meiosis

Question 1

why are gametes described as haploid

Answer 1

this is due to them only having one copy of the chromosomes

Question 2

first stage of meiosis

Answer 2

the DNA unravels and replicates so there are two copies of each chromosome, called chromatids

Question 3

second stage of meiosis

Answer 3

the DNA condenses to form double-armed chromosomes, each made from two sister chromatids. The sister chromatids are joined in the middle by a centromere

Question 4

meiosis I

Answer 4

first division - the chromosomes arrange themselves into homologous pairs which are then separated, halving the chromosome number

Question 5

meiosis II

Answer 5

the pairs of sister chromatids that make up each chromosome are separated (centromere is divided)

Question 6

what is produced at the end of meiosis

Answer 6

four haploid cells that are genetically different from each other

Question 7

chromatids crossing over

Answer 7

during meiosis I, homologous pairs of chromosomes come together and pair up

the chromatids twist around each other and bits of chromatids swap over

the chromatids still contain the same genes but now have a different combination of alleles

Question 8

two ways during meiosis that lead to genetic variation

Answer 8

crossing over of chromatids

independent segregation of chromosomes

Question 9

what occurs during the independent segregation of chromosomes

Answer 9

each homologous pair of chromosomes in your cells is made up of one chromosome from your mum and one chromosome from your dad

when the homologous pairs are separated in meiosis I, it’s completely random which chromosome from each pair ends up in which daughter cell

so the four daughter cells produces by meiosis have completely different combinations of those maternal and paternal chromosomes

Question 10

outcomes of mitosis

Answer 10

produces cells with the same number of chromosomes as the parent cell

daughter cells are genetically identical to each other and to the parent cell

produces two daughter cells

Question 11

outcomes of meiosis

Answer 11

produces cells with half the number of chromosomes as the parent cell

daughter cells are genetically different from one another and the parent cell

produces four daughter cells

Question 12

what increases the rate of mutation

Answer 12

mutagenic agents such as ultraviolet radiant and ionising radiation

Question 13

what is substitution

Answer 13

one or more bases are swapped for another

Question 14

what is deletion

Answer 14

one or more bases are removed

Question 15

what is addition

Answer 15

one or more bases are added

Question 16

what is duplication

Answer 16

one or more bases are repeated

Question 17

what is inversion

Answer 17

a sequence of bases is reversed

Question 18

what is translocation

Answer 18

a sequence of bases is moved from one location in the genome to another
this could be movement within the same chromosome or movement to a different chromosome

Question 19

what happens if the amino acid sequence changes

Answer 19

a polypeptide may change the tertiary structure of the protein, which could mean that it doesn’t work properly

Question 20

what controls the transcription of genes

Answer 20

controlled by protein molecules called transcription

Question 21

how do transcription factors work

Answer 21

they move from the cytoplasm to the nucleus where they bind to specific DNA sites near the start of their target genes

they control the expression of the gene by controlling the rate of transcription

activators - stimulate or increase the rate of transcription
repressors - inhibit or decrease the rate of transcription

Question 22

how do activators work

Answer 22

example - they help RNA polymerase bind to the start of the target gene and activate transcription

Question 23

how to repressors work

Answer 23

example - they bind to the start of the target gene, preventing RNA polymerase from binding, stopping transcription

Question 24

how can oestrogen initiate transcription

Answer 24

it is a steroid hormone that can affect transcription by binding to a transcription factor called an oestrogen receptor, forming an oestrogen-oestrogen receptor complex

the complex moves from the cytoplasm into the nucleus where it binds to specific DNA sites near the start of the target gene

the complex can act as an activator of transcription, such as helping RNA polymerase bind to the start of the target gene