Variation and Evolution Flashcards
what are the three main factors variation (differences in phenotype) between individuals is caused by?
Differences in genotype – genetic factors.
•Different epigenetic modifications - but same genotype.
•Differences in environment – environmental factors
Why is variation important to the survival of an organism?
because it means that they are more likely to adapt and survive changes in the environment
what does discontinuous variation?
A particular phenotype can be controlled by one gene
What is continuous variation?
A particular phenotype can be controlled by more than one gene
what is non-heritable variation (environmental)? (2)
- The environment can affect the way an organism’s genes are expressed, i.e. phenotypic variation.
-This variation cannot be passed to offspring unless an epigenetic change occurs.
If the variation is not passed on to the offspring, then the variation is non-heritable.
Explain how the environment could lead to an epigenetic change:
-An environmental factor (e.g. diet) alters DNA methylation or histone modification.
-This then leads to changes in the expression of the genes
what is genetic variation also known as
heritable variation
what may genetic variation be increased as a result of?
Crossing over between homologous chromosomes during meiosis.
Independent assortment of chromosomes during meiosis.
Independent assortment of chromatids during meiosis.
Mixing of two different parental genotypes at fetilisation.
what does sexual reproduction do compared with mutations?
Sexual reproduction establishes new combinations of already present alleles.
Mutations produce new alleles. These often have a more significant impact on natural selection.
what can enter an inter and intra specific competition have an effect on?
breeding success and survival.
What can competition do?
Competition (e.g. for food/nutrients) can place selective pressures on the survival of different phenotypes and therefore breeding success.
what is the definition of selective pressure?
an environmental factor that can alter the allele frequencies of the alleles present at a particular gene locus in a population
what is the definition of selective agencies?
exert selection pressure, for example, Climate, Human impact, Supply of food, Breeding sites
Who are more likely to survive?
Organisms with well-adapted phenotypes (those whose alleles are selected for and give them a selective advantage) are more likely to survive than those whose phenotypes are less well adapted (those whose alleles mean they are selected against).
what are the phenotype which increase the chance of organism surviving also likely to do?
likely to give a higher breeding success
What selection pressure led to the increase of dark moths during the industrial revolution?
Soot from the factories led to tree bark becoming darker – dark form moths were camouflaged – reduced predation.
if a dominant allele produces a phenotype which gives a selective disadvantage what will happen to the frequency of the dominant allele in the gene pool?
-The frequency of the allele will decrease and it may disappear from the gene pool.
-As any organism with it will have the disadvantageous phenotype so is less likely to breed and pass on the allele
Will the effect be the same for a recessive allele that produces a selective disadvantage? Explain your answer.
No, organisms who are heterozygous will not have the disadvantageous phenotype, so will survive and breed and pass the allele on.
This means the recessive allele will remain at a low frequency in the population.
Only homozygous recessive have a disadvantageous phenotype
what is the gene pool?
the total of all alleles for all of the genes in a population
what is allele frequency?
Number of copies of that allele with all the alleles for that gene
what is the allele frequency equation?
Frequency of dominant allele + frequency of the recessive allele = 1
In a population of 65 organisms, 25 are homozygous dominant and 30 are heterozygous.
What is the frequency of the dominant allele in the gene pool? Show your working.
Total number of allele = 65 x 2 = 130
Number of dominant alleles = 25 x 2 (homozygous ) + 30 (heterozygous)
Number of dominant alleles = 80
Dominant allele frequency = number of dominant alleles /
total number of alleles
What is the hardy Weinberg principal state?
that the frequencies of dominant and recessive alleles and genotypes will remain constant from one generation to the next, if certain conditions remain true
What do the conditions include?
•a large population (100+ individuals);
•no selection for or against any phenotype;
•random mating throughout the population;
•no mutations;
•the population is isolated, i.e. no immigration or emigration.
