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Do Now Incomplete or Codominance? 1 2 3 4 5
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Human Genetics: Patterns of Inheritance for Human Traits
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We will be discussing 5 Patterns of Inheritance for Human Traits 1. Autosomal Dominant 2. Autosomal Recessive 3. Sex Linked (X-Linked) 4. Multiple Alleles 5. Polygenic Traits
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Autosomal Traits Traits that are determined by a dominant or recessive allele on an autosome (any chromosome other than the sex chromosomes) 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
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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.
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1. Dominant Allele Disorders Achondroplasia Dwarfism Person grows no taller than 4’4
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1. Dominant Allele Disorders Polydactyly The presence of more than the normal number of fingers or toes. Can usually be corrected by surgery.
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2. Recessive Allele Disorders Albinism Lack of pigment in skin, hair, and eyes Mutation in one of several genes which produce proteins in charge of making melanin (pigment in skin).
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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.
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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
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3. Sex Link Traits: Genes on the X and Y chromosomes
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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)
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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 Thomas Morgan experimented with the eye color of fruit flies (Drosophilia) to determine X- linkage
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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? X R X r and X R Y
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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
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Examples of X-linked traits: 1. Color Blindness 2. Hemophilia 3. Muscular Dystrophy 4. Icthyosis simplex (scaly skin)
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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.
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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.
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Hemophilia Hemophilia- Lacking in the ability to clot blood –There is a gene on the “X” chromosome that controls blood clotting –People who have hemophilia are missing the protein to clot blood –They can bleed to death by minor cut.
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Muscular Dystrophy - Results in weakening/ loss of muscles - Caused by defective version of gene that codes for muscle
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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
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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)
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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
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Blood has both Multiple Alleles and is CoDominant If you have I A I B as you genes, you have both Type A and Type B blood, also known as Type ABIf you have I A I B as you genes, 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 bloodIf 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.
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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.
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