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Mr Ellis BIOLOGY > 6.3. MEIOSIS > Flashcards

6.3. MEIOSIS Flashcards

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1
Q

What are homologous chromosomes?

A
  • a pair of ‘identical’ chromosomes, one from dad and one from mum.
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2
Q

What is the main component of homologous chromosomes?

A
  • do not have same base sequence
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3
Q

Why would sister chromosomes not have the same base sequence?

A
  • copying errors with DNA polymerase
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4
Q

What is a gene?

A
  • section of DNA that codes for a polypeptide
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5
Q

What is an allele?

A
  • variation of a gene
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6
Q

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A

yes

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7
Q

What is the Locus (loci for plural)?

A
  • where all alleles for a gene are at the same place on the same chromosome
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8
Q

Summarise mitosis:

A
  • reduces chromosome number from diploid to haploid
  • produces four daughter cells
  • AKA reduction cell division
  • has two stages
  • generates genetic variation in gametes by independent assortment and crossing-over
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9
Q

What are gametes?

A
  • sex cells
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10
Q

What is the haploid number of chromosomes?

A
  • n= 23
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11
Q

What is the diploid number in chromosomes?

A
  • 2n= 46
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12
Q

What are the two stages of Meiosis?

A
  • meiosis 1
  • meiosis 2
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13
Q

What happens during prophase 1?

A
  1. chromosomes have been replicated during S phase
  2. homologous chromosomes pair up to form a BIVALENT
  3. centrioles begin to form spindle fibres that will bind to the centromeres and drag the bivalents onto the metaphase plate.
  4. nuclear envelope disintegrates
  5. crossing over happens
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14
Q

What happens in Metaphase 1?

A
  1. nuclear envelope has gone
  2. spindle fibres have bound to the centromeres and arranged the bivalents on the Metaphase plate
  3. orientation of each bivalent is independent of other bivalents.
  4. independent assortment shuffles alleles and not genes because in humans we all have the same genes.
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15
Q

How do you calculate the number of ways homologous pairs can be arranged by independent assortment?

A

2 to the power of 23.

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16
Q

What happens during Anaphase 1?

A
  1. Bivalents pulled apart by contracting spindle fibres and the centromeres remain intact.
  2. Homologous chromosomes pulled to opposite parts of the cell
  3. the effects of crossing over become apparent
17
Q

What happens during Telophase 1?

A
  1. new nuclear envelopes form around each of the chromosomes
  2. a new cleavage furrow forms and cytokinesis happens
  3. each nucleus is now haploid and the reduction of the chromosome number is complete
  4. centrioles are replicated
18
Q

What happens during prophase 2?

A
  1. nuclear envelope disintegrates
  2. centrioles move to pole of each cell
  3. spindle fibres form and bind to centromeres, dragging chromosomes onto the metaphase plate.
19
Q

What happens during metaphase 2?

A
  1. spindle fibres have aligned the chromosomes on the metaphase plate
  2. due to crossing over, the chromosomes are not identical, so independent assortment happens again.
20
Q

What happens during anaphase 2?

A
  1. spindle fibres contract and separate the centromeres
  2. chromatids now become chromosomes and are puled to the poles of the cell
21
Q

What happens during telophase 2?

A
  1. new nuclear envelopes form
  2. chromosomes will un-condense and form chromatin to fill the volume of the nucleus
  3. a new cleavage furrow forms and 4 daughter cells are made, each gamete is haploid.
22
Q

When does crossing over happen?

A
  • in prophase 1, the effects are shown in anaphase 1.
23
Q

What is crossing over (see diagram in folder for detail)?

A
  • in prophase 1, one chromatid arm is broken on one of the homologous pair chromatids.
  • the breaks are random and multiple along all 4 chromatids
  • ends re-join but with other sister chromatids to form a chiasma
  • in anaphase 1, crossing over creates genetic variation by shuffling alleles

Mr Ellis BIOLOGY (36 decks)

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