meiosis Flashcards
describe the difference between meiosis and mitosis.
meiosis produces four genetically different daughter cells with half the number of chromosomes as parent cells.
mitosis produces two daughter cells that are genetically identical to parent cells.
explain the importance of meiosis.
it maintains constant number of chromosomes in a cell - creates variation.
what is a diploid cell?
has 2 complete sets of chromosomes, represented as 2n.
what is a haploid cell?
has a single set of unpaired chromosomes, represented as n,
how does meiosis lead to genetic variation?
- crossing over
- independent assortment of chromosomes
- random fertilisation
what is independent assortment of chromosomes?
- occurs in metaphase 2 and anaphase 2.
- any half of the chromosomes can end up in the haploid gamete, the separation of one homologous pair is not affected by the separation of any other pair.
what is random fertilisation?
any sperm can meet with any egg - another opportunity to create a unique genetic combination.
explain why the number of chromosomes is halved during meiosis.
homologous chromosomes are separated during meiosis 1.
explain how crossing over creates genetic variation.
- homologous pairs of chromosomes associate.
- chiasmata form.
- alleles exchange between chromosomes.
- which creates new combinations of alleles on chromosomes.
explain how independent assortment creates genetic variation.
- homologous pairs randomly align on the equator.
- creating different combinations of maternal and paternal chromosomes in daughter cells.
other than mutation and meiosis, explain how genetic variation within a species is increased.
random fertilisation - creates new allele combinations.
briefly describe how a cell divides by meiosis.
meiosis 1 - separates homologous chromosomes - arrange in pairs, cross over, and independent assortment.
meiosis 2 - separates chromatids.
explain the different outcomes of mitosis and meiosis.
mitosis produces 2 daughter cells, whereas meiosis produces 4 daughter cells.
mitosis maintains the chromosome number, whereas meiosis halves the number of chromosomes (e.g diploid to haploid).
mitosis produces genetically identical daughter cells, whereas meiosis produces genetically different (due to independent assortment and crossing over).
how can you recognise where mitosis and meiosis occur in a life cycle?
mitosis occurs between stages where chromosome number is maintained.
meiosis occurs between stages where chromosome number halves.
describe how mutations in the number of chromosomes arise.
by chromosome non-disjunction - homologous chromosomes fail to separate during meiosis, so some gametes have an extra copy of a particular chromosome and others have none (gamete contains one more than the haploid number)
do all mutations result in a change in amino acid sequence - why?
no - due to the degenerate nature of the genetic code, many mutations do not affect the amino acid sequence of a polypeptide.
