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28 Cards in this Set
- Front
- Back
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Asexual vs. sexual reproduction
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Asexual:
• one parent • genetically identical offspring • mitosis Sexual: • 2 parents • genetically variable offspring • sperm and egg made by meiosis |
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What contributes to genetic variation in sexual reproduction?
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1) cross-over AKA genetic recombination
2) independent assortment of chromosomes 3) random fertilization |
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Independent assortment
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Homologous pairs orient on the metaphase plate, so that the poles can receive either paternal or maternal chromosomes
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Haploid
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• n = 23
• one set of chromosomes • gametes |
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Diploid
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• 2n = 46
• two sets of chromosomes paired to one another • somatic cells |
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Gametes
What is it? Haploid or diploid? Undergoes mitosis or meiosis? |
• Sperm or egg
• haploid • undergoes meiosis |
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Zygote
What is it? Haploid or diploid? Undergoes mitosis or meiosis? |
• a fertilized egg
• diploid • undergoes mitosis |
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Why does meiosis reduce the number of chromosomes by half?
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So that when the gametes sperm and egg join as a zygote, the zygote will have 46 chromosomes
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Karyotype
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• The particular set of 23 homologous chromosome pairs in an individual
• in diploid cells |
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Autosomes
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• The first 22 pairs of a karyotype
• contains the genes that code for the body's proteins |
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Sex chromosomes
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• pair 23 of a karyotype
• contains the genes that code for sex characteristics |
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What determines the sex of the baby?
4 |
The sperm
• the egg always has an X chromosome • the sperm can either have and X or Y chromosome • XX = female • XY = male |
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Gonads
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• Ovaries and testis
• where meiosis occurs to produce gametes (sperm and egg) |
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Germ cells
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• diploid cells
• become haploid gametes through meiosis • located within the gonads |
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What is the difference between meiosis I and meiosis II?
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Meiosis I:
• s phase produces sister chromatids • prophase I pairs homologues • anaphase I divides # of chromosomes in half: homologues separated, sister chromatids remain intact • results in 2 daughter cells Meiosis II: • no s phase • anaphase II splits separates sister chromatids • results in 4 daughter cells |
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After which division are cells genetically variable, and after which are they identical?
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During meiosis I daughter cells are identical
During meiosis II daughter cells are genetically variable |
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Homologous pairs
Similarities/differences Also are... |
2 chromosomes of the:
1) Same size 2) Same banding pattern 3) Same genes 4) Different alleles Are non-sister chromatids (not identical to one another) |
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Homologous pairs vs. sister chromatids
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Homologous pairs:
• 1 chromosome from each parent • the same except for alleles Sister chromatids: • identical copy of a chromosome |
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Synapsis
When does this occur? Does this occur in mitosis? |
• When homologues pair up
• Occurs during prophase I • Does not occur during mitosis |
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Synaptonemal complex
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• meiosis-specific cohesin proteins that glue homologues together
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Tetrad
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• when homologous pairs pair up, they are in the form of sister chromatid b/c chromosomes previously replicated in S phase
• this forms a structure of 4 chromosomes |
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Crossing over
What? Alters... Adds to... Occurs when? |
• when homologues/non-sister chromatids of a tetrad exchange genetic information
• sister-chromatids are no longer identical • adds to genetic variation • occurs during synapsis in prophase |
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Chiasmata (pl.) / chiasma (s.)
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The sites of crossing over on homologous pairs
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Metaphase I
What occurs Difference from mitosis |
• Homologous pairs line up at the metaphase plate
• in contrast to mitosis, where sister chromatids line up |
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Anaphase I
What occurs (2) Difference from mitosis |
• homologous pairs are pulled to opposite poles
• sister chromatids, still attached to one another, are pulled to the same pole • in contrast to mitosis, where sister chromatids are pulled to opposite poles |
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Telophase I
Difference from mitosis (3) |
In contrast to mitosis
• sister chromatids together in the 2 daughter cells • each daughter cell has half the number of chromosomes as the parent cell |
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Separation of chromosomes in meiosis II:
Occurs as in meiosis I or as in mitosis? What is the 1 difference it has to this? |
Occurs as in mitosis, except that the cell did not have a second S phase and so haploid cells are produced
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How many daughter cells are produced in meiosis?
Are they identical or variable? |
4 genetically variable cells
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