IB BIOLOGY Topic 10: Genetics and Evolution

Meiosis

The process of cell division that results in the formation of four haploid cells with half the chromosome number of the parent cell.

Haploid cells

Cells that have half the chromosome number of the parent cell.

Crossing over

The exchange of genetic material between homologous chromosomes during prophase I of meiosis.

Independent assortment

The random orientation of chromosomes on the equatorial plate during metaphase I, leading to diverse genetic combinations in gametes.

Replication

The process of DNA duplication during the interphase of the cell cycle before meiosis or mitosis.

Centromere

A specific region where microtubules attach during cell division, ensuring proper chromosome segregation.

Bivalent chromosome

A structure formed during prophase I of meiosis, consisting of two homologous chromosomes aligned side by side.

Chiasma formation

The point of adherence between non-sister chromatids during meiotic crossing over, facilitating the exchange of genetic material.

Law of Independent Assortment

The separation of one pair of alleles during the formation of gametes is independent of the separation of another pair of alleles.

Dihybrid cross

A genetic cross that involves the simultaneous consideration of two different traits or gene pairs.

Linkage

The tendency of two genes located on the same chromosome to be inherited together, defying the law of independent assortment.

Gene pool

The total collection of genes and their alleles present in a population at a particular time.

Hardy-Weinberg equation

An equation used to calculate allele frequency in a population.

Directional selection

Selection that favors one extreme phenotype over the other, leading to a shift in the population towards the favored phenotype.

Stabilizing selection

Selection that favors the intermediate phenotype over the extremes, reducing genetic diversity.

Disruptive selection

Selection that favors both extreme phenotypes over the intermediate, leading to the formation of distinct subpopulations.

Balancing selection

Selection that maintains genetic diversity by favoring multiple alleles in a population.

Reproductive isolation

Barriers that prevent gene flow between populations, including geographical, temporal, and behavioral isolations.

Polyploidy

A cause of speciation where an organism has more than two complete sets of chromosomes.

Gradualism

A theory of speciation that suggests slow, continuous changes over time.

Punctuated equilibrium

A theory of speciation that suggests quick changes followed by minimal subsequent changes.