Human Genetics Patterns of Inheritance for Human Traits

Human Genetics: Patterns of Inheritance for Human Traits Chapter 14 sec. 14. 1 p. 341 -348

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

Single Allele Genes Regular traits that are either determined by a dominant or recessive allele on an autosome 1. 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

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.

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

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

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.

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.

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

3. Sex Link Traits: Genes on the X and Y chromosomes Chapter 14 section 14. 2 p 349 -353

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)

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, Y 0. • Y-linked genes are found on the Y chromosome, symbolized by X 0, Y R, Y r • Thomas Morgan experimented with the eye color of fruit flies (Drosophilia) to determine Xlinkage

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 recessive male • What will the genotypes be? • XRXr and XRY

Here’s the results • 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. R X r X XR XR Xr Y 0 XR Y 0 Xr Y 0

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

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.

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.

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.

Muscular Dystrophy - Results in weakening/l oss of muscles - Caused by defective version of gene that codes for muscle

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

4. 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)

Check out the possible genotypes and phenotypes of blood below: Genotypes Phenotypes IAIA or IAi Type A IBIB or IBi Type B I AI B Type AB ii Type O

Blood has both Multiple Alleles and is Co. Dominant • 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.

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.