Here are 3 practice questions on multiple alleles: 1. A woman with blood type AB marries a man with blood type A. What are the possible blood types of their children? - Type A, Type B, Type AB 2. A woman with blood type O marries a man with blood type B. What are the possible genotypes and phenotypes of their children? Genotypes: BO, OO Phenotypes: Type B, Type O 3. A woman with blood type A marries a man with blood type AB. What are the possible offspring genotypes and phenotypes? Genotypes: AO, BO, AB Phenotypes: Type A, Type B, Type AB

1. PTC Taster Gene
Scientific
Investigation

2. Types of
Inheritance

3. Mystery of evolution -
why some people like
Brussels sprouts but
others hate them.

4. Substances similar to PTC
give a bitter taste to green
vegetables such as Brussels
sprouts, broccoli and cabbage
They have found that a gene in
modern humans that makes some
people dislike a bitter chemical called
phenylthiocarbamide, or PTC,
But they are also present in
some poisonous plants, so having
a dislike for it makes
evolutionary sense.
"The sense of bitter taste
protects us from ingesting toxic
substances," the report said.
a recessive variant of the TAS2R38
gene which made some of them
unable to taste PTC - an inability
they share with around one third of
modern humans.
"This feature ... is a mystery of
evolution," said the report.
"These (bitter) compounds can be toxic
if ingested in large quantities and it is
therefore difficult to understand the
evolutionary existence of individuals
who cannot detect them."

5. •Blame it on
your
Genes?
•Blame it on
your
Parents?

6. Bitter

9. Homozygous
Dominant
Homozygous
Recessive
Heterozygous
Dominant

10. 1. Complete dominance
2. Sex Linked
3. Codominance
4. Incomplete Dominance 5.
Multiple Alleles
In a nutshell!
Types of
Inheritance

11. 1. Complete Dominance

12. Dominant/Recessive
• One allele is
dominant over the
other (capable of
masking the
recessive allele)
PP = purple pp = white Pp = purple

13. Dominant/Recessive
• In pea plants, purple flowers (P) are dominant
over white flowers (p) show the cross between
two heterozygous plants. Monohybrid Cross
P
p
P p
pp
Pp
Pp
PP
- PP (1); Pp (2); pp (1)
- ratio 1:2:1
- purple (3); white (1)
- ratio 3:1
GENOTYPES:
PHENOTYPES:

14. 2. Sex Linked Inheritance
• Genes found only on
Your sex chromosomes,
Chromosome pair 23.

15. X – Linked traits
• Colour Blindness * Haemophilia
Question: Drawing a monohybrid cross for a homozygous
recessive female x dominant male for Haemophilia,
determine the genotypes and phenotypes of all offspring.

16. 3. Codominance

18. Codominance
• The heterozygous condition, both
alleles are expressed equally
• Sickle Cell Anemia in Humans
CN
CN
=
normal cells
CS
CS
= sickle
cells
CN
CS
=
some of each

19. Problem: Codominance
• Show the cross between an individual with
sickle-cell anemia and another who is a
carrier but not sick.
CN
CS
CS
CS
CN
CS
CN
CS
CS
CS
CS
CS
- NS (2) SS (2)
- ratio 1:1
- carrier (2); sick (2)
- ratio 1:1
GENOTYPES:
PHENOTYPES:

20. 4. Incomplete Dominance

21. Incomplete Dominance

23. Incomplete Dominance
• A third (new) phenotype appears in the
heterozygous condition.
RR = red rr = white Rr = pink

24. Problem: Incomplete
Dominance
• Show the cross between a pink and a
white flower.
- Rr (2); rr (2)
- ratio 1:1
- pink (2); white (2)
- ratio 1:1
R r
r
r
rrRr
rrRr
GENOTYPES:
PHENOTYPES:

25. So is PTC taster gene
Incomplete Dominance?

26. • Since all people have two copies of
every gene, combinations of the bitter
taste gene variants determine whether
someone finds PTC intensely bitter,
somewhat bitter, or without taste at all.

27. • To people who are tasters, the paper
tastes very bitter, but to non-tasters, it
just tastes like paper

28. • More precise analysis of the
phenotype indicated that the "taster"
gene is incompletely dominant to the
"nontaster" gene, so that people with
two copies of the taster gene have a
lower threshold of sensitivity to PTC
than people with only one copy.

29. • When there is a T allele present, this
usually predicts the ability of PTC
tasting
• The heterozygotes tend to be weak
tasters compared to the homozygous
dominant genotype.

30. • other studies have indicated that
another gene may determine taste
sensitivity.
• The frequency of PTC taster and non-
taster allele vary in different human
populations

31. t
t
T t
Tt tt
Tt tt
1. Name the 3
possible
genotypes and
phenotypes for
the PTC gene?
Refer to the
Monohybrid
cross below.
2. What are the
offspring
genotypes?
3. What are their
phenotypes?
4. Draw a
Monohybrid
cross for a
Supertaster
crossed with a

32. Complete PTC Gene Scientific
Investigation
Refer back of task sheet and remember to look at criteria sheet
carefully
•Title Pg.
•Introduction (including secondary data and in-text referencing) and justified
hypothesis
•Materials
•Method (third person past tense)
•Results (see format from draft sheet)
•Discussion – observation of results, refer back to introduction and
hypothesis. Analyse data, find relationships and justify your conclusions.
•Conclusion – Summary
•Bibliography

33. Extra on Multiple alleles if time

34. Red blood cell compatibility table[60][61]
Recipint[1]
Donor[1]
O− O+ A− A+ B− B+ AB− AB+
O− Y N N N N N N N
O+ Y Y N N N N N N
A− Y N Y N N N N N
A+ Y Y Y Y N N N N
B− Y N N N Y N N N
B+ Y Y N N Y Y N N
AB− Y N Y N Y N Y N
AB+ Y Y Y Y Y Y Y

35. • http://www.youtube.com/watch?v=NJHgZhbn8

36. 5. Multiple Alleles
• There are more than two alleles for
a trait
• Blood type in humans
• Blood Types?
–Type A, Type B, Type AB, Type O
• Blood Alleles?
–A, B, O (in book – IA
, IB
, I)

37. Rules for Blood Type
• A and B are codominant
–AA = Type A
–BB = Type B
–AB = Type AB
• A and B are dominant over O
–AO = type A
–BO = type B
–OO = type O

38. Problem: Multiple Alleles
• Show the cross between a mother who has
type O blood and a father who has type AB
blood.
- AO (2) BO (2)
- ratio 1:1
- type A (2); type B (2)
- ratio 1:1
GENOTYPES:
PHENOTYPES:
O O
A
B
AO
BO
AO
BO

39. Problem: Multiple Alleles
• Show the cross between a mother who is
heterozygous for type B blood and a father who is
heterozygous for type A blood.
-AB (1); BO (1);
AO (1); OO (1)
- ratio 1:1:1:1
-type AB (1); type B (1)
type A (1); type O (1)
- ratio 1:1:1:1
GENOTYPES:
PHENOTYPES:
A O
B
O
AB
OO
BO
AO

40. Exercises
• Textbook pg. 77. q. 1 to 4, 6, 7, 9