Question

A purple flower with an unknown genotype is crossed with a white flower. Determine the genotype of the purple flower if purple (P) is dominant and white (p) is recessive

Answer 1

Do you have the Punnet Square resulting of the cross ?

Answer 2

@Romona......First of all, Welcome to OPEN STUDY.....

well....The question is about a test cross.

Definition of a test cross:
Generally a cross involving a homozygous recessive individual. When a single trait is being studies, a test cross is a cross between an individual with the dominant phenotype but of unknown genotype (homozygous or heterozygous) with a homozygous recessive individual. If the unknown is heterozygous, then approximately 50% of the offspring should display the recessive phenotype.

If the individual is homozygous all the progeny will have the dominant phenotype.

James' suggestion to use show the result of the two possible crosses with a Punnet square is a great suggestion.

Answer 3

Or informations about the phenotype of the offsprings.
And @Koikkara is right :)

Answer 4

If you are unfamilar with a Punnet square or how to write one, check out this website.

@MagaliH...... @Romona....refer

http://utahscience.oremjr.alpine.k12.ut.us/sciber00/7th/genetics/sciber/punnett.htm

Answer 5

Thanks for your Sharing of thougths.....Congratulations for the team Work....!!

Answer 6

@Koikkara ;)
@Romona So remember, in your case, to know the exact genotype of the purple flower, you need the phenotype (or the genotype) of the offsprings. Do you have it ?

Answer 7

Is it possible to help me do the pungent square for it?

Answer 8

No magaliH I'm new to all of this ,it is a white20 mark question.

Answer 9

Ok :)
You have two possibilities. The purple flower can have a genotype (Pp), which is an heterozygous genotype, or (PP), which is an homozygous one. Indeed, this flower needs to have at least one P allele (without it, the purple color could not be expressed), but as P is dominant, this flower can have also a p allele, because the P allele would be expressed anyway.

Tu know which possibility out of those two is the real genotype of the purple flower, we need to analyse the phenotype/genotype of the offsprings. If you don't have it, you can just talk about the two possibilities (but this would be strange because the exercise wouldn't mention the white flower and the test-cross if you don't have informations about the offspring).

Answer 10

Is it possible to help me do the pungent square for it?

Answer 11

Of course ! But you don't have the genotype of the purple flower, so the Punnet Square looks like that :


On the top, the two alleles that the white flower can give : have you understood why ? If yes, explain it to me, if not, tell me and I will explain it to you.
On the left, the two alleles that the purple flower can give : same advices :)
In the center, the genotype of the four possible offsprings.

Answer 12

How do i go about. Getting the genotype?

Answer 13

Which genotype ?

Answer 14

Gosh I'm confused so will what u just sent me be the answer to my question?

Answer 15

Ahaha, I see that, please keep calm and don't panic, everything will be alright :D
The square in my previous message is the square that corresponds to the cross of the purple flower and the white one.

If you don't know how to get a genotype, here is a clue :
You're studying a gene that codes for the color of a flower. This gene has two versions, called "alleles". Each flower has two alleles : it may be the same two alleles (the flower is called "homozygous") or two different alleles (the flower is called "heterozygous").
One of the alleles is called "dominant" because when it is present in the flower, it is always expressed, no matter what is the second allele. Here, the P (that codes for purple) is domainant. The other version of the gene is callled "recessive", what means it needs to be present twice in the flower to be expressed.
The genotype is written like that :
(allele1oftheflower allele2oftheflower)
If the flower has :
(PP), it is homozygous and purple because only P alleles are present and they code for purple
(pp), it is homozygous and white because only p alleles are present and they code for white. As p is recessive, this is the only case in which the flower is white
(Pp), it is heterozygous and the flower is purple because the two versions of the gene coexist and P is dominant on p, so only P is expressed and the flower is purple.

Here, you have a purple flower and a white one. As we just said, the white one must be (pp), but the purple one can be (Pp) or (PP).

Have I lost you yet ?

Answer 16

Ok i understand so far

Answer 17

Great.
To draw a Punnet square, you have to take the two alleles that are present in the flower. On the top of the square, you write the two alleles of one flower. On the left, you write the two alleles of the other flower. Even if the flower is homozygous (and have the same two alleles), you have to write the two alleles.

Does it make you understand this square ? On top, te white flower. On left, the purple one.
If you combine the column with the line for each central little square, you get the genotype of the children.