Dominant Alleles and rule of addition vs multiplication.

[NewtoBiology]

Hello Biologists!

I am have just studying about Mendel and his genetic variations on pea plants. Now I have to apply the rule of addition and the rule of multiplication to a question. WOULD YOU ALL BE SO KIND TO ASSIST.....

Rule of addition: when one event can occur in two or more alternative ways. Is this correct? Anyone have a simpler way of explaining?
Rule of multiplication: used when trying to predict the probability of compound events? Is this correct?

My QUESTION:

Dwarfism is caused by a dominant allele. A female dwarf (whose mother was also a dwarf) marries a man of normal height..
So if I understand correctly the female dwarf would be Dd?? Is this correct?

a. What are their chances of having a child of normal stature? Using Pinnett square I calculated that there are Dd genotype and dd genotype therefore there is 50% chance that they will have a child of normal stature?????

b. What are their chances of having four children who are dwarves?
1/2 x 1/2 x 1/2 x 1/2 = 1/16 of a chance of having 4 children who are dwarves??

Any help or clarification would be so greatfully appreciated!!!

Thank you
NewtoBiology

[mith]

think of the rule of addition as when two events are not dependent on each other such as

whether a coin lands heads/tails OR a dice lands on 6 = 1/2 + 1/6


then the rule of multiplication would be when two events are dependent on each other

whether a coin lands heads/tails AND a dice lands on 6 = 1/2 *1/6

Of course things get a bit more complicated if they're not mutually exclusive.