Question

Mendel's Laws: n this chapter we learned not only about the importance of Mendel's Laws (segregation and independent assortment) to heredity, but also that there are a number of exceptions to Mendel's Laws. Inheritance follows some basic ideas, but can certainly appear to be a tricky thing if you don't fully understand the basis of how the traits of living things come about. This discussion, therefore, will focus on the exceptions to Mendel's Laws so that it will help you better understand how traits come about. You should look up more information on an exception and provide us with a better understanding of it in your postings. Different examples, importance, effects on traits including diseases, and other things can certainly be addressed.I need an outside source with this with in paragraph citation as well as a reference citing at the end..

Answer 1

The exception to Mendel's Law:

1) Co-dominance: It refers to when two alleles of a gene are clearly and equally expressed in the phenotype. Example- AB blood type in humans where I^A and I^B are present.

2) Incomplete dominance: It refers to when two alleles of a gene are blended into the phenotype. Example- Cross of Red snapdragons and White snapdragons gives Pink snapdragon in an F1 hybrid.

3) Polygenic Inheritance: It refers to some genes having three or more alleles but only two alleles define the trait. Example- From 3 alleles, I^A- dominant, I^B- dominant and i- recessive there are 4 phenotypes A, B, AB, O. A person can have only two alleles expressing the blood type.

4) Lethal genes: It refers to some genes which are lethal when present in a homozygous condition. Example- In mice, yellow coat color is dominant to grey. When crossing hybrid mice Yy x Yy, using Punnett square,

	Y	y
Y	YY	Yy
y	Yy	yy

where YY genotype is lethal, mice having these genotypes do not survive.

5) Pleiotropy: One gene defect can affect the body as the gene product (protein) is affected. Example- Sickle cell anemia where single amino acid is altered affecting hemoglobin genes.

6) Epistatic genes: These genes interferes with the expression of another gene which functions perfectly. Example- Albinism where individuals lack melanin pigment in their body.