetic diversity. Understanding their behavior is essential for grasping how alleles segregate during gamete formation.
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Mendel's Law of Segregation

Mendel's Law of Segregation states that during the formation of gametes, the two alleles for a trait separate from each other so that each gamete carries only one allele for each gene. This principle explains how offspring inherit one allele from each parent. The law is illustrated during meiosis when homologous chromosomes are separated, ensuring that each gamete receives only one allele from each gene pair.
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Meiosis and M Phase

Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in four haploid gametes. The segregation of alleles occurs during the M phase of meiosis, specifically in Anaphase I, when homologous chromosomes are pulled apart to opposite poles of the cell. This stage is critical for ensuring that each gamete receives a unique combination of alleles, reflecting Mendel's law.
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Related Practice
Textbook Question

A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.

Draw a pedigree of this family, including the woman, the man, their siblings, parents, and grandparents.

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Textbook Question

A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.

On the pedigree, write the genotypes (GG, Gg, or gg) for each person who has been tested or for whom you can deduce a genotype. If a genotype cannot be determined completely, list the alleles you know or deduce must be present.

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Textbook Question

A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.

Explain why you are able to assign genotypes to the man's parents despite their not being tested.

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Textbook Question

Suppose crossover occurs between the homologous chromosomes in the previous problem. At what stage of M phase do alleles D and d segregate?

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Textbook Question

If a man and a woman are each heterozygous carriers of a mutation causing a disease on the RUSP list, what do you think are the three or four most important factors they should consider in their decision making about having children?

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Textbook Question

Suppose a man and a woman are each heterozygous carriers of a mutation causing a fatal hereditary disease not on the RUSP list. Prenatal genetic testing can identify the genotype of a fetus with regard to this disease and can identify fetuses with the disease. What do you think are the three or four most important factors this couple should consider in their decision making about having children?

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