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Human Genetics

Human Genetics. Problems of studying human genetics: May take 75 years to produce 3 generations of humans (months for peas, weeks for fruit flies) Each pair of humans only produce a few offspring (peas and ff: 100’s)

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Human Genetics

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  1. Human Genetics • Problems of studying human genetics: • May take 75 years to produce 3 generations of humans (months for peas, weeks for fruit flies) • Each pair of humans only produce a few offspring (peas and ff: 100’s) • Ethical concerns prevent scientists from using the same techniques used with other organisms

  2. Ways to study Human Genetics • Population Sampling: scientists select a few individuals (10’s—1000’s) that represent the population they want to study—use formulated statistical rules to get accurate results • Example: to find the % of people in the US that could taste the chemical PTC (phenylthiocarbamide) they randomly selected a few 1000 individuals and tested them and came up with the data that 65% are “Tasters”—can detect a bitter taste and 35% are “Non-tasters”—cannot detect a taste

  3. Identical Twin studies • Researchers study identicaltwins (those from 1 zygote and have identical DNA) to distinguish between genetic and environmental influences on specific traits • Especially are interested in those raised apart to study NATURE vs NURTURE • Some researchers feel a baby is a blank slate (TABULA RAZA) and turns out a certain way due to its environment

  4. Pedigree studies • Geneticists analyze inheritance patterns in families • Pedigrees often reveal a carrier—someone who is heterozygous for a trait, so doesn’t have the disease, but can pass the rec gene on to their children • Many diseases can be tracked through families with pedigrees

  5. Single Allele traits • Traits that are coded by a single allele—you inherit that one allele and you get that trait (disease) • Sickle Cell Anemia is where the dom allele A produces normal hemoglobin (round RBC) • A‘ is a codominant allele that codes for abnormal hemoglobin (sickle/crescent shaped RBC) • AA = normal RBC • AA‘ = normal and abnormal RBC (live with disease) • A‘A‘ = all abnormal RBC (death) • Sickle cells clump together and clog capillaries—causes great pain due to improper flow of oxygen • Normal RBC live ~120 days—sickle cells live 10-20 causing chronic shortage of RBC--anemia

  6. Huntington’s Disease • HD starts as mild forgetfulness in 30’s/40’s, leads to loss of muscle control, severe mental illness, death • Since it is a dominant trait, anyone receiving the gene will develop HD • Really scary because you don’t know you have it until you have already had children (usually) and passed it on to them • Gene found on the tip of the arm of chromosome 4 • H = HD h = normal • H h • h Hh hh • h Hh hh • 50/50 chance of passing it on to children

  7. Multiple AlleleTraits • Human blood types (A, B, AB, O) are coded by several alleles found on chromosome 9 • A and B are codominant when they are together and both are dominant over O • Genotype Blood type • AA or AO A • BB or BO B • AB AB • OO O • Universal donors—type O • Universal recipient—type AB • Actually 8 blood types when you use the Rh factor: + or – • A type O male marries a type AB female; what would the possible blood types be for their children?

  8. Sex-linked Traits • Alleles for these traits appear only on the X chromosome • Males have only 1 X (females 2) so whatever is on that 1 chromosome will be expressed • There are no complimentary genes on the Y chromosome to mask any rec genes • Females have 2 X’s so the rec allele can be masked by the dom allele • This is why males are more likely to express rec sex-linked traits/diseases • Colorblindness and hemophilia are 2 examples • Since these conditions only deal with the X chromosome, we use the capital letter X with a superscript to signify dom/rec alleles

  9. Colorblindness • Can’t distinguish colors • Most common: red-green colorblindness---can’t tell the difference between these 2 colors • Use a superscript “c” to show the allele for colorblindness • XcXn carrier female • XcY colorblind male • XnXn normal female • XnY normal male • Carrier female marries a colorblind male—what % of females will be colorblind? Carrier? • What % of males will have normal vision? • With sex-linked problems you have to pay attention to what the problem is asking—boy, girl or child---the % will be different

  10. Hemophilia • Disease where the blood lacks a clotting factor (Factor VIII) • Without this clotting factor a hemophiliac could bleed to death from a bump or scrape • During Victorian England, the disease ran through the Royal houses in Europe, due to the way the English princesses (carriers) were married off to other Royal families in other countries • Change the superscript to a lowercase “h” for hemophilia • XhXn carrier female • XhY hemophiliac male • Normal clotting male marries a carrier female—what are the chances of them having a hemophiliac CHILD?

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