Download Genetics - Kawameeh Middle School

Genetics
Genes and alleles…
O Our traits are controlled by genes
O Alleles (different forms of a gene) can be
dominant or recessive
O Organisms get two alleles for each trait – one
from each parent
O If an organism has at least one dominant allele
for a trait, that trait will show
O A trait controlled by a recessive allele will only
show if the dominant allele is not present
Genotypes
O The actual genetic makeup of an organism
is called it’s genotype
O We use letters to represent the different
alleles
O Capital letters are used for dominant traits
O Ex/ Brown hair (B)
O Lower case letters are used for recessive
traits
O Ex/ Blonde hair (b)
Phenotypes
O The phenotype is the physical trait (what you
see)
O It depends on the genotype
O Homozygous dominant (BB) - brown
O Heterozygous (Bb) - brown
O Homozygous recessive (bb) - blonde
Practice..
O Is it homozygous or heterozygous?
O Tt _____________
tt______________
O What phenotype will result?
O Tall is dominant to short plants
O Tt -______________________
O TT - _____________________
O tt- ______________________