10/21/2011

 A herd of cows vary in color. Some are black, some are white with black spots, some are white. The color and pattern on each cow are distinct from those of its parents and siblings. What process is responsible for the differences seen in each cow?  Replication  Translation  Mitosis  Meiosis  What are the two gametes in the human body?  Sperm and egg  Sperm and ovary  X and Y  Egg and ovary

 The type of inheritance we learned about before was called complete dominance. One trait was completely dominant over the other, like tall is dominant to short, with no in-between. We only used one letter to stand for the trait, with upper case for the dominant and lower case for the recessive.

 These are called Mendelian traits because this is the type of traits studies by Mendel when he worked with pea plants.  Today we will learn about non-Mendelian traits. For these, we will use two capital letters to stand for the different alleles, and both letters to stand for the hybrid (heterozygote).

 Incomplete Dominance – neither allele is completely dominant over the other, the combination of alleles creates a new phenotype that is a blend of the others.  For example, a certain plant shows incomplete dominance. It can have red flowers, white flowers, or pink flowers. Let’s assign letters to the alleles: RR = red, WW = white, RW = pink  Make a Punnett square showing a cross between a red flowered plant and a pink flowered plant:

 Codominance – both alleles are dominant and both will show in a hybrid (heterozygote).  In guinea pigs, black and white fur colors are codominant. A hybrid will show black and white spots. Let’s assign letters to the alleles: BB = black fur,WW = white fur, BW = black and white spotted fur  Make a Punnett square showing a cross between a white guinea pig and a spotted guinea pig:

 Polygenic traits are traits that are influenced by several genes. Examples include human height and skin color, which are both influenced by dozens of genes.  As a result of polygenic traits, a lot of intermediate conditions exist.

 Genes with 3 or more alleles are said to have multiple alleles. An example of multiple alleles is human blood type.  The four blood types are A, B, AB, and O. A and B are codominant and O is recessive. They are sometimes written with the letter I : I A, I B, i O  Since O is recessive, this means that if A is with O, A will be the blood type. If B is with O, then B will be the blood type. But if A is with B, then the blood type is AB.

Blood TypeAllele Combinations AAA or AO (I A I A or I A i) BBB or BO (I B I B or I B i) ABAB only (I A I B ) OOO only (ii)

 What blood types can be donated? It depends on the blood types of the receiver and the donor.  Type A can give to A or AB, because both contain A  Type B can give to B or AB, because both contain B  Type AB can give to AB only, because only AB contains both A and B  Type O can give to all blood types since it is recessive.  AB is considered the universal acceptor, O is the universal donor.

 Make a Punnett Square showing a cross between a woman with Type A homozygous blood and a man with Type B heterozygous blood:  Make a Punnett Square showing a cross between a woman with Type A heterozygous blood and a man with Type O blood: