Q6: Meiosis Flashcards
Meiosis
Usually produces four daughter cells, each with half the number of chromosomes as the parent cell.
Gene
A length of DNA that codes for a polypeptide
Locus
The position of a gene on a chromosome or DNA molecule
Allele
One of the different forms of a particular gene
Homologous chromosomes
A pair of chromosomes, one maternal, one paternal, that have the same gene loci
Gamete
sex cell
In sexual reproduction two gametes fuse…
to give rise to new offspring
Diploid number
Each cell contains two of each chromosome, one from each parent.
Every diploid organism has …
two complete sets of chromosomes, one provided by each parent
Zygote
Formed from two gametes from fertilisation, divides and develops into a new organism.
Gametes number of chromosomes
haploid
Diploid number
in algebra
2n
Haploid number
one copy of each chromosome
During sexual reproduction, fertilisation is…
random
The mixing of genetic material in sexual reproduction increases…
genetic diversity within a species
Random fertilisation produces zygotes with…
different combinations of chromosomes to both parents
Meiosis occurs in
the reproductive organs
What happens before meiosis starts?
the DNA unravels and replicates, so there are two copies of each chromosome -chromatids
The DNA condenses to form…
double-armed chromosomes, each made from two sister chromatids which are joined by a centromere.
Meiosis 1
first division
What happens in meiosis 1
- the chromosomes arrange themselves into homologous pairs,
- these homologous pairs are then separated, halving the chromosome number,
Meiosis 2
second division
What happens in meiosis 2
- The pairs of sister chromatids that make up each chromosome are separated and the centromere divides
- Four haploid cells (gametes) that are genetically different from each other are produced
How many homologous pairs in humans?
23
Crossing over
During meiosis 1,
The chromatids of homologous pairs twist round each other and bits of chromatids swap over.
Difference in chromatids after crossing over
the chromatids contain the same genes but have a different combination of alleles
