Chapter 10 Sexual Reproduction & Genetics Part 1: Meiosis.
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Transcript of Chapter 10 Sexual Reproduction & Genetics Part 1: Meiosis.
![Page 1: Chapter 10 Sexual Reproduction & Genetics Part 1: Meiosis.](https://reader035.fdocuments.net/reader035/viewer/2022062309/5697bff51a28abf838cbda9e/html5/thumbnails/1.jpg)
Chapter 10 Sexual Reproduction
& GeneticsPart 1: Meiosis
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Concepts for Concepts for ReviewReview• Chromatin is the relaxed form of
DNA• Chromosome is the coiled form of
DNA• Sister chromatids are identical copies
of DNA (after S-phase/replication)
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Key Terms Key Terms • Homologous chromosomes are
chromosomes that make up a pair, one from each parent– Not necessarily identical but…– Are the same length– Have the same genes
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Key Terms Key Terms • Diploid refers to complete
chromosome sets in a cell (or 2N)– N= the number of chromosomes in a
gamete (sex cell)– N chromosomes from the female
parent + N chromosomes from the male parent= 2N
– For humans, 2N = 46
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Key Terms Key Terms • Haploid refers to single
chromosomes in a cell (or N)– One-half of the 2N set (the maternal
N or the paternal N)– Gametes (i.e. sperm, egg sex cells) are
haploid cells– For humans, N = 23
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Bottom Line
• diploid means that there are the full number of chromosomes where as haploid means that there are half the number of chromosomes.
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Key Terms Key Terms • Meiosis is a type of cell division
that reduces the number of chromosomes – Forms gametes (i.e. sex cells)– Occurs in the reproductive structures
of organisms that reproduce sexually– Occurs in 2 consecutive cell divisions:
meiosis I and meiosis II
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Before meiosis Before meiosis Interphase occurs….Interphase occurs….• Replication of DNA occurs.• Chromosomes Condense
Sounds familiar right???
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Meiosis I: Meiosis I: “Reduction “Reduction Division”Division” Reducing
2N cells
to…
N cells
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PROPHASE I• Homologous
chromosomes pair up• Crossing over occurs• Nuclear envelope
breaks down• Spindles form
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Crossing Over
• Chromosomal segments (genetic information) are exchanged between a pair of homologous chromosomes
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METAPHASE I
• Spindle fibers attach to the centromeres
• Homologous Chromosomes Line up at the equator
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ANAPHASE I
• Homologous chromosomes separate and move to the opposite poles of the cell
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TELOPHASE I
• The cell divides• The result is two
daughter cells. • Each daughter cell is
haploid.• The daughter cells are
not genetically identical
**During Telophase I Cytokinesis occurs at the same time!!**
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Meiosis II: “Mitotic Meiosis II: “Mitotic Division”Division”
Separatin
g sister
chromatid
s
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• Nucleus breaks up• Spindles form and
attach to centromere
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• Sister chromatids randomly align at middle of cell
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• Sister chromatids separate
• Chromosomes move to opposite poles of cell
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• Cells divide• 4 haploid
daughter cells result
• Each cell is genetically different
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Summary of Key Summary of Key ConceptsConcepts• Chromosomes contain genes (humans
have 46 chromosomes or 23 homologous pair)
• Homologous chromosomes may contain different forms of the same genes
• Meiosis reduces chromosome # by ½ and results in sex cells (gametes)
• Crossing-over increasing genetic variation
Click here for detailed animation of meiosis
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which set of chromatids illustrates the result of a single crossover of the homologous chromosomes?