3.1.9 Genetic Diversity may Arise by Meiosis Flashcards

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1
Q

What are the gametes in plants?

A

Ovum and pollen

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2
Q

Why do diploid cells (ones that divide into gametes) have to half their number of chromosomes?

A

Gametes have to fuse with another gamete to make a full set of genes to code for all the proteins

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3
Q

Explain how sexual reproduction increases genetic diversity within a species?

A

Fertilisation of gametes is random & produces zygotes with different combinations of chromosomes to both parents

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4
Q

Where does meiosis take place in?

A

Reproductive organs

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5
Q

What happens before meiosis starts?

A

DNA unravels and replicates, forming 2 copies of each chromosomes = called chromatids

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6
Q

How are sister chromatids joined?

A

By centromere in the middle

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7
Q

Describe what happens in meiosis 1

A
  1. Prophase 1
    • Chromosomes condense and super coil
  2. Metaphase 1
    • Chromosomes line up along the centre of nucleus with their homologous pair (bivalents)
  3. Anaphase 1
    • One of each homologous pair get pulled to either side of nucleus
  4. Telophase 1
    • Nuclear envelope reforms to make 2 separate nuclei
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8
Q

Describe what happens in meiosis 2

A
  1. Prophase 2
    • Chromosomes condense and super coil
  2. Metaphase 2
    • Chromosomes line up along centre of nucleus still attached at centromere
  3. Anaphase 2
    • Each chromatid gets pulled to either side of nucleus (centromere is divided)
  4. Telophase 2
    • Nuclear envelope reforms to make 4 operate nuclei each with single copy of each chromosome
  5. End up with 4 haploid non-identical daughter cells (n)
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9
Q

What is genetic variation?

A

Differences in the genes of individual organisms

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10
Q

Describe what is happening in this diagram & what this means

A
  1. Crossing over
  2. Between chromatids of homologous chromosomes
  3. (Chromatid twist around each other & bits of chromatids swap over)
  4. Chromatids still contain same gene but now have different combination of alleles
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11
Q

Name 2 ways how meiosis produces cells that are genetically different

A
  1. Crossing over of chromatids
  2. Independent segregation of chromosomes
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12
Q

Describe how crossing over of chromatids increases genetic variation

A

Each of 4 daughter cells formed from meiosis contains a different chromatid with a different set of alleles

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13
Q

Describe how independent segregation increases genetic variation

A
  • We don’t know which maternal or paternal chromosomes will get pulled to each side
    • i.e. we don’t know which chromosome (from each pair) ends up in which daughter cell
  • ∴ 4 daughter cells produced have different combinations of those maternal and paternal chromosomes
  • (Leads to genetic variation in any potential offspring)
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14
Q

What is chromosome mutation?

A

When cell produced in meiosis contains variation in numbers of whole chromosomes or parts of chromosomes

(caused by errors during meiosis)

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15
Q

Describe and explain the appearance of this chromosome

A
  • Chromsome is formed of 2 chromatids
  • ∵ of DNA replication
  • Sister chromatids are held together by centromere
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16
Q

What is the role of the centromere (2x)?

A
  • Holds chromatids together
  • Allows chromatids to be separated
17
Q

This cell produces gametes by meiosis. Draw a diagram to show the chromosomes in one of the gametes.

A

3 chromosomes - one from each homologous pair

18
Q

Crossing over of chromatids is ________

A

infrequent/rare

19
Q

Name 3 advantages of variation (caused by meiosis) to species

A
  • Different adaptations
  • Passing on alleles/genes
  • Allows for changing environment
20
Q

Explain why Plant A (has 42 chromosomes) is fertile while Plant B (has 21 chromosome) is not

A
  1. Plant A’s cells are diploid - have 2 copies of each chromosome
  2. Plant A’s chromosomes can produce haploid gametes
  3. Plant A’s gametes receive a copy of every chromosome
21
Q

Explain the role of independent segregation in meiosis

A
  • To provide genetic variation
  • Allows different combinations of maternal and paternal chromosomes
22
Q

How do you calculate the number of different types of gametes that can be produced from a diploid cell?

A

Use this formula:

2n

n = number of gene pairs

23
Q

Calculate the number of different types of gametes that can be produced in a species with a diploid number of 24

A

212 = 4096

24
Q

Assuming random fertilisation, calculate the number of different combinations of maternal and paternal chromosomes in the zygotes of this species (with a diploid number of 24)

A

4096 x 4096 = 16 777 216

25
Q

Unit 5

During meiosis, when the X and Y chromosomes pair up, they do not form a typical bivalent as do other chromosomes. Explain why. (2)

A
  • X and Y chromosomes are different sizes / shapes
  • Chromatids unable to line up and form bivalent / only short pairing region / most of length not homologous