1. Human Genetics: Patterns of Inheritance for Human Traits
Chapter 14
sec.14.1 p

2. We will be discussing 5 Patterns of Inheritance for Human Traits
1. Single Allele Dominant
2. Single Allele Recessive
3. Sex Linked (X-Linked)
4. Multiple Alleles
5. Polygenic Traits

3. Single Allele Genes
Regular traits that are either determined by a dominant or recessive allele on an autosome
Autosomal Dominant examples:
a. Huntington’s Disease
b. Achondroplasia (dwarfisim)
c. Polydactyly (extra fingers and toes)
2. Autosomal Recessive examples:
a. Albinism
b. Cystic Fibrosis
c. Sickle Cell Anemia

4. 1. Dominant Allele Disorders
Huntington’s Disease (HD)
Results in loss of muscle control and mental deterioration
No signs are shown until 30’s
Brain degeneration
Treatment: No cure, but drug treatments are available to help manage symptoms.

5. 1. Dominant Allele Disorders
Achondroplasia
Dwarfism
Person grows no taller than 4’4

6. 1. Dominant Allele Disorders
Polydactyly
The presence of more than the normal number of fingers or toes.
Can usually be corrected by surgery.

7. 2. Recessive Allele Disorders
Albinism
Lack of pigment in skin, hair, and eyes
Mutation in one of several genes which provide the instructions for producing one of several proteins in charge of making melanin.

8. 2. Recessive Allele Disorders
Cystic Fibrosis (CF)
Caused by recessive allele on chromosome 7
Small genetic change (removes one Amino Acid)  changes protein
Results in: Excess mucus in the lungs, liver and digestive tract, gets infection easily, and early death unless treated.

9. 2. Recessive Allele Disorders
Sickle Cell Disease
Red blood cells are bent and twisted
Get stuck in capillaries  damage tissues
Results in weakness, damage to brain and heart

10. 3. Sex Link Traits: Genes on the X and Y chromosomes Chapter 14 section 14.2 p 349-353

11. Lets recall how we determine gender…
How do we determine the sex of an individual?
 through sex chromosomes
Sex Chromosomes: X and Y
Female: XX
Male: XY
Who is responsible for gender determination in the child?
The father because he gives an X or Y to the gametes. The mother only gives an X to the gamete
Which sex chromosome is bigger?
 the X chromosome (y is much smaller)

12. What are sex-linked genes?  genes found on a sex chromosome
X-linked genes are genes found on the X chromosome, symbolized by Xr, XR, Y0.
Y-linked genes are found on the Y chromosome, symbolized by X0, YR, Yr
Thomas Morgan experimented with the eye color of fruit flies (Drosophilia) to determine X-linkage

13. X-linked Genes
X-linked recessive traits will show up more often in males because they have only 1 X chromosome
Let’s do a punnett square for a female carrier of an x-linked gene and a dominant male
What will the genotypes be?
XRXr and XRY

14. Here’s the results XR Xr XR XR XR Xr Y0 XR Y0 Xr Y0
For girls: 0% have the trait
For boys 50% have it.
Probability is higher for boys because whatever X they get determines the trait, for girls they have to get 2 recessive X’s. XR Xr
XR XR
XR Xr Y0
XR Y0
Xr Y0

15. Examples of X-linked traits:
1. Color Blindness
2. Hemophilia
3. Muscular Dystrophy
4. Icthyosis simplex (scaly skin)

16. Colorblindness
A person with normal color vision sees a number seven in the circle above.
Those who are color blind usually do not see any number at all.

17. Colorblindness RED-GREEN COLORBLINDNESS:
People with red-green color blindness see either a three or nothing at all.
Those with normal color vision see an 8.

18. Hemophilia Hemophilia- Lacking in the ability to clot blood
There is a gene on the “X” chromosome that control blood clotting
People who have hemophilia are missing the protein to clot blood
They can bleed to death by minor cut.

19. Muscular Dystrophy - Results in weakening/loss of muscles
- Caused by defective version of gene that codes for muscle

20. Sex-influenced Traits
Sex-Influenced traits are those that are on autosomes, but occur because of the sex hormones in male and female bodies.
Examples: Facial hair
Baldness

21. 4. Multiple Alleles
Multiple Alleles – any gene that has 3 or more alleles (not just 1 dominant and 1 recessive)
Example: Blood type has 3 alleles:
IA= Type A blood (dominant)
IB= Type B blood (dominant)
i = Type O blood (recessive)

22. Check out the possible genotypes and phenotypes of blood below:
IAIA or IAi
Type A
IBIB or IBi
Type B
IAIB
Type AB ii
Type O

23. Blood has both Multiple Alleles and is CoDominant
If you have IAIB as you genes, you have both Type A and Type B blood, also known as Type AB
If you have IAi, i is recessive to IA, so you have type A blood
Q. When would you have Type O blood?
A. When you have ii as your genotype.

24. 5. Polygenic Traits – traits controlled by 2 or more genes that interact, forming the trait
Usually show a wide range of phenotypes
Ex: Skin color, eye color, foot size, height
Wide range of skin colors because there are more than 4 genes that control this trait.
These may also be influenced by the environment, for example height. If not given the proper nutrition as a child, they might not be as tall as their genes dictate.