3.7 Genetics , populations , evolution and ecosystems (A- level only) Flashcards
what is a genotype?
The genetic constitution of an organism.
What is a phenotype?
The expression of the genes and its interaction with the environment.
What is a homozygous allele?
A pair of homologous chromosomes carrying the same alleles for a single gene.
What is a heterozygous allele?
A pair of homologous chromosomes carrying two different alleles for a single gene.
What is a recessive allele?
An allele only expressed if no dominant allele is present .
What is a dominant allele?
An allele that will always be expressed in the phenotype.
What is multiple alleles?
More than two alleles for a single gene.
What is sex - linkage ?
A gene whose locus is on the X chromosome.
What is autosomal linkage?
Genes that are located on the same chromosome ( not the sex - chromosomes).
What is epistasis?
When one gene modifies or masks the expression of a different gene at a different locus.
What is monohybrid inheritance?
Genetic inheritance cross of a characteristic determined by one gene.
What is dihybrid inheritance?
Genetic inheritance cross for a characteristic determined by two genes .
What is co dominance ?
Both alleles are equally dominant and expressed in the phenotype.
What is gene pool?
All the alleles of all genes within a population at one time.
What is population ?
All the individuals of one species in one area at one time.
What is allele frequency ?
The proportion of an allele within the gene pool.
What is the Hardy - Weinberg principle ?
The mathematical model which can be used to predict the allele frequencies within a population.
What is the accuracy / conditions of the hardy - weinberg principle?
It assumes that there will be no change in the allele frequency between generations within a population , so it’s not perfectly accurate.
What are the assumptions of the hardy - weinberg principle ?
• No migration to introduce or removal of alleles from the population.
• No mutations to create new alleles
• No selection favouring particular alleles.
• Mating is random ( no inbreeding)
• The population is large
What is the hardy - weinberg equation?
p^2 + 2pq + p^2 = 1
p^2 = frequency of homozygous dominant genotype.
2pq = frequency of heterozygous genotype.
q^2 = frequency of homozygous recessive genotype.
p+q= 1
p = frequency of dominant allele
q = frequency of recessive allele
What causes variation within a population of species ?
- main source is mutation
- meiosis (crossing over and independent segregation)
- random fertilisation
What are the three types of selection?
- Stabilising
- Directional
- Disruptive
What is disruptive selection ?
- Individuals which contain the alleles coding for either extreme trait are more likely to survive and pass on their alleles.
- Allele frequency changes and more individuals possess the allele for the extreme trait.
- middling trait allele becomes less frequent
- continued disruptive selection can ultimately lead to speciation
What is speciation ?
Speciation is the process that results in the creation of new species
How does speciation happen?
•One original population of the same species becomes reproductively isolated.
•This means that there are now two populations of the same species but they cannot breed together.
• Results in the accumulation of differences in their gene pool
What are the two ways that populations can become reproductively isolated ?
• Allopatric speciation
- Geographical barrier
• Sympatric speciation
- Changes in the reproduction mechanisms
What is sympatric speciation?
Populations can become reproductively isolated due to differences in their behaviour
How can sympatric speciation occur?
- Due to random mutation which could impact reproductive behaviour such as may cause to perform different courtship behaviour
- Due to this , individuals will not reproduce together so no gene flow between the two groups within the population
- Overtime these reproductively isolated populations will accumulate different mutations to the extent that their DNA is so different they can’t interbreed therefore classed as two different species
What is genetic drift?
This is the change in the allele frequency within a population between generations.
What can result in evolution?
- Continuous , substantial genetic drift can result in evolution
- the smaller the population is the bigger the impact allele frequency have and this is why evolution occurs more rapidly in smaller populations
