Eukaryotic cell cycle and division

Question 1

cell cycle

Answer 1

interphase - the time taken between divisions
mitosis - separation of the chromatids of each chromosome to form two new nuclei
cytokinesis - division of the cytoplasm

Question 2

Interphase

Answer 2

G1 - first growth phase
- organelles replicate protein synthesis cell size grows - respiration
S - synthesis
- DNA replication
- each chromosome becomes two chromatids attached at the centromere
G2 - second growth phase
- G1 + error checking

Question 3

State the cell divisions in mitosis

Answer 3

prophase, metaphase, anaphase and telophase

Question 4

Prophase

Answer 4

• replicated chromosomes super coil ( shorten and thicken )
• nuclear envelope breaks down and disappears
• centrioles divide into two and each daughter centriole moves to form a spindle

Question 5

Metaphase

Answer 5

• chromosomes line up and move to the central region of the spindle known as the equator
• each chromosome becomes attached to the spindle thread by its centrosome

Question 6

Anaphase

Answer 6

• replicated sister chromatids that make up the chromosome separate from each other when the centromere holding them splits
• each of the sisters becomes an individual chromosome
• spindle fibre shorten

Question 7

Telophase

Answer 7

• as the separated sister chromatids reach the poles of the cell, a new nuclear envelope forms around each cell
• the spindle breaks down and disappears
• chromosomes uncoil, so you can no longer see them under a light microscope

Question 8

Cytokinesis - after mitosis

Answer 8

• the whole cell now splits to form two new cells, each one containing a full set of chromosomes identical to that found in original parent cell

Question 9

where is mitosis commonly observed ?

Answer 9

mammals: tissues - epithelial tissues such as the skin and the lining of the intestine
plants: meristems - the actively growing tips of shoots and roots

Question 10

In prokaryotic cells, cell division ..

Answer 10

occurs by a process known as binary fission

Question 11

In eukaryotic cells, cell division ..

Answer 11

part of a regulated process called the cell cycle

Question 12

what is asexual reproduction ?

Answer 12

the formation of new organisms that does involve the fusion of gametes

Question 13

gene

Answer 13

a base sequence of DNA that codes of the amino acid sequence of a polypeptide or a functional RNA molecule

Question 14

allele

Answer 14

versions of genes

Question 15

chromosome

Answer 15

structure in a cell that contains genetic material also known as DNA

Question 15

chromatid

Answer 15

one of the two identical halves of a chromosome that has been replicated in preparation for cell division

Question 16

centromere

Answer 16

a constricted region of a chromosome to which the microtubules of the spindle attach during cell division

Question 17

chromatin

Answer 17

a mixture of DNA and proteins that form the chromosomes found in the cells of humans and other higher organisms

DNA + histone = chromatin

Question 18

how many daughter cells does meiosis produce ?

Answer 18

4 daughter cells

Question 19

differences between mitosis and meiosis

Answer 19

meiosis:
- have half the number of chromosomes as the parent cell
- genetically different

mitosis:
- same chromosomes complement as the parent cell
- genetically identical to each other - clones

Question 20

where does meiosis occur in humans ?

Answer 20

occurs in the gonads - testes and ovaries - and results in the formation of haploid gametes that fuse at fertilisation to form a diploid zygote

Question 21

what is a haploid ?

Answer 21

contains only one chromosome from each of its homologous series

Question 22

overview of meiosis

Answer 22

in meiosis 1, homologous chromosomes are separated
in meiosis 2, the chromatids of each chromosome are separated

Question 23

Meiosis 1

Answer 23

• prophase 1 (early )
• prophase 1 ( mid )
• prophase 1 ( late )
• metaphase 1
• anaphase 1
• telophase 1

Question 24

prophase 1 ( early )

Answer 24

during interphase the chromosomes replicate into chromatids held together by a centromere ( the chromatids are not visible ). NOW, the chromosomes condense ( shorten and thicken ) and become visible

Question 25

prophase 1 ( mid )

Answer 25

homologous chromosomes pair up ( becoming bivalents ) as they continue to shorten and thicken. Centrioles duplicate.

Question 26

prophase 1 ( late )

Answer 26

Homologous chromosomes repel each other. Chromosomes can now be seen to consist of chromatids. Sites where chromatids have broken and rejoined, causing crossing over, are visible as chiasmata

Question 27

metaphase 1

Answer 27

nuclear membrane breaks down. Spindle forms. Bivalents line up at the equator, attached by centromeres

Question 28

anaphase 1

Answer 28

homologous chromosomes separate. Whole chromosomes are pulled towards opposite poles of the spindle, centromere first ( dragging along the chromatids )

Question 29

telophase 1

Answer 29

nuclear membrane re-forms around the daughter nuclei. The chromosome number has been halved. The chromosomes start to decondense

Question 30

Meiosis 2

Answer 30

prophase 2 metaphase 2 anaphase 2 telophase 2

Question 31

prophase 2

Answer 31

the chromosomes condense and the centrioles duplicate

Question 32

metaphase 2

Answer 32

the nuclear membrane breaks down and spindle forms. The chromosomes attach by their centromere to spindle fibres at the equator of the spindle

Question 33

anaphase 2

Answer 33

the chromatids separate at their centromeres and are pulled to opposite poles of the spindle

Question 34

telophase 2

Answer 34

the chromatids ( now called chromosomes ) decondense. The nuclear membrane re-forms . The cells divide

Question 35

what is meiosis a major source of ?

Answer 35

genetic variation in organisms

Question 36

the cells produced by meiosis are genetically different because of two different reasons :

Answer 36

independent assortment and crossing over

Question 37

Independent assortment

Answer 37

bivalents line up at the equator of the spindle in meiosis 1 entirely at random

Question 38

Crossing over

Answer 38

exchange in DNA between chromatids of homologous chromosomes

Question 39

w/hat is a chromosome mutation ?

Answer 39

a change in the number or the sequence of genes can be brought about in a number of different ways

Question 40

chromosome translocation

Answer 40

part of a chromosome breaks and re-joins a completely different chromosome

Question 41

chromosome non disjunction

Answer 41

the members of a homologous pair fail to be separated during meiosis

Question 42

polysomy

Answer 42

a zygote with more copies of this chromosome than usual

Question 43

monosomy

Answer 43

a zygote with only one copy of this chromosome

Question 44

Turner's syndrome - monosomy

Answer 44

- only one case of full monosomy in humans - Women have only one X chromosome rather than the normal two (represented XX)

Question 45

Down's syndrome - polysomy

Answer 45

non disjunction of chromosome 21 during gamete production - total of 47 chromosomes