Biodiversity & natural selection Flashcards
What are linked genes?
How do they function
are genes that are carried on the same chromosome and are inherited together.
Linked genes cannot assort independently (unlike genes on different chromosomes) as they are physically linked to each other on the same chromosome and cannot separate (randomly) during meiosis. This reduces genetic variation because different allele combinations for the linked genes cannot occur unless crossing over happens. (Note: this means the expected phenotype ratios of a dihybrid cross (e.g. 9:3:3:1 or 1:1:1:1) do not occur for linked genes)
Define and explain Genetic Diversity,
Why is it important for survival?
Genetic diversity is variations in the genetic make-up / genotypes / total number of genetic characteristics in a population / gene pool
Differences in alleles for genes between individuals is what gives a population or gene pool its genetic diversity. If there are many different forms of alleles (a large range of alleles) then the population/gene pool has a high genetic diversity.
Having many different combinations of alleles may offer a survival advantage if conditions change. Due to the high genetic diversity there is a chance some individuals may have combinations of alleles (therefore phenotypes) that allow them to survive despite any changes in environmental conditions, thus ensuring the
survival of the species
Define:
-Gene pool
-Allele frequency
^ how to calculate allele frequency
Gene Pool = the sum total of all alleles available to a population
Allele Frequency = the percentage of each allele in a gene pool
total number of specified allele / total number alleles x 100
Define Evolution,
what processes result in it?
Evolution: Is the change in allele frequencies in populations over time
-Mutation
-Migration
-Genetic Drift
-Natural Selection
What are the changes in gene pools that can occur?
-increase or decrease in allele frequency of a particular allele
-An allele may become LOST from the gene pool
-AN allele may become FIXED in the gene pool (meaning it’s frequency would be 100%)
What is the difference between small and large gene pools?
-Large gene pools have a high amount of genetic diversity – this is generally due to having a large population size. There are more individuals therefore greater chance of random mating which will result in greater diversity.
-Small gene pools have low genetic diversity – generally due to having a small population size. Smaller gene pools - any gene pool changes will have a larger proportional effect. Allele frequencies are more likely to change with any small changes. Alleles are more likely to become lost or fixed. there is the possibility of inbreeding between closely related individuals and this can further lead to low diversity.
Define natural selection
Natural selection – Natural variation exists in a population, where some individuals may have phenotypes (adaptations) that are better suited to the
environmental conditions. These individuals have a better chance of survival and reproduction. This means they pass on their more favourable alleles to the next
generation.
What are selection pressures?
The factors that determine which phenotype/s is favourable (those that increase survival and reproductive success) are known as selection pressures. These can include environmental conditions, predators, prey, competition, disease.
What is the process of Natural Selection?
how does it change gene pools over time?
Variation
-due to random mutations
Adaption
-offer phenotype advantages so favourable adaption
Reproduction
-good alleles = more reproduction
Passing on
-offspring inherit good alleles
allele frequency of the favourable alleles, will increase in frequency in the gene pool over time.
What is artificial selection?
Give examples
This practice, called artificial selection or selective breeding, involves breeding (selecting) from
individuals with the most desirable phenotypes.
wild brassica –> broccoli, cauliflower, Brussel sprouts , cabbage etc
wolf –> silly dogs
Natural selection vs artificial selection?
Artificial = people select not environment, faster, inbreeding
Natural = good alleles passed down, environmental factors are selecting agents
