Unit 3- Eukaryotic Cell Division

Question 1

What is chromatin?

Answer 1

• coiled DNA wrapped around a histone protein

Question 2

How is chromatin different to chromosomes

Answer 2

Chromatin are bundles of histone proteins wrapped in DNA

Chromosomes are millions of coiled up chromatins

Question 3

Where are chromatids joined?

Answer 3

At the centromere

Question 4

Why can we see chromosomes in a light microscope?

Answer 4

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

Question 5

What is the product of mitosis?

Answer 5

2 genetically identical daughter cells

Question 6

What is mitosis used for?

Answer 6

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

Question 7

What are the 3 phases of the cell cycle?

Answer 7

Mitosis
Cytokinesis
Interphase

Question 8

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

Answer 8

Interphase

Question 9

Describe interphase:

Answer 9

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

Question 10

Summary of mitosis phase:

Answer 10

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

Question 11

Summary of cytokinesis:

Answer 11

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

Question 12

Prophase: (3)

Answer 12

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

Question 13

Metaphase:

Answer 13

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

Question 14

Anaphase: (3)

Answer 14

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

Question 15

Telophase: (3)

Answer 15

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

Question 16

Cytokinesis, how it differs in plants and animals:

Answer 16

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

Question 17

What are the products of meiosis?

Answer 17

4 genetically different haploid daughter cells

Question 18

Describe the differences in division 1 of meiosis:

Answer 18

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

Question 19

What are bivalents and where are they found?

Answer 19

Meiosis division 1:

2 homologous chromosomes joined together

Question 20

How does meiosis differ from mitosis?

Answer 20

In meiosis the chromosome number is halved

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

Question 21

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

Answer 21

As fertilisation later restores the haploid number to diploid

Question 22

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

Answer 22

Crossing over

Independent assortment

Question 23

When does crossing over occur?

Answer 23

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

Question 24

What is crossing over?

Answer 24

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

Question 25

How come chromosomes stay the same length in crossing over?

Answer 25

Equal amounts of the chromosomes cross over

Question 26

When does independent assortment occurs?

Answer 26

Metaphase 1 of meiosis

Question 27

What is independent assortment?

Answer 27

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

Question 28

What are the 2 different types of chromosome mutations?

Answer 28

Nondisjunction and translocation

Question 29

What is non-disjunction?

Answer 29

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

Question 30

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

Answer 30

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

Question 31

What is Down syndromes link to non-disjunction?

Answer 31

- when a gamete with an extra chromosome fertilises a normal gamete the zygote will show trisomy - 3 copies of the smallest chromosome 21

Question 32

Symptoms of Down’s syndrome

Answer 32

- recognisable facial features - short height - heart defects - poor vision - learning difficulties

Question 33

What is Turner syndrome caused by?

Answer 33

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

Question 34

Symptoms of Turner syndrome?

Answer 34

Female sex organs don’t mature at adolescence

Question 35

What is monosomy and trisomy?

Answer 35

- having only 1 copy of a chromosome | - having 3 copies of a chromosome

Question 36

What is polyploidy?

Answer 36

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

Question 37

What is translocation mutation?

Answer 37

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

Question 38

When do translocation mutations occur?

Answer 38

During interphase

Question 39

What causes translocation?

Answer 39

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

Question 40

Why are translocation mutations most often harmless?

Answer 40

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

Question 41

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

Answer 41

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