Genetic Variation level 2 key definitions

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