Biology Chapter 2.2. Meiosis I in Human Genetics

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Questions and Answers

What is the term used to describe the pairing of homologous chromosomes during prophase I?

Chiasma

Crossover

Tetrad

Synapsis (correct)

What is the primary purpose of genetic crossing over during meiosis?

To increase genetic diversity (correct)

To reduce the chromosome number

To ensure identical offspring

To enhance the chances of asexual reproduction

Sister chromatids undergo crossing over during meiosis.

False

Nondisjunction can lead to chromosomes having an incorrect number of copies in a gamete.

True Signup and view all the answers

What is the role of the synaptonemal complex during meiosis?

To hold homologous chromosomes together during synapsis. Signup and view all the answers

Define 'linkage' in genetics.

Linkage refers to the tendency for genes to be inherited together due to their proximity on a chromosome. Signup and view all the answers

During prophase I, the chromatin condenses into __________.

chromosomes Signup and view all the answers

During _____ I, homologous pairs align at the metaphase plate.

metaphase Signup and view all the answers

Match the following terms to their descriptions:

Tetrad = A group of four chromatids formed during synapsis Chiasma = The point of contact where crossing over occurs Crossover = The exchange of genetic material between homologous chromosomes Homologous chromosomes = Chromosomes that are similar in shape, size, and genetic content Signup and view all the answers

Match the stage of meiosis with its description:

Prophase I = Homologous chromosomes exchange genetic material Anaphase I = Homologous pairs separate Metaphase II = Chromosomes line up on the metaphase plate Telophase II = Nuclear membrane forms around each new nucleus Signup and view all the answers

How many chromatids are present after the S phase?

92 Signup and view all the answers

Crossing over can increase genetic variety in gametes.

True Signup and view all the answers

What unit is used to measure the distance between genes on a chromosome?

Centimorgans Signup and view all the answers

What major process occurs at the chiasmata during meosis I?

Crossing over Signup and view all the answers

Meiosis results in the creation of diploid daughter cells.

False Signup and view all the answers

What happens during anaphase I of meiosis?

Homologous chromosomes are separated and pulled to opposite poles of the cell. Signup and view all the answers

Homologous chromosomes are made up of one chromosome inherited from each __________.

parent Signup and view all the answers

During _____ II, sister chromatids are separated from one another.

meiosis Signup and view all the answers

What is the primary difference between sister chromatids and homologous chromosomes?

Sister chromatids are identical, while homologous chromosomes are not. Signup and view all the answers

Which of the following describes a key difference between meiosis and mitosis?

Meiosis involves crossing over; mitosis does not. Signup and view all the answers

Study Notes

Meiosis I Overview

Human genome consists of 23 homologous pairs of chromosomes, resulting in 46 chromosomes total.
Sister chromatids are identical DNA strands connected at the centromere, while homologous pairs are not identical and come from each parent.

Prophase I

Chromatin condenses into distinct chromosomes; spindle apparatus forms; nucleoli and nuclear membrane disappear.
Synapsis occurs, where homologous chromosomes intertwine to form tetrads consisting of four chromatids.
The synaptonemal complex holds homologous chromosomes together.
Crossing over occurs at chiasmata, allowing chromatids to exchange DNA, increasing genetic diversity.
Genetic recombination unlinks linked genes, enhancing variation in gametes, a crucial benefit of sexual reproduction.

Mapping Genes

The frequency of gene unlinking during crossing over helps in mapping the distance between genes on chromosomes, measured in centimorgans.
Each daughter cell from meiosis will possess a unique combination of alleles from maternal and paternal sources.
Crossing over maintains Mendel's second law of independent assortment, asserting that the inheritance of one allele does not affect others.

Metaphase I

Tetrads align at the metaphase plate with each chromosome attached to a separate spindle fiber via its kinetochore.
Unlike mitosis, where chromosomes align individually, homologous pairs line up across from each other in meiosis.

Anaphase I

Homologous pairs are separated during disjunction, upholding Mendel's first law of segregation.
Random distribution of homologous chromosomes to daughter cells occurs, ensuring genetic diversity.

Telophase I

Nuclear membrane forms around each new nucleus; chromosomes remain as sister chromatids connected at centromeres.
Each daughter cell is haploid, containing 23 chromosomes after homologous separation.
Cytokinesis occurs, followed by a potential interkinesis phase where chromosomes partially uncoil.

Nondisjunction Impact

Nondisjunction may occur during anaphase I or II, leading to gametes with abnormal chromosome numbers, which can result in conditions like Down syndrome and other syndromes caused by sex chromosome anomalies.

Meiosis II Overview

Meiosis II resembles mitosis, focusing on the separation of sister chromatids rather than homologous chromosomes.

Prophase II

Nuclear envelope dissolves, centrioles migrate to poles, and the spindle apparatus begins to form.

Metaphase II

Chromosomes align at the metaphase plate.

Anaphase II

Centromeres divide, separating sister chromatids, which are pulled to opposite poles by spindle fibers.

Telophase II

Nuclear membranes form around new nuclei, followed by cytokinesis, producing up to four haploid daughter cells from one gametocyte.
Oogenesis may result in fewer than four cells, particularly if an egg remains unfertilized after ovulation.

Key Concepts Comparison

Mitosis results in diploid cells (2n) maintaining chromosome number, while meiosis results in haploid cells (n), halving the chromosome count.
Meiosis occurs exclusively in sex cells, allows crossing over, and homologous chromosomes align on opposite sides of the metaphase plate.

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Description

This quiz focuses on the process of Meiosis I, emphasizing the role of homologous chromosomes and sister chromatids in the human genome. It addresses key terminology and the organization of chromosomes and chromatids post-S phase. Test your understanding of genetic variations and the mechanics of cellular division!