Meiosis and Genetic Variation Flashcards
Why is meiosis important
In sexual production 2 gametes fuse to give rise to the new off spring. If each gamete had a full set of chromosomes ( diploid number) then the cell that they produce has double this number.
In order to maintain a constant number of chromosomes in the adults of a species, the number of chromosomes must be halved at some age in the life cycle. This Halving occurs as a result of meiosis
What happens to the diploid cell of an organism that has two complete sets of chromosomes, one set provided by each parent?
During meiosis, homologous pairs of chromosomes separate so that only one chromosome from each pair enters a daughter cell. This is known as the haploid number of chromosomes (23 in humans ).
What happens when two haploid gametes dude at fertilisation
The diploid number of chromosomes is restored
How does meiosis bring about genetic variation (2 ways)
Independent segregation of homologous chromosomes
New combinations of maternal and paternal alleles by crossing over
What’s a gene
A length of dna that codes for a polypeptide
What’s a locus
The position of a gene on a chromosome or dna molecule
What’s an allele
One of the different forms of a particular gene
What’s a homologous chromosomes
A pair of chromosomes, one Maternal and one paternal, that have the same gene loci
What’s independent segregation of chromosomes
Each homologous pair of chromosomes in your cells is made up of one chromosome from your mum and one chromosome from your dad
When the homologous pairs are separated in meiosis 1, it’s completely random which chromosome from each pairs ends up in which daughter cell
So the 4 daughter cells produced by meiosis have completely different combinations of those Maternal and paternal chromosomes
How does crossing over of the Chromatids cause genetic variation
The Chromatids of each pair become twisted around one another
During this twisting process tensions are created and portions of the Chromatids break off
These broken portions might then rejoin with the Chromatids of its homologous partner
Usually it is equivalent portions of homologous chromosomes that are exchanged
In this way new genetic combinations of Maternal and paternal alleles are produced
What is recombination
When the broken off portions of Chromatids recombine with another chromatid
What’s the formula to determine the number of possible combinations of chromosomes for each daughter cell
2 to the power of n
N=the number of pairs of homologous pairs
Formula used to determine number of possible chromosome combinations in zygotes due to random fertilization.
2 to the nth power all squared.
What happens during crossing over
Pairing up homologous chromosomes (synapsis) to form a bivalent
Cross over region is the chiasma
Equal sections of non sister Chromatids are exchanged between Maternal and paternal chromosomes ( recombination); creating new combinations of alleles
what does non disjunction mean
it is the failure of homologous chromosomes or sister chromatids to separate properly during cell division
