Meiosis & Sexual Life Cycle Chapter 13. Slide 2 of 20 AP Essential Knowledge Essential knowledge...
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Transcript of Meiosis & Sexual Life Cycle Chapter 13. Slide 2 of 20 AP Essential Knowledge Essential knowledge...
![Page 1: Meiosis & Sexual Life Cycle Chapter 13. Slide 2 of 20 AP Essential Knowledge Essential knowledge 3.A.2: In eukaryotes, heritable information is passed.](https://reader036.fdocuments.us/reader036/viewer/2022062722/56649f295503460f94c42279/html5/thumbnails/1.jpg)
Meiosis & Sexual Life Cycle
Chapter 13
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Slide 2 of 20
AP Essential Knowledge
Essential knowledge 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization.
b. Mitosis passes a complete genome from the parent cell to daughter cells.4. Mitosis is a continuous process with observable structural
features along the mitotic process. Students must know the order of the processes
(replication, alignment, separation).
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AP Essential Knowledge
c. Meiosis, a reduction division, followed by fertilization ensures genetic diversity in sexually reproducing organisms. Gametes have a haploid set of chromosomes Homologous chromosomes are paired and then
separated ensuring haploid set of chromosomes During meiosis (Prophase I), homologous chromatids
exchange genetic material via a process called “crossing over” which increases genetic variation in the resultant gametes.
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Homologous Chromosomes
2 chromosomes that have same length, centromere position, and staining pattern
Autosomes Non-sex chromosomes Chromosomes that do not determine gender
Sex Chromosomes Chromosomes that determine gender
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Chromosomes
Human somatic cell = 44 autosomes + 2 sex chromosomes
Human gamete = 22 autosomes + 1 sex chromosome
Sex Chromosomes Can be XX or XY XX = Homologous chromosomes XY = Not homologous chromosomes
Egg must contain X, sperm may contain X & Y Hence, males determine the gender of offspring
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Unnecessary Censorship
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Slide 7 of 20
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Meiosis
2 Stages of Meiosis Meiosis I & Meiosis II
Much of Meiosis resembles Mitosis
Chromosomes are replicated only once Before Meiosis I
4 daughter cells are produced
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Meiosis: An Overview
Assume that an organism has:1 Homologous Pair = 2 Chromosomes(Diploid cell – 2n)
STEP 1: Each of the chromosomes is replicated in Interphase
STEP 2: Chromosome pairs of copies separate in Meiosis I(Haploid cell – n)BUT 2 copies of each one
STEP 3: Each of the copies (sister chromatids) in a cell separates creating 4 haploid cells(Haploid cell with only 1 copy)
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Slide 10 of 20
What is different in Prophase I?
What is different in Anaphase I?
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Meiosis I
Prophase I Longest phase Homologous pairs align Crossing-Over may occur Synapsis – pairing of homologous pairs tied tightly
together Tetrads form (4 chromosomes = 2 pairs)
Each tetrad has 1 or more chiasmata Criss-crossed regions where crossing over has occurred
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Meiosis I (Page 2)
Metaphase I Tetrads are aligned at the metaphase plate Each chromosome pair faces a pole
Anaphase I Homologous chromosomes (composed of 2 copies of
each chromosome called chromatids) are pulled apart
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Slide 13 of 20
What is different between Meiosis I & II?
This division is sometimes called the Mitotic division, why?
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Meiosis vs. Mitosis
Tetrads align in Prophase I, Chromosomes align in Prophase mitosis
Chromosomes position @ metaphase plate (Mitosis) Tetrads position @ metaphase plate (Meiosis)
Homologues separate in Meiosis I
Sister chromatids separate in Meiosis II & Mitosis
Crossing over = Meiosis NOT mitosis
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Mitosis Meiosis
DNA replicates in interphase
1 division
No synapsis
2 Diploid cellsGenetically identical cells
Responsible for:-- Zygote growth into multicellular organism
DNA only replicates in Pre-meiotic interphase
2 divisions
Synapsis occurs during prophase I forming tetrads
Crossing over occurs now
4 haploid cellsGenetically different cells
Responsible for:-- Gamete production-- Genetic variation
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Genetic Diversity
The reason for meiosis + sexual reproduction
Mutations are the original source of genetic diversity
3 main sources of Genetic Diversity
1. Independent Assortment of Chromosomes
2. Crossing Over
3. Random Fertilization
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Each daughter cell has a 50% chance of getting maternal chromosome (or its copy)
Similarly, 50% chance of getting paternal chromosome (or its copy)
Independent assortment - each chromosome is positioned independently of the other chromosomes
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When homologous pairs are formed in Prophase I, a recombinant chromosome can be formed -- A chromosome that has DNA from 2 different parents
2 chromosome segments trade places (cross over) producing chromosomes with new combos of maternal & paternal genes
1-3 times per chromosome in humans
Increases genetic variation
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Random Fertilization
Egg + sperm cells are genetically different from parent cells
Their combination (fertilization) increases variation even more