Unit 5: Genetics

True breeding

over many generations of self-pollination the plants produce same variety as parent plant

Hybridization

mating of two different true breeding varieties

Testcross

breeding organism of unknown genotype with recessive homozygote to reveal its genotype

Incomplete dominance

when heterozygous condition expresses a third phenotype, no dominance, heterozygous = blend (ex. snap dragon flower color, red + white = pink)

Codominance

when heterozygous condition expresses both conditions simultaneously, equally dominant, heterozygous = both (ex. brown horse + white horse = brown and white speckled horse)

Multiple alleles

when there are more than two alleles for a gene, creates hereditary (ex. blood type)

Polygenic inheritance

when more than one gene contributes to expression of particular trait, multiple genes control trait, bell curve/rainbow (ex. height, skin/eye color)

Sex-linked

trait only appears with one type of chromosome

Pleiotrophy

when one gene has multiple effects on the physiology of an organism

Epistasis

when 2 or more genes control the expression of a single trait

Penetrance

the likelihood of a genotype expressing a phenotype in an organism (or population), what is the chance it shows up

Expressivity

the extent to which a trait is expressed in an organism, what is the effect

Epigenetics

refers to any heritable trait that is not determined by DNA sequence

Phenotypic plasticity

ability of a genotype to produce different phenotypes based on environmental factors

Nondisjunction

chromosomes do not seperate during anaphase

Large scale rearrangement

segments of chromosomes get altered during DNA replication

Aneuploidy

abnormal number of a particular chromosome

Monosomic

missing chromosome

Trisomic

extra chromosome

Deletion

removes segment

Duplication

repeats segment

Inversion

reverses segment

Translocation

crossing over between segments that shouldn’t

Trisomy-21

Down syndrome, extra chromosome in 21st pair

Turner syndrome

X0, missing X or Y chromosome, always female because of lack of Y

Klinefelter syndrome

XXY, extra X chromosome, always male because has Y

What probability rule should you use if you see AND?

multiplication rule

What probability rule should you use if you see OR?

addition rule

X inactivation

in every female cell, one X is turned off, becomes bar body, random