Genetics Basic rules… Lots of info is being researched by the Human Genome Project….
Genetics ~ the study of traits or genes that are passed from parent to offspring • Each parent gives 1 gene to the child for a total of 2 genes per trait Ex: hair color: B from mom + B from dad BB for child Blood type: A from mom + B from dad AB for child
Dominant ~ the gene that “shows up”, or takes over (dominates) • Recessive ~ the gene that does not “show up”, or is hidden. Unless there are 2 of them together. Ex: eye color Dominant: Brown (B) BB - brown Recessive: Blue (b) bb - blue Bb - brown http://faculty.southwest.tn.edu/jiwilliams/Human_Traits.htm
Genotype: genetic make up of a trait; gene pair (2 letters that represent genes) • You receive 1 gene from each parent for a total of two genes per trait Ex: AA Bb tt
Phenotype: physical appearance, as a result of the gene pair (genotype) Ex: type A blood Brown hair Type B blood blue eyes
Genotypes vocabulary: • Heterozygous – a gene pair with two different genes; one dominant and one recessive Ex: Aa, Rr, Bb, Pp • Hybrid – a synonym for heterozygous Ex: Aa, Rr, Bb, Pp • Homozygous – a gene pair with two of the same genes; either 2 recessives, or 2 dominants Ex: aa, AA, RR, rr • Pure – a synonym for homozygous Ex: aa, AA, RR, rr • Writing a key: for each genetics problem, start by writing the key for the traits. You ALWAYS use the letter of the dominant trait for both dominant and recessives. Ex: Trait: Yellow – dominant key: Y – yellow Green – recessive y- green
Punnett Square ~ a tool used to determine probability of offspring traits 1. Put mom’s 2 genes in the spaces on top of the square (1 gene over each square) 2. Put dad’s 2 genes in the spaces along the side of the square (1 gene next to each square) 3. Bring down the genes in mom’s column 1 to both squares underneath, then column 2 to both squares underneath 4. Bring over the genes in dad’s column 1 to both squares next to it, then column 2 to both squares next to it.
Punnett Square practice B – black fur (dominate) b – brown fur (recessive) B B
Mom’s genotype: BB phenotype: black Dad’s Genotype: Bb phenotype: black Possible offspring: Genotype: Phenotype: _BB____ % __50_____ black___ % ___100_____ __Bb___ % __50 ___ brown___ % ____0____ __bb___ % ___0____