Chapter 20 - Inheritance + Variation Flashcards
What is a Phenotype?
The physical expression of an organism’s genetic consitution
How can meiosis bring about genetic variation?
- Random arrangement of chromosomes during lining up (independent assortment)
- Crossing over of chromatids before the first division
How does random fertilisation bring about genetic variation
- Gametes = haploid (only contains half a person’s DNA)
- Determined by meiosis - every gamete contains different DNA - therefore same 2 organisms can produce genetically different offspring
What is Monogenic Inheritance?
Where one phenotypic characteristic is controlled by a single gene
What is Dihybrid Inheritance?
Where 2 phenotypic traits are determined by 2 different genes present on two different chromosomes at the same time.
What is sex-linkage?
When an allele is located on one of the sex chromosomes, meaning expression depends on the sex of the individual
What is multiple alleles?
A gene with more than two alleles
What are codominant alleles?
When two dominant alleles both contribute to the phenotype, either by showing a blend of characteristics, or showing both together.
What is autosomal linkage?
When two or more alleles are located on the same non-sex chromosome. In this case, only one homologous pair is needed for all four alleles to be present.
What is epistasis?
Where two non-linked genes interact, with one gene either masking or supressing the other gene
What is the Chi-squared test?
A statistical test to find out whether the difference between observed and expected data is due to chance or real effect.
How can the number of genes coding for a characteristic influence variation?
- Discontinuous variation = characteristic determined by 1 gene
- Continuous variation = characteristic determined by more than 1 gene.
What is stabilising selection?
occurs when environment stays the same - individual closest to the mean are favoured. Low diversity.
What is directional selection?
Occurs when environmental conditions change. Individuals with phenotypes suited to new conditions + pass on genes. Over time the population will move towards these characteristics.
What is Genetic Drift?
Change in a population’s mean characteristics due to chance rather than selective pressures.
What is a genetic bottleneck?
Where a catastrophic event dramatically reduces the size of a population - thereby decreases allele variety in gene pool - causes large changes in allele frequencies.
What is meant by the founder effect?
Small number of individuals of a population become isolated - limited gene pool - allele frequency differs from original population.
What is the Hardy-Weinberg equation?
P+ Q = 1
Where P = Dominant alleles
and Q = recessive alleles
What does the Hardy-Weinberg equation allow for?
Allows us to estimate allele frequency in a population + if allele freq. is changing over time.
What is speciation?
When the genetic makeup of two isolated groups of a species becomes so different that they can no longer interbreed and create fertile offspring.
What is allopatric speciation?
Speciation from a physical barrier, resulting in 2 different environments with different selection pressures, resulting in different favoured alleles.
What is sympatric speciation?
Speciation from non-physical barrier - e.g. mutation that no longer allows two organisms to produce fertile offspring.
What is artificial selection?
selective breeding
humans choosing particular organisms to breed in order to produce a desired characteristic in offspring
What are the 5 factors affecting evolution?
Mutation Natural Selection Gene Flow Sexual Selection Genetic Drift
What are the 5 assumptions for the Hardy Weinberg Principle
- No mutation
- no immigration / emmigration
- no selection pressures
- mating is random
- population is large
(i. e. unrealistic expectations)
What is Gene Pool ?
The total sum of all the alleles in a population at any one time.
What is a gene?
a section of DNA that codes for a polypeptide or protein in an organism
What is an allele?
one of multiple different forms of a gene
