1. Materials: none
Catalyst: Beyonce and Jay Z are having another baby. Both parents are heterozygous for Hitchhiker’s thumb. Hitchhikers thumb is dominant to no Hitchhiker’s thumb. What are the possible genotypes and phenotypes of their offspring and in what percentages will they be seen?

2. Materials: none
Catalyst: Compare and contrast Codominance with Incomplete Dominance. You may use a table or Venn Diagram to help you out.

3. Announcements Unit 3 Test this week (Thurs/Fri)
If you do well you get to go to Six Flags in May!!
Unit 3 Study guide due on Wednesday
Can be found online at msnay.weebly.com
LAST WEEK TO TURN IN LATE WORK FOR UNIT 3! No work/Mutant Makers projects will be accepted past Friday!
Grades post tomorrow!
Tutorial Today 3:15 – 4:30

4. Star Quiz 14

5. Objectives
I can explain the concepts of codominance and incomplete dominance.
I can determine the genotypes and phenotypes of codominant and incompletely dominant traits in offspring.
I can explain the concept of sex-linked traits in mammals.

6. Codominance: (NOTES) RR’ BB’
Both alleles are expressed on different parts of the organism.
Heterozygous = see both phenotypes
CO means BOTH SHOW!
RR’
BB’

7. Codominance Example: (NOTES)
There are 3 alleles to classify blood type in humans (A, B, O).
Blood type AB = codominant

9. Incomplete dominance: (NOTES)
No dominant allele
Blending of traits
Heterozygous = blended phenotype

10. Example: snapdragon flower color:
RR = red
Rr = pink
rr = white

11. How is Incomplete Dominance Shown on a Punnett Square?
When the heterozygous genotype is shown, label it as having the “blended” phenotype.
Ex: RR Rr heterozygous cross
Rr rr Red= RR= 25%
Pink=Rr=50%
White=rr=25%

12. Silent Practice
The color of pythons is a codominant trait. A dark brown python (BB) mates with a light brown python (B’B’). What are the genotypes and phenotype probabilities of the offspring?

13. Genetic Disorder Inheritance
A heterozygote for a recessive disorder is a carrier.
Disorders caused by dominant alleles are uncommon.
(dominant)

14. Sex-linked traits
Genes on sex chromosomes are called sex-linked genes.
Y chromosome genes = male characteristics.
X chromosome genes = many traits.

15. Male mammals have an XY genotype
All of a male’s sex-linked genes are expressed.
If a disorder is carried on the X chromosome, the male will express it.

16. Female mammals have an XX genotype
Females must have 2 copies of a recessive sex linked trait to express the disorder.

17. Examples of Sex Linked Disorders
Red – Green Colorblindness
Recessive trait
Found on the x chromosome
Male Pattern Baldness
Hemophilia

19. Sex Linked Disorders Summary (LISTEN)
Males express sex linked traits more frequently than females. (XY vs. XX)
If the gene is found on the X chromosome, it will be expressed in males no matter if it is dominant or recessive.
For females, they must have 2 copies of the gene to express that disorder.

20. Classwork 3.11
Directions: complete the worksheet using your notes to correctly answer the questions.
REMEMBER:
Co means both show!
Incomplete = blend
When you are done, turn it in to the blue tray and work on your Unit 3 Study Guide!