genetic diversity and adaptation Flashcards
What is a mutation
random change to quantity or base sequence of DNA
genes and chromosome mutations
gene- changes to nucleotide bases or sequence of bases in DNA (micro)
chromosome (macro)- can have changes to whole chromosomes-occur when organisms have three or more sets of chromosomes, rather tham the usual two. Condition is called polyploidy and occurs mostly in plants
-can have changes to number of individual chromosomes. sometimes homologous pairs fail to seperate during meiosis. Called non-disgunction and results in a gamete having one more or one fewer chromosome. On fertilisation of a gamete with normal number of chromosmes, forms offspring with one more or one fewer chromosome in all body cells. An example is down syndrome
Types of mutation
Substition of bases- nucleotide is replaced with another. Can result in multiple outcomes. May have no effect as code is degenerate, but if protein is functional protein eg enzyme could alter active site and stop protein working
insertion and deletion- shift reading frame so may result in whole new amino acid sequence.
READING FRAME- way of dividing the sequence of nucleotides on DNA or RNA into consecutive, non-overlapping triplets
genetic diversity
total number of different alleles in a population (gene pool)
population
group of individuals of the same species that live in the same place and can interbreed
Natural selection process
1- variation exists within gene pool. New alleles will be created by mutations
2- best adapted survive and reproduce (have more reproductive success)
3-best alleles are passed on
4- new generation with mutated allele more likely to survive so allele passed on again and this repeats over multiple generations
5- successful allele frequency increases as these alleles give the organism an advantage over other individuals within the population and the non-advantages allele frequency decreases
what is selection
process by which organisms that are better adapted to their environment tend to survive and breed, while those who are less well adapted tend not to
directional selection
Occurs as a result of a change in the environment. Favours individuals varying in 1 direction from the mean (extreme phenotypes)
Results in a change in characteristics within the population with more organisms having the extreme phenotype
This causes normal distribution curve to shift to left or right but remain the same shape
IF environmental change is great enough may beno phenotype suited to new conditions so population will die out
stabilising selection
If environmental conditions remain stable it is individuals with phenotypes closest to the mean that are favoured.
These individuals are more likely to pass on their alleles to the next generation and those individuals with extreme phenotypes are less likely to
causes normal distribution curve to become narrower or higher but mean does not change
Stabilising selection therefore tends to eliminate phenotypes at the extreme
Disruptive selection
occurs when both extreme traits are favoured in an environment. Disruptive selection increases genetic and phenotypic diversity in a population, since more than one phenotype, or physical trait, is favoured.
eg short tails help keep predators from catching you on the ground and long tails are good for balance in trees but medium tails dont help
sexual selection
involves random mutations affecting what is considered to be sexually attractive when there is competition for mates
Types of adaptations
1- behavioural- eg mating rituals, hibernation, migration
2-anatomical- structural changes to help survival eg thicker fur in artic foxes compared to those in warmer climates
3-physiological- changes to internal organs, tissues and cells to help survival eg oxidation of fat rather than carbohydrates in kangaroo rats to produce additional water in dry dessert environments, venom production in snakes
why will a mutation to DNA be more damaging than a mutation of RNA
-errors in DNA will may be inherited and therefore have a permanent affect on the whole organism. Errors in transcription usually only affected specific cells, are temporary and are not inherited, so are therefore less dangerous
recombination
- when the broken off portions of chromatid, during crossing over , recombine with another chromatid
-usually equivalent portions of homologous chromosomes are exchanged
equation to calculate number of possible combinations of chromosomes for each daughter cell
2^n
where n= number of pairs of homologous chromosomes
when gametes come from two different parents can use: (2^n)^2
these still assume no crossing over has occurred and all chromosomes remain intact
