Meiosis and genetic variation Flashcards
Are normal body cells diploid or haploid?
Diploid (2n)
Why are human cells diploid?
Each cell has two of each chromosome, one from mother and one from father
What is a homologous pair?
Two chromosomes that have the same genes but can have different alleles
What is the diploid number for humans?
46
Are gametes diploid or haploid?
Haploid (n)
What is the haploid number for gametes?
23
What occurs at fertilisation?
Haploid sperm fuses with a haploid egg making a normal diploid number of chromosomes
What does random fertilisation produce?
Zygotes with different combinations of chromosomes
How does fertilisation produce genetic diversity?
The random fertilisation causes the mixing of genetic material
Where does meiosis take place?
Reproductive organs
What type of cells divides in meiosis?
Normal diploid cells
What type of cells are formed in meiosis?
Haploid gametes
What happens before meiosis occurs?
The DNA unravels and replicates so there are to copies of each chromosomes called chromatids, cell becomes 2 x 2n
What is the second stage that takes place before meiosis?
The DNA condenses to form double-armed chromosomes, each made from two sister chromatids which are joined in the middle by a centromere
What happens during Meiosis 1?
Chromosomes arrange themselves in homologous pairs
The homologous pairs are then separated, halving the chromosome number
What is the chiasma?
The point at which recombination occurs
What is recombination?
During meiosis 1, the chromatids of the homologous chromosomes cross over each other and swap bits of chromatids
How does recombination create genetic variation?
Creates different combinations of alleles
Each of the 4 daughter cells contain chromatids with different alleles
What happens during Meiosis 2?
The pairs of sister chromatids that make up each chromosome are separated as the centromere is divided
What is produced from meiosis?
4 haploid daughter cells, each genetically different from each other
What is independent segregation?
When the homologous pairs separate in meiosis 1, it is completely random which chromosome from each pair ends up in each daughter cell
How does independent segregation produce genetic variation?
The daughter cells have completely different combinations of those maternal and paternal chromosomes, leads to genetic variation in potential offspring
How can you tell if a cell has halved?
If the number of chromosomes in the daughter cells are half that of the parent cells
What are the three outcomes of meiosis?
- 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 4 daughter cells
