1. BEYOND MENDEL’S LAWS Lesson 2.
Mendel studied traits that were purely dominant or recessive. Unfortunately, in nature, there exists more than simply two choices for some traits.
Snapdragons can be white, red, pink, yellow, or orange.
Incomplete dominance
Codominance
Multiple alleles
Polygenic inheritance
Linked genes
Sex-linked inheritance
Lesson 2.

2. INCOMPLETE DOMINANCE Neither trait is dominant or recessive.
A heterozygous individual is a blend of the two traits.
Ex. Snapdragons
Instead of using R and r, we use FR and FW to show
incomplete dominance.
Red = FR FR
Pink = FR FW
White = FW FW

3. INCOMPLETE DOMINANCE
Cross a Red Flower with a White flower: If we crossed two plants from F1, we would get:

4. CO-DOMINANCE
BOTH alleles for a trait are dominant, a heterozygous individual expresses both traits.
Ex. Black rooster FBFB x white hen FWFW.
The F1 are all ‘barred’ (FBFw
black and white feathers)

5. EXAMPLE
In four o’clock plants, red flowers are incompletely dominant over white flowers. Heterozygous flowers are pink. If a red flower is crossed with a white flower what is the colour of:
The F1 generation?
The F1 generation crossed with the red parent?
The F1 generation crossed with the white parent?

6. EXAMPLE
A cross between a yellow snake & a blue snake produces offspring that are all green: 
What are the genotypes of the parent generation (P)?
What are the genotypes of the F1 generation?
What would be the phenotypic ratios of offspring produced by two green snakes?

7. What is Sickle Cell Anemia (SCA)?
First described in Chicago in 1910 by James Herrick as an inherited condition that results in a decrease in the ability of red blood cells to carry oxygen throughout the body
Sickle red blood cells become hard and irregularly shaped (resembling a sickle)
Become clogged in the small blood vessels and therefore do not deliver oxygen to the tissues.
Lack of tissue oxygenation can cause excruciating pain, damage to body organs and even death.

8. Some Genetic History
The error in the hemoglobin gene results from a genetic mutation that occurred many thousands of years ago in people in parts of Africa, the Mediterranean basin, the Middle East, and India.
A deadly form of malaria was very common at that time
Malaria epidemics caused the death of many
In areas where malaria was a problem, children who inherited one sickle hemoglobin gene and who, therefore, carried the sickle cell trait - had a survival advantage.
Unlike the children who had normal hemoglobin genes, they survived the malaria epidemics they grew up, had their own children, and passed on the gene- for sickle hemoglobin.

9. Genetics HbS –Recessive S=Sickle A=Normal
2 copies of the gene for Hb (each parent)
HbS –Recessive
S=Sickle
A=Normal

10. Multiple Alleles: Human Blood Groups
In humans a single gene controls a person’s ABO blood type
This gene determines what type of an antigen protein is attached to membrane of a red blood cell
Three alleles A,B and O
Combination of three alleles make 4 different blood types ___________

11. BLOOD TYPES
A human blood group or “type” is a group of red blood cells that have the same antigen protein markers on the cell surface
There are four human blood groups:
A, B, AB, O

12. Type A produces antibodies against Type B antigens
Type AB produces no antibodies against blood antigens
Type B produces antibodies against Type A antigens
Type O produces antibodies against both Type A & Type B antigens

13. BLOOD TYPES Blood Type % Amongst Canadians Can Receive From
Can Donate To A 42
A, O
A, AB B 9
B, O
B, AB AB 3
A, B, AB, O O 46
AB = Universal recipient (can receive from anyone)
O = Universal donor (can donate to anyone)
Each blood type has + and – versions (Rh factor)
+ = Universal recipient (can receive from anyone)
– = Universal donor (can donate to anyone)

14. EXAMPLE
If a woman has AB blood, and a man has type A blood, what are the possible blood types of their offspring?

15. Sickle Cell Trait
Sickle haemoglobin (S) + Normal haemoglobin (A) in RBC
Adequate amount of normal Hb (A) in red blood cells
RBC remain flexible
Carrier
Do Not have the symptoms of the sickle cell
Heterozygous advantage (HbA HbS)

16. Polygenic Inheritance
Display continuous variation, in which phenotypes vary gradually from one extreme to another
Height, skin colour, eye colour
Variation is controlled by more than one gene; polygenic trait

17. Polygenic inheritance explains this…

18. Or this…

19. Inheritance of linked genes

20. Lack of independent assortment with linked genes

21. Only way for Pl and pL is crossing over – 3% of the time

22. SEX-LINKED INHERITANCE
Using fruit flies as
test subjects, Thomas
Morgan studied eye
colour using simple
monohybrid crosses.
Red eyes (R) are
dominant over white
eyes (r).

23. SEX-LINKED INHERITANCE
When he crossed
purebred white-eyed
males with red-eyed
females, he was unable to
produce a female with
white eyes.
He concluded that the
gene must be located on
the X chromosome.

24. SEX-LINKED INHERITANCE
Some traits are located on the sex chromosomes, so the inheritance of these traits depends on the sex of the parent carrying the trait.

25. SEX-LINKED INHERITANCE
Most known sex-linked traits are X-linked (carried on the X chromosome). This is probably because the X chromosome is much larger than the Y chromosome

26. SEX-LINKED DISORDERS
Some sex-linked traits are associated with disorders.
Most are found on the X chromosome, Y-linked disorders are rare.
Males are at a much greater risk for inheriting sex-disorders because they only inherit one X, so if the X has the allele for the disorder, they will suffer from the disorder.
Recessive lethal X-linked traits result in death.

27. EXAMPLES OF SEX-LINKED TRAITS and DISORDERS
Red-green colour vision deficiency (CVD) , hemophilia, X-linked severe combined immunodeficiency (SCID)

28. Hemophilia
Condition that affects body’s ability to produce proteins involved in blood clotting
X-linked recessive
“Royal Disease”

29. Symptoms Uncontrolled bleeding “bleeds”
Most bleeding is internal and often into joint spaces
Prior to 1960, life expectancy was 11 years.
Today, life expectancy only 10 years shorter than an unaffected male

30. SEX-LINKED INHERITANCE
Punnett squares are used to predict the outcome of sex-linked inheritance.
Assume the trait is X-linked unless told otherwise!
Most disorders are recessive, some are dominant, the question will tell you.
A “carrier” is a female who is heterozygous for the trait.

31. EXAMPLE
Hemophilia is a recessive X-linked trait. What is the probability of a couple having a hemophiliac child if the man does not have hemophilia and the woman is a carrier?

32. Determining sex-link patterns in a pedigree
This pedigree shows the inheritance of red-green CVD in a family. Identify the genotype of each family member.
How does the inheritance pattern support X-linked inheritance?
Hint Start with a legend

33. Barr Bodies: Inactive X Chromosomes
In females every cell only has one functioning X chromosome
Early in embryo development one X chromosome is condensed tightly into a Barr body
Occurs randomly in each cell
Explains calico and tortoiseshell cats (50% of cells have active X with allele for black, and 50% have and active X allele for orange)
All calicos are female, male calicos are sterile. Why?