Genetics

Basic rules…

Lots of info is being researched by theHuman Genome Project….

• Genetics ~ the study of traits or genes that are passedfrom 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

http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/chooser.shtml

• 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 - brownRecessive: 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 recessiveEx: Aa, Rr, Bb, Pp

• Hybrid – a synonym for heterozygousEx: Aa, Rr, Bb, Pp

• Homozygous – a gene pair with two of the same genes; either 2 recessives, or 2 dominantsEx: aa, AA, RR, rr

• Pure – a synonym for homozygousEx: 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____