Question

How to solve SsBb x ssbb

Answer 1

The SsBb represents the alleles on the two S and two B chromosomes of the first parent. And the ssbb represents the alleles on the two S and two B chromosomes of the second parent.

The key is, each parent has four chromosomes. Each letter represents one of those chromosomes. The offspring will get one of those two S chromosomes and one of those two B chromosomes from each parent. Which chromosome the offspring actually gets is random.

So for the first parent, you come up with all possible combinations of chromosome the offspring might inherit. For example, the first parent can pass on the S chromosome with the dominat allele (S) with either of its B chromosomes - the possible combinations are SB or Sb. Same thing for the second S chromosome with the recessive allele on it - the possible combinations with that one are sB and sb. Along the top of your Punnett square, you put those four combinations.

Along the side of the Punnett square, you put all possible combinations of chromosomes from the other parent. In this case (because the alleles are all the same), the possible combinations are sb, sb, sb and sb. Not very interesting but easy.

Clear?

Answer 2

thanks that helps

Answer 3

Sure, not a problem. ;D

Answer 4

is the problem in math

Answer 5

The cross you are being asked to preform is a Test Cross. What you are testing is whether your first individual (SsBb) is heterozygous (Ss) or a homozygous dominant (SS) as both of these genotypes produce the same phenotype (the dominant phenotype resulting from S). Since our eyes cannot see objects as small as chromosomes (of which there are only two in this example, making the example organism, like humans, diploid) we observers of the natural world (scientists are also, by definition, practitioners of the art of falsehood identification and epistemologically believe themselves incapable of identifying truth – instead recognizing the simple fact that the universe fails to conform to the intuition of the uninformed mind) choose to observe phenotype. If we do observe genotype, we do so indirectly through robots equipped to perform biochemistry (most usefully in my experience Real Time Reverse Transcriptase Polymerase Chain Reactions)

Soooo..... I will post a visual aid for understanding this simple test cross very soon.... and there are only two chromosomes in this example!

To truly understand the test cross you must appreciate this simple fact: the only time genotype can be directly inferred from the phenotype of an individual is when a recessive phenotype is observed and the observer can conclude that the genotype of the individual is homozygous recessive (ss). A test cross is needed to distinguish SS from Ss as both look like the dominant S trait for which this imaginary gene was named.