Heredity
The passing of traits from parent to offspring
Gene
Specific length of DNA on a chromosome that has information to determine a particular protein which is a characteristic
Allele
Alternative form of a gene that has a specific base sequence
Genotype
Genetic makeup of an organism for a characteristic shown by the 2 alleles
Phenotype
Physical expression of the trait in the individual
Gene pool
All the alleles that are present in the population
Allele frequency
number of times that an allele occurs in a gene pool as a percentage of the total occurrence of all alleles for that gene in that gene pool
Genetic biodiversity
The range of all the alleles present in the gene pool, the greater the number of different alleles the greater the genetic biodiversity
Natural selection
When the environment changes those individuals with adaptations and the favourable alleles are selected for and reproduce which shifts the allele frequency
Mutation
Permanent change in the DNA base sequence which can produce a .new protein therefore create a new allele
Meiosis
a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes
Somatic cell
Body cell which contains a full set of chromosomes
Gametic cell
Sex cell which contains half the number of chromosomes as the body cells
Homologous chromosomes
Pair of chromosomes that are the same size, same appearance and same genes. One comes from the father (paternal) one comes from the mother (maternal)
Locus
position of a gene on a chromosome
haploid
Contains half the number of chromosomes shown as n
diploid
contains homologous pairs of chromosomes shown as 2n
zygote
the cell created after fertilisation
independant assortment
process when homologous chromosomes line up in a random order during meiosis
How does independant assortment increase genetic variation?
Since only one chromosome from each homologous pair is placed in the gametes, each new cell has a different combination of chromosomes
Crossing over
is the exchange of alleles on segments of chromosomes between homologous chromosomes. Crossing over can only take place between homologous chromosomes because they share the same genes at the same loci on the chromosomes
How does crossing over increase genetic variation?
each new cell has a different combination of alleles from each other which increases genetic variation
Segregation
only one chromosome from each homologous pair is placed into the new cells when the gametes made. Homologous chromosomes separate and move to the cells poles during meiosis.
How does segregation increase genetic variation?
During gamete formation, alleles for each gene separate from each other, so that each gamete carries one allele per gene. Therefore, genetic variation is increased because each new cell has a different combination of alleles from each other, and only half the chromosomes of the parent cell.
Linked genes
Genes located on the same chromosome that tend to be inherited together.
Recominant chromosome
after crossing over a chromosome that has both paternal and maternal DNA
Parental chromosome
chromosome containing DNA from only one parent
Fertilisation
Fusing of a male gamete with a female gamete to restore the cell to be diploid
Monohybrid cross
inheritance of one characteristic controlled by one gene
Complete dominance
the dominant allele is always expressed in the phenotype if present. It will mask the presence of a recessive allele
Homozygous
having two identical alleles for a trait eg bb or BB
Heterozygous
having two different alleles for a trait eg Bb
Purebred
the individual is homozygous for a trait so will only pass down one type of allele
test cross
the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype
incomplete dominance
Neither allele is dominant. The heterozygous individual is a blend of the two alleles eg red and white makes pink
Co-dominance
Both alleles are equally dominant. The heterozygous individual shows both alleles eg red and white makes spots
Multiple alleles
When a gene has more than 2 alleles. An individual will only inherit 2 of the alleles eg blood type
Lethal alleles
Alleles that cause an organism to die when present in homozygous condition.
Dihybrid inheritance
The inheritance of two characteristics which are controlled by two different genes on different chromosomes
Genetic change
the change in the frequency of alleles for that population
Gene flow
Movement of alleles into or out of a population due to the migration of individuals to or from the population
Genetic drift
A change in the allele frequency of a population as a result of chance events rather than natural selection.
Founder effect
genetic drift that occurs after a small number of individuals colonize a new area such as an island. Genetic diversity reduces
Bottleneck effect
genetic drift that occurs following a dramatic reduction in the size of a population. Genetic diversity reduces
Dominant
This allele is shown in the phenotype even if the recessive is present
Recessive
This allele is only shown in the phenotype when there are two copies and no dominant allele
population
group of individuals of the same species that can breed to produce offspring
genetically isolated
individuals in the two populations cannot mate and produce offspring so their gene pools are separate and there is no gene flow
genetic diversity
variations in genetic make up in a species/population
evolution
a change in the gene pool of species over time
adaptations
inherited, genetically determined characteristics that ensure an organism is able to exist to maximise its survival and reproductive success
evolutionary fitness
measure of how well adapted to its current environment an organism is in order to survive