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Genes and Heredity > Meiosis > Flashcards

Meiosis Flashcards

1
Q

What happens in early prophase I?

A

Chromatin condenses. Each replicate chromosome pairs up with its homolog. The synaptonemal complex zips the chromosomes together in synapsis.

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2
Q

What happens in midprophase I?

A

The pairs of chromosomes are fully fused along the lengths to form a tetrad. Crossing over occurs in the mid arms. DNA repair occurs in single chromosomes or across the synaptonemal complex causing non-sister chromatids to join together.

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3
Q

What happens in late prophase I?

A

The synaptonemal complex breaks down but homologs stay attached at the chiasmata.

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4
Q

What happens in metaphase I?

A

Homologous pairs are aligned at the metaphase plate by spindle fibres. Kinetochores only form on one side of the external centrosome.

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5
Q

What happens in anaphase I?

A

Spindle microtubules and kinesin motors pull homologs apart. Chiasmata resolve towards the ends of the chromosome. Crossing over results in reciprocal exchange of genetic material.

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6
Q

What does meiosis I result in?

A

Two genetically distinct haploid cells.

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7
Q

What happens in metaphase II?

A

Spindle microtubules align chromosomes at central plane of the cell in a bipolar fashion.

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8
Q

What happens in anaphase II?

A

The sister chromatids are separated. Ploidy isn’t exchanged but each chromosome contains only one chromatid.

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9
Q

What happens in telophase II?

A

The nuclear envelopes reform around four haploid groups of chromosomes. Chromatin decondenses.

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10
Q

What are the mechanisms of genetic diversity in gametes?

A
  • Crossing over
  • Random independent sorting of homologous chromosomes into daughter cells
  • Random sorting of sister chromatids in meiosis II
  • Crossing over
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11
Q

What is spermatogenesis?

A

Production of sperm.

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12
Q

What is a primary spermatocyte?

A

The cell that enters meiosis.

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13
Q

How many cells does a primary spermatocyte produce?

A

4 genetically diverse spermatids.

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14
Q

What is Oogenesis?

A

The production of egg cells.

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15
Q

How many cells does the first meiotic division in oogenesis produce?

A

2

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16
Q

What does uneven cytokinesis in the first meiotic division of oogenesis result in?

A

One cell getting the majority of cell material resulting in only one egg cell and one redundant polar body.

17
Q

How many gametes are produced in oogenesis?

A

One

18
Q

What do mutations in early embryogenesis result in?

A

Mosaicism

19
Q

What mechanisms of diversity are employed by asexual reproduction?

A

Mutations and horizontal gene transfer.

20
Q

What errors occur in gametes?

A

Non-disjunction errors.

21
Q

What are non-disjunction errors caused by?

A

The breakdown of cohesion.

22
Q

What non-disjunction error can occur in anaphase I?

A

Homologous pairs fail to separate.

23
Q

What non-disjunction error can occur in anaphase II?

A

Sister chromatids fail to separate correctly.

24
Q

What do non-disjunction errors result in?

A

Aneuploidy - extra or fewer chromosomes in the cell.

25
Q

What does the fusion of a polyploidy or monoploidy gamete with an unaffected cell lead to?

A

Either miscarriage or Down’s syndrome.

26
Q

What is Down’s caused by?

A

Trisomy 21 or translocation of the chromosome 21.

27
Q

What does XXX result in?

A

A sterile female.

28
Q

What does XXY result in?

A

Klinefelter’s syndrome

29
Q

What does X0 result in?

A

Turner’s syndrome

30
Q

What does 0Y result in?

A

A non viable pregnancy.

31
Q

What does the self fertilisation of triploid plants result in?

A

Auto polyploidy

32
Q

How is crossover regulated?

A

By formation of programmed meiotic DNA double strand breaks. (DSBs)

33
Q

What is a chiasma?

A

Joints between non-sister chromatids.

Genes and Heredity (6 decks)

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