Honors Biology - Unit 6

Gregor Mendel

the father of modern genetics; an Austrian monk who studied pea plants to understand how traits are inherited

true-breeding

organisms that always pass down the same traits to offspring when self-pollinated

P generation

the parent generation; two true-breeding plants with contrasting traits

F1 generation

the first generation of offspring from the P generation; all are hybrids

F2 generation

the second generation from self-fertilized F1 hybrids; shows a 3:1 trait ratio

gene

a segment of DNA that codes for a specific trait

allele

an alternative form of a gene found at the same locus on homologous chromosomes

principle of dominance

one allele can mask the effect of another; dominant hides recessive

principle of segregation

alleles separate during gamete formation and reunite randomly at fertilization

genotype

the genetic makeup of an organism (e.g., Aa, BB)

phenotype

the observable physical traits of an organism (e.g., blue eyes)

homozygous

having two of the same alleles for a gene (e.g., TT or tt)

heterozygous

having two different alleles for a gene (e.g., Tt)

punnett square

a diagram used to predict the outcome of a genetic cross

monohybrid cross

a cross that follows a single trait with two variations(e.g., Tt vs tt).

principle of independent assortment

alleles of different genes assort independently during gamete formation

dihybrid cross

a genetic cross that follows two traits; F2 ratio is 9:3:3:1

probability

the likelihood that a specific genetic event will occur

rule of addition

used to calculate the probability of either of two mutually exclusive events

rule of multipluication

used to calculate the probability of two independent events both occurring

testcross

a cross between an individual with an unknown genotype and a homozygous recessive to determine the unknown genotype

phenotypic plasticity

when the same genotype can result in different phenotypes due to environmental conditions

polygenic inheritance

traits controlled by multiple genes, showing continuous variation (e.g., skin color)

pleiotropy

a single gene affects more than one trait

multiple alleles

a gene with more than two possible alleles (e.g., blood type alleles: A, B, O)

incomplete dominance

the heterozygous phenotype is a blend of the two homozygous phenotypes (e.g., wavy hair)

codominance

both alleles in a heterozygote are fully expressed without blending (e.g., AB blood type)

epistasis

one gene affects or masks the expression of another gene

ABO blood group system

an example of codominance and multiple alleles; determines blood type

genotype dictates phenotype

genes (DNA) determine proteins, which in turn influence the organism’s traits and functions