Genetic Diversity, adaptation and meiosis Flashcards
Define mutation?
Any change in the quantity or base sequence of DNA
Why do not all mutations result in changes in amino acid sequence?
Due to the degenerate nature of genetic code.
Different types of gene mutation?
Substitution or deletion
What usually has worse consequences substitution or deletion?
Deletion
Each base has been shifted to the left causing the sequence to be read differently.
What is a mutagenic agent?
Something that increases the likelihood of mutation occurring eg. UV radiation
What are chromosome mutations?
Changes in the number or structure of whole chromosomes
What are polyploidy mutations.
Changes in whole sets of chromosomes
Where organisms have more than the two normal sets of chromosomes
What are non disjunction mutations?
When individual homologous pairs of chromosomes fail to separate during meiosis.
Leading to organisms having one more or less of this particular chromosome
What type of mutation is downs syndrome
Disjunction as human’s have an extra chromosome 21
What’s the importance of meosis?
Allows genetic variation and maintains a constant number of chromosomes by producing haploid daughter cells.
Process of meiosis
DNA replicates and unravels so there are two copies of each chromosome
In Meiosis 1 the chromosomes arrange themselves into homologous pairs. There chromatids wrap around each other and crossing over may occur leading to genetic recombination.
In the first division it is the homologous pairs that are separated.
In the second division the sister chromatids are separated - same process as mitosis
Result is 4 haploid daughter cells
How does meiosis lead to genetic variation?
Genetic recombination by crossing over:
When homologous chromosomes come together and pair up the chromatids twist around each other and bits swap over.
This leads to different combinations of alleles
Independent segregation of homologous chromosomes:
Random separation of maternal and paternal chromosomes into daughter cells.
Define gene
A sequence of DNA bases that code for a polypeptide
Define locus
The position of a gene on a chromosome or DNA molecule
Define allele
Version of a particular gene
Define homologous chromosome
A pair of chromosomes, one maternal and one paternal that have the same gene loci
Causes of genetic variation?
Independent segregation of homologous chromosomes
Genetic recombination via crossing over
Random fertilisation of gametes
Mutation
Different types of natural selection?
Directional selection
Stabilising selection
What is directional selection?
Occurs when the environmental conditions change.
One extreme of the phenotype is selected for and one is selected against.
When this phenotype causes an advantage the organism is more likely to survive and reproduce.
Over time there is a higher proportion of the population with this allele. Therefore, the mean will then move in the direction of these individuals.
What is stabilising selection?
Occurs when environmental conditions are not changing.
Extremes of the phenotype are selected against and therefore these alleles are less likely to be passed on due to lower survival rates.
Therefore, over time the alleles will stabilise towards the mean and there is less variation at the extremes.
