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

• 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 χ^2test

Contributors and Attributions

• Dr. Todd Nickle and Isabelle Barrette-Ng (Mount Royal University) The content on this page is licensed under CC SA 3.0 licensing guidelines.