3. classical genetics

genotype

the genes of an individual

allele

an alternate form of a gene

phenotype

the physical appearance or outward expression of the genotype

one-trait cross

examines the patterns of inheritance of only a single set of alleles for a single characteristic

(WW x Ww)

two-trait cross

considers the inheritance of 2 characteristics (WWTT x WwTT)

genotypic ratio

the number of offspring with the same genotype

phenotypic ratio

the number of offspring with the same outward appearance

dihybrid cross

2 traits

autosomal dominant

genetic disorder— AA or Aa will have the disorder

autosomal recessive

genetic disorder— only aa will have the disorder

polygenic traits

controlled by several sets of alleles (ex: skin color and height)

multifactorial traits

controlled by polygenes subject to environmental influences (ex: skin color is influenced by sun exposure)

incomplete dominance

occurs when the heterozygote is immediate between the 2 homozygotes (ex: CC x CS = CS curly hair)

codominance

occurs when the alleles are equally expressed in a heterozygote (Ex: AA x BB = AB type AB blood)

sex linked inheritance

traits are controlled by genes on the sex chromosomes

x-linked disorders

color blindness, muscular dystrophy, hemophilia