IB Biology HL Topic 10

linked genes

Genes located on the same chromosome that tend to be inherited together in genetic crosses

gene loci

specific locations of genes along the chromosome

Discrete variation

Inherited characteristic that have a limited number of variations, such as the ability or inability to roll one's tongue

Continuous variation

An assemblage of measurements of a phenotypical characteristic which forms from a continuous spectrum of values, such as body height, skin color or hair curl

Polygenic inheritance

An additive effect of two or more gene loci on a single phenotypic character

chi-square test

A statistical method used to calculate whether the observed and expected genotype frequencies of a population are significantly different.

dihybrid cross

A cross between two individuals, concentrating on two definable traits, for example pea color and height of pea plant

recombinants

Offspring whose phenotype differs from that of the parents; also called recombinant types

diploid

(genetics) an organism or cell having two sets of chromosomes or twice the haploid number

gametes

A haploid cell such as an egg or sperm. Gametes unite during sexual reproduction to produce a diploid zygote

crossing over

Process in which homologous chromosomes exchange portions of their chromatids during meiosis

fusion of gametes

occurs when two haploids (an egg and sperm) join to form one zygote (first cell of life)

non-disjunction

meiosis in which there is a failure of paired homologous chromosomes to separate

random orientation

the random position of each pair of chromosomes in the nucleus when the spindle microtubules become attached. Their random orientation will eventually result in which chromosomes end up where

haploid

(genetics) an organism or cell having only one complete set of chromosomes

bivalents

A structure in which 2 pairs of homologous sister chromatids have synapsed with one another

fertilisation

Male sex cell (sperm) unites with female sex cell into one cell (46 chromosomes -- 23 from each)

non-sister chromatids

Chromatids from opposite members of a homologous pair. These cross over at prophase I

chiasmata

The X-shaped, microscopically visible region representing homologous chromatids that have exchanged genetic material through crossing over during meiosis

allele exchange

During crossing over, the switch of alleles for the same genes

independent assortment

the random distribution of the pairs of genes on different chromosomes to the gametes

synaptomenal complex

where cross over occurs between two non-sister chromatid to allow for cross-over

gene pool

The gene pool is the set of all genes, or genetic information, in any population, usually of a particular species

allelic frequency

The percentage of all alleles at a given locus in a population gene pool represented by a particular allele

reproductive isolation

Separation of species or populations so that they cannot interbreed and produce fertile offspring

speciation

An evolutionary process in which one species splits into two or more species

polyploidy

A chromosomal alteration in which the organism possesses more than two complete chromosome sets. Found in plants

directional selection

Natural selection in which individuals at one end of the phenotypic range survive or reproduce more successfully than do other individuals

stabilising selection

Natural selection in which intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes

disruptive selection

form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

punctuated equilibrium

Pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change

gradualism

A proposed explanation in evolutionary biology stating that new species arise from the result of slight modifications (mutations and resulting phenotypic changes) over many generations

hybrid vigour

the increased vigour (eg: growth, litter size, milk production) of crossbred animals