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A Level Bio Edexcel > Unit 3- Eukaryotic Cell Division > Flashcards

Unit 3- Eukaryotic Cell Division Flashcards

1
Q

What is chromatin?

A
  • coiled DNA wrapped around a histone protein
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2
Q

How is chromatin different to chromosomes

A

Chromatin are bundles of histone proteins wrapped in DNA

Chromosomes are millions of coiled up chromatins

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3
Q

Where are chromatids joined?

A

At the centromere

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4
Q

Why can we see chromosomes in a light microscope?

A

They are short very wide bundles of chromatin that are so thick and coiled we can see them

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5
Q

What is the product of mitosis?

A

2 genetically identical daughter cells

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6
Q

What is mitosis used for?

A
  • Growth
  • replacement
  • repair
  • asexual reproduction in some eukaryotic organisms
  • artificial cloning of plants and animals
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7
Q

What are the 3 phases of the cell cycle?

A

Mitosis
Cytokinesis
Interphase

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8
Q

What phase do cells spend the majority of their time in?

A

Interphase

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9
Q

Describe interphase:

A

Growth 1 phase: cell grows to original size, organelles are replicated and genes are expressed
Synthesis phase: DNA and histone are replicated
Growth 2 phase: spindle and proteins are synthesised

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10
Q

Summary of mitosis phase:

A

Nucleus divides to make 2 nuclei with identical copies of DNA
This is subdivided into PMAT

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11
Q

Summary of cytokinesis:

A

The division of the cytoplasm to form 2daughter cells, with 1 nucleus each

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12
Q

Prophase: (3)

A
  • Chromosomes condense becoming visible
  • centrioles move to opposite poles of cell
  • nucleoli disappears
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13
Q

Metaphase:

A
  • nuclear envelope disappears
  • chromosomes align along equator of cell
  • spindle fibres connect centrioles to chromosomes
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14
Q

Anaphase: (3)

A
  • centromere splits, chromatids separate
  • spindle fibres shorten pulling chromatids towards poles, centromere first
  • some spindle fibres lengthen pushing the poles further apart
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15
Q

Telophase: (3)

A
  • spindle fibres disperse
  • nuclear envelope forms around 2 sets of chromosomes
  • chromatids (chromosomes) uncoil becoming too thin to see
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16
Q

Cytokinesis, how it differs in plants and animals:

A

Animals: ring of actin filament forms around cell equator and tightens squeezing the cell into cleavage furrow which splits into 2 cells
Plants: vesicles move to cell equator, line up and fuse a cell plate down the middle which developers into a cell wall

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17
Q

What are the products of meiosis?

A

4 genetically different haploid daughter cells

18
Q

Describe the differences in division 1 of meiosis:

A

Prophase: homologous chromosomes join together to for bivalents
Metaphase: bivalents line up on equator of cell
Anaphase: bivalents are separated and homologous chromosomes are pulled to opposite poles of the cell (chromatids don’t separate)
Telophase: chromosomes don’t uncoil

19
Q

What are bivalents and where are they found?

A

Meiosis division 1:

2 homologous chromosomes joined together

20
Q

How does meiosis differ from mitosis?

A

In meiosis the chromosome number is halved

In meiosis chromosomes are rearranged to form new combinations of alleles, this os genetic recombination

21
Q

Why are does meiosis produce gametes with a haploid number of chromosomes?

A

As fertilisation later restores the haploid number to diploid

22
Q

What are the 2 processes that occurs in meiosis that result in genetic variation?

A

Crossing over

Independent assortment

23
Q

When does crossing over occur?

A

Prophase 1 of meiosis, when homologous chromosomes bind to form bivalents

24
Q

What is crossing over?

A

When homologous chromosomes join together to form bivalents, sections of sister chromatids cross over, resulting in the swapping of alleles

25
Q

How come chromosomes stay the same length in crossing over?

A

Equal amounts of the chromosomes cross over

26
Q

When does independent assortment occurs?

A

Metaphase 1 of meiosis

27
Q

What is independent assortment?

A

When the random line up of bivalents along the cell equator gives rise to genetic variation by recombination of alleles

28
Q

What are the 2 different types of chromosome mutations?

A

Nondisjunction and translocation

29
Q

What is non-disjunction?

A

This is when chromatids or chromosomes remain stuck together in anaphase 1 or 2, moving together to one pole of the cell

30
Q

What is the product of nondisjunction? And what if the gamete fuses with the other gamete?

A

Gametes with extra chromosomes or missing chromosomes, if this gamete fertilises the zygote shows polysomy

31
Q

What is Down syndromes link to non-disjunction?

A
  • when a gamete with an extra chromosome fertilises a normal gamete the zygote will show trisomy
  • 3 copies of the smallest chromosome 21
32
Q

Symptoms of Down’s syndrome

A
  • recognisable facial features
  • short height
  • heart defects
  • poor vision
  • learning difficulties
33
Q

What is Turner syndrome caused by?

A

When a gamete with a missing X chromosome fertilises a normal gamete
The zygote shows monosomy

34
Q

Symptoms of Turner syndrome?

A

Female sex organs don’t mature at adolescence

35
Q

What is monosomy and trisomy?

A
  • having only 1 copy of a chromosome

- having 3 copies of a chromosome

36
Q

What is polyploidy?

A

When all the chromosomes remain stuck together in meiosis, forming a gamete with 2 copies of every single chromosome which fertilises a normal haploid gamete resulting in a Triploid gamete

37
Q

What is translocation mutation?

A

When a part of a chromosome is swapped with a part of a completely different non-homologous chromosome.

38
Q

When do translocation mutations occur?

A

During interphase

39
Q

What causes translocation?

A

Radiation, virus’ or chemicals which spontaneously break the DNA molecules and the DNA ligase joins the DNA back in the wrong place

40
Q

Why are translocation mutations most often harmless?

A

Exactly the same genes and alleles are still present, just located on different chromosomes

41
Q

Cells with translocation mutations have difficulties with meiosis, why is this?

A

Homologous chromosomes are no longer homologous (eg, paternal chromosomes may have swapped over sections)
True bivalents cannot form, so the gametes produced from these bivalents are unviable and cause miscarriages

A Level Bio Edexcel (51 decks)

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