6.1.2 Inheritance Key Terms Flashcards
Genotype
The genetic constitution of an organism (the alleles it has for a gene)
Phenotype
The expression of the genes and its interaction with the environment
Homozygous
A pair of homologous chromosomes carrying the same alleles for a single gene
Heterozygous
A pair of homologous chromosomes carrying two different alleles for a single gene
Recessive allele
An allele only expressed if no dominant allele is present
Dominant allele
An allele that will always be expressed in the phenotype
Codominant
Both alleles are expressed in the heterozygous resulting in a different phenotype
Multiple alleles
More than two alleles coding for a single gene
Sex linkage
A gene whose locus of on the X (or Y) chromosome
Autosomal linkage
Genes that are located on the same chromosome (not sex-chromosomes)
Epistasis
When one gene modifies or masks the expression of a different gene at a different locus
Monohybrid
Genetic inheritance cross of characteristics determined by one gene
Dihybrid
Genetic inheritance cross for characteristics determined by two genes
Chi squared conclusion
The x^2 value (…) is more/less than the critical value at the 5% level (…) at (…) degrees of freedom
Therefore the null hypothesis can be accepted/rejected
The difference between what we expected and observed is statistically significant/insignificant- the differences are/aren’t due to chance
Continuous variation
A characteristic with continuous values.
Due to genetics and the environment, many genes are involved (polygenic)
E.g mass and height of organisms
Discontinuous variation
A characteristic with categorical (discrete) values.
Due to genetics only.
One or two genes involved.
E.g. blood group
Directional selection
One of the extremes has the selective advantage.
Occurs when there’s a change in the environment.
The modal trait changes.
E.g, antibiotic resistance in bacteria
Stabilising selection
The modal trait has the selective advantage.
Occurs when there’s no change in the environment.
Modal trait remains the same
Standard deviation decreases as individuals with the extreme trait decrease.
E.g. human birth weight
Genetic drift
Change in allele frequency I thin a population between generations.
The smaller the population, the bigger the impact allele frequency changes have proportionally-occurs more rapidly.
Genetic bottlenecks
Caused by events that kill almost all of the population, leaving only a few individuals left.
Results in a very small gene pool.
Many alleles for genes are lost, the remaining breeding population pass on the same alleles.
Lack in genetic diversity, genetic diseases that exist are more likely to be passed on.
Founder effect
When a few individuals from an existing population relocate to an isolated area.
This results in a small population breeding together-small gene pool.
Natural selection
Wide range of variations in a phenotype within a population. Due to genetic and environmental factors
Primary source of genetic variation is mutation.
Predation, disease, competition result in selection pressures.
Organisms with phenotypes providing advantages are likely to survive.
Also likely to produce more offspring and pass on their favourable alleles to the next generation.
Effect is a change in allele frequency (evolution)
Artificial selection
Humans select plats or animals with favourable characteristics and deliberately breed them together.
Manipulates the gene pool so the favourable alleles become more common than the less favourable.
Prevalent in creating dog breeds with popular features.
Ethical issues, due to certain selected features, health problems are likely to arise and affect their lives.
Gene banks
A way of maintaining genetic material for use in selective breeding.
Stores of biological samples (plant seeds, animal semen or eggs).
Used to help increase genetic diversity by outbreeding (breeding unrelated individuals)
Reduces the frequency of homozygous recessive disease in the offspring.
