NCEA level 2 Biology 2.5 Key words

gene pool

all alleles present in the population

homozygous

If both alleles are the same (ff, FF)

Emmigration

------> migrate out of population

Immigration

<------ migrate into population

Crossing over

Alleles that occur on the same chromosome are linked. Linked alleles may be separated by this process..

Meiosis

Process of cell division that occurs in the sex organs and produces gametes (sperm and ova)

Metaphase 2

Stage one of meiosis 2- Chromosomes, still as two chromatids line up randomly along the spindle fibres, attach to get to chromosomes

Telophase 2

Stage three of meiosis 2- 4 Haploid gametes are formed: all genetically different

Anaphase 2

Stage two of meiosis 2- Spindle fibres contract, breaking the centromere; chromatids separate, being drawn to each end of the cell

Genetic change

The change in frequency of alleles in a gene pool of a population. the process of mutation, natural selection and genetic drift

Dihybrid inheritance

The inheritance of 2 characteristics controlled by two genes.

Monohybrid inheritance

The inheritance of one characteristic controlled by one gene on homologous chromosomes

Fertilisation

The mixing of alleles from different individuals in sexual reproduction

Random assortment

The mixing up of parental chromosomes and alleles in meiosis. Two sets of chromosomes one from mother and one from the father.

Segregation

The separation of sets of chromosomes and alleles in gamete formation

Test cross

To determine if an individual for a breeding program is homozygous dominant or heterozygous dominant for pure breeding

Bottleneck effect

When a population's size is greatly reduced. Genetic drift will have an effect on the population. When the population size is reduced, gene frequencies in the population are likely to change just by random chance and many genes may be lost from the population, reducing the population's genetic variation.

Founder effect

changes in gene frequencies, starting a new population from a small number of individuals. The newly founded population is likely to have quite different gene frequencies than the source population because of genetic drift. The newly founded population is also likely to have a less genetic variation than the source population.

Genetic drift

changes in the frequency of alleles in the gene pool of a small population as the result of change

Somatic cells

have pairs of homologous chromosomes. each chromosome is identical. Cells have 23 pairs (46 chromosomes)

heterozygous

if allele are different (fF)

natural selection

individuals that have adaptations best suited for the environment to survive to reproduce and pass their alleles on to the next generation

lethal alleles

occur when a mutation results in an allele that produces a non-functional version of an essential protein. If an individual inherits this they will die before or shortly after birth

Co-dominance

occurs when both alleles are equally expressed. When both alleles are present in the heterozygous genotype, they are both expressed in the phenotype

multiple alleles

occurs when genes have more than two different alleles

Incomplete dominance

occurs when neither allele dominates the other. When both alleles are present in the heterozygous genotype both contribute to produce a phenotype that is an intermediate blend of genetic information.

Complete dominance

occurs when one allele completely dominates another allele when both are present in the genotype

Evolution

process by which new species of organisms develop from earlier forms

Telophase 1

stage four of meiosis 1- Cell has completed division. Two new cells have been made

Prophase 1

stage one of meiosis 1- Chromosomes condense forming visible chromatids joined by a centronome. Homologous chromosomes come together to form tetrads. Nuclear membrane disappears to form a spindle

Anaphase 1

stage three of meiosis 1- Spindle fibres contract and the homologous pairs are separated being drawn to each side of the cell. Cytoplasm begins to constrict between the chromosomes

Metaphase 1

stage two of meiosis 1- Nuclear membrane has disappeared, spindle is fully formed. Tetrads line up at the equator, crossing over occurs

Migration

when individual organisms migrate from one population to another, their alleles are lost from the gene pool