3.4.3 genetic diversity can arise as a result of mutation or during meiosis Flashcards
1
Q
what can a gene mutation involve?
A
- change in the base sequence of chromosomes
- can arise spontaneously
2
Q
what are the types of gene mutation?
A
deletion and substitution
3
Q
why do some substitution mutations not result in a mutation?
A
- due to the degenerate nature of the genetic code
- some amino acids are coded for by more than one DNA triplet code
- not all substitutions result in a change in the primary structure
4
Q
what are mutagenic agents?
A
- external influences that induce mutations
5
Q
how do mutagenic agents increase the rates of mutations?
A
- certain chemicals can remove groups from nucleotide bases
- other chemicals can add groups to nucleotides
6
Q
what does meiosis produce?
A
daughter cells that are genetically different from each other
7
Q
outline interphase
A
- happens before meiosis
- chromosomes replicate to form 2 sister chromatids joined at a centromere
8
Q
outline prophase I
A
- chromosomes condense and become visible
- homologous pairs of chromosomes come together to form a bivalent
- adjacent chromatids exchange genes during crossing over
9
Q
outline metaphase I
A
- nuclear membrane broken down
- spindle fibres produced at centrioles
- bivalents move to the equator of the cell
- centromeres attach to spindle
- positioning of homologous pairs is random ( independent segregation)
10
Q
outline anaphase I
A
- homologous chromosomes are pulled apart
- by contraction of spindle fibres
11
Q
outline telophase I
A
- chromosomes group together at the poles of the cell
- the spindle disappears
- nuclear envelope reforms
12
Q
outline prophase II
A
- 2 haploid cells divide a 2nd time
- new spindle begins to form in each cell
13
Q
outline metaphase II
A
- chromosomes line up on the equator of the spindle
- chromatids may not be identical but instead recombinants
14
Q
outline anaphase II
A
- chromatids are pulled apart by protein spindles contracting
- centromeres divide and chromatids move to opposite poles of the cell
15
Q
outline telophase II
A
- spindle fibres breakdown
- nuclear envelope reforms around separated chromosomes
16
Q
outline the importance of meiosis
A
- reduces number of chromosomes in a cell before fertilisation
- fusion of gametes restores diploid number
- results in new combinations of alleles increasing genetic diversity
17
Q
how does random fertilisation increase genetic diversity?
A
random fertilisation produces a zygote with different combinations of chromosomes and so different combinations of alleles
