4.1 Inheritance, Selection and Speciation Flashcards
Define: Phenotype
The appearance of a characteristic due to the expression of the genotype and its interaction with the environment.
What is a genotype?
The genetic makeup of an organism. Refers to alleles present.
Define: alleles
Different forms of the same gene.
Define: locus
The position of a gene on a chromosome.
Alleles occupy the same locus on each member of a pair of homologous chromosomes.
Define: dominant allele
Always expressed in the phenotype.
Define: recessive allele
Only expressed when the genotype is homozygous recessive.
Define: Codominance
Both alleles are expressed in the phenotype. Both contribute to the appearance.
Define: multiple allelism?
More than two alleles of a particular gene. Only two can be present in a genotype.
Define: sex linked gene
Where the gene is carried on only one type of sex chromosome, usually the X chromosome.
Why is the observed ratio different to the expected ratio?
The fusion of gametes is random.
What is a test cross?
The crossing of an organism with a homozygous recessive.
Define: gene pool
All the alleles of all the individuals of a population at any one time.
Define: allelic frequency
The number of times an allele of a particular gene occurs within a gene pool.
What are the principals of the Hardy Weinberg equilibrium?
Population is large Mating is random No mutations occur No selection Population is isolated
What do p and q represent in the Hardy Weinberg equation?
p= frequency of dominant allele
q= frequency of recessive allele
What do p^2, q^2 and 2pq represent in the Hardy Weinberg equation?
p^2 = frequency of homozygous dominant genotype
q^2 = frequency of homozygous recessive genotype
2pq = frequency of heterozygous genotype
Describe natural selection.
Variation is present in a population due to mutations.
A change in the environment results in some being better adapted.
Organisms with higher differential reproductive success will survive and breed and pass on these alleles to offspring.
The frequency of the beneficial allele increases in the gene pool.
When are two organisms considered different species?
When they breed, infertile offspring are produced.
Describe speciation.
Variation is present due to mutations and the population is split by geographical isolation.
Different environmental conditions result in different advantageous alleles (selection).
There is no gene flow between gene pools.
Eventually, gene pools become so different they become different species.
Different alleles increase in frequency.
What is stabilising selection?
Selection when the environment isnt changing, usually when an allele is advantageous
Favours those in middle of range
What is directional selection?
Selection when the environment is changing, selects for those with alleles for a phenotype towards extreme of a range
Results in change in range until new optimum is established
