genetics, populations and evolution Flashcards
What is a gene?
A sequence of DNA bases that codes for a protein (polypeptide).
What is an allele?
A different version of a gene caused by a difference in base sequence.
What is a genotype?
The genetic constitution (alleles) of an organism.
What is a phenotype?
The expression of the genotype and its interaction with the environment.
What is a dominant allele?
An allele whose trait appears in the phenotype even with only one copy present.
What is a recessive allele?
An allele whose trait only appears in the phenotype if two copies are present.
What are codominant alleles?
Two alleles that are both expressed in the phenotype.
What is a locus?
The fixed position of a gene on a chromosome.
What is a homozygote?
An organism with two identical alleles at a gene locus.
What is a heterozygote?
An organism with two different alleles at a gene locus.
What is a carrier?
A person who carries a recessive allele but does not express it in the phenotype.
What is a monohybrid cross?
A genetic cross involving one gene with two alleles.
What is a dihybrid cross?
A genetic cross involving two genes. The typical F2 phenotypic ratio is 9:3:3:1.
Why might actual ratios deviate from expected ratios in a dihybrid cross?
Due to sex linkage, autosomal linkage, or epistasis.
How does the ABO blood group system work genetically?
It involves 3 alleles: IA, IB (codominant), and IO (recessive).
What is sex linkage?
When a gene is located on a sex chromosome, often the X chromosome.
Why are males more likely to express X-linked recessive traits?
Males have only one X chromosome, so recessive alleles are always expressed.
What is autosomal linkage?
When genes are on the same autosome and are inherited together unless separated by crossing over.
What is epistasis?
When one gene masks or suppresses the expression of another gene.
Example of epistasis?
Baldness gene masking the gene for widow’s peak — baldness is epistatic.
What is the chi-squared test used for in genetics?
To determine whether observed results significantly differ from expected ratios.
What is the null hypothesis in a chi-squared test?
There is no significant difference between observed and expected values.
How do you calculate degrees of freedom in chi-squared tests?
Number of categories - 1.
When do you reject the null hypothesis in chi-squared tests?
When the chi-squared value is greater than or equal to the critical value.
What is the gene pool?
The complete set of alleles in a population.
What is allele frequency?
The proportion of a particular allele in a population, usually given as a percentage.
What are the Hardy-Weinberg equations?
Allele frequency: p + q = 1
Genotype frequency: p² + 2pq + q² = 1
What conditions must be met for Hardy-Weinberg to apply?
No mutations, large population, random mating, no selection, no migration.
What causes genetic variation?
Mutation, crossing over, independent assortment, random fertilisation.
What causes phenotypic variation?
Genetic factors, environmental factors, or a combination of both.
What is natural selection?
The process where individuals with advantageous traits survive and reproduce, passing on their alleles.
What is stabilising selection?
Favours average phenotypes, reducing variation. Occurs in stable environments.
What is directional selection?
Favours one extreme phenotype. Occurs during environmental change.
What is disruptive selection?
Favours both extremes over the average. Leads to increased variation.
What is speciation?
The formation of new species due to reproductive isolation.
What is allopatric speciation?
Speciation due to geographic isolation and different selection pressures.
What is sympatric speciation?
Speciation without geographic isolation, due to random mutations.
What is seasonal isolation?
When organisms breed at different times of the year.
What is mechanical isolation?
Mating is prevented by incompatible reproductive organs.
What is behavioural isolation?
Differences in courtship behaviours prevent mating.
What is genetic drift?
A change in allele frequencies due to random chance, not selection.
In which populations does genetic drift have the greatest effect?
Small populations.
What are the consequences of genetic drift?
Loss of genetic variation, fixation or loss of alleles.
