Genetic divesity Flashcards
Homologous chromosomes
Two chromosomes with the same sets of genes
Can have different alleles
What is a mutation
An alteration to the DNA base sequence that often arises spontaeously iduring DNA replication
Why might a mutation not lead to a change in the amino acid sequece?
+Genetic code is degenerate so mutation may end up coding for the same amino acid as the original triplet
-Mutation may occur in an intron
What is a substitustion mutation?
-When a nucleotide in the DNA sequence is replaced by another. This is more likely to be a silent mutation
What is a deletion mutation
When a nucleotide in a DNA sequence is lost.
More likely to be harmful, as it leads to a frameshift where the entire amino acid sequence will be different
mutagenic agent
Factors that increase the rate of gene mutation
Examples of mutagenic agents
X-rays
UV lights
Gamma rays
Certain chemicals e.g in alchohol and tobatoc
Polypoloidy chromosome mutation
Where an individual has three or more sets of chromosomes instead of two
What is a chromosome non-disjunction?
When chromosomes fail to seperate correctly in meiosis, resulting in gametes with one more or less chromosome than normal
Meiosis
A form of cell division that produces 4 genetically different haploid cells known as gametes
Haploid
Cells with half the number of chromosomes found in the parent cell
Diploid
Cells that contain two complete sets of chromosome
How does meiosis differ from mitosis
-Meiosis produces four genetically different cells with half the number of chromosomes as the parent cells
-Mitosis produces 2 genetically identical cels with the same number of chromosome as the parent cells
What happens during Meiosis 1
- Homologous chromosomes pair to form bivalents
- Corssing over (exchange of sections of genetic material) occurs at the chiamata
- Cells divide in two. Homologous chromosomes separate randomly in independant segregation. Each cell contains either maternal or paternal copy
What happens during meiosis 2
- Division
Population
All of the organisms of a particular species that live in the same place
Allele
Different forms of a particular gene, found at the same locus on a chromosome
Genetic diversity
The total number of different alleles in a population
What advantage does a high genetic diversity provide
Ability to adapt to a change in environment: allows natural election to occur
Explain how natural selection results in the 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 recieve the new allele and frequency continues to increase over many generationd
What is directional selection
Occurs when environmental conditions change
Individuals with phenotypes suited to the new conditions will survive and pas on their genes
Over time the mean of the population will move towards these characteristics
Example of directional selection
Antibiotic resistance
Stabilising selection
Occurs when environmental conditions stay the ame
Individuals closest to the mean are favoured, and any new characteristics are selected against
Results in low diversity
Example of stabilising selection
Birth weight
