7. You are investigating the inheritance of petal shape in tulips. There are two

Question

7. You are investigating the inheritance of petal shape in tulips. There are two types of flowers, those with entire (smooth) edges and those with feathered edges. You carry out the following three crosses: Cross Parent Phenotypes Progeny Phenotypes Smooth x Smooth 2 Smooth x Feathered Smooth x Feathered 40 Smooth, 7 Feathered 20 Smooth, 35 Feathered 200 Smooth, 195 Feathered 1 3 On the basis of these results, what is the most likely mode of inheritance of the smooth edge phenotype? A. B. Give the most likely genotypes of the parent in each cross. Use a chi-square test to evaluate the fit of the observed numbers of progeny to the number of expected on the basis of your proposed genotypes for cross number 1. C.

Explanation / Answer

Cross

Parent phenotype

Progeny Phenotype

1.

Smooth X smooth

40 Smooth, 7 feathered

2.

Smooth X feathered

20 smooth, 35 feathered

3.

Smooth X feathered

200 smooth, 195 feathered

Cross 1 is having 40 smooth and 7 feathered progeny, which shows that most of the progeny inherited dominant character. And hence, the pattern of inheritance of smooth edge phenotype is dominant inheritence

Cross 2 is having 20 smooth and 35 feathered, so, it is clearly seen that the feathered edges are twice the smooth no., hence it is case of sex linked recessive inheritance.

Cross 3 is 50% smooth and 50% feathered, which is a autosomal recessive inheritence.

cross 1

Dd X Dd

DD, Dd, Dd, dd

Cross 2

Ddc X dcdc

Ddc, Ddc, dcdc, dcdc

Cross 3: Dd X dd

Dd, Dd, dd, dd

In case of autosomal dominance the ratio expected is 3:1

Observed

expected

(O-E)2

(O-E)2/E

Smooth

40

¾*40=30

(40-30)2=100

100/30=3.3

Feathered

7

¼*7 = 1.75 ~2

(7-2)2= 25

25/2=12.5

Chi square = 15.8

Degree of freedom = 2-1 =1

At P = 0.05 and degree of freedom the value is 3.841

This chi square value is much larger than the tabular critical value,

So the hypothesis is rejected.

Cross

Parent phenotype

Progeny Phenotype

1.

Smooth X smooth

40 Smooth, 7 feathered

2.

Smooth X feathered

20 smooth, 35 feathered

3.

Smooth X feathered

200 smooth, 195 feathered

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