Post on 14-Sep-2020
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11-4 MeiosisLecture 4: Meiosis and
Gene Linkage (11-4/11-5)
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11-4 Meiosis
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Phases of Meiosis
Meiosis I
Prophase I Metaphase I Anaphase I Telophase I and
Cytokinesis
Interphase IMeiosis I
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Phases of Meiosis
DNA replicates → forming duplicate chromosomes
Interphase I
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Phases of Meiosis
1) Tetrads form
•Homologous chromosomes pair
•4 chromatids per tetrad
2) Crossing-over occurs
MEIOSIS I Prophase I
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11-4 Meiosis
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Phases of Meiosis
Crossing over = tetrads exchange portions of their chromatids
•produces new combinations of alleles
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Phases of Meiosis
1) Spindle fibers attach to the chromosomes.
2) Chromosomes line up along metaphase plate
MEIOSIS I Metaphase I
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Phases of Meiosis
MEIOSIS I Anaphase IThe fibers pull the
homologous chromosomes toward opposite ends of the cell.
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Phases of Meiosis
MEIOSIS I Telophase I and Cytokinesis1) Nuclear membranes
form.
2) The cell separates into two cells.
•chromosomes and alleles that are different from parent cells
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11-4 Meiosis
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Phases of Meiosis
Meiosis II
•The 2 cells produced by meiosis I now enter Meiosis II
•NO chromosome replication•Each of the cell’s chromosomes has 2 chromatids.
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11-4 Meiosis
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Phases of Meiosis
Meiosis II
Telophase II and
CytokinesisProphase II
Metaphase II Anaphase IITelophase I and Cytokinesis I
Meiosis II
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Phases of Meiosis
Cell prepares for division MEIOSIS IIProphase II
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Phases of Meiosis
The chromosomes line up in the center of cell.
MEIOSIS II Metaphase II
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Phases of Meiosis
The sister chromatids separate and move toward opposite ends of the cell.
MEIOSIS II Anaphase II
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11-4 Meiosis
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Phases of Meiosis
Meiosis II results in four haploid (N) daughter cells.
MEIOSIS II Telophase II and Cytokinesis
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Phases of Meiosis
What happens during the process of meiosis?
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Phases of Meiosis
Phases of Meiosis
Meiosis = •Number of chromosomes per cell is cut in half
•Separates the homologous chromosomes in a diploid cell
•2 Phases: Meiosis I and Meiosis II
•Results in 4 haploid cells
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Gamete Formation
Gamete FormationIn males, meiosis results in four equal-sized gametes called sperm.
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Gamete Formation
In females, one egg results and three polar bodies
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Principle of Gene Linkage:1. Each chromosome is a set of linked genes.
2. Chromosomes assort independently not individual genes.
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Gene maps
a) Map that shows the relative position of a gene on a chromosome.
b) The closer the genes are the less likely they will be separated during a crossing.
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Answer the following questions to summarize the lecture:
1. Describe the purpose and stages of meiosis.
2. Determine the stage crossing over occurs and why crossing over is important to the survival of our species.
3. Relate gene linkage to Mendel’s law of segregation and independent assortment.
4. Describe a gene map.
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