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Biology > 10.1 Meiosis > Flashcards

10.1 Meiosis Flashcards

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1
Q

Where do chromosomes replicate before meiosis?

A

Interphase

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2
Q

What are the 3 cell cycle phases in interphase?

A
  • G1
  • S
  • G2
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3
Q

What happens in the S phase of interphase?

A

DNA is repilicated so that each chromosome consits of two chromatids

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4
Q

At the start of meiosis, what do the chromosomes do?

A

They condense and are visible as two chromatids, called sister chromatids

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5
Q

Where do pairing or synapsis occur in meiosis?

A

Occurs where homologous chromosomes come to align beside each other

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6
Q

What a tetrad?

A

The combination of chromatids as it is composed of four chromatids
Also a homologous pair

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7
Q

What is a tetrad also referred to as and why?

A

Bivalent - as it is composed of a homologous pair

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8
Q

What is the protein-based structure that forms between the homologous chromosomes called?

A

Synaptonemal complex

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9
Q

In what type of cells do synaptonemal complexes form?

A

Eukaryotic cells

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10
Q

What is crossing over?

A

The exchange of DNA material between non-sister homologou chromatids

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11
Q

When do breaks in the DNA occur in meiosis?

A

Prophase I

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12
Q

What happens during crossing over?

A

Non-sister chromatids “invade” a homologous sequence on a non-sister chromatid and bind in the region of the break

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13
Q

What are the connection points where crossing over occured called?

A

Chiasmata (P) or Chiasma (S)

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14
Q

What does the chiasmata formation between non-sister chromatids in a bivalent result in?

A

An exchange of alleles

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15
Q

What are the two consequences of chiasmata formation?

A
  • Increased stability of bivalents at chiasmata
  • Increase genetic variability if crossing over occurs
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16
Q

What are the two consequences of chiasmata formation?

A
  • Increased stability of bivalents at chiasmata
  • Increase genetic variability if crossing over occurs
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17
Q

What chromosomes are exchanged in crossing over?

A

The process of crossing over results in the exchange of DNA between the maternal and paternal chromosomes

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18
Q

What leads to independent assortment?

A

Crossing over can decouple linked combinations of alleles and therefore lead to independent assortment

19
Q

How many times can crossing over occur?

A

Multiple times and between different chromatids within the same homologous pair.

20
Q

When does crossing over and independent assortment occur?

A

Crossing over - Prophase I
Independent assortment - Metaphase I

21
Q

What are the 3 methods by which meiosis creates genetic variation?

A
  • Crossing over - Prophase I
  • Independent assortment - Metaphase I
  • Random Fusing of gametes
21
Q

What are the 3 methods by which meiosis creates genetic variation?

A
  • Crossing over - Prophase I
  • Independent assortment - Metaphase I
  • Random Fusing of gametes
22
Q

How are recombinant chromatids fromed?

A

When exchange of alleles occurs due to crossing over

23
Q

Compared to before, what do recombinant chromatid still contain? Whats different?

A

Recombinant chromatids still contain the same genes but a different combination of alleles

24
Q

After crossing over, what are chromatids of each chromosome no longer?

A

They are no longer genetically identical

25
Q

What are the 3 features shared between homologous chromosomes?

A
  • Same length
  • Same centromere position
  • Same gene content
26
Q

What is a difference between homologous chromosomes?

A

They will have different combinations of alleles

27
Q

What is a chiasma?

A

An X-shaped knot-like strcuture that forms where crossing over has occurred

28
Q

What do chiasmata do to homologous chromosomes?

A

They hold homologous chromosomes together for a while

29
Q

What do chiasmata do to homologous chromosomes?

A

They hold homologous chromosomes together for a while

30
Q

Which round of meiosis resembles mitosis?

A

The first meiotic division is unique while the second round resembles mitosis

31
Q

How does meiosis 1 differ from mitosis and meiosis 2?

A
  1. Sister chromatids remain associated with each other
  2. The homologous chromosomes behave in a coordinated fashion in prophase
  3. Homologous chromosomes exchange DNA leading to genetic recombination
  4. Meiosis I is a reduction division in that it reduces the chromosome number by half
32
Q

Which stage of meiosis initiates the processes that result in the creation of genetic variety of gametes?

A

Meiosis 1

33
Q

When does the segregation of homologous chromosomes occur?

A

During anaphase I, resulting in two haploid cells, each with only one copy of each homologous pair

34
Q

How does independent assortment occur?

A

independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis I

35
Q

What is independent orientation?

A

The direction in which one pair is facing does not affect the direction in which any of the other pairs are facing. This is called independent orientation

36
Q

If an organism is heterozygous for a gene, how would you expect their chromosomes to be like in a cell?

A

In its cells, one chromosome in a pair will carry one allele of the gene and the other chromosome will carry the other allele

37
Q

How is it determined which allele moves to which pole in meiosis?

A

The orientation of the pair of chromosomes will determine which allele moves to which pole

38
Q

What is the chance of each allele moving to a particular pole?

A

50%

39
Q

By is there a 50% chance of an allele moving to a particular pole?

A

Because there is random orientation of chromosome pairs

40
Q

What are separated in meiosis II?

A

Sister chromatids

41
Q

What do daughter cells of meiosis I not do before entering meiosis II?

A

After meiosis I, the daughter cells enter meiosis II without passing through interphase

42
Q

How is meiosis II similar to mitosis?

A

The replicated chromosome is separated into chromatids

43
Q

Why are the sister chromatids separated in meiosis II likely to be non-identical?

A

Due to the occurrence of crossing over

Biology (57 decks)

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