WHAT IS THE PHENOTYPIC RATIO OF A SIMPLE DOMINANT-RECESSIVE CROSS? plz help!!!!10 points!!?

Question

hi... i'm having some trouble with biology homework.

For a trait with intermediate inheritance, what is the phenotypic ratio for f2 off spring of a monohybrid cross? How is that different from a simple dominant-recsesive cross?


for the phenotypic ratio for f2 offspring of a monohybrid cross i got 1:2:1.. is that correct?
now i just need to know.. how is that different from a simple dominant-recessive cross

Answer 1

yes you got the right ratio of 1:2:1.

the F2 generation is the second generation which means the offsprings of the offsprings of the original parent while the simple dominant recessive cross is the first generation offsprings or F1.

you said the parents are simple dominant recessive cross..

so

BB- dominant parent
bb- recessive parent

The F1 (1st generation offsprings using the square would be all Bb).

Bb- all F1 parents

The F2 generation (2nd generation offsprings using the punnett square would be:

1 BB
2 Bb
1 bb

with the ration of 1:2:1

Note: The person above me who gave a ratio of 1:1:1:1 was wrong because you are looking for a phenotypic ratio which means how the organism would look like.

bB and Bb since B is the dominant trait would be the same....

Answer 2

Here's the difference:

Intermediate inheritance means that the trait shows incomplete dominance and the heterozygous ones have an intermediate or "in between" phenotype. An example is red x white = pink.
Parents: RR x rr
F1: all Rr = all pink
F2: RR, Rr, rR, rr = 1 red: 2 pink: 1 white

Simple dominance means that the alleles that control the trait are the dominant and recessive and the heterozygous ones have the dominant phenotype. An example is tall/short in peas where tall (T) is dominant to short (t).
Parents: TT x tt
F1: all Tt = all tall
F2: TT, Tt, tT, tt = 3 tall: 1 short

Whenever you get a ratio of 1:2:1, the trait must be incompletely dominant or codominant. When the ratio is 3:1, the trait is simple dominance.

Answer 3

i don't know what you mean by intermediate inheritence but i don't think that affects the answer to your question.

P generation: AA x aa
F1 progeny: all Aa
F2 progeny from Aa x Aa brother-sister matings: AA Aa aA aa (in equal ratios 1:1:1:1)

or the genotypic ratios will be 1:2:1 as you said. Because "A" is dominant the phenotypic ratio will be 3:1

In your example, "A" is the dominant allele and "a" is the recessive allele. Based on your wording I see no difference. By the above cross you established which allele was the "dominant allele" (A) and which allele was the "recessive allele" (a).

Answer 4

phenotypic is the external out look
1:2:1 ------- codominance as in case of december flowers 1 red ,1 white ,2 punk
if 1:3--------- its simple domonance in case of tall and short of peas i short and 3 short
genotypic:
1 For codominance ---------1:2:1
2 For simple dominance-----1:2:1