Chapter 8 - Inheritance and Selection Flashcards
What is meant by the term ‘phenotype’?
The visible characteristics of an organism.
What is meant by the term ‘genotype’?
Genetic composition of an organism. Genotype describes all the alleles that organism contains.
What are multiple alleles?
A gene with more than two possible alleles.
How is sex determined genetically?
By chromosomes. Female XX (all gametes same as both have X chromosome) Male XY (produce 2 types of gamete - half have X, half have Y)
What is sex linkage?
Any gene carried on X or Y chromosome. In males, any recessive alleles on X chromosome will appear more frequently in phenotype because have one X chromosome.
How are sex linked diseases (e.g. haemophilia) inherited?
From mothers who are either homozygous recessive (haemophilia is recessive) or heterozygous (carrier). Males only obtain X chromosome from mother. Males cannot pass onto sons (who receive Y chromosome) but can to daughters, who would become carriers.
How does co-dominance affect the inheritance of characteristics?
Both alleles are ‘dominant’ so would be expressed in the phenotype. Neither is dominant (H) though nor is one recessive (h) as they are both expressed. Represent them differently (R=red and W=white) on the letter representing the gene (C=colour).
What is co-dominance?
This is when both alleles are equally dominant.
What is meant by the term ‘gene pool’?
All of the alleles of all genes of all individuals in a population at any one time.
What is meant by the term ‘allelic frequency’?
The number of times an allele occurs within the gene pool.
State the Hardy-Weinberg principle.
An equation used to calculate the frequencies of the alleles of a particular gene in a population. It predicts this will remain constant over generations assuming it following these 5 conditions:
- No mutations arise
- No migration
- No selection
- Large population
- Random mating
What is the Hardy-Weinberg equation?
p2 + 2pq + q2 = 1.0
p + q = 1.0
p = dominant allele q = recessive allele 2pq = heterozygous
What is the affect of reproductive success on allele frequency?
- Population contains variety of alleles (diversity).
- Some individuals are better adapted to environment than others. They have a selective advantage.
- Individuals with the less advantageous alleles less likely to survive.
- Those with advantageous alleles survive and breed.
- Passing on advantageous alleles to the offspring.
- Allele frequency increases in population.
What is selection?
The process by which organisms that are better adapted to their environment survive and breed, while those less well adapted fail to do so.
What is stabilising selection?
Should environmental conditions stay stable, individuals closest to the mean (of graph) are favoured and the individuals with phenotypes at the extremes are less likely to pass on alleles than others.
