Genotype: Phenotype: The genetic composition of an individual How the alleles express themselves. Ex. Two black calves might have the same phenotype, but different genotypes. One may be Heterozygous (Bb) One may be Homozygous (BB)

Homozygous: Heterozygous: Genes that possess two dominant alleles or two recessive alleles. Alleles are traits. TT or tt Heterozygous: Genes that possess one dominant and one recessive allele. Tt

ACTVITY: Probability in Genetics Probability: The likelihood that a particular event is going to happen. Get Two Pennies Heads = “A” for attached earlobes Tails = “a” for free-hanging earlobes Flip them 20 times and record your genotypes.

Tt Tt Tt Tt Mendel's pea plants Tall = TT T T Short = tt t P1 Generation Tt Tt F1 Generation

TT Tt Tt tt Mendel's pea plants Tall = Tt T t T F1 Generation t

“Penny Punnett Square Lab”

Gender Determination The sex (or gender) of an animal is determined by the sex chromosomes. There are two types: X shaped chromosomes Y shaped chromosomes Vertebrate males have XY Vertebrate females have XX

Sex-linked Genes Fruit Flies inherit sex chromosomes (X and Y) the same as humans. Sex chromosomes determine what the gender will be. (XX = female, XY = male) Traits located on the sex chromosomes are called sex-linked traits, and are located on the X chromosomes.

Male Fruit Flies Phenotype = White Eyes Genotype = Xr Y R = Red Eyes r = White Eyes Male Fruit Flies Phenotype = White Eyes Genotype = Xr Y Female Fruit Flies Phenotype = Red Eyes Genotype = XR XR

NOTE: The gene is never carried on the Y chromosome! Xr Y XRXr XRY XR XRXr XRY

XR Y XRXR XRY XR Xr XRXr XrY

Incomplete Dominance When traits are inherited incompletely, or they mix. Red Carnations Genotype (RR) White Carnations Genotype (WW)

Incomplete Dominance When they reproduce, the offspring are pink in color. The new phenotype occurs because the trait that controls pigment is affected.

W W R RW RW RW RW

R W R W RR RW RW W

Codominance The full expression of both alleles Neither one of the alleles are dominant or recessive, and is expressed in its true form in the offspring. Example: In some chickens, alleles for feather color are codominant.

Alleles are written with superscripts, similar to sex-linked traits. Genotype = FB Phenotype = Black Genotype = FW Phenotype = White

FB = Black Feathers FW = White Feathers FB FW FBFW FBFW FBFW FBFW

Another example of codominance: Shorthorn Cattle