L6 outcomes of meiosis Flashcards
How does meiosis cause genetic variation?
Meiosis results in genetic variation by shuffling and crossing over maternal (mum) and paternal (dad) chromosomes
In each cell that meiosis occurs, 4 haploid gametes are produced (each that contain 23 chromosomes – half the normal number required)
No daughter cells formed are genetically identical to either mother or father.
What are the 4 outcomes of variability?
- Reduction in chromosomes
- Independent assortment
- Crossing over
- Random fertilization
What is reduction in chromosomes?
During meiosis 1, pairs of homologous chromosomes are separated to create two cells containing sister chromatids.
Meiosis two separates these chromatids as they are not genetically identical anymore to create gametes that contain individual chromosomes with half the number of DNA.
This allows the gamete to join with another gamete through fertilization to get the full chromosomal number.
What is independent/random assortment?
During meiosis I, homologous chromosomes (one maternal, one paternal), line up in the middle of the cell in their pairs.
The chromosomes in each pair lines up on either side of the centre of the cell.
This means when the cell separates, there is a random assortment of chromosome from each parent in the new daughter cells.
What is crossing over?
Crossing over/genetic recombination is the process of genes being exchanged on homologous chromosomes.
During prophase/metaphase in meiosis I, homologous chromosomes exchange genes. This results in new alleles on chromatids that are different from the original parent.
This can occur because genes found on the same chromosome are ‘linked’.
This causes the mixing of paternal and maternal genes which increases the number of combinations on genes that can be passed on.
What is random fertilization?
Sperm and ovum are the daughter cells produced during meiosis
These daughter cells are produced in meiosis each contain a single set of chromosomes (23 chromosomes)
This means that when sperm and eggs combine, they will contain the full (diploid) number of chromosomes.
How does crossing over contribute to genetic variation in organisms?
The process of crossing over in meiosis 1 contributes to genetic variation in organisms. During the metaphase, the homologous pairs with the same gene on each homologous chromosome swap 3 genes per chromosome resulting in a completely genetically different chromosomes. Each haploid daughter cell produced at the end of meiosis 2 will be genetically different because of the different genes it received from metaphase one.
