genetics (week 2)

Question 1

diploid vs haploid

Answer 1

diploid = 2 copies of each chromosome (46)

gametes = 23 = haploid

Question 2

process forming sperm and egg

Answer 2

male gametes = spermatogenesis (turns a single diploid cell into 4 haploid)

eggs = oogenesis (oocyte - immature egg goes through meiosis to form one egg cell and 3 polar bodies)

Question 3

meiosis 1- prophase 1

Answer 3

prophase 1 - chromosomes condense, spindle fibres form

homologous chromosomes seek each other out and pair up = synapsis forming tetrads (4 chromosomes)

tetrads perform crossing over - exchanging lengths of DNA at chiasmata

Question 4

meiosis 1 - metaphase + anaphase + telophase

Answer 4

tetrads line up on the equator

tetrads split and each half of a cell receives different DNA

sister chromatids are still intact

chromosomes decondense, nuclear membrane reforms and cytokinesis occurs at the cleavage furrow

Question 5

interkinesis

Answer 5

seperates meiosis 1 and 2 where no DNA replication occurs

Question 6

meiosis 2

Answer 6

prophase 2 - nuclear membrane dissipates, spindle forms

metaphase 2 - chromosomes align themselves on equator

anaphase 2 - centromeres + kinetochores break and chromosomes move to opposite ends of the cell

telophase - spindle breaks down and nuclear membrane reforms

cytokinesis

Question 7

how meiosis introduces genetic variability

Answer 7

independent assortment - metaphase 1

genetic recombination - prophase 1

random fertilisation

Question 8

non disjunction

Answer 8

during meiosis 1 = one daughter cell has an extra chromosome and the other has one less

end of meiosis 2 = some daughter cells will not contain a particular chromosome while others have xtra

Question 9

trisomy vs monosomy

Answer 9

trisomy = fertilisation using an extra chromosome forms a zygote with 3 copies of a chromosome eg: Down’s syndrome

Every cell has an extra chromosome

monosomy = cell missing a chromosome from a pair

Question 10

non disjunction in sex chromosomes

Answer 10

females with 1 X = turners

3 X = metafemale syndrome

male = XXY = klinfelters syndrome

Question 11

chance of children having black hair eg: calculation

Answer 11

blakc = 1/4
2 children = 1/4 x 1/4 = 1/16

Question 12

intermediate inheritance - sickle cell

Answer 12

eg: sickle cell anaemia
(single aa in a haemoglobin chain is abnormal)

SS = normal

ss = severe respiratory problems (no haemoglobin carries enough O2)

Ss = hetero
produce both normal + sickle hameoglobin so symptomless until high respiratory demand

Question 13

sex linked inheritance

Answer 13

y chromosome shorter so has less genetic info

x linked traits are always expressed in males as it is coded for on a bit of x chromosome with no corresponding piece on Y chromosome eg: r/g colour blindness

Question 14

polygenic inheritance

Answer 14

multiple genes needed to change phenotypes

some genes are only expressed in some environmental conditions eg freckles + sunlight

• nature + nurture

Question 15

mutations

Answer 15

point mutation vs frameshift (insertion/deletion)

occur as a mistake during DNA replication in meiosis

Question 16

Meiosis 1-2 detailed

Answer 16

Prophase 1 - chromosomes condense
Homologous chromosomes pair up closely forming tetrads (4 chromosomes) via synapsis
Crossing over at chiasmata of non sis chromatids

Metaphase 1 - tetrads line along equator
Microtubules from one pole attach
to one chromosome of each pair (and opposite pole for other)

Anaphase 1 - homologous chromosomes pulled to opposite poles (centromeres attached)

Telophase 1 and cytokinesis - cleavage furrow

Meiosis 2
Same
Metaphase 2 - chromosomes line up individually on equator
Anaphase 2 centromeres split and sister chromatids pullled to opposite poles

Telophase / cytokinesis - nuclear envelope reforms
Contractile ring at cleavage furrow