In a cross between a black guinea pig and a white guinea pig, all members of the fi generation are black. the f2 generation is made up of approximately 3/4 black and 1/4 white guinea pigs.
a) diagram this cross, showing the genotypes and phenotypes.
b) if two fz white guinea pigs are crossed, what will be the appearance of the offspring?

In F0, we have two blacks guinea pigs this tells us that they have at least one allele for the color black (B).

In F1, they tell us that everyone is black, so everyone also has the allele for the color black (B).

In F2, they tell us that there are 1/4 whites, which means that there is a second possibility of color, recessive (w).

The only way for a second allele to appear is that these characteristics are heterozygous. If you draw Punnett's square(photo) you'll find:

a)

F0: BB x Bw = BB BB Bw Bw= 4/4 black

F1: Bw x Bw = BB Bw Bw ww= 3/4 black 1/4 white.

White guinea pigs: ww

b)

If you cross two white Guinea pigs, you only have the recessive allele, so all of the offspring will be also white.

1.  The enzyme dicer cleaves dsRNA to form

small interfering RNA (siRNA).

2.  The siRNA binds to a special protein,  

which degrades one strand.

3. One strand of siRNA associates with the

protein to form an RNase complex.

4. The RNase complex binds to a specific

mRNA and degrades it.