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Biology > Meiosis > Flashcards

Meiosis Flashcards

1
Q

What is the name of the cell at the beginning of the cell cycle

A

Parent Cell

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2
Q

What is the parent cell at the start of the cell cycle

A

A diploid (2n) cell

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3
Q

How many chromosomes are present in a haploid cell

A

n

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4
Q

Define Homolgous

A

Chromosomes of a similar length with the same genes at the same loci

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5
Q

What is a diploid cell

A

A cell containing paired chromosomes one from each parent

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6
Q

Which way round are mother and father chromosomes

A

Mum on left, Dad on right

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7
Q

What does n refer to when talking about cells

A

The quantity of DNA within the cell

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8
Q

How does meiosis produce daughter cells that are genetically different from each other and to the parent cell​

A

the processes of independent assortment and crossing over​

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9
Q

What is independent assortment

A

The production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase I

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10
Q

How come the allele a gamete received for one gene does not influence the allele received for another gene​

A

Because homologous chromosomes line up in random orientations at the middle of the cell at metaphase as they prepare to separate, meaning that the same parent cell can produce different combinations of chromosomes in the daughter cells​

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11
Q

Do paternal and maternal chromosomes in a homologous pair contain the same genes at the same loci

A

Yes, though they may contain different alleles

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12
Q

What do homologous chromosomes replicate to form

A

pairs of sister chromatids (genetically identical), that are linked by a specialised DNA sequence known as a centromere.

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13
Q

What are non sister chromatids

A

chromatids of homologous chromosomes that are not identical and may contain different alleles at the same gene loci. ​

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14
Q

How can you distinguish between sister and non sister chromatids

A

Non sister chromatids are not joined by a centromere​

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15
Q

Why are non sister chromatids important

A

They play an important role in one of the key events of meiosis that results in variation​s

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16
Q

How can we distinguish between the phases in Meiosis I and Meiosis II

A

Roman numerals are used e.g. There are two Prophases - Prophase I and Prophase II

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17
Q

What is crossing over

A

The process whereby a chromatid breaks during meiosis and rejoins to the chromatid of its homologous chromosome so that its alleles are exchanged​. Resulting in recombinant chromatids.

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18
Q

what is a chiasma

A

X-shaped points of attachment between two non-sister chromatids of a homologous pair.

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19
Q

What occurs during prophase I

A

DNA condenses and becomes visible as chromosomes​
DNA replication has already occurred so each chromosome consists of two sister chromatids joined together by a centromere​
The chromosomes are arranged side by side in homologous pairs​
As the homologous chromosomes are very close together the crossing over of non-sister chromatids may occur
In this stage centrioles migrate to opposite poles and the spindle is formed​
The nuclear envelope breaks down and the nucleolus disintegrates​

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20
Q

When does crossing over occur

A

Meiosis I (Prophase I)

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21
Q

When does chiasma break separating chromosomes

A

Anaphase I

22
Q

What occurs during metaphase I

A

The bivalents line up along the equator of the spindle in a completely random nature, with the spindle fibres attached to the centromeres​. on some occasions, the paternal chromosome will be facing a particular pole of the cell and on other occasion, it will be the maternal chromosome that faces that pole​

23
Q

What are bivalents

A

A pair of homologous chromosomes

24
Q

What occurs during Anaphase I

A

The homologous pairs of chromosomes are separated as spindle fibres contract and so microtubules pull whole chromosomes to opposite ends of the spindle​
The centromeres do not divide

25
Q

What occurs during telophase I

A

Spindle fibres start to break down​

Nuclear envelopes form around the two groups of chromosomes and nucleoli reform​

Some plant cells go straight into meiosis II without reformation of the nucleus in telophase I​

Although there are two nuclear divisions and two sets of cytoplasmic divisions during cytokinesis, interphase only occurs once at the beginning of the cell cycle.

26
Q

What is cytokinesis

A

When the division of the cytoplasm occurs

27
Q

How does cytokinesis occur in animal cells

A

the cell surface membrane pinches inwards creating a cleavage furrow in the middle of the cell which contracts, dividing the cytoplasm in half​

28
Q

How does cytokinesis occur in plant cells

A

Vesicles from the Golgi apparatus gather along the equator of the spindle (the cell plate). The vesicles merge with each other to form the new cell surface membrane and secrete a layer of calcium pectate which becomes the middle lamella. Layers of cellulose are laid upon the middle lamella to form the primary and secondary walls of the cell​

29
Q

What is the product of cytokinesis in meiosis I:

A

Two haploid cells - They are haploid because they contain half the number of centromeres​

30
Q

What occurs during prophase II

A

The nuclear envelope breaks down and chromosomes condense​

A spindle forms at a right angle to the old one​

31
Q

What occurs during metaphase II

A

Chromosomes line up in a single file along the equator of the spindle​

32
Q

What occurs during anaphase II

A

Centromeres divide and individual chromatids are pulled to opposite poles​

This creates four groups of chromosomes that have half the number of chromosomes compared to the original parent cell​

33
Q

What occurs during telophase II

A

Nuclear membranes form around each group of chromosomes​

34
Q

What occurs after Telophase II

A

Cytokinesis - Cytoplasm divides as new cell surface membranes are formed creating four haploid cells​ genetically different to each other and to the parent cell which began the cell cycle​

35
Q

What is having genetically different offspring advantageous for

A

Natural Selection

36
Q

What mechanisms of meiosis increase the genetic diversity of gametes produced

A

Both crossing over and independent assortment (random orientation) result in different combinations of alleles in gametes​

37
Q

How does the entanglement in crossing over cause non sister chromatids to swap DNA

A

The entanglement places stress on the DNA molecules​
As a result of this a section of chromatid from one chromosome may break and re-join with the chromatid from the other chromosome​

38
Q

How many chiasmata are usually present in each bivalent during meiosis

A

At least one, if not more, chiasmata present in each bivalent during meiosis​

39
Q

Where is crossing over most likely to occur

A

further down the chromosome away from the centromere​

40
Q

What is the number of homologous chromosomes in humans

A

23

41
Q

What would the calculation and answer be for the number of possible chromosomal combinations in a human

A

2^23 = 8 388 608 possible chromosomal combinations​

42
Q

How can cells undergoing meiosis be observed and photographed

A

Using specialised microscopes

43
Q

What can the stages of meiosis be identified with and why

A

The stages can be identified from photomicrographs or diagrams because each stage has distinctive characteristics

44
Q

How can you distinguish between meiosis I and meiosis II on a photomicrograph or diagram

A

Homologous chromosomes pair up side by side in meiosis I only. If there are two new cells forming it is meiosis I but if there are four new cells forming it is meiosis II​

45
Q

What does meiosis do in comparison to mitosis

A

Mitosis contributes to the growth of an organism or to replace dead/dying cells. Meiosis produces genetically different gametes for sexual reproduction​

46
Q

How many daughter cells do does meiosis make in comparison to mitosis

A

Mitosis = 2​
Meiosis = 4​

47
Q

Ploidy (number of chromosomes) of daughter cells in meiosis compared to mitosis

A

Mitosis = 2n​
Meiosis = n​

48
Q

Are the daughter cells genetically identical to each other in mitosis and meiosis

A

Mitosis = yes​
Meiosis = no​

49
Q

Why is it important that mitosis produces 2 daughter cells genetically identical to each other and the parent cell

A

This is important so that growth and cell replacement can occur within a body continually​

50
Q

What similarity does every cell in our bodies have

A

Every cell in an organism’s body (other than gametes) contain exactly the same genetic material - the full genome​

51
Q

Why is it important that meiosis produces 4 daughter cells genetically unidentical to each other and the parent cell

A

This is important for genetic variation within families and the population. ​Genetic variation can reduce the risk of inheriting genetic diseases​

Biology (28 decks)

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