meiosis Flashcards

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1
Q

define ‘meiosis’

A

cell division which produces gametes (sex cells) that contain half the number of chromosomes making them haploid

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2
Q

why is meiosis a reduction division?

A

It enables the chromosome number to be halved as the parent cells are diploid but the daughter cells are haploid meaning they only have one chromosome from each homologous pair present

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3
Q

For humans, what is the diploid and haploid number?

A

diploid = 46
haploid = 23

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4
Q

How do you know what the haploid number is of a cell from a diagram?

A

Haploid number is how many different sizes of chromosomes are present in the cell.
The cell becomes diploid when the matching size pairs join

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5
Q

What is the gene loci?

A

The position on the chromosome where the gene is found

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6
Q

define ‘gene’

A

The DNA sequence which codes for a polypeptide which when folded into its tertiary protein structure, gives rise to a characteristic. E.g eye colour or hair texture

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7
Q

define ‘allele’

A

Alternative versions of a gene due to slight variations in DNA sequence of the polypeptide leading to a variation in the final protein

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8
Q

What are homologous chromosomes?

A

Chromosomes that share the same structural features e.g size, same genes at same loci position, but alleles may be different

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9
Q

What’s the state given to homologous chromosomes that carry the same alleles and the state when carrying different alleles?

A

-Same alleles = Homozygous state
-Different alleles = Heterozygous state

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10
Q

summarise prophase 1

A
  • x shaped chromosomes condense
  • homologous chromosomes pair up and form bivalents
  • crossing over occurs at chiasmata
  • nuclear envelope breaks down
  • nucleolus disappears
  • centrioles separate
  • spindle fibres form
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11
Q

summarise metaphase 1

A
  • bivalents line up in middle of cell
  • this is independent assortment
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12
Q

summarise anaphase 1

A
  • homologous pairs pulled apart to poles (random segregation)
  • sister chromatids remain attached at centromeres
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13
Q

summarise telophase 1

A
  • chromosomes assemble at either pole
  • nuclear envelope forms to make two haploid nuclei
  • chromosomes diffuse
  • cytokinesis and cleavage furrow
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14
Q

summarise prophase 2

A
  • chromosomes condense
  • nuclear envelope breaks down
  • centrioles separate
  • spindle is formed
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15
Q

summarise metaphase 2

A
  • chromosomes line up at equator
  • independent assortment of chromatids
  • the spindle is attached at centromeres
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16
Q

summarise anaphase 2

A
  • centromeres replicate
  • random segregation of chromatids
17
Q

summarise telophase 2

A
  • chromatids assemble at poles
  • nuclear envelope forms
  • 4 haploid nuclei
  • cytokinesis
18
Q

how does prophase 1 cause genetic variation

A
  • chromatids from different homologous pairs interweave at chiasmata points and form bivalents
  • produces variation as genetic material is exchanged between homologous chromosomes producing new combinations of alleles
19
Q

how does metaphase 1 cause genetic variation?

A
  • independent assortment = when homologous chromosomes move to the equator the alignment of each chromosome is random
  • when homologous chromosomes are separated in anaphase 1, many different chromosome combinations can be formed in the daughter cells
20
Q

how does metaphase 2 cause genetic variation

A
  • independent assortment: chromosomes lines up at the cell equator but the side on which each sister chromatids is positioned is random
  • this causes genetic variation as sister chromatids are no longer identical
21
Q
A