✅9 - Genetic Diversity Flashcards
What is a mutation?
A change to the base sequence of DNA
What is substitution?
When one nucleotide is exchanged for another
What does the significance of a substitution mutation depend on?
The importance of the original amino acid
How can a substitution affect the amino acid sequence?
If the codon is altered to code for a different amino acid, then the sequence will be altered and the polypeptide changed
What is a deletion mutation?
When a nucleotide is lost from the normal DNA sequence
What can deletion cause?
Frame shift
What are chromosome mutations?
Changes in the structure or number of whole chromosomes
What are the two forms of chromosome mutation?
Changes in whole sets of chromosomes
Changes in the number of individual chromosomes
When do changes in whole sets of chromosomes occur?
When organisms have three or more sets of chromosomes rather than the usual two, called polyploidy
When do changes in the number of individual chromosomes occur?
When chromosomes fail to separate in meiosis, and organisms get one more or one less chromsome
What is mitosis?
Produces two daughter cells with the same number of chromosomes as the parent cell and as each other
What is meiosis?
Usually produces four daughter cells. each with half the number of chromosomes as the parent cell
Why is meiosis important?
Otherwise the number of chromosomes would double each time the gametes fused
What happens in the first division of mitosis?
The homologus chromosomes pair up and their chromatids wrap around each other - crossing over may occur
What happens in the second division of meiosis?
The chromatids move apart and four cells form
How does meiosis being about genetic variation?
Independent segregation of homologus chromosomes
Crossing over
How does independent segregation occur?
The chromosomes arrange themselves randomly as they line up and which of each pair goes into the daughter cell depends on how they are lined up
How does crossing over occur?
The chromosomes become twisted around each other and tensions are created, causing portions to break off. These portions may rejoin with the chromatids of the homologus partner, creating new genetic combinations
What is genetic diversity?
The total number of different alleles in a population
What is allelic frequency?
The relative frequency of an allele in a population
What is selection?
The process by which organisms that are better adapted to their environment tend to survive and breed
What is directional selection?
Favouring alleles to one side of the mean, phenotypes to one extreme
What is an example of directional selection?
Antibiotic resistance of bacteria
What is stabilising selection?
Favouring phenotypes around the mean, eliminating extremes
What is an example of stabilising selection?
Birthweight of babies
What are anatomical adaptions to the environment?
Shorter ears and thicker fur in arctic foxes
What are physiological adaptions to the environment?
Oxidising of fat rather than carbohydrates in kangaroo rats to product additional water in dry areas
What are behavioural adaptions to the environment?
Autumn migration of swallows from the UK to Africa
