1. 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)

2. 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

3. 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.

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

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

6. “Penny Punnett Square Lab”

7. 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

8. 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.

9. 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

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

11. XR Y
XRXR
XRY XR Xr
XRXr
XrY

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

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

14. W W R RW RW RW RW

15. R W R W RR RW RW W

16. 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.

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

18. FB = Black Feathers
FW = White Feathers FB FW
FBFW
FBFW
FBFW
FBFW

19. Another example of codominance:
Shorthorn Cattle