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Supplementary Material . Lecture 2. Inheritance . If a gene has a two or more variants then these are called alleles; alleles are the result of mutations in gene. The presence of such alleles is the basis of differences between members of a species; Tall/dwarf [in certain plants] .
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Supplementary Material Lecture 2
Inheritance • If a gene has a two or more variants then these are called alleles; alleles are the result of mutations in gene. • The presence of such alleles is the basis of differences between members of a species; Tall/dwarf [in certain plants] . • Therefore each trait (phenotype/physical manifestation ) has two alleles associated with it. One on the chromosome from the male and one from the female; or one on each chromosome [in the chromosome pair]
Types of alleles-> Phenotype • Dominant/recessive system • the dominant allele is capitalised/ recessive is lower case • In heterozygous only the dominant trait is seen. • In the homozygous it depends it can be either. • Homozygous dominant: DD (Tall) • Homozygous recessive: dd (dwarf ) • Heterozygous: Dd (Tall) • Incomplete / semi-dominance (snap dragon) • No allele dominant and mixed phenotype (red and white giving pink) • Co-dominant (e.g. blood groups) • The phenotype of both alleles are equally expressed; AB, AA, BB, OO
Classical (autosomal) Mendelian Inheritance Somatic Monohybrid cross Adapted from ref [1] p42
Inheritance: Questions • This is a dominant/recessive inheritance system. • F1: stands for cross-pollination. • What conclusion can you draw from F1 results? • F2 is self pollination: • How the ratios are obtained. • For each example determine: • Which is the dominant/recessive trait. Adapted from ref [1] p. 39
X-linked inheritance • Haemophilia: (a classical case is son Alexei of last tzar of Russia who was related to queen Victoria) • X chromosome has the normal/defective gene (H/h) • Y chromosome has no gene (smaller in size) • Defective allele is recessive • Male is XY and Female is XX • Homozygous defective results in the disease • This includes a defective allele in males • Homozygous/heterozygous normal results in no physical effects.
