1. Exceptions to Mendel

2. Sometimes, genetic traits don’t work in a straight dominant or recessive manner. Here are 5 exceptions to Mendel.

3. 1. Co-Dominance Both alleles contribute to the phenotype so you see both traits. Both alleles contribute to the phenotype so you see both traits. For example, a brown goat and a white goat making a baby that is brown and white. For example, a brown goat and a white goat making a baby that is brown and white.

4. Brown and White Roan Coat http://www.spinone.com/genetics.htm

5. Orange and White Roan Coat http://www.spinone.com/genetics.htm

6. 2. Incomplete Dominance One allele is not completely dominant over the other allele, and the phenotype is in between. One allele is not completely dominant over the other allele, and the phenotype is in between. For example, red and white flowers make pink flowers. For example, red and white flowers make pink flowers.

7. 4 o’clock Flowers – red and white makes pink. http://www.goldiesroom.org/Note%20Packets/18%20Genet ics/04%20Genetics--Lesson%204.htm Notice how two letters are being used. R – red W – white This is done so a person can tell the trait is not a straightforward dominant/recessive trait. Sometimes you might also see R – red R’ – white (you say this R prime) This telling a person the same thing - that it is not a straight dominant/recessive trait.

8. Think about this….. Could two pink flowers make a red flower? If so, what is the likelihood? Could two pink flowers make a red flower? If so, what is the likelihood? The likelihood would be 25%

9. Shorthorn Cattle also show incomplete dominance A black bull and a white cow make gray offspring. Again, notice how two different letters are being used for each allele. A black bull and a white cow make gray offspring. Again, notice how two different letters are being used for each allele. http://media.nasaexplores.com/lessons/02-064/images/image2.jpg

10. Think about this…… If the 4 o’clock flowers and the shorthorn cattle had co-dominant traits instead of incomplete dominance, what color offspring would each have? If the 4 o’clock flowers and the shorthorn cattle had co-dominant traits instead of incomplete dominance, what color offspring would each have? The flower offspring would be red and white spotted. The shorthorn cattle offspring would be black and white spotted. You would see both traits, not an in between phenotype as in incomplete dominance. The flower offspring would be red and white spotted. The shorthorn cattle offspring would be black and white spotted. You would see both traits, not an in between phenotype as in incomplete dominance.

11. 3. Multiple Alleles Some genes are coded for by more than two alleles. Some genes are coded for by more than two alleles. For example, blood type is coded for by three alleles. You will get two alleles for blood type, but there are three possible choices… the A allele, the B allele, or the O allele. For example, blood type is coded for by three alleles. You will get two alleles for blood type, but there are three possible choices… the A allele, the B allele, or the O allele.

12. Blood Type http://www.enh.org/uploadedimages/antigens.jpg If mom gives you the A allele and so does dad, you would be Type A. If mom gives you the A allele and dad gives you the B allele you would be Type AB (this is because they are co- dominant). If mom gives you the B allele and dad gives you the O allele, you would be Type B (this is because O is the recessive form). To be Type O, mom and dad would both need to give you the O allele.

13. 4. Polygenic Several genes interact to determine a trait. Several genes interact to determine a trait. For example, skin color is controlled by several genes and how they interact together. For example, skin color is controlled by several genes and how they interact together.

14. Skin Color Variations are a Polygenic Trait Controlled by Many Genes. http://anthro.palomar.edu/adapt/adapt_4.htm (Sub-Saharan African, Indian, Southern European, and Northern European) Skin color being polygenic helps explain why there are some many colors in the human population, and not just two or three.

15. 5. Multifactorial Inheritance Phenotype is determined by genotype and environmental factors (nutrition, health, etc.). Phenotype is determined by genotype and environmental factors (nutrition, health, etc.). For example, height and predisposition to developing diabetes or cardiovascular disease are controlled by genes and the environment. For example, height and predisposition to developing diabetes or cardiovascular disease are controlled by genes and the environment.

16. Height Your DNA will only allow you to grow so tall, but if you have poor nutrition, will you reach that maximum height? Probably not. Your DNA will only allow you to grow so tall, but if you have poor nutrition, will you reach that maximum height? Probably not. http://www.personal.psu.edu/afr3/blogs/siowfa13/2013/10/you-are-growing-like-a-weed.html

17. Cardiovascular Disease and Type 2 Diabetes You may have a genetic predisposition to developing these disorders, but if you exercise and watch what you eat, will you get them? Hopefully not. You may have a genetic predisposition to developing these disorders, but if you exercise and watch what you eat, will you get them? Hopefully not. This picture shows environmental factors that can affect your likelihood of developing Type 2 Diabetes. http://www.metacure.com/about-diabetes-2/type-2-diabetes-mellitus-t2dm/