Bio (Genetic Variation)

Meiosis

Cell division that occurs in the sex organs to produce sex cells/gametes

Crossing over

when homologous pairs of chromosomes exchange sections of DNA and alleles creating recombinant chromosomes

somatic mutation

mutation in any cell except a sex cell eg skin cell

gametic mutation

mutation that occurs in a gamete/sex cell

random fertilisation

random as to which sperm will fertilise which egg

independant assortment

homologous chromosome pairs line up at the cell equator randomly and independently

Mitosis

cell division that makes exact copies of your body cells for growth and repair

pure breeding

contains only one type of allele in the genotype

test cross

to determine whether an individual with a dominant phenotype is homozygous dominant or heterozygous

incomplete dominance

neither allele is completely dominant, so the heterozygote has an intermediate phenotype. eg RR (red) x WW (white) = RW (pink)

incomplete dominance phenotype ratio in F2

1:2:1

co-dominance

both alleles are equally expressed in the phenotype rather then one masking another.

complete dominance

dominant allele is always expressed in the phenotype if present in the genotype.

complete dominance phenotype ratio in F2

3:1

multiple alleles

when a gene has two or more possible alleles in the population.

lethal alleles

alleles that cause an organism to die before or shortly after birth. leads to non-functional protein. 2:1 ratio

dyhybrid inheritance

Tracks how two different traits are passed from parent to offspring at the same time

non-linked genes

DNA is found on different homologous chromosomes. They assort independently.

linked genes

DNA is found on the same chromosome. Can’t independently assort. To get different allele combinations they need to cross over.

gene pool

the total number of different alleles that exist for a population

genetic drift

the change in allele frequency due to chance. affects smaller population

evolution

change in the gene pool of a population over a period of time.

immigration

alleles moving into a gene pool

emigration

alleles moving out of a gene pool

founder effect

when a small group of individuals emigrate from a population and become geographically isolated from the original population

bottleneck effect

the original population is reduced to a small size suddenly due to a catastrophic event

natural selection

occurs when there is an environmental change eg change in climate or selection pressure eg predators that causes some individuals to survive and some not to survive.

law of segregation

allele pairs separate during meiosis and randomly unite during fertilization