Genetic Diversity Flashcards
Give two types of gene mutation, describe them
Substitution - one base replaced by another
Deletion - nucleotide lost = frame shift
What is non disjunction?
Where within meiosis the homologous pairs fail to separate, leads to +/- one chromosome in the gametes
What is the overall effect of meiosis?
1 diploid cell becomes four haploid cells
What happens in meiosis 1 ?
Homologous chromosomes pair up
Then separate into two cells with one chromosome from each pair.
What happens in meiosis 2?
Chromatids move apart into two separate cells
Each cell has the haploid number
What is a homologous chromosome?
A pair of chromosomes one maternal and one paternal that have the same gene loci
Describe genetic variation by independent segregation
The orientation of homologous pairs is random
Therefore when meiosis 1 occurs the maternal and paternal chromosomes will be segregated randomly
Which produces new combinations of alleles
Describe random fertilisation as a means of genetic variation
Any gamete can fuse with any other gamete (of opposite sex)
Mating occurs at random
Describe crossing over as a means of genetic variation
Homologous pairs line up
Chromatids twist round each other
In twisting process bits may be broken off
Broken sections may rejoin with homologous partner
Give a formula for the number of potential chromosome combinations within offspring produced from two haploid gametes
(2^n)^2
Where n is the number of chromosome pairs
What is the formula for the number of chromosome pairs within a daughter cell produced by meiosis from diploid cells
2^n
Define genetic diversity, what is the advantage of high genetic variation ?
Total number of different alleles in a population
Greater genetic variation = increased chance of survival upon climactic change
Describe the process of natural selection
1) population has a gene pool with wide variety of alleles
2) random mutation leads to new alleles being formed
3) the new allele may be advantageous making the organism better adapted and hence increasing the chance of survival
4) therefore it has a better chance of breeding
5) the allele frequency of this allele increases at the expense of the less advantageous alleles
What is directional selection?
Where environmental conditions favour those organisms who are away from the mean.
E.g. Conditions change - get colder, thicker furred organisms survive.
What is stabilising selection?
Conditions remain the same
Individuals close to the mean are favoured
