Ch. 13 - Meiosis

Freeman - Biological Science 8th Edition

Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook

Freeman 8th Edition

Ch. 13 - Meiosis

Problem 9

Chapter 13, Problem 9

Meiosis results in independent assortment of egg-derived and sperm-derived chromosomes. If 2𝑛=4 for a given organism, and there is no crossing over, what is the chance that a gamete produced by this diploid organism will receive only sperm-derived chromosomes? In domestic cats, 2𝑛=38. What is the chance that a cat gamete contains only egg-derived chromosomes?

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Identify the number of chromosomes in a haploid set for the given organism. Since 2n=4, the haploid number n=2.

Understand that each gamete receives one of each chromosome pair, and each chromosome can be either egg-derived or sperm-derived. The total number of combinations of chromosome origins in the gametes is 2^n.

Calculate the probability of all chromosomes in a gamete being sperm-derived. Since each chromosome independently has a 1/2 chance of being sperm-derived, the probability for all chromosomes being sperm-derived is (1/2)^n.

Apply the same logic to the domestic cat scenario where 2n=38, thus n=19. Calculate the probability of all chromosomes in a cat gamete being egg-derived using the formula (1/2)^n.

Interpret the results to understand the rarity of a gamete receiving only sperm-derived or only egg-derived chromosomes, especially as the number of chromosomes increases.

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Key Concepts

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

Meiosis

Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in four genetically diverse gametes. It consists of two sequential divisions: meiosis I and meiosis II. During meiosis, homologous chromosomes are separated, and independent assortment occurs, which contributes to genetic variation. This process is crucial for sexual reproduction, as it ensures that offspring receive a mix of genetic material from both parents.

Independent Assortment

Independent assortment is a principle of genetics that describes how different genes independently separate from one another when reproductive cells develop. In meiosis, the orientation of homologous chromosome pairs during metaphase I determines which chromosomes are distributed to gametes. This means that the combination of chromosomes in gametes is random, leading to a variety of genetic combinations in offspring, which is essential for evolution and adaptation.

Gamete Formation and Probability

Gamete formation involves the production of sperm and egg cells through meiosis, where each gamete receives a random assortment of chromosomes. The probability of a gamete containing only chromosomes from one parent can be calculated based on the number of chromosome pairs. For an organism with 2n=4, there are two pairs of chromosomes, leading to a 1 in 4 chance for a gamete to receive only one parent's chromosomes. In domestic cats with 2n=38, the same principle applies, but the calculations involve more chromosome pairs.

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Textbook Question

If you followed a woman's cells through meiosis, at what stage of meiosis would the amount of DNA in one of these cells be equal to the amount of DNA in one of her G1 phase (before DNA replication) kidney cells?

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Textbook Question

Norway rats have 42 chromosomes in their diploid cells. If such a cell enters meiosis, how many chromosomes and double-helical molecules of DNA will be present in each daughter cell at the end of meiosis II?

a. 21 chromosomes and 21 double-helical DNA molecules

b. 21 chromosomes and 42 double-helical DNA molecules

c. 42 chromosomes and 42 double-helical DNA molecules

d. 42 chromosomes and 84 double-helical DNA molecules

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Textbook Question

Triploid (3n) watermelons, which are seedless, are produced by crossing a tetraploid (4n) strain with a diploid (2n) plant. Explain why this mating produces a triploid individual.

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Textbook Question

A species of rotifer, a small freshwater invertebrate, lost the ability to reproduce sexually millions of years ago. A remarkable feature of its life cycle is the ability to withstand dry conditions. When the rotifer's environment dries out, so does the rotifer, and it can be blown to a new area. Rotifers that land in water will rehydrate and resume an active life. A major pathogen of these rotifers is a species of fungus that cannot survive drying. Some scientists hypothesize that drying rids the rotifers of this pathogen. Design an experimental study to test this hypothesis.

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Textbook Question

A species of rotifer, a small freshwater invertebrate, lost the ability to reproduce sexually millions of years ago. A remarkable feature of its life cycle is the ability to withstand dry conditions. When the rotifer's environment dries out, so does the rotifer, and it can be blown to a new area. Rotifers that land in water will rehydrate and resume an active life. A major pathogen of these rotifers is a species of fungus that cannot survive drying. Some scientists hypothesize that drying rids the rotifers of this pathogen. Why might the ability to withstand drying reduce any potential advantage of sexual reproduction in this rotifer species?

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Textbook Question

Select True or False for each statement.

T/FLinked genes are always inherited together.

T/FGenetic map distances measure the number of nucleotides between a pair of genes.

T/FThe farther apart genes are on a chromosome, the more likely there is to be a crossover between these genes during meiosis.

T/FCrossing over occurs between genes on different homologs of a homologous chromosome pair.

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