1. Punnett Squares

2. DOMINANT/RECESSIVE
Dominant allele is represented by a capital letter. (usually the first letter of the trait)
Recessive allele is represented by the SAME letter except in lower-case.
EX: (Trait: height)
Tall = T
Short = t; not s for short

3. Misconceptions About Dominant Alleles

4. The genetic makeup (set of 2 alleles) of an organism is its genotype
Genotype & Phenotype
The genetic makeup (set of 2 alleles) of an organism is its genotype
The physical appearance of an organism is its phenotype

5. Genotype vs. Phenotype

6. Talk to a Partner: Determine the genotype and phenotype of each flower

7. HOMOZYGOUS & HETEROZYGOUS
When both alleles in the pair are the same, the organism is homozygous (purebred)
EX: TT or tt
When both alleles in the pair are different, the organism is heterozygous (hybrid or carrier)
Ex: Tt

8. Which chromosome set is heterozygous?

9. Punnett Squares (PSq) Developed in 1905 by Reginald Punnett.
Used to predict & compare possible genetic variations resulting from a cross
Probabilities, not exact results

10. PROBABILITY
____________________ is the liklihood that a particular event will occur
It can be written as a:
Fraction ____
Percent ____
Ratio ____
(dominant : recessive)
1/4
25%
1:3

11. Symbols used in PSq Original parents  P1 generation
Offspring of the parent plants  F1 generation
Offspring of the F1 generation  F2 generation

12. Explaining Mendel’s Results using Punnett Squares
Creating Pure breeding P generation
PP X PP
pp X pp

13. Explaining Mendel’s Results using Punnett Squares
Creating F1 generation:
PP X pp

14. Explaining Mendel’s Results using Punnett Squares
Creating F2 generation:
Pp X Pp

15. Practice Problem: Monohybrid Crosses: Working w/ PS #1

16. Now try problems on: Punnett Squares Practice: Monohybrid Crosses
STOP !!

17. Non-Mendelian Genetics
Patterns that don’t follow Mendel’s Rules

18. 1) Incomplete Dominance
Two different alleles BLEND to form a new phenotype
Ex: Colors in flowers, red + whitepink

20. 2) Codominance
Two different alleles of the same trait are completely and fully expressed
EX: Red flower & white flower produces a red and white striped flower

21. Examples

22. 2. Codominance & Multiple Alleles
Classic Ex: Human blood types - A, B, AB, O
Alleles: IA, IB, i
IA & IB are codominant
i - recessive (ii = type O blood)

23. Genotype IA IA or Iai IB IB or Ibi IA IB ii
Phenotype

24. IA IA or IAi A IB IB or IBi B IA IB A and B AB ii none O
Genotypes
Surface Proteins
Phenotypes
IA IA or IAi A
IB IB or IBi B
IA IB
A and B AB ii
none O

25. A and AB see A as “like me” as Different!
DONOR BLOOD
A and AB see A as “like me”
B and O see A
as Different!
IMMUNE SYSTEM ATTACKS!
Body images modified from:

26. B and AB see B as “like me” as Different!
DONOR BLOOD
B and AB see B as “like me”
A and O see B
as Different!
IMMUNE SYSTEM ATTACKS!
Body images modified from:

27. O ____ can donate to EVERY BLOOD TYPE = _____________________
DONOR BLOOD O
____ can donate to EVERY BLOOD TYPE
= _____________________
Nothing on surface to
recognize as “NOT SELF”
UNIVERSAL DONOR
YOU DON’T HAVE ANYTHING I DON’T HAVE!
Body images modified from:

28. AB can only GIVE to AB BUT . . .
______ can RECEIVE FROM
EVERY BLOOD TYPE
= ________________________
UNIVERSAL RECIPIENT
Body image modified from:

29. Comparison
Codominance
Incomplete dominance

30. Practice Problem: Incomplete Dominance Working w/ PS #3,4 & 6

31. Now try problems on: Punnett Squares Practice: Incomplete/Codominant
STOP !!

32. Non-Mendelian Genetics
Patterns that don’t follow the rules
Incomplete Dominance
Codominance

33. 3) Sex-linked traits
Traits carried on the sex chromosomes (mostly the x chromosome)

34. Ex. Colorblindness, hemophilia

35. 4) Polygenic traits
Trait produced from many alleles on more than one chromosome
Ex. Hair color, skin color, eye color, height

36. The more genes that contribute to the trait, the more complicated the pattern of expression

39. Practice Problem: Incomplete Dominance Working w/ PS #2, 5

40. Now try problems on:
Punnett Squares Practice:
Sex-Linked
STOP !!