4.2 (9) - Genetic Diversity Flashcards
Mutations Meiosis and genetic variation Genetic diversity and adaptations Types of selection
What is a gene mutation?
Any change to one or more nucleotide bases, or a change in the sequence of bases, in DNA
What is base substitution?
Where a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base
How does base substitution affect the final polypeptide?
The final polypeptide will differ only in 1 amino (codon with 3 bases) - the significance of this depends upon the exact role of the original amino acid
What is base deletion?
Where a nucleotide is lost from the normal DNA seuqence
How does base deletion affect the final polypeptide?
The DNA’s sequence of bases is read differently because each has been shifted to the left by 1 base, causing the final polypeptide to function incorrectly
What is a chromosome mutation?
A change in the structure/number of whole chromosomes
What are 2 types of chromosome mutations?
Changes in:
- whole sets of chromosomes
- number of individual chromosomes
When does a change in whole sets of chromosomes occur?
Occurs when organisms have 3 or more sets of chromosomes (polyploidy), rather than 2
When does a change in the number of individual chromosomes occur?
Occurs when individual chromosomes fail to separate during meiosis, which usually results in a gamete having ±1 chromosome
What is meiosis?
The special form of cell division used to produce gametes (sex cells)
What is the purpose of meiosis?
- To form haploid cells with half the chromosome number
- To re-arrange the chromosomes with a new combination of alleles
Describe the process of meiosis 1 in 6 stages
1) Interphase
- start with 2 single chromatids
- DNA is copied
2) Prophase 1
- the doubled chromosomes pair up
- recombination (crossing over) occurs
3) Metaphase 1
- Chromosomes line up at the equator
4) Anaphase 1
- Chromosomes are pulled apart by meiotic spindle
5) Telophase 1
- Cell pinches in the middle
6) Cytokinesis
- Cells separate, due to a ring of protein filament around the cell that tightens - results in 2 daughter cells
Describe the process of meiosis 2 in 5 stages
1) Prophase 2
- 2 daughter cells
2) Metaphase 2
- Chromosomes line up at the equator of each cell
3) Anaphase 2
- Sister chromatids are pulled apart by meiotic spindle
4) Telophase 2
- Both cells pinch in the middle
5) Cytokinesis
- Cells separate, due to a ring of protein filament around the cells that tightens - results in 4 granddaughter cells
Describe the process of meiosis in 11 stages
1) Interphase
- start with 2 single chromatids
- DNA is copied
2) Prophase 1
- the doubled chromosomes pair up
- recombination (crossing over) occurs
3) Metaphase 1
- Chromosomes line up at the equator
4) Anaphase 1
- Chromosomes are pulled apart by meiotic spindle
5) Telophase 1
- Cell pinches in the middle
6) Cytokinesis
- Cells separate, due to a ring of protein filament around the cell that tightens - 2 daughter cells
7) Prophase 2
- 2 daughter cells
8) Metaphase 2
- Chromosomes line up at the equator of each cell
9) Anaphase 2
- Sister chromatids are pulled apart by meiotic spindle
10) Telophase 2
- Both cells pinch in the middle
11) Cytokinesis
- Cells separate, due to a ring of protein filament around the cells that tightens - results in 4 granddaughter cells
What are the 2 sources of genetic variation in sexual reproduction?
- Genetic recombination by crossing over
- Independent segregation of homologous chromosomes
What is a chiasma?
The point at which chromatids are in contact during crossing over
What is the point at which chromatids are in contact during crossing over called?
Chiasma
What is crossing over?
- In prophase 1, the chromatids become twisted around each other
- During the twisting, tensions are created and portions of the chromatids break off - they may re-combine with their homologous partner (recombination)
- There are always equal amounts crossed over, so chromosomes stay the same length
What is the purpose of crossing over?
Maternal and paternal alleles can be mixed (provides new combinations of alleles)
What is independent segregation?
In meiosis 1, chromosomes can line up along the cell’s equator in any order, resulting in different possible combinations
What is non-disjunction?
When pairs of homologous chromosomes fail to separate during meiosis
How do you work out the number of combinations of chromosomes?
2∧n, where n = the number of pairs of homologous chromosomes
What does genetic diversity mean?
The number of different alleles in a population
What is a population?
A group of individuals of the same species that live in the same place and can interbreed
What is allele frequency?
The number of times a specific allele occurs
What are 2 types of selection?
- Directional selection
- Stabilising selection
What is directional selection?
Directional selection is where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce
What is stabilising selection?
Stabilising selection is where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce
What are three adaptations based on natural selection?
- Anatomical
- Physiological
- Behavioural
What is an anatomic adaptation? Give an example
An adaptation to do with physical features (eg. thicker fur or short ears)
What is an physiological adaptation? Give an example
An adaptation to do with the inner workings of the body (eg. oxidising fat rather than carbohydrates to produce water)
What is an behavioural adaptation? Give an example
An adaptation to do with an organism’s behaviour (eg. migration)
