1. Segregation diagrams are useful because they allow geneticist to make predictions.

2. Example: What is the chance that this brown-eyed couple will have a blue-eyed baby?Bb BB B b B B BB BB Bb Bb
0% chance

3. The ability to make predictions becomes important when dealing with genetic disorders/diseases.

4. The man and the woman below have achondroplasia (dwarfism)
The man and the woman below have achondroplasia (dwarfism). If this couple has children, will the children also have achondroplasia?

5. To answer this question, we have to figure out if the disorder is dominant or recessive.

6. The FGFR3 gene codes for cartilage protein
mutation
ONE COPY
ACHONDROPLASIA
IS DOMINANT
From Dad
From Mom

7. Achondroplasia = A; regular height = a
fatal
Aa:
dwarf
aa:
regular
FGFR3
FGFR3
mutation
mutation
From Dad
From Mom A a a A

8. If these two people have a baby, how will the baby turn out?Aa Aa
AA:
25%
Aa:
50% A a A a
aa:
25% AA Aa Aa aa

9. This explains the family below:
AA:
25%
Aa:
50%
aa:
25%

10. However, we cannot say with absolute certainty what the outcome of this cross will be. We can only determine the probability.

11. Probability 50% chance of heads 50% chance of tails
The chance that an event will occur; expressed as a percentage. C P

12. Probability Practice Female: 6/8 = 3/4 = 75% Solid: 4/8 = 1/2 = 50%
Black/solid:
2/8
= 1/4
= 25%
Black nose:
8/8
= 100%
male
male
female
female
female
female
female
female

13. Segregation diagrams are not the only way to determine probability
Segregation diagrams are not the only way to determine probability. You can also use a Punnett square.

14. Punnett Square
Diagram that shows the probable outcome of a genetic cross; used by geneticists to make predictions. P P

15. gametes
Offspring

16. Offspring (two alleles)
Curly = H; straight = h HH
Gametes (one allele) hh H H
Probabilities:
HH: 0% h Hh Hh
Hh:
100%
hh: 0%
Curly:
100% h Hh Hh
Straight: 0%
Offspring (two alleles)

17. Make a blank Punnett square in your notes
Make a blank Punnett square in your notes. Include the probabilities section:
Probabilities:
HH:
Hh:
hh:
Curly:
Straight:

18. Use the Punnett square to solve the genetics problem below.Hh
Probabilities: hh H h
HH: 0% h Hh hh
Hh:
50%
hh:
50%
Curly:
50% h Hh hh
Straight:
50%

19. #48 in SG: Mendel’s P generation cross.
Probabilities: t t
TT: 0% T Tt Tt
Tt:
100%
tt: 0%
Tall:
100% T Tt Tt
Short: 0%
FI generation

20. In genetics, an organism can be described by its genotype or its phenotype.
Tall
Tall
Short TT Tt tt

21. Genotype Tall Tall Short TT Tt tt
An organism’s allele combination. Geno = gene. A G

22. Phenotype Tall Tall Short TT Tt tt
The way the organism looks. Pheno = physical. L P

23. What is the genotype of person A?B C
Brown
Brown
Blue BB Bb

24. What is the phenotype of person B?C
Brown
Brown
Blue BB Bb

25. What is the phenotype of person C?B C
Brown
Brown
Blue BB Bb

26. A B C What is the only possible genotype for a blue-eye phenotype?
Brown
Brown
Blue BB Bb bb

27. A B C Which two people have the same phenotype? Brown Brown Blue BB Bb

28. A B C Do they also have the same genotype? No! Brown Brown Blue BB Bb

29. Two organisms can have the same phenotype, but different genotypes.
Tall
Tall
Short TT Tt tt

30. Brown (B) is dominant; black (b) is recessive
What is the phenotype of dog #2?
Black 1 4 2 3 5 6
Brown (B) is dominant; black (b) is recessive

31. Brown (B) is dominant; black (b) is recessive
What is the genotype of dog #2? bb 1 4 2 3 5 6
Brown (B) is dominant; black (b) is recessive

32. Brown (B) is dominant; black (b) is recessive
What is the phenotype of dog #6?
Brown 1 4 2 3 5 6
Brown (B) is dominant; black (b) is recessive

33. Brown (B) is dominant; black (b) is recessive
What are two possible genotypes for dog #6? BB
or Bb 1 4 2 3 5 6
Brown (B) is dominant; black (b) is recessive

34. A genotype may either be homozygous or heterozygousTT Tt tt

35. Homozygous TT Tt tt
Genotype with the same alleles. Homo = same. S A S

36. Heterozygous TT Tt tt
Genotype with different alleles. Hetero = different. D A D

37. A B C Which people have a homozygous genotype? Brown Brown Blue BB Bb

38. A B C What word describes person B’s genotype? Heterozygous Brown
Blue BB Bb bb

39. Which person is homozygous dominant?B C
Brown
Brown
Blue BB Bb bb

40. Which person is homozygous recessive?A B C
Brown
Brown
Blue BB Bb bb

41. To have a recessive phenotype, the genotype must be homozygous.
Blue
Short tt bb

42. Genetics Problem #3: Black Parents, White Baby
Dark skin (D) is dominant; light skin (d) is recessive

43. Create a Punnett square showing how this type of inheritance is possible.
Probabilities: D d
DD:
25%
Dd:
50% D DD Dd
dd:
25%
Dark:
75% d Dd dd
Light:
25%

44. 45. If this couple decides to have another baby, what is the probability that the baby will have light skin?
46. If this couple decides to have another baby, what is the probability that the baby will have dark skin?
47. If this couple decides to have another baby, what is the probability that the baby will be a carrier?
25%
75%
50%