meiosis and genetic variation

Question 1

what are gametes

Answer 1

gametes are the sperm cells in males and egg cells in females. They join together at fertilisation to form a zygote, which divides and develops into a new organism

Question 2

what diploid number do normal body cells have

Answer 2

2n of chromosomes meaning each cell contains two of each chromosome, one from the mother and one from the father

Question 3

what number of chromosomes do gametes have

Answer 3

they are a gametes so they have (n) number of chromosomes, there’s only one copy of each chromosome

Question 4

what occurs at fertilisation

Answer 4

a haploid sperm fuses with a haploid egg, making a cell with the normal diploid number of chromosomes.half these chromosomes are from the father (the sperm) and half are from the mother (the egg)

Question 5

what does random fertilisation produce

Answer 5

zygotes with different combinations of chromososmes to both parents. The mixing of genetic material in sexual reproduction increases genetic diversity within a species

Question 6

is fertilisation random

Answer 6

yes any sperm can fertilise any egg

Question 7

what is meiosis

Answer 7

meiosis is a type of cell division. it takes place in reproductive organs. cells that divides by meiosis are diploid to start with,but the cells that are formed from meiosis are haploid. The chromsosome number halves. without meiosis youd get double the number of chromosomes when the gametes fuse

Question 8

what happens without meiosis

Answer 8

youll get double the number of chromososmes when gametes fuse

Question 9

what happens to DNA before meiosis starts

Answer 9

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

Question 10

what happens after the DNA unravels and replicates so that there are two copies of each chromosomes called chromatids

Answer 10

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

Question 11

what happens in meiosis 1 (first division)

Answer 11

the chromosomes arrange themselves into homologous pairs. These homologous pairs are then separated, halving the chromosome number

Question 12

what occurs in meiosis 2 (second division)

Answer 12

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

SO in result four haploid cells (gametes) that are genetically different from eachother are produced

Question 13

how many chromososmes do humans have

Answer 13

46 total chromosomes 23 pairs

one chromososome in each pair came from a mother and the other the father e.g. there are two number ones, two number 2’s etc. the chromosomes that make up each pair are the same size and have the same genes although they could have different versions of those genes (called alleles). these chromososmes are called homologous pairs