Human Genetics:Patterns of Inheritance for Human Traits
We will be discussing 5 Patterns of Inheritance for Human Traits1. Single Allele Dominant2. Single Allele Recessive3. Sex Linked (X-Linked)4. Multiple Alleles 5. Polygenic Traits
Single Allele GenesRegular traits that are either determined by a dominant or recessive allele on an autosome
Autosomal Dominant examples: a. Huntingtons Disease b. Achondroplasia (dwarfisim)c. Polydactyly (extra fingers and toes)
2. Autosomal Recessive examples: a. Albinismb. Cystic Fibrosisc. Sickle Cell Anemia
1. Dominant Allele DisordersHuntingtons Disease (HD)Results in loss of muscle control and mental deteriorationNo signs are shown until 30sBrain degenerationTreatment: No cure, but drug treatments are available to help manage symptoms.
1. Dominant Allele DisordersAchondroplasiaDwarfismPerson grows no taller than 44
1. Dominant Allele DisordersPolydactyly The presence of more than the normal number of fingers or toes. Can usually be corrected by surgery.
2. Recessive Allele DisordersAlbinismLack of pigment in skin, hair, and eyesMutation in one of several genes which provide the instructions for producing one of several proteins in charge of making melanin.
2. Recessive Allele DisordersCystic 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 DisordersSickle Cell DiseaseRed blood cells are bent and twistedGet stuck in capillaries damage tissuesResults in weakness, damage to brain and heart
3. Sex Link Traits:Genes on the X and Y chromosomes
Human Chromosomes: 2 Sex Chromosomes
Human Chromosomes:44 Autosomes
GenderWe determine the gender of an individual through sex chromosomesSex Chromosomes: X and Y Female: XX Male: XYThe father gives an X or Y to the gametes. The mother only gives an X to the gameteThe X chromosome is larger than the Y chromosome.
What are sex-linked genes? genes found on a sex chromosomeX-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
Sex-Linked TraitsIt 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
Lets 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
Heres the resultsFor girls: 0% have the traitFor 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 Xs.
Examples of X-linked traits:1. Color Blindness2. Hemophilia3. Muscular Dystrophy4. Icthyosis simplex (scaly skin)
ColorblindnessA 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.
People with red-green color blindness see either a three or nothing at all.
Those with normal color vision see an 8.
HemophiliaHemophilia- Lacking in the ability to clot bloodThere is a gene on the X chromosome that control blood clottingPeople who have hemophilia are missing the protein to clot bloodThey can bleed to death by minor cut.
- Results in weakening/loss of muscles
- Caused by defective version of gene that codes for muscle
Sex-influenced TraitsSex-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: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:
Blood has both Multiple Alleles and is CoDominantIf you have IAIB as your genotype, 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 traitUsually show a wide range of phenotypesEx: Skin color, eye color, foot size, heightWide 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.