1. Chapters 6 and 7; Patterns of Heredity
I. Patterns of Heredity; These can be traced through
generations using a pedigree.
A. Complete dominance; Anytime the dominant allele appears, you see it’s phenotype.
The only time you see the recessive phenotype is when the genotype is homozygous recessive.

2. B. Incomplete dominance; Neither allele is completely dominant.
A new phenotype appears in an intermediate form of the original phenotypes.
ie. RR (red) X R'R' (white) produces RR' (pink)
This occurs in snapdragon flowers and four o’ clock flowers.

3. R R R R’ R R’ R’ R R’ phenotype; pink R R’
Incomplete dominance; R – red R' – white RR x R' R'
R R
R R’
R R’ R’
phenotype; pink
R R’
R R’

4. R R’ R R R R’ R R’ R R’ phenotype; red, pink and white R’ R’
Incomplete dominance; R R’ – Pink R R’ x R R'
R R’
R R
R R’ R R’
phenotype;
red, pink and
white
R R’
R’ R’

5. C. Codominance; Neither allele is completely dominant
C. Codominance; Neither allele is completely dominant. Both traits are expressed.
ie. RR (red) X WW (white) produces RW (red and white) This produces roan cattle, and
BB (black) X WW (white) produces “erminette” (speckled) chickens

6. R R R W R W W R W Phenotype F1; red and white (roan) R W
Codominance; R – red W – white RR x WW
R R
Phenotype F1;
red and white
(roan)
R W
R W W
R W
R W

7. R W R R R W R W R W Phenotype F2; Red, white and roan W W
Codominance; R – red W – white RW x RW
R W
R R
R W R W
Phenotype F2;
Red, white and
roan
R W
W W

8. Both of these are controlled by codominant alleles
Roan cow
Both of these are controlled by
codominant alleles
Rhododendron flower

9. Blood type is also controlled by codominance.
There are four major blood groups: A, B, AB and O.
Blood types are determined by the absence or presence of certain molecules on the surface of red blood cells.
Gene I is the gene for blood type. It codes for a molecule that attaches to a membrane protein found on the surface of red blood cells.

10. There are two types of antigens
(surface molecules) that can be found on
red blood cells. They are type A and type B.
The surface molecules (antigens) attract antibodies that are recognized as the same kind. Foreign antigens are attacked by the antibodies in a person’s blood.

11. If a blood transfusion of the wrong type occurs, antibodies will not recognize the foreign antigens and will cause the person’s blood to clot.

12. Blood Groups Phenotype (blood type) Genotype Antigen on Red Blood Cell
Safe Transfusions To
From A B AB O
IAIA or
IAi
A, AB A
A, O B
IBIB
or IBi
B, AB
B, O
A and B
IAIB AB
A, B, AB, O ii
none
A, B, AB, O O

13. Is it possible for a type A(IAIA or IAi) person and a type
B (IBIB or IBi) person, to produce a type O offspring?
Consider each possible combination
IAIA x IBIB
IA i x IBIB
IA i x IB i
and IAIA x IB i
You can set up a Punnett square for each situation.
IA i
IA i x IB i IB i
IA IB
IB i
IA i
i i

14. A person with type AB blood is known as a universal recipient, because they can receive blood from any donor.
A person with type O blood is known as a universal donor, because they can safely give blood to any recipient.

15. D. Sex-linked inheritance; Traits are controlled by genes
D. Sex-linked inheritance; Traits are controlled by genes located on the sex chromosomes.
In humans there are 22 pair of autosomes (the homologous pair look alike)
The 23rd pair are the sex chromosomes (X and Y chromosomes)
Females always have two X chromosomes, but males will have an X and a Y.
The X chromosome is larger than the Y chromosome, and carries more genetic information.
Females may carry a trait, but not express it. If it is passed to a male offspring, it may be expressed because the male does not have a corresponding section of chromosome to hide the trait.

16. Sex linked traits were first discovered in 1910 by Thomas Hunt Morgan, who was working with fruit flies.

17. XR Y XR XR XR Y XR Xr XR Xr phenotypes; XR XR female red
Sex Linked; X female XR XR red XR Xr red Xr X r white
Y male XR Y red Xr Y white
XR Y
phenotypes;
XR XR female red
XR Xr female red
XR Y male red
Xr Y male white
XR XR
XR Y XR Xr
XR Xr
Xr Y

18. Xr Y XR Xr XR Y XR XR Xr phenotypes; XR Xr female red 0 female white
Sex Linked; X female XR XR red XR Xr red Xr X r white
Y male XR Y red Xr Y white
Xr Y
phenotypes;
XR Xr female red
female white
XR Y male red
male white
XR Xr
XR Y XR
XR Xr
XR Y

19. Xr Y XR Xr XR Y XR Xr Xr Xr phenotypes; XR Xr female red
Sex Linked; X female XR XR red XR Xr red Xr X r white
Y male XR Y red Xr Y white
Xr Y
phenotypes;
XR Xr female red
Xr Xr female white
XR Y male red
Xr Y male white
XR Xr
XR Y XR Xr
Xr Xr
Xr Y

20. In humans, we see sex linked in heritance with red/green color blindness and royal hemophilia in males.
The probability of a female having one of these disorders is very low.

21. E. Polygenic inheritance; trait is controlled by two or more genes.
Each gene may have two or more alleles that control the trait on that particular gene.
None of the alleles are dominant, or recessive. Each can be expressed equally with heterozygotes as intermediates.

22. ie. Gene 1 has AA, Aa, or aa
Gene 2 has BB, Bb, or bb
Gene 3 has CC, Cc, or cc
The trait has 3 genes (6 alleles) that control it.
Using plant height as an example;
A plant that is homozygous for short alleles at all three genes would have a genotype of aabbcc, and grow to be 4 feet tall.
A plant that is homozygous for tall alleles at all three genes would have a genotype AABBCC, and grow to be 16 feet tall.

23. A 16 foot plant is crossed with a 4 foot plant
A 16 foot plant is crossed with a 4 foot plant. The resulting F1 generation has a genotype of AaBbCc. Each tall gene contributes 2 feet of height, to the base height of 4 feet.
The difference between the tallest plant (16 ft) and the shortest plant (4 ft) is 12 feet, or 2 feet per allele.
The F1 generation of this cross would be an intermediate size of 10 feet tall.

24. Examples of polygenic inheritance in humans includes hair color, eye color and skin color.