punnett squares, inheritance and other stuff (quiz two, unit two, semester two)

character

a heritable feature that varies among individuals

trait

each variant for a character

true-breeding

over generations of self pollination plants produced the same variety as the parent plant

hybridization

mating/crossing of two true-breeding varieties

allele

alternative versions of genes (organisms inherit two versions, one from each parent)

law of segregation

two alleles for a heritable character segregate, during gamete formation and end up in different gametes.

punnett square

diagrammatic device predicting the allele of all offspring resulting from a cross between individuals with known genetic makeup

phenotype vs. genotype

• observable physical and physiological traits

• genies in a given organism

testcross

cross of homozygous recessive with an organism showing dominance to determine the phenotypic dominants genotype

monohybrids

heterozygous for one given characteristic

dihybrid

individuals heterozygous for two characters being followed in the cross

law of independent assortment

two or more genes assort independently - each allele pair segregates independently from other pairs during gamete formation

co-dominance

both alleles are expressed at the same time

incomplete dominance

• neither allele is expressed in the offspring

• offspring has a their phenotype as a result of mixing the two

• the mixed trait is heterozygous

blood types

A - II with A’s IA i

B - II with B’s IBi

O - ii

barr bodies

• only one x is expressed in somatic cells the second condenses to become a barr body

• barr body = inactivated X

  • becomes reactivated during gamete production (bad x’s aren’t always the ones turned off)

epistasis

the phenotypic expression of a gene at one locus alters that of a gene at a second locus

quantitative characters

traits that vary in the population in graduations along a continuum

polygenic inheritance

an additive effect of two or more genes on a single phenotypic character

• phenotype can also differ when its environment and genotype dependent