1. Human Inheritance

2. Single Gene Traits Many Human traits are controlled by a single gene with one dominant and one recessive allele This yields two distinct phenotypes for the three different genotypes (TT, Tt, tt) –I.e.: Widow’s peak vs. straight hairline or tall and short When two alleles are Co-dominant, they produce an intermediate phenotype that is some mix of the homozygous parents Also known as Incomplete Dominance

3. Incomplete Dominance Produces a phenotype that appears to be a mix between the 2 homozygous parents –It’s not a mix like paint, there are lots of “spots” which look like one parent or the other –The distribution and size of these can give different looking combinations in different organisms that can look like a mixture –The Punnett Squares for incomplete dominance are different as well

4. Both letters are capitals but one was an added apostrophe called prime For example –Cross of a red (FF) four o’clock flowers with white (F’F’) ones –The results are pink (FF’) flowers. –The pink is really lots of small red and white dots intermixed. FF F’FF’ F’FF’

5. Multiple Alleles Some single gene traits have more than two alleles – Multiple Alleles, which will yield more than three phenotypes –Blood type has three alleles (A, B & O) and thus 4 main blood types: A, B, AB, O –O is recessive to A and B but they are co- dominant with each other, thus giving AB. –A person with A-type blood has AA or AO –B-type would be BB or BO and O-type is OO

6. Polygenic (Multi-Gene) Traits Some Human traits show a large number of phenotypes because the traits are controlled by many genes. The genes act together to produce a single trait Height, eye hair, skin color are examples. This allows for numerous combinations of genes and alleles and thus many variations in the phenotypes Other environmental factors, such as diet, can contribute as well, affecting height etc.

7. Traits and Chromosomes Gender (sex) is controlled by chromosomes: female = XX male = XY Male parent donates an X or a Y and thus determines the offspring’s sex. Genes on the X and Y chromosomes are called sex-linked genes and the resulting traits are also sex-linked. The Y chromosome does not carry alleles for these traits.

8. Sex-linked Traits Since males have only one X chromosome, they are more likely to have a sex linked trait that is controlled by a recessive allele. This is because they can have only one recessive allele and not have a dominant allele mask the trait. Red-Green colorblindness is an example. A Carrier is someone who has one recessive and one dominant allele. A Carrier does not have the trait but can pass it to her offspring Only females can be carriers of sex-linked traits because males only have one allele (on the X- Chromosome).

9. Sex Linked Recessive Traits Father does not have trait (X H Y) XHXH Y XHXH XHXHXHXH XHYXHY XhXh XHXhXHXh XhYXhY XHXH Y XhXh XHXhXHXh XhYXhY XhXh XHXhXHXh XhYXhY Mother is a carrier Some sons will have trait Mother has the trait All sons will have trait

10. Sex Linked Recessive Traits Father does have trait (X h Y) XhXh Y XHXH XHXhXHXh XHYXHY XhXh XhXhXhXh XhYXhY XhXh Y XhXh XhXhXhXh XhYXhY XhXh XhXhXhXh XhYXhY Mother is a carrier Some children could have it Mother has the trait. All children will have trait

11. Sex Linked Recessive Traits Father does have trait (X h Y) XhXh Y XHXH XHXhXHXh XHYXHY XHXH XHXhXHXh XHYXHY Mother does not have trait but all daughters are carriers!

12. Pedigree In studying inheritance patterns, geneticist trace traits through many generations To do this they use a Pedigree –A pedigree is a chart or “family tree” that tracks which members of a family have a particular trait Note that inheritance patterns don’t always follow the predicted probabilities from Punnett squares!