Unit 1.6

Question 1

Centromere?

Answer 1

specialised region where chromatids join

Question 2

Chromosome?

Answer 2

A long thin structure of DNA and protein, in the nucleus of eukaryotic cells, carrying the genes

Question 3

Haploid?

Answer 3

having 1 complete set of chromosomes
(egg cell / sperm cell)

Question 4

Chromatid?

Answer 4

one of the 2 identical copies of a chromosome joined at the centromere prior to cell division

Question 5

Diploid?

Answer 5

having 2 complete sets of chromosomes
(body cells)

Question 6

Polyploid?

Answer 6

multiple sets of chromosomes
triploid - banana

Question 7

Tetraploid?

Answer 7

4 sets
potato

Question 8

Hexaploid?

Answer 8

6 sets
wheat

Question 9

Octoploid?

Answer 9

strawberries

Question 10

Homologous?

Answer 10

chromosomes that are identical in shape + size + have the same gene locus

Question 11

What are not homologous?

Answer 11

X Y chromosomes

Question 12

Mitosis

Answer 12

a type of cell division in which the 2 daughter cells have the same number of chromosomes that are genetically identical with each other and the parent cell

Question 13

Cell cycle?

Answer 13

the sequence of events that takes place between one cell division and the next

Question 14

Interphase?

Answer 14

period of synthesis and growth

Question 15

Cytokinesis?

Answer 15

division of the cytoplasm + to form 2 daughter cells

Question 16

Prophase?

Answer 16

the longest stage of mitosis
(1hr)
chromosomes condense + become shorter, thicker + visible
centrioles = separate in prophase + move to the opposite ends
spindle fibres radiate from centrioles between the pairs
Nuclear envelope disintegrates
nucleolus disappears
pairs of chromatids = visible in the cytoplasm

Question 17

Metaphase?

Answer 17

chromosomes attach to the spindle fibres at the centromere
the chromosomes align on the equator

Question 18

Anaphase?

Answer 18

shortest stage
centromere divides
spindle fibres shorten
chromatids = pulled to the pores - centromere first

Question 19

Telophase?

Answer 19

final stage of mitosis
chromosomes uncoil + lengthen
spindle fibres break down, nuclear envelope reforms + nucleolus reappears

Question 20

Cytokinesis?

Answer 20

division on the nucleus by mitosis to make 2 separate cells
animal cell?
cytokinesis occurs by constricting the parent cell around the equator from the outside in
plant cell?
cell wall material
( cellulose) forms a cell plate across the equator of the parent cell from the centre outwards

Question 21

Significance of mitosis?

Answer 21

produces cells that are genetically identical to the parent
provides genetic stability
allows organisms to increase their cell number for tissues replacement + repair
Body cells = produced by mitosis are genetically identical
Adult mammals constantly lose skin cells + gut lining cells which are replaced by mitosis
mitosis occurs continually in bone marrow, producing red white blood cells
mitosis occurs in nail beds + hair folices

Question 22

Where is mitosis in plants?

Answer 22

growing region known as the meristem
roots and shoots

Question 23

A sexual reproduction?

Answer 23

Genetically identical
examples -
unicellular organisms such as yeast
bacteria
carry out sexual reproduction, some flowering plants such as strawberries + potatoes
most plants can reproduce by sexual reproduction as well

Question 24

Damage + disease?

Answer 24

if genes are damaged, cells may fail to divide or may divide too frequently
Radiation + toxic chemicals can mutate DNA

Question 25

methotrexate?

Answer 25

becomes incorporated into DNA + prevents replication

Question 26

Deorubicin?

Answer 26

inhibits enzymes essential for the cell cycle

Question 27

Vinblastine + Vinocristine?

Answer 27

prevents spindle formation

Question 28

Formation of a tumour?

Answer 28

Genes that control the cell cycle act as a brake, preventing the cell cycle from repeating continually
if brake = damaged the cell repeats rounds of mitosis

Question 29

Forming solid + tissue tumour?

Answer 29

if this occurs in the bone marrow, immature blood cells accumulate + spill out into the general circulation, causing leukaemia

Question 30

Genes that prevent cancer?

Answer 30

tumour suppressor gene

Question 31

Gene that causes cancer?

Answer 31

oncogenes

Question 32

Meiosis?

Answer 32

2 stage cell division in sexually reproducing organisms
which produces 4 genetically distinct daughter cells each with half the number of chromosomes in the patient cell

Question 33

Where does meiosis take place?

Answer 33

in the reproductive organs of plants + animals + Protoctista
Diploid number of chromosomes = halved to haploid 2n to n
2 haploid gametes fuse at fertilisation so the zygote has 2 complete sets of chromosomes

Question 34

Independent assortment?

Answer 34

either of pair of homologous chromosomes faces to either pole at metaphase I of meiosis , independently of the chromosomes of other homologous pairs.
Either a pair of chromatids face to either pole at metaphase II, independently of the chromatids of other chromosomes

Question 35

Interphase?

Answer 35

DNA = replicated, followed by Meiosis I and Meiosis II
between the 2 divisions there = no more DNA replication

Question 36

Bivalent?

Answer 36

the association of the 2 chromosomes of a homologous pair at Prophase I of meiosis

Question 37

Chiasma?

Answer 37

which chromosomes exchange DNA in genetic crossing over

Question 38

Meiosis I

Question 39

prophase I?

Answer 39

maternal + paternal chromosomes unite in homologous pairs
(where the locus on genes are the same)
Pairing of chromosomes = synapses
each homologous chromosome pair = bivalent
chromosomes condense, becoming shorter, thicker + visible
centriole separate + move to the pores
microtubules radiate spindle fibres
chromatids wrap around each other at the chiasmata
(region where DNA = exchanged)
The swapping of DNA = crossing over + is a source of genetic variation as it mixes the genes of 2 parent on a single chromosome
crossing over can occur at several places along the chromatid, extending the genetic combinations
nuclear envelope disintegrates
nucleolus disappears

Question 40

Metaphase I?

Answer 40

pairs of homologous chromosomes align along the equator
1 chromosome from the mother + one from the father lie randomly
this is known as independent assortment
( creating variation)
If independent assortment with 2 pairs of chromosomes
there are 4 possible combinations

Question 41

Anaphase I?

Answer 41

the chromosomes in each bivalent separate and as the spindle fibres shorten, one of each pair is pulled to one pole and the other to the opposite pole.
Each pole receives only one of each homologous pair of chromosomes and because of their random arrangement at metaphase I, there is a random mixture of maternal and paternal chromosomes

Question 42

Telophase I?

Answer 42

in some species, the nuclear envelope reforms around the haploid group of chromosomes and the chromosomes decondense and no longer visible.
But in many species, the chromosomes stay in their condensed brother

Question 43

Cytokinesis?

Answer 43

the division of the cytoplasm occurs making 2 haploid cells

Question 44

Meiosis II?

Answer 44

there is no pairing of homologous chromosomes and it is the chromatids rather than the homologous chromosomes that separate at anaphase

Question 45

Prophase II?

Answer 45

the centrioles separate and organise a new spindle at right angles to the old spindle

Question 46

Metaphase II?

Answer 46

chromosomes line up on the equator with each chromosome attached to a spindle fibre by its centromere
Independent assortment happens because the chromatids of the chromosomes can face either pole/

Question 47

Anaphase II?

Answer 47

the spindle fibres shorten + the centromeres separate, pulling the chromatids to opposite poles

Question 48

Telophase II?

Answer 48

at the poles, chromatids lengthen and can no longer be distinguished in the microscope
the spindle disintegrates + the nuclear envelope and nucleoli re-form

Question 49

The significance of Meiosis?

Answer 49

Meiosis keeps the chromosome number constant from 1 generation to the next
Meiosis generates genetic variation in the gametes + therefore the zygotes that they produce
there are 2 ways this happens
a) crossing over during prophase I
b) Independent assortment at
Metaphase I - so that the daughter cells contain different combinations of maternal and paternal chromosomes
Metaphase II- so daughter cells have different combinations of chromatids
In the long term, if a species is to survive in a constantly changing environment and to colonise new environments, sources of variation = essential

Question 50

Comparison of Mitosis and Meiosis?

Answer 50

Mitosis
Number of divisions = 1
Number of daughter cells = 2
Chromosome number in daughter cells = same as parent cell
Ploidy of daughter cells of parent cell = Diploid
Chiasmata = absent
Genetic crossing over = none
Independent assortment = none
Genetic composition = genetically identical with parent cell and each other
Meiosis
Number of divisions = 2
Number of daughter cells = 4
Chromosome number in daughter cells = half of parent cells
Ploidy of daughter cells of parent cell= haploid
Chiasmata = present
Genetic crossing over = in prophase I
Independent assortment = In metaphase I and metaphase II
Genetic composition = Genetically different