Topic 11: Mitosis and Meioisis

Question 1

What is the relationship between DNA molecules, chromosomes and chromatids?

Answer 1

DNA molecules wrap around histones and become beads on a string (nucleosomes), which then coil to become a solenoid, which scrunch together to form a chromatid.

A chromatid has a p arm and a q arm and before DNA replication, chromosomes have 1 chromatid and 2 chromatid after DNA replication.

Question 2

What is the structure of a chromosome?

Answer 2

Each replicated chromosome consists of 2 chromatids

Question 3

What is a centromere?

Answer 3

Consists of repetitive sequences and links the chromatids

Question 4

What is a telomere?

Answer 4

Repeated sequences at each end

Question 5

What is the difference between gene and allele?

Answer 5

Genes are DNA sequences, and alleles are different variants of genes.

Question 6

What are the 4 stages of cell cycle?

Answer 6

G1, S, G2, M

Question 7

What are the 2 stages of M phase?

Answer 7

Mitosis and cytokinesis

Question 8

What is mitosis?

Answer 8

Cell division for somatic cells that produces 2 identical daughter cells

Question 9

What are the 5 stages of mitosis?

Answer 9

Prophase, prometaphase, metaphase, anaphase, telophase

Question 10

What are the 2 things that happen in early prophase?

Answer 10

Chromosome condensation and centrosome separation

Question 11

What are the 2 things that happens in late prophase?

Answer 11

Chromosome condensation and nuclear envelope breakdown

Question 12

What are the 3 events in prometaphase?

Answer 12

Nuclear envelope breakdown 
Mitotic spindle assembly (centrioles moved to pole of the cell and spindle fibers connect to kinetochores)
Chromosome capture (by spindle fibers and kinetochore)

Question 13

What are the 2 events in metaphase?

Answer 13

Bipolar chromosome attachment

Chromosome alignment at metaphase plate

Question 14

What is the event at anaphase?

Answer 14

Sister chromatid separation (centromeres divide and sister chromatids move to opposite poles)

Question 15

What are the 3 events at telophase?

Answer 15

Nuclear envelope reformation (2!)
Chromosome decondensation
Spindle disassembly (spindle fibers disappear)

Question 16

What happens during cytokinesis?

Answer 16

Cytoplasm divides and parent cell becomes 2 daughter cells with identical generic information

Question 17

What is nondisjunction?

Answer 17

Missegregation of chromosomes - instead of sister chromatids going to opposite poles, the whole chromosome goes to one pole leading to aneuploidy which is an unusual amount of chromosomes

Question 18

What if mitotic nondisjunction happens during first post-zygotes division (from the fertilized cell)?

Answer 18

From a normal cell with 46 chromosomes, it divides but nondisjunction happens so one cell has 47 chromosomes and one has 45.

The one with 45 chromosome (monosomy) cell line is usually lost but the one with 47 will continue to proliferate

Leads to a non-mosaic phenotype - all cells are chromosomally similar (all have 47 chromosomes)

Question 19

What if mitotic nondisjunction occurs in later post-zygotes division?

Answer 19

There’ll be some cells with normal 46 chromosomes, but some with 47 chromosomes (monosomy cell lines are lost)

Leads to mosaicism, presence of 2 or more cell lines in an individual

Question 20

What is meiosis?

Answer 20

Special cell division for germ line cells that produces four non-identical daughter cells

Question 21

What are the 2 main process of meiosis?

Answer 21

Meiosis 1 and 2

Question 22

What is meiosis 1?

Answer 22

Homologous pairs of chromosomes line up and separate

Question 23

What are the 4 stages of meiosis 1?

Answer 23

Prophase I, metaphase 1, anaphase 1, telophase 1

Question 24

What are the 3 events of prophase I?

Answer 24

Nuclear envelope breaks down
Homologous chromosomes pair up
Crossing over of genetic material occurs (recombination = daughter chromosomes are a mixture of parental chromosomes)

Question 25

What is the event during metaphase I?

Answer 25

Homologous chromosomes pairs (tetrad - 4 chromatids) line up on the spindle

Question 26

What is the event during anaphase 1?

Answer 26

Homologous chromosomes pairs get separated, moves to opposite poles of the cell

Question 27

What are the 2 events during telophase 1?

Answer 27

Chromosomes gather at the poles of the cells | Nuclear membrane forms

Question 28

What happens during cytokinesis?

Answer 28

Cytoplasm divides

Question 29

What are the 2 events during prophase II?

Answer 29

New spindle forms around the chromosomes | Nuclear envelope disintegrates

Question 30

What happens during metaphase II?

Answer 30

Chromosomes line up at the equator

Question 31

What are the 3 events that happen during anaphase II?

Answer 31

Centromeres divide Separation of chromatids Chromatids move to the opposite poles of the cells

Question 32

What happens during telophase II?

Answer 32

Nuclear envelope forms around each set of chromosomes

Question 33

What happens during cytokinesis?

Answer 33

Cytoplasm divides

Question 34

What are the differences between meiosis I and meiosis II?

Answer 34

In meiosis I, homologous pairs of chromosomes line up and separate. In meiosis II, chromosomes line up and chromatids separate

Question 35

What is spermatogenesis?

Answer 35

Cell division to produce male gametes Spermatocyte (diploid) to 4 sperms (haploids)

Question 36

How long does spermatogenesis take?

Answer 36

1 spermatocyte forms 4 sperms in approximately 60 days

Question 37

What is oogenesis?

Answer 37

Cell devision to form female gametes 1 oocyte to form 1 egg and 3 polar bodies

Question 38

How long does oogenesis take?

Answer 38

1 oocyte to 1 egg + 3 polar bodies in 12-50 years

Question 39

What are 6 key differences between mitosis and meiosis?

Answer 39

1. Mitosis 4 stages meiosis 8 stages 2. Mitosis happens in somatic cells meiosis happens in germ cells 3. Purpose of mitosis is cellular proliferation purpose of meiosis is sexual reproduction 4. Product of mitosis is 2 diploid daughter cells product of meiosis is 4 haploid daughter cells 5. Number of chromosomes after mitosis is same number of chromosomes halved after meiosis 6. Mitosis doesn’t affect genetic variation but meiosis increases genetic variation

Question 40

What are the 2 ways that genetic variation created during meiosis?

Answer 40

1. Crossing over of genetic material in prophase 1 | 2. Random assortments of chromosomes in metaphase 1

Question 41

What happens if there is nondisjunction in meiosis I?

Answer 41

Produces 2 gametes with 2 chromatids and 2 gametes without that chromosome Upon fertilization by a normal gamete, produces 2 zygotes with trisomy and 2 with monosomy

Question 42

What happens if there is non disjunction in meiosis Ii?

Answer 42

Produce 1 gamete with 2 chromatids, 1 gamete without that chromosome, 2 normal gametes with 1 chromatid each Upon fertilization by normal gamete, produces 1 zygote with trisomy, 1 with monosomy, 2 normal gametes

Question 43

What are 3 consequences of faulty meiosis?

Answer 43

Miscarriages, infertility and leading cause of mental retardation