1. Incomplete & co-dominance
GENETICS
Incomplete & co-dominance

2. Incomplete Dominance
Incomplete Dominance occurs when the offspring show a combination of recessive and dominant characteristics
Pure Red flowers crossed with White flowers produce all pink flowers in the F1 generation.

3. All RW (Roan) Offspring are produced
Looking at incomplete dominance when pure bred (homozygous) red and white cattle are bred. P1
Red Bull
White cow
Genotype RR WW R W
Gametes F1
All RW (Roan) Offspring are produced

4. Now what if the F1 generation (all roan) interbred?X RW RW R W
gametes F2 RR RW
1 out of 4 Red R
2 out of 4 Roan RW WW W
1 out of 4 White
Possible offspring

5. Co-dominance: Inheritance of Blood Groups
The difference in blood groups is due to antigens on the surface of blood cells
e.g. “A” blood group has
A antigens on the surface
of blood cells
There are 4 main types of blood group:
A; B; AB and O A

6. Inheritance of Blood Groups
Three alleles are involved: A; B and O
Alelles A and B are co-dominant over O
For example a person with type “A” blood group can have AA or AO genotype
If the genotype is AO, the person will have type “A” blood group because the O gene is recessive
Note the O allele is a capital letter although it is recessive

7. Blood Group
Genotype A
A AA or AO B
B BB or BO A B
AB AB
O OO

8. Look at the possible blood groups from a male AO and female BO genotypes
male gametes A O
Blood groups
AB; B;
A and O
are possible B AB BO
female gametes O AO OO
Possible offspring

9. Mendel & Dihybrid Cross
GENETICS
Mendel & Dihybrid Cross

10. Mendel’s Experiments
Gregor Mendel is regarded as the father of modern genetics. His experiments with pea plants has formed the basis of genetics. We will look at one of these experiments with pea plants

11. Dihybrid Cross This involves the inheritance of two characteristics
These characteristics are linked to each other as they occur on the same chromosome

12. Dihybrid Cross
In pea plants, the gene for colour ( Yellow or Green) and the gene for skin type ( Round or Wrinkled) occur on the same chromosome Y
Yellow (Y) is dominant Green (y) is recessive
Round (R) is dominant Wrinkled (r) is recessive R

13. What will the seeds of the following look like?Y R Y r y y r y R r
Yellow Round
Yellow Wrinkled
Green Wrinkled
Green Round

14. Pure bred Yellow-Round Seeded plant crossed with Green-Wrinkled Seeded plant
PHENOTYPE Y R y r
GENOTYPE Y R y r
Possible Gametes

15. Yellow Round Green Wrinkled PHENOTYPE GENOTYPE Possible Gametes
OFFSPRING
ALL Yellow Round

16. Now if YyRr is crossed with YyRr female gametes from YyRr
yellow,round
YYRr
YyRR
YrRr
YYrr
yellow,wrinkled
YyRr
yyRR
green,round
yyRr
Yyrr
yyrr
green,wrinkled
male gametes from YyRr

17. Here are all the possible types of seed in the F2 generation
Try to work out colour and skin of other crosses
What seed result when YR and YR gametes fuse?
Here are all the possible types of seed in the F2 generation
Count the seed the different seed types- How many?
yellow, round: yellow,wrinkled:
green, round: green, wrinkled: 9 3 3 1 YR Yr yR yr
YYRR
yellow,round
YYRr
YyRR
YrRr
YYrr
yellow,wrinkled
YyRr
yyRR
green,round
yyRr
Yyrr
yyrr
green,wrinkled

18. Sex determination & Sex-linked Inheritance
GENETICS
Sex determination & Sex-linked Inheritance

19. What are the chances of producing a boy or a girl?
SEX DETERMINATION
What are the chances of producing a boy or a girl?

20. Males have an X and a Y chromosome Females have TWO X chromosomes
SEX CHROMOSOMES X X X Y
Males have an X and a Y chromosome
Females have TWO X chromosomes

21. Males produce X and Y sperm cells by meiosisXY XX
Males produce X and Y sperm cells by meiosis X X X X
As women are XX, they produce only X egg cells by meiosis

22. XY XX If an X sperm fuses with the egg cell , it’s a GIRL
If an Y sperm fuses with the egg cell , it’s a BOY

23. X Y X XX XY X XX XY Punnett square of sex determination
male gametes X Y X XX XY
There is a 50% chance of having a boy or a girl
female gametes X XX XY
Possible offspring

24. SEX-LINKED INHERITANCEY
Some Characteristics, like the gene for colour vision are found attached to the X chromosome.
This means that the gene for that characteristic is linked to the sex of the individual.

25. SEX-LINKED INHERITANCEY
In humans, the gene for colour vision is sex-linked.
The gene is linked to the X chromosome.
The gene for normal colour vision (B) is dominant over the gene for colour blindness (b)

26. SEX-LINKED INHERITANCEY
If the female parent (XX) has normal vision (BB) and the male (XY) is colour blind (b –only on the X)…
How do we link the colour blind genes to the sex chromosomes ?

27. SEX-LINKED INHERITANCEB B b Y
Normal Female
BB on the X chromosomes
Colour Blind male
b on the X chromosome only

28. Normal Female x Colour Blind MaleY
Colour Blind Male
Normal Female
XBXB
XbY
Colour blind male possible sperm cells X B X B
Normal female possible egg cells
Normal Female x Colour Blind Male

29. Normal Female x Colour Blind MaleY Y
Colour Blind Male
Normal Female
XBXB
XbY X B X B X B X X B X B b Y
Normal Female but carries the (b) colour blind gene
Normal Male
Normal Female x Colour Blind Male

30. Carrier female gametes
What are the possible offspring that would result from a carrier female and normal male ?
Normal male gametes
PHENOTYPE XB Y
1 Normal female 1 2 XB
XBXB
XBY
2 Normal male
Carrier female gametes
3 Carrier female 3 4 Xb
XBXb
XbY
4 Colour blind male
Possible GENOTYPE