1. Exceptions to Mendel

2. Not all genes show simple patterns of dominant and recessive alleles
Genetics is more complicated in most organisms

3. 4 Exceptions to Mendel’s Genetics
Incomplete dominance
Codominance
Multiple alleles
Polygenic traits

4. Incomplete Dominance
One allele is not completely dominant over another
The heterozygous phenotype is somewhere in between the two homozygous phenotypes
Examples: four-o’clock flowers, betta fish

5. RR = red
WW = white
RW = pink

6. B1B1 = green
B2B2 = steel blue
B1B2 = royal blue

7. Codominance Both alleles are dominant and contribute to the phenotype
Example: roan cattle, appaloosa horses, human blood type (AB)

8. RR = red
WW = white
RW = roan
GG = gray
WW = white
GW = appaloosa

9. Type AB is codominant

10. Multiple Alleles Genes that have more than two alleles
No individual can have more than two alleles, but more than two alleles can exist in a population
Examples: human blood type = 3 different alleles

12. Polygenic Traits Poly = many genic = genes
Traits are controlled by two or more genes
Examples: eye color (3 diff. genes, human skin color (4 diff. genes)

13. At least 3 different genes determine eye color in humans
Order of dominance: brown > green > blue.
At least 3 different genes determine eye color in humans

14. An epistatic gene can interfere with other genes.
Example: albinism

15. Phenotype is a combination of genotype and environment
Examples:
sea turtles male or female
height amount of nutrition
hair color effects of sunlight

16. Pedigrees & Karyotypes 7.4

17. Pedigrees
A pedigree chart is used to trace the phenotypes and genotypes throughout a family.
Boxes = males
Circles = females
Shaded shape = person shows the trait
White shape = person doesn’t show trait
Half-shaded = person is a carrier

19. Karyotypes A karyotype is a picture of all the chromosomes in a cell.
X Y

20. Karyotypes can show changes in chromosomes.
deletion or loss of chromosome
extra chromosomes or duplication of part of a chromosome
duplication
deletion