Human Genetics: Patterns of Inheritance for Human Traits

What is the difference between heterozygous and homozygous alleles?

What is the difference between dominant and recessive traits?

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

What is genotype? What is phenotype?

3. Sex Link Traits: Genes on the X and Y chromosomes

Human Chromosomes: 2 Sex Chromosomes

Human Chromosomes: 44 Autosomes

Gender  We determine the gender of an individual through sex chromosomes  Sex Chromosomes: X and Y Female: XX Male: XY The father gives an X or Y to the gametes. The mother only gives an X to the gamete  The X chromosome is larger than the Y chromosome.

What are sex-linked genes?  genes found on a sex chromosome X-linked genes are genes found on the X chromosome, symbolized by X r, X R, Y 0. Y-linked genes are found on the Y chromosome, symbolized by X 0, Y R, Y r

Sex-Linked Traits It is possible for a female to be a carrier of an X- linked trait, but not express it Men will express all X-linked traits they inherit because they have one X chromosome X-linked recessive, carrier mother Unaffected son Unaffected daughter Affected son Carrier daughter Unaffected father Carrier mother Carrier Affected Unaffected

X-linked Genes Let’s do a punnett square for a female carrier of an x-linked gene and a recessive male What will the genotypes be? X R X r and X R Y

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. XRXR XrXr XRXR XRXRXRXR XRXrXRXr Y0Y0 X R Y 0 XrY0XrY0

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

Colorblindness 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 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/ loss 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 Multiple Alleles – any gene that has 3 or more alleles (not just 1 dominant and 1 recessive) Example: Blood type has 3 alleles: Example: Blood type has 3 alleles: I A = Type A blood (dominant) I B = Type B blood (dominant) I B = Type B blood (dominant) i = Type O blood (recessive) i = Type O blood (recessive)

Check out the possible genotypes and phenotypes of blood below: GenotypesPhenotypes I A I A or I A iType A I B I B or I B iType B IAIBIAIB Type AB iiType O

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