biology homework. please help. maybe you can explain answer?

Question

In certain breeds of dogs, deafness is due to a recessive allele (d) of a particular gene, and normal hearing is due to its dominant allele (D). What is the percentage of the offspring of a normal heterozygous (Dd) dog and a deaf dog (dd) would be expected to have normal hearing?

oh ok. thank you. I understand it.

Answer 1

ok so you inherit one allele from each parent. there is a 1/2 chance that a puppy will inherit the D gene from the normal heterozygous dog and 1/2 chance that it will inherit the d gene. From the other parent there is a 1/1 chance that it will inherit the d gene.
Therefore when we multiply the probabilities there is a 1/2 chance of being Dd and 1/2 of being dd. so 50% would be expected to have normal hearing.

We can also do this the Punnit (spelling?) Square method

We place the possible alleles for one parent on one side and the other parent on the other side

  D      d
d

d

Now we bring fill in the blanks by bringing the alleles down or sideways.

  D     d
d Dd dd

d Dd dd

We see that 50% are Dd and 50% are dd.

Answer 2

Oh, I use to know how to do this. I can't remember exactly how to calculate it--you're suppose to diagram it somehow in a box. Your teacher will help, I'm sure, but if the normal heterozygous dog carries the recessive allele (as indicated by the "d"), and it mates with a dog that has "dd" in its genetic code, then it seems like the offspring would be 75% likely to be deaf.

(There are a total of 4 d's in this equation. If 3 are "d" and only one is "D", then normal hearing makes up 1/4 of the combined genes.)

I THINK this is right. I just wish I could remember how to calculate it for sure.

Answer 3

This Punnet square shows to possible combinations of genes in the children of parents with one having Dd and the other dd..
If your puppy inherited a recessive gene from each parents, then both of her parents must have the recessive gene “d” in their genotypes. However, if only one of them has normal hearing,only one has the dominant gene “D”.

With one parent that have the genotype Dd, there are two possible outcomes for the genotypes of the puppies.

Two out of four (or 50%) will likely have the genotype “dd” (deafness)
Two out of four (or 50%) will likely have the genotype “Dd” (normal hearing)

````d`````d
D Dd Dd
d dd dd

Answer 4

there are four possibilities:
DD
Dd
dD
dd
as you can see a normal dog could be represented by a D no matter it is DD, Dd or dD, so the % of a normal dog is 75% and a deaf dog 25%

Answer 5

you need to set up a punnett square, and if there is only 4 different ways it can be set up, wouldn't it only be 25%?