Unit 1.6 Flashcards
Centromere?
specialised region where chromatids join
Chromosome?
A long thin structure of DNA and protein, in the nucleus of eukaryotic cells, carrying the genes
Haploid?
having 1 complete set of chromosomes
(egg cell / sperm cell)
Chromatid?
one of the 2 identical copies of a chromosome joined at the centromere prior to cell division
Diploid?
having 2 complete sets of chromosomes
(body cells)
Polyploid?
multiple sets of chromosomes
triploid - banana
Tetraploid?
4 sets
potato
Hexaploid?
6 sets
wheat
Octoploid?
strawberries
Homologous?
chromosomes that are identical in shape + size + have the same gene locus
What are not homologous?
X Y chromosomes
Mitosis
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
Cell cycle?
the sequence of events that takes place between one cell division and the next
Interphase?
period of synthesis and growth
Cytokinesis?
division of the cytoplasm + to form 2 daughter cells
Prophase?
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
Metaphase?
chromosomes attach to the spindle fibres at the centromere
the chromosomes align on the equator
Anaphase?
shortest stage
centromere divides
spindle fibres shorten
chromatids = pulled to the pores - centromere first
Telophase?
final stage of mitosis
chromosomes uncoil + lengthen
spindle fibres break down, nuclear envelope reforms + nucleolus reappears
Cytokinesis?
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
Significance of mitosis?
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
Where is mitosis in plants?
growing region known as the meristem
roots and shoots
A sexual reproduction?
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
Damage + disease?
if genes are damaged, cells may fail to divide or may divide too frequently
Radiation + toxic chemicals can mutate DNA
methotrexate?
becomes incorporated into DNA + prevents replication
Deorubicin?
inhibits enzymes essential for the cell cycle
Vinblastine + Vinocristine?
prevents spindle formation
Formation of a tumour?
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
Forming solid + tissue tumour?
if this occurs in the bone marrow, immature blood cells accumulate + spill out into the general circulation, causing leukaemia
Genes that prevent cancer?
tumour suppressor gene
Gene that causes cancer?
oncogenes
Meiosis?
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
Where does meiosis take place?
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
Independent assortment?
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
Interphase?
DNA = replicated, followed by Meiosis I and Meiosis II
between the 2 divisions there = no more DNA replication
Bivalent?
the association of the 2 chromosomes of a homologous pair at Prophase I of meiosis
Chiasma?
which chromosomes exchange DNA in genetic crossing over
Meiosis I
prophase I?
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
Metaphase I?
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
Anaphase I?
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
Telophase I?
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
Cytokinesis?
the division of the cytoplasm occurs making 2 haploid cells
Meiosis II?
there is no pairing of homologous chromosomes and it is the chromatids rather than the homologous chromosomes that separate at anaphase
Prophase II?
the centrioles separate and organise a new spindle at right angles to the old spindle
Metaphase II?
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/
Anaphase II?
the spindle fibres shorten + the centromeres separate, pulling the chromatids to opposite poles
Telophase II?
at the poles, chromatids lengthen and can no longer be distinguished in the microscope
the spindle disintegrates + the nuclear envelope and nucleoli re-form
The significance of Meiosis?
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
Comparison of Mitosis and Meiosis?
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
