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Define Meiosis (more thorough explanation) (4pts)
- - the form of cell division by which gametes, with the number of chromosomes are produced
- - 2n —meiosis-> 4 n
- - Gametes (male + female) combine to form zygote (sexual reproduction) Ensuring differentiation and variability.
- - It has two division (meiosis I and meiosis II
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What is Meiosis 2 key outcomes, describe what the 2 outcomes are?
- 1) Reduction division - produces daughters with fewer chromosomes than the parent (2n —> n)
- 2) Recombination - chromosomes mix and cells have different genetic combinations than parent (variation)
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In mammal, where are the gametes produced?
who produces gametes for female and male? (2pts)
Are mitosis and meiosis similar?
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What happens in the G1 phase of Interphase? (3pts)
- - the (newly formed) cell growth period
- - a high amount of protein synthesis occurs and the cell grows (about double its original size
- - more organelles are produce and the volume of cytoplasm increases.
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What is the S phase of Interphase?
- Responsible for the synthesis of DNA copy (copies are made of paternal and maternal DNA producing sister chromatids)
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What is the G2 phase of Interphase?
-Rebuilds energy reserves, organelles and proteins necessary for cell division are produced
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What happens in Interphase I (4pts)
- - Similar to mitosis Interphase, but occurs in the germ cells (gametes reproducing)
- - Chromosomes replicate (S phase) and Cells grow (G1 and G2)
- - Each duplicated chromosomes consist of two identical sister chromatids attach at their centromere
- - Centriole pairs also replicated.
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Meiosis has two stages, Meiosis I and Meiosis II. Describe briefly what happens in those stages (2pts)
- Meiosis I - reduction division (2n —> n)
- Meiosis II - separation of chromosomes (to 2 chromatids)
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Define Crossing over (2pts)
- Crossing over is the process of two homologous non sister chromatids pair up with each other and exchange different segments of genetic information forming two recombinant chromosome sister chromatids.
- - segments of non sister chromatids (at specific locus) break and reattach to the other chromatid.
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What is aster fibers and who grows them
Aster fibers are grown by centrioles (along with microtubule spindle fibers). They position centrioles.
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What is Metaphase I? (4pts)
- - the shortest phase of meiosis
- - Spindle fibre attaches to centromere
- - tetrad align on the metaphase plate (equatorial plate)
- - independent assortment occurs
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What is independent assortment, what does it result to and how does this affect anaphase.
When does independent assortment occur?
During Metaphase I of Meiosis I, Independent assortment occurs, it is the random orientation of paternal chromosome and maternal chromosome (/homologous chromosomes) at the equatorial plate.
- Independent assortment results into variation
- The random orientation describes how pairs of chromosomes are separate during Anaphase I
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What is Anaphase I? (2pts)
- - Spindle fibres shortens, homologous chromosome separate and move towards the pole
- - Chromatids remain attach to their centromeres (chromosomes remain double stranded)
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What is Telophase I? (3pts)
- - Each pole has haploid set of chromosomes
- - Nuclear membrane begins to form around chromosomes and spindle fibres disappear
- - Cytokinesis occurs and two haploid daughters cells are formed
- - Each daughter cell is different/ has a different pair of chromosomes.
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What happens in Meiosis II? (4pts)
- - No more interphase (or very short - no more DNA replication)
- - Meiosis II is very similar to mitosis
- - Occurs at the same time in each daughter cell
- - Centromere binding pair of chromatids will break, the chromatids will move to opposite poles.
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What happens in Prophase II?
The same as Prophase in mitosis
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What happens in Metaphase I?
the same as Metaphase in mitosis
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What happens in anaphase II? (2pts)
- - The same as Anaphase in mitosis
- - sister chromatids separate
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What happens in Telophase II (4pts)
- - the same as Telophase in mitosis
- - nuclear membrane forms
- -cytokinesis
- - 4 haploid gametes cells are produce from each mitotic division.
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Why is Variation (Genetic recombination) important and what do each cell have? (2pts)
- - Variation is important to population as it is the raw material for natural selection
- - Each cell has one chromosome from father, and one chromosome from mother
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Variation is caused by what three events?
- - Independent assortment
- - Crossing Over
- - Nondisjunction disorder
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Define disjunction disorder (4pts)
- - two homologous chromosomes goes to the same pole during anaphase I or II. One daughter cell has an extra chromosome, the other is missing one
- - Cells that have too much information, or not enough = problems
- - Nondisjunction can produce
- :one gamete cell with 22 chromosomes
- : one gamete cell with 24 chromosomes
- - Once a zygote with an abnormal number of chromosomes begins to divide; each cell of the body will contain an abnormal number of chromosomes
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Define Monosomy
Zygote contains 45 chromatids. one set of homologous chromatid pairing will not be complete (eg. Turner Syndrome)
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Define Trisomy (2pts)
- - The presence of 3 homologous chromatids in every cell
- - Zygote contains 47 chromatids (not 46), one pair will have three chromatids instead of normal pair
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