1. Review What does homozygous dominant mean?
Example:
What does heterozygous mean?
What is another word for heterozygous?
Where do male genes go on a punnet square?
Where do female genes go on a punnet square?

2. Chapter 11 Introduction to Genetics 11-3 Exploring Mendelian Genetics

3. Does that happen independently of other genes?
Mendel had
another question…
When a pair of
alleles (genes
segregate (separate)
in the formation of
sex cells:
What did he do?
Does that happen independently of other genes?
He crossed 2 plants where he could follow 2 different traits as they passed from one generation to the next.
For example: Seed shape-seed color
ROUND YELLOW x wrinkled green
RR YY x rr yy

4. The 1st generation was hybrid for each trait
Now that he had a hybrid plant, he crossed 2 of them
RrYy
Round/Yellow
RrYy x RrYy
Round/Yellow x Round/Yellow

5. How do 2 hybrid genes separate during the formation of sex cells?
RrYy
RY, Ry
rY, ry

6. RY Ry rY ry RY Ry rY ry RrYy RRYY RRYy RrYY RRYy RRyy RrYy Rryy rrYy
Round/Yellow Round/Yellow Round/Yellow Round/Yellow
RRYy
RRyy
RrYy
Rryy
Round/Yellow Round/green Round/Yellow Round/green
rrYy
RrYY
RrYy
rrYY
Round/Yellow Round/Yellow wrinkled/Yellow wrinkled/Yellow
RrYy
Rryy
rrYy
rryy
Round/Yellow Round/green wrinkled/Yellow wrinkled/green

7. Because 4 phenotypes were produced, it proves that the alleles
RY Ry rY ry 1 RY Ry rY ry
RrYy
RRYY
RRYy
RrYY
Round/Yellow Round/Yellow Round/Yellow Round/Yellow 2
RRYy
RRyy
RrYy
Rryy
Round/Yellow Round/green Round/Yellow Round/green 3
rrYy
RrYY
RrYy
rrYY
Round/Yellow Round/Yellow wrinkled/Yellow wrinkled/Yellow 4
RrYy
Rryy
rrYy
rryy
Round/Yellow Round/green wrinkled/Yellow wrinkled/green
Because 4 phenotypes were produced, it proves that the alleles
separated independently of each other when sex cells were formed.

8. Count how many of each there are
List the 4 phenotypes
Count how many of each there are
Round Yellow
Round green
wrinkled Yellow
wrinkled green
9 RY
3 Ry
3 rY
1 ry
Ratio of a DIHYBRID Cross:
9:3:3:1

9. THE LAW OF INDEPENDENT ASSORTMENT
Why is this important?
Genes for different traits separate (segregate) independently from each other in the formation of sex cells
explains why we are so different

10. Summary of Mendel’s Principles
The inheritance of traits is determined by genes passed from parent to offspring
Some genes are dominant, others are recessive
Each trait is governed by 2 genes or alleles, one from each parent.
These genes are segregated (separated from each other) when sex cells (gametes) are formed
These genes, or alleles, segregate independently from each other

11. Exceptions to the Law of Independent Assortment
Why are there exceptions to the Law of Independent Assortment
What are the exceptions?
Not all traits are governed by 2 genes
Some genes are not dominant or recessive
Incomplete Dominance
Codominance
Multiple Alleles

12. Incomplete Dominance Rr Rr r
r r Rr Rr

13. Incomplete Dominance Which gene is dominant? In 4 o’clock flowers:
RR = red
Rr =pink (not RED as expected)
rr = white
The hybrid phenotype is a blend of both dominant and recessive
Neither.

14. Incomplete Dominance

15. Both genes (alleles) contribute to the appearance (phenotype)
Codominance
Both genes (alleles) contribute to the appearance (phenotype)
In certain chickens
The gene for Black feathers is codominant with the gene for white feathers
Hybrids are speckled black and white and called “erminette”

16. So more than 2 genes contribute to the phenotype Rabbits can be
Multiple alleles
More than 2 alleles can exist in a population, not in a single organism
So more than 2 genes contribute to the phenotype
Rabbits can be
CC - Full color
cch cch - Chinchilla - partial defect in pigmentation
ch ch - Himalayan - color in certain parts of the body
cc -albino - no color, recessive D O M I N A T

17. Full color (CC)

18. Chinchilla (cchcch) Partial defect in pigmintation

19. Himalayan (chch) - color in certain parts of the body

20. Albino (cc) - no color recessive to others

23. Can chinchillas hide all?
Why do the following genotypes all appear ‘full color’?
Ccch - full color
Cch - full color
Cc - full color
The gene for full color dominates all the others
Can chinchillas hide all?
Full Color Chinchilla Himalayan albino

24. Do Mendel’s genetic principles apply to animals as well?
Are genes the ONLY factor that determine an organisms characteristics?
Yes. No
The environment also plays a role
Example:
Identical twins brought up in different environments can be very different
Plants with genes for good height and color also depend on soil and water for optimal growth

25. Homework
p. 274 # 1, 2, 4
Genetics crossword
Genetics test practice – 50 questions
All to be completed by Thursday – end of class
can collaborate with teams on this day
TEST – Monday March 2nd

26. There are 3 alleles for the human blood type:
IA Type A
IB Type B
ii Type O (recessive blood type)
Type A genes: IAIA, IAi
Type B genes: IBIB, IBi
Type AB genes: IAIB (co-dominant)
Type o genes: ii

29. Create your own dihybrid cross
Create the gene chart
TT - tall
Tt - tall
tt - short
Write the hybrid genotype for each parent.
Independently assort to create gametes for each parent
Set up the punnett square
What are the answers-offspring?