Mendel pea plant experiment questions - Help? (1 Viewer)

[florence1996]

Could anyone explain to me how to answer these questions? Thanks.

A student repeated one of Mendel's experiments. A plant with green pods was self fertilised and produced a first generation consisting of 793 plants with green pods and 275 with yellow pods.

Approximately how many of the 793 green-pod plants would be expected to be homozygous for pod color?

a) 0
b) 100
c) 250
d) 500
e) 793

If the original plant is fertilised by a yellow pod plant, what proportion of the offspring can be expected to be yellow pod plants?

a) 0
b) 1/4
c) 1/2
d) 3/4
e) 1

In certain plant species, the trait T is dominant to the dwarf t and the color red R is dominant to white r. To determine whether a particular tall red plant is heterozygous or homozygous for both characteristics, the plant would be best crossed with which of the following?

a) TTRR
b) TtRr
c) ttRR
d) TTrr
e) ttrr

 

[tohriffic]

Could anyone explain to me how to answer these questions? Thanks.

A student repeated one of Mendel's experiments. A plant with green pods was self fertilised and produced a first generation consisting of 793 plants with green pods and 275 with yellow pods.

Approximately how many of the 793 green-pod plants would be expected to be homozygous for pod color?

a) 0
b) 100
c) 250
d) 500
e) 793

If the original plant is fertilised by a yellow pod plant, what proportion of the offspring can be expected to be yellow pod plants?

a) 0
b) 1/4
c) 1/2
d) 3/4
e) 1

In certain plant species, the trait T is dominant to the dwarf t and the color red R is dominant to white r. To determine whether a particular tall red plant is heterozygous or homozygous for both characteristics, the plant would be best crossed with which of the following?

a) TTRR
b) TtRr
c) ttRR
d) TTrr
e) ttrr

Hi, not sure if you have answered the questions by now.. but here is one way on how you can do it. Sorry I don't actually know how to draw tables on this.. s: -noob-

1)
If a plant with green pods self fertilised and managed to produce offspring with yellow pods, this indicates it must have been heterozygous.
With this information we are able to draw up a punnet square.

Let the allele for green pods be represented by G. Therefore let the allele for yellow pods be represented by g.

S G p g ace
G GG Gg
g Gg gg

This gives us a ratio of 3 green: 1 yellow. Or in genotype terms, 1 GG: 2 Gg: 1 gg. Therefore, if there are 275 with yellow (gg) we would expect about 275 homozygous green pods (GG) which is closest to C - 250.

2)
Using the knowledge that the original plant was heterozygous we are able to draw another punnet square.

Let the allele for green pods be represented by G. Therefore let the allele for yellow pods be represented by g.

S G p g ace
g Gg gg
g Gg gg

The phenotypic ratio here is 1 green: 1 yellow. So we would expect 1/2 to be yellow pod plants. (C)

3)
Take this question in parts: first we have height of the plant and the colour.
Starting with the height, the plant can either be homozygous tall (TT) or heterozygous tall (Tt). You can draw punnet squares to help you out. If you take a step back and have a think about it, the key word here is best. It is definitely not ideal to cross it with a homozygous dominant because the dominant allele will characterise its phenotype and thus if it really is heterozygous, the recessive allele will never be expressed. Therefore a), c) and d) are eliminated leaving you with b) and e).

So each answer will give you two cases:

If the plant is homozygous tall:
Case 1 with b):

S T p T ace
T TT TT
t Tt Tt

Case 1 with e)

S T p T ace
t Tt Tt
t Tt Tt

With both cases giving us offspring with phenotype of being tall (as T is dominant)

If the plant is heterozygous:

Case 2 with b)
S T p t ace
T TT Tt
t Tt tt

Case 2 with e)

S T p t ace
t Tt tt
t Tt tt

Both answers also provide us with an accurate representation of the genotype the red tall plant however we can note that e) has a greater chance of providing the recessive trait (if it is heterozygous). Therefore, the best answer will be e) as you can do the same thing with the red colour genotype. Note, for the last question you don't need draw the punnet squares, I just did for the sake of explanation.