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Bio > Meiosis Review > Flashcards

Meiosis Review Flashcards

1
Q

what is meiosis

A
  • form of cell division by which gametes: with 1/2 the number of chromosomes are produced
  • meiosis is sexual reproduction with 2 divisions

(SPERM-23)+(EGG-23)=(ZYGOTE-46)

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2
Q

Sex cells divide to

A

produce gametes (sperm or egg), gametes have 1/2 the number of chromosomes,

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3
Q

where does meiosis occur

A

in the gonads (testes or ovaries)

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4
Q

male (sperm) process

A

spermatogenesis- production of 4 haploid sperm cells

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5
Q

female (ovary) process

A

oogenesis- production of one egg and 3 polar bodies that die and are reabsorbed/recycled by the body

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6
Q

INTERPHASE 1

A
  • chromosomes replicate in S phase
  • one duplicated chromosome=2 identical sister chromatids attached at their centromeres
  • centriole pairs also replicate

INTERPHASE 1: nucleus and nucleolus visible

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7
Q

Process of meiosis

A
  • cell division that reduces the chromosome number by 1/2: the four phases
  • prophase 1
  • metaphase 1
  • anaphase 1
  • telophase 1
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8
Q

(general) PROPHASE 1

A
  • longest and most complex phase (90%)
  • chromsomes condense
  • synapsis occurs (formation of tetrad with 2 homologus chromsomes)
    tetrad= 2 chromosomes/ four chromatids (sister and non-sister chromatids)
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9
Q

Non-sister chromatid homologs

A
  • homologs contain DNA that codes for the same genes. but different versions of those genes
  • genes occur at the same loci
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10
Q

Sister Chromatids vs Homologs Chromosomes

A

Sister: exact replicas

Homlogus: not exact replicas-regions code for the same gene

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11
Q

Homologus Chromosomes

A
  • pair of chromsomes: maternal and paternal that are similar in shape and size
  • homologs pairs (tetrads) carry the genes controlling the exact same region on the homologus
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12
Q

how many pairs of homologus chromsomes do humans have

A

22- autosomes pairs
1- sex chromosome pair

= 23 total

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13
Q

Crossing Over- PROPHASE 1

A
  • crossing over MIGHT occur between non-sister chromatids at chiasmata
  • Crossing Over: segments of non-sister chromatids break and re-attach to the other chromatid
  • Chiasmata are where chromosomes touch and exchange genes (CROSSING OVER)
  • Causes genetic recombination
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14
Q

GENERAL EVENT MEIOSIS 1

A

-homologs separate

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15
Q

Prophase 1

A
  • nucleus and nucleolus disappear
  • spindle forms
  • chromosomes coil and synapsis (pairing) occurs
  • tetrads form and crossing over occurs
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16
Q

Metaphase 1

A
  • shortest phase
  • tetrads align on the equator
  • independent assortment occurs: chromosomes separate randomly causing genetic recombination
17
Q

In terms of independent assortment, how many different combinations of sperm could a male produce

A

ANS: using 2^n

2n=46 (Number of human chromsomes)

n=23, 2^23= around 8 million

18
Q

Anaphase 1

A
  • homologous chromsomes separate and move towards the poles
  • sister chromatids remain attached at their centromeres
19
Q

Telophase 1

A
  • each pole now has a haploid set of chromosomes
  • cytokinesis occurs and 2 haploid daughter cells are formed
20
Q

Meiosis 2 main event

A
  • sister chromatids separate
  • no interphase 2 (or its very short)
  • dna replication
  • MEIOSIS 2 IS SIMILAR TO MITOSIS
21
Q

Prophase 2

A
  • same as prophase in mitosis
  • nucleus and nucleolus disappear, chromosomes condense, spindle fibres form
22
Q

Metaphase 2

A
  • same as metaphase in mitosis (chromosomes not homologous line up at the equator now)
23
Q

Anaphase 2

A
  • same as anaphase in mitosis
  • sister chromatids separate
24
Q

Telophase 2

A
  • same as telophase in mitosis
  • nuclei. and nucleoli reform, spindle disappears
  • cytokinesis occurs
  • 4 haploid daughter cells are produced=GAMETES
25
Q

Genetic recombination/variation

A
  • raw material for natural selection
  • ensure all organisms are not alike
  • strongest “most fit’ traits survive and are passed along

OCCURS THROUGH:
- crossing over (prophase 1)
- independent assortment (metaphase 1)
- random fertilization

26
Q

A cell containing 20 chromosomes (diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?

A

10 chromosomes (haploid=n)

20 chrom as diploid=40 haploid
40/2=20 first phase
20/2=10 second phase

27
Q

Karyotypes

A
  • organized picture of chromosomes arranged in pairs by size from largest to smallest
  • pairs 1-22= autosomes
  • last pair= sex chromsomes
28
Q

What is fertilization?

A
  • the fusion of a sperm and egg to form a zygote
  • a zygotę is a fertilized egg
29
Q

A cell containing 40 chromatids at the beginning of meiosis would, at its completion, produce how many cells containing chromosomes?

A

10 haploid cells

chromatid=haploid
40/2=20 first phase
20/2=10 second phase

30
Q

how does meiosis involve genetic variation

A

independent assortment, crossing over, and random fertilization

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