Mendelian Inheritance

Conclusions: Purple colour is dominant White colour is recessive The cause of the white colour is not diluted, but co-exists with the purple colour

Mendel’s Model Alternative versions of genes account for variations in inherited characteristics Purple or white flowers For each characteristic, an organism inherits two alleles – one from each parent If two alleles at a locus differ, one is dominant and the other is recessive The two alleles separate during gamete formation

Helpful definitions Gene Locus Allele Segments of DNA on a chromosome in the genome that specify the sequence of a protein Locus The specific location of a gene on a chromosome in the genome Allele any one of a number of versions of a gene occupying a given locus Each cell has 2 copies of a chromosome Therefore there are two possible alleles for every gene

More definitions Homozygous Heterozygous Genotype Phenotype Pleiotropy Organism with a pair of identical alleles Heterozygous Organism with two different alleles for a particular gene Genotype The genetic make-up of an individual Phenotype The displayed traits of an individual Pleiotropy occurs when a single gene influences multiple phenotypic traits

Genotype vs. Phenotype

Performing a Testcross

Independent Assortment

But….then there is incomplete dominance

Or….co-dominance…or even multiple alleles

Epistasis - the gene at one locus alters the phenotype resulting from another gene at a separate locus B – black b – brown C – colour c – no colour Black (B) is dominant Colour (C) is dominant cc will be albino (no colour)

Quantitative trait locus a region of DNA that is associated with a particular phenotypic trait underlie continuous traits - the trait could have any value within a range (e.g. height) a single phenotypic trait is usually determined by many genes QTLs are often found on different chromosomes Nature vs. Nurture

Pedigree Charts