Genetic Diversity Flashcards
What is a mutation?
An alteration to the DNA base sequence. Often arise spontaneously during DNA replication
Why might a mutation not lead to change in the amino acid sequence?
Genetic code is degenerate so mutations may end up coding for the same amino acid as the original triplet
Mutation may occur in an intron
What is a substitution mutation?
When a nucleotide in the DNA sequence is replaced by another. This is more likely to be a quiet mutation, meaning no change occurs in the amino acid sequence
What is a deletion mutation?
When a nucleotide in the DNA sequence is lost. This is more likely to be harmful and significant as it leads to a frame shift which means the entire amino acid sequence will be different
What is a mutagenic agent? Give examples of this
Factors that increase the rate of gene mutation. X-rays, UV light, gamma rays, certain chemicals e.g alcohol and tobacco
What is a polyploidy chromosome mutation?
Where an individual has three or more sets of chromosomes instead of two
What is chromosome non-disjunction?
When chromosomes fail to separate correctly in meiosis, resulting in gametes with one more or less chromosome than normal
What is meiosis?
A form of cell division that produces four genetically different haploid cells (cells with half the number of chromosomes found in the parent cell) known as gametes
How does meiosis differ from mitosis?
Meiosis produces four genetically different cells with half the number of chromosomes as the parent cells
Mitosis produces two genetically identical cells with the same number of chromosomes as the parent cells
What happens during meiosis I?
- Homologous chromosomes pair to form bivalents
- Crossing over (exchange of section of genetic material) occurs at chiasmata
- Cell divides into two. Homologous chromosomes separate randomly. Each cell contains either maternal or paternal copy
What happens during meiosis II?
- Independent segregation of sister chromatids
2. Each cell divides again, producing 4 haploid cells
In which two ways does meiosis produce genetic variation?
- Crossing over during meiosis I
- Independent assortment of homologous chromosomes and sister chromatids
Results in new combinations of alleles
Define population
All the organisms of a particular species that live in the same place
What is an allele?
Different forms of a particular gene, found at the same locus on a chromosome. A single gene could have many alleles
Define genetic diversity
The total number of different alleles in a population
What advantage does a high genetic diversity provide?
The ability to adapt to a change in environment; allows natural selection to occur
Explain how natural selection results in development of new characteristics
Random mutations result in new alleles
Some alleles provide an advantage, making an individual more likely to survive and reproduce
Their offspring receive the new allele and frequency continues to increase over many generations
What is directional selection?
Occurs when environmental conditions change. Individuals with phenotypes suited to the new conditions will survive and pass on their genes. Over tim the mean of the population will move towards these characteristics
Give an example of directional selection
Antibiotic resistance. Bacteria with a mutation allowing them to survive in the presence of antibiotics will reproduce. Therefore frequency of this allele will increase and the population will shift to have greater antibiotic resistance
What is stabilising resistance?
Occurs when environmental conditions stay the same. Individuals closest to the mean are favoured and any new characteristics are selected against
Results in low diversity
Give an example of stabilising selection
Birth weight; babies that weigh around 3kg are more likely to survive than those at lower or higher weights
Define a niche
The role of a species within its environments. Species sharing the same niche will compete with each other
What are three types of adaptation? Give examples of each
Anatomical: changes to the body structure e.g oily fur
Physiological: changes to bodily processes e.g venom production
Behavioural: changes to action e.g hibernation
