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 identical twins (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 causing chronic shortage of RBC--anemia

6. 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
50/50 chance of passing it on to children
Huntington’s Disease

7. Multiple Allele Traits
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?
Multiple Allele Traits

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
Colorblindness

10. 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?
Hemophilia