Question

In pea plants, purple flowers (P) are dominant over white flowers (p) and tall stems (T) are dominant over short stems (t). Complete a dihybrid cross for parents with the genotypes: PpTT × ppTt and answer the following in complete sentences.

Describe how you would set up a Punnett square for this cross.
List the likelihood of each possible offspring genotype.
List the likelihood of each possible offspring phenotype. @niels5x9

Answer 1

what do u think the answer is ?

Answer 2

@Rushwr I honestly don't know

Answer 3

do you know what a punnet square is?

Answer 4

@niels5x9 yes I do know what a punnet square is

Answer 5

do you know how to make a punnet square of a dihybrid cross?

Answer 6

I very vaguely know how to make it :(

Answer 7

okey here is an example:

Answer 8

Cool @niels you are there... ,I'll leave

Answer 9

Yeah I know what it looks like and stuff

Answer 10

@Devingee23 1st u would have to write down the gametes for each parent.

Answer 11

It's pretty much just finding the probabilities that trips me up

Answer 12

okey

Answer 13

So it would be PT pT pT and pt?

Answer 14

the number of times a genotype shows up in the square devided by the total number of squares is the probability of a certain genotype

Answer 15

So I had it right? for that part @niels5x9

Answer 16

o sorry no it is PT, PT, pT and pT. No pt

Answer 17

for PpTT parent it would be PT and pT
for ppTt ------> pT and pt
Now it's just the matter of punnet square

Answer 18

because there is no little t in the starting genotype

Answer 19

Okay so it is PT, PT, pT, and pT?

Answer 20

oh hehe i think I understood you wrong I thought you meant on one side... you are right no problem

Answer 21

so now what do I do?

Answer 22

one side has PT and pT and the other has pT and pt

Answer 23

you draw a square like that and you fill up the square combining the 2 genotypes (so the top left one is PpTT)

Answer 24

THe next one would be PpTt? @ niels5x9

Answer 25

exactly!! great

Answer 26

So now what we just fill in the rest of the square?

Answer 27

exactly

Answer 28

okay so all of them together are PpTT, PpTt, ppTt and ppTT?

Answer 29

and then we can go on to determine the likelyhood of every genotype:

the genotypes we have are:
PpTT
PpTt
ppTT
pptT
the total number of genotypes is four and every genotype comes up one time. what do you think is the probability of every genotype showing up?

Answer 30

yes is is

Answer 31

25%?

Answer 32

magnificent. now for the last question do you know what dominent and resisive means?

Answer 33

I know for resecisve you have to have two of that one gene right? @niels5x9

Answer 34

*dominant and ressesive exuse my english

Answer 35

when you have two genes in a pair one can be dominant over another, like P is dominant over p. that means that if you have the genotype Pp your fenotype will be P and not p. p is the ressesive gene here.

do you understand?

Answer 36

KInd a

Answer 37

@ niels5x9

Answer 38

okey you have two genes P and p. some people have PP, they will have a fenotype P. some people have pp, they will have a fenotype p. But an organism can have only one fenotype so one should be dominant over another meaning that in case of Pp one should come out as the phenotype.

Answer 39

@Devingee23

Answer 40

So if it is Pp it will be purple but if it is pp it will be white?

Answer 41

exactly

Answer 42

yeah PP also means that its purple.

Answer 43

a lot of genetic disorders are also recessive and that means that somebody can have one of the genes for the disease but not notice it, but when they have children with another person with one gene of the disease their child might get the dissease.

Answer 44

now what?

Answer 45

so getting back to the exersize, you now work out what the fenotype of those 4 genotypes is

Answer 46

How do I do that?

Answer 47

okey so in the first one: PpTT

in Pp P is dominant so phenotype: P
in TT: T
so the phenotype is: TP

Answer 48

Well I know no matter what it will be a tall plant right?

Answer 49

exactly!!

Answer 50

So in the second one it will be purple and tall

Answer 51

yes it will

Answer 52

the third white and tall and in the last white and tall?

Answer 53

yess certainly!!

Answer 54

so really there is a 50% chance that it will be purple or white right?

Answer 55

now what do you think is the next step in getting the chance in phenotype

Answer 56

?

Answer 57

WOuld it be 50% @niels5x9

Answer 58

@niels5x9 r u still there?

Answer 59

sorry i was distracted yes it is!!

Answer 60

SO are we done then?

Answer 61

so now you have all the questions answered

Answer 62

btw sorry @shreehari499 I just realised that this might have been more of your area of expertise.

Answer 63

Yeah it might be but you've done a good job..! Bravo!

Answer 64

thanks!!