3.S: Genetic Analysis of Single Genes (Summary)

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A diploid can have up to two different alleles at a single locus. The alleles segregate equally between gametes during meiosis.
Phenotype depends on the alleles that are present, their dominance relationships, and sometimes also interactions with the environment and other factors.
Classical geneticists make use of true breeding lines, monohybrid crosses, Punnett squares, test crosses, reciprocal crosses, and the chi-square test.
Sex-linked genes are an exception to standard Mendelian inheritance. Their phenotypes are influenced by the type of sex chromosome system and the type of dosage compensation system found in the species.
The male/female phenotype (sex) can be determined by chromosomes, genes, or the environment.

Key Terms

allele

Mendel’s First Law

Law of Equal Segregation

homozygous

heterozygous

hemizygous

wild-type

variant

locus

genotype

phenotype

dominant

recessive

complete dominance

incomplete (semi) dominance

co-dominance

ABO blood group

haplosufficiency

haploinsufficiency

classical genetics

molecular genetics

true breeding lines

monohybrid cross

Punnett Square

test cross

tester

sex-linked

dosage compensation

X-linked genes

autosomal genes

reciprocal cross

Z-linked genes

hermaphrodites

parthenogenesis

hormonal

cell-autonomous

sexual gynandro-morphs

sexually dimorphic

gynandromorphy

mosaic

chimera

G + E = P

penetrance

expressivity

sampling effects

chi-square χ²test