Mitosis and Meiosis

Question 1

Define Diploid Cell

Answer 1

A cell that contains two sets of chromosomes. One set of chromosomes is donated from each parent (n=46).

Question 2

Define Germ Cell

Answer 2

Cells that lead to the production of gametes. Produced by meiosis.

Question 3

Define Haploid Cell

Answer 3

A cell that contains one complete set of chromosomes (n=23).

Question 4

Define Meiosis

Answer 4

A type of cellular reproduction that results in the formation of four haploid cells from one diploid cell. Contains two cellular divisions that follow only one round of DNA replication. The type of reproduction that produces germ cells.

Question 5

Define Mitosis

Answer 5

The five-step process by which a cell separates replicated chromosomes before cytokinesis creates two identical daughter cells from one original cell. The five steps of mitosis are: prophase, prometaphase, metaphase, anaphase, telophase.

Question 6

What are the five steps of mitosis?

Answer 6

Prophase, Prometaphase, Metaphase, Anaphase and Telophase

Question 7

Define Somatic Cell

Answer 7

Any plant or animal cell that is not a germ cell. The class of cell formed during mitosis

Question 8

What are Stem Cells?

Answer 8

Biological cells that can differentiate into other types of cells and can divide to produce more of the same type of stem cells. They are always and only found in the multicellular organisms.

Question 9

What are the three principle types of protein fibres (filaments and tubules) that make up the cell skeleton (cytoskeleton)?

Answer 9

Microfilaments (thin ~8nm diameter) actin filaments)

Microtubules (thicker ~20mn diameter) made of tubulin)

Intermediate filaments (intermediate thickness e.g. keratin in skin cells)

Question 10

What does the cytoskeleton do?

Answer 10

Maintains cell shape, gives the cell strength and toughness, moves the cell and its organelles

Question 11

What happens during early prophase?

Answer 11

Cell rounds up into a ball

Chromatin begins to condense

Nucleolus disappears

Centrioles begin to move to opposite poles of the cell

Microtubules (MTs) dissolve and reassemble (polymerise) around the centrosomes, from which they extend

Question 12

What happens during prometaphase?

Answer 12

Chromosomes condensed and arranged in sister pairs (chromatids)

Chromosomes begin to move

Centrioles begin to move to opposite poles of the cell

Microtubules have formed the mitotic spindle; proteins attach to the centromeres to form kinetochores; spindle Mts attach to kinetochores and pull on chromosomes

Nuclear envelope disperses

Question 13

What happens during metaphase?

Answer 13

Paired chromatids align along the cell equator (or midline of the nucleus) by the mitotic spindle

This (imaginary) midline is called the mitotic plate

Question 14

What happens during anaphase?

Answer 14

Paired chromosomes separate at their kinetochores and move to opposite poles (the kinetochores move along the microtubules)

Question 15

What enzyme degrades the cohesin proteins that hold two sister chromatids together?

Answer 15

separase

Question 16

What does the degradation of cohesin cause?

Answer 16

The abrupt separation of the sister chromatids

Question 17

What happens during Telophase?

Answer 17

Chromosomes arrive at opposite poles

New nuclear envelopes form around each daughter nucleus

Mitotic spindle disperses

Chromosomes disperse as their chromatin becomes diffuse (and invisible under the light microscope)

Question 18

What is cytokinesis?

Answer 18

Cytokinesis is the physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells.

Question 19

What causes cytokinesis in animal cells?

Answer 19

The actin ring causes a cleavage furrow

Question 20

What holds pairs of homologous chromosomes together?

Answer 20

Synapsis

Question 21

What allows chromosomes to be bound tightly together and in perfect alignment?

Answer 21

A protein lattice called a synaptonemal complex and by cohesin proteins at the centromere

Question 22

What is the result of crossover?

Answer 22

An exchange of genetic material between homologous chromosomes.

Question 23

What is homologous recombination?

Answer 23

Homologous recombination is the process by which two chromosomes, paired up during prophase 1 of meiosis, exchange some distal portion of their DNA.

Question 24

What is crossover?

Answer 24

Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and then reconnect but to the different end piece.

Question 25

What are primordial germ cells (PGCs)?

Answer 25

Earliest recognisable precursors of gametes

Question 26

When are primordial germ cells recognisable?

Answer 26

Primordial Germ Cells are recognisable at 24 days after fertilisation in the endodermal layer of the yolk sac

Question 27

When germ cells exit from the yolk sac where do they migrate to?

Answer 27

The dorsal mesentery until they reach the primordia of the gonads