Meiosis
Gametes
Unique haploid cells used in sexual reproduction - no two are identical due to processes in meiosis
Point Mutation
A change to a single base pair in the DNA sequence
Complete Dominance
Inheriting only one copy of the dominant allele for a gene results in the expression of the dominant trait eg. Bb in eye colour creates brown eyes
Pure Breeding
An individual is homozygous for the trait eg. BB or bb
Gene Pool
All of the alleles present in a breeding population
Genetic Drift
Loss or fixation of alleles due to random chance events. This has a bigger impact on small populations.
Cells that only contain one of each homologous chromosome pair
Block Mutation
A large section of DNA on a chromosome changes/is deleted/is inserted/gets flipped over
Multiple Alleles
When a gene has more than two different allele possibilities this increases the number of possible phenotypes eg. Blood type has three alleles and four possible phenotypes
Linked genes
Genes that are close together on the same chromosome so get inherited together - this decreases genetic diversity since some allele combos cannot be split apart
Allele Frequency
Measure of how popular an allele is in a population. Any change in allele frequency is a sign that evolution is taking place.
Natural Selection
Increase in frequency of beneficial alleles that help survival and decrease in frequency of alleles that harm survival
Homologous chromosomes
Chromosomes with the same genes on them but not necessarily the same alleles, one is inherited from mum and the other from dad
Heritable Mutation
A permanent change in the base pair sequence of a gene that can create new alleles if it occurs in a gamete cell
Incomplete Dominance
Inheriting the heterozygous genotype results in the expression of a blend between the dominant and recessive traits eg. Rr in snapdragons creates a pink phenotype
Parental Type
Gametes that contain the same two linked alleles that the parent who made them has
Gene Flow
Selection Pressure
Any environmental factor that some individuals will be better adapted for surviving than others eg. predation
Crossing Over
Step in meiosis that creates new combinations of alleles - homologous chromosomes pair up and swap over alleles where they touch
Alleles
Different versions of the same gene caused by random mutations eg. blue, brown, and green eye colour alleles
Co-Dominance
Inheriting the heterozygous genotype results in the expression of both the dominant alleles simultaneously in patches eg. BW in chickens creates splotchy feathers
Recombinant Type
Gametes that have new combinations of alleles due to crossing over occurring between the linked genes - these are underrepresented in offspring because they are rare
Fixed Allele
An allele that has become 100% frequent - no other alleles exist for that gene any more - this decreases genetic variation
Bottleneck event
Loss of alleles due to a near-extinction event in a population. This massively decreases genetic diversity.
Independent Assortment
Process in meiosis that creates new combinations of alleles - the order in which each homologous pair lines up is unique and independent of any other pair
Genetic Variation
The variety of different alleles and genes present in a population
Lethal Alleles
Inheriting the homozygous genotype (can be recessive or dominant) results in death eg. bb in Manx cats
Unlinked Genes
Genes that are either on completely separate chromosomes so the alleles can segregate during meiosis without crossing over occurring
Lost allele
Allele that has become 0% frequency in a population - it no longer exists in the gene pool
Founders Effect
Change in allele frequency due to a small subsample of alleles from a larger population moving and establishing a new gene pool - they do not represent the allele frequency seen in the mainland population