Human Genetics: Patterns of Inheritance for Human Traits

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  • 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

  • X-linked Genes

    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.

  • Muscular Dystrophy

    - 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.