Section 4 - Genetic information, variation and relationships between organisms: 9. Genetic diversity Flashcards
What is a mutation
A change in the arrangement of the bases in an individual gene, or in the structure of the chromosome (leading to changes in the arrangement of genes)
What are gene mutations
Changes in the sequence of bases
What are the 3 types of gene mutations
- Substitution
- Deletion
- Insertion
What is a substitution
When one nucleotide is replaced by another, changing one base in the sequence
What is the potential impact of a base substitution
- May have no impact, due to the degenerate code (could code for the same amino acid)
- If the amino acid does change, minimal impact as only one is different
What is a deletion
When one nucleotide is lost, so one base is missing from the sequence
What is an insertion
When one nucleotide is added, giving an extra base in the sequence
What is the potential impact of a base deletion/insertion
Causes a frameshift, as the following triplet codes are all moved along by one, impacting each of the following amino acids
(can completely change the protein structure)
What are chromosome mutations
Changes in the structure or number of whole chromosomes
What are the 5 types of chromosome mutations
- Deletion
- Duplication
- Inversion
- Translocation
- Whole chromosome mutations
What is Gene deletion
When a section of a chromosome is removed
What is Gene duplication
When a section of chromosome is added from its homologous partner, giving one chromosome 2 copies of one gene
What is Gene inversion
When a section of a chromosome is reversed
What is Translocation
When sections of chromosomes are swapped between two chromosomes
What are whole chromosome mutations
When an entire chromosome is lost or replaced
What is Polyploidy
The process (Chromosome mutations) leading to becoming Polyploid (having more that two sets of chromosomes)
Mainly in plants
What is Non-disjunction
When pairs of chromosomes fail to separate in meiosis, leading to one more/less chromosome
Eg. Downs syndrome: Additional chromosome 21
What are the possible effects of mutations
- Production of new/superior proteins (Reproductive advantage)
- Neutral mutation (No change, due to degenerate code)
- Production of no/inferior proteins (potentially causing disease and fatality)
What is meiosis
Cell division producing 4 daughter cells, each with half the number of chromosomes as the parent
What happens during meiosis 1
Homologous chromosomes separate into different cells
What happens during meiosis 2
Chromatids from the homologous chromosomes are separated into 4 cells
(same as mitosis, but splits into 4, rather than 2)
What is the importance of meiosis
Allows for gametes to be produced with half the number of chromosomes (Haploid number), so when they fuse during fertilisation, the off-spring has the correct diploid number.
What is Independent segregation (random assortment)
During meiosis 1, each of the chromosomes in the homologous pair will randomly pass to each daughter cell
What is the effect of Independent segregation (random assortment)
As each chromosome will have a different allele of the same gene, the arrangement of the pair before separation in meiosis 1, and the following division of meiosis 2, will impact the allele of the daughter cell
What is genetic recombination by crossing over
- When lined up before separation in meiosis 1, chromatids of the homologous chromosomes can become twisted
- This leads to portions of the chromatids being broken off and exchanged between the chromosomes, producing new combinations of alleles
What is the chiasma
The point where two chromatids cross during genetic recombination
How many possible chromosome combinations can occur in the daughter cell as a result of meiosis (not regarding genetic recombination, which would increase this)
2^n
(n = number of homologous pairs)
How many possible chromosome combinations can occur as a result of sexual reproduction (not regarding genetic recombination, which would increase this)
(2^n)^2
(n = number of homologous pairs)
What is genetic diversity
The total number of different alleles in a population
What is the benefit of greater genetic diversity
Greater chance of some individuals within a population surviving an environmental change
What is natural selection
The process by which organisms that are better adapted to their environment tend to survive and breed, passing on their advantageous characteristics
What is the selection pressure
The changed environmental factor that determines which traits (and therefore alleles) are more advantageous
What is a polygenetic trait
A characteristic that is influenced by more than one gene, most impacted by natural selection
What is the process of natural selection
- Gene pool within a population contains a variety of alleles
- A Selection pressure will favour a certain group of alleles, due to their advantageous characteristics
- Individuals with these alleles are more likely to survive and breed, passing on their desired characteristics to the next generations
- This repeats over many generations, resulting in adaptation and evolution
What are the 3 types of selection
- Directional
- Disruptive
- Stabilizing
What is Directional selection
When one of the extremes of the characteristic is favoured by the selection bias, causing the mode to move in that direction
What is an example of Directional selection
- Giraffe evolution: Longer necks could reach leaves
- Pepper moths: darker trees due to soot in the industrial revolution was advantageous for dark coloured moths
What is Disruptive selection
When both extremes of the characteristic are favoured, so the current mode is selected against
What is an example of Disruptive selection
- Breeding Fish: Large males mate by brute force, small makes ‘sneak’ in an fertilise the eggs
- Prey animals: Large are too big to attack, small can hide
What is Stabilizing selection
When environmental conditions remain stable, favouring phenotypes closest to the mean
What is an example of stabilizing selection
- Baby weights: Small will lose heat quickly, Large is heavy and hard to pass through the pelvis
- Oyster colour: Too light/too dark, don’t blend and are eaten
What are the 3 types of adaptation that can arise from natural selection
- Anatomical (Physical): eg. Thick fur
- Physiological (Biology): eg. Oxidising fats instead of carbs, to give extra water
- Behavioural: eg. Migration patterns
