1. INTRODUCTION

Mendel had determined the dihybrid inheritance by carried out crossing

between two parents that differ in two traits at the same time. . He used dihybrid

cross to observed whether traits of pea plants such as seed shape, seed color,

flower position were inherited independently. In dihybrid cross, the expected

phenotypic ratio is 9:3:3:1. Alleles of different genes are assorted independently

of one another during gametes formation. From these results, Mendel proposed

the second law of inheritance which rewritten as Law of Independent

Assortment. It states that during gamete formation, each member of a pair of

alleles may combine randomly with either member of another pair of alleles (Teh

Lay Hong, Lee Ching, Wong Tzyy Woei & Chan Suan Khin, 2006).

The objectives for this experiment are:

1. To understand the Mendel’s Law of segregation & independent assortment by

analyzing the two traits in ear of corn.

2. To gather data from F2 ears of corn.

3. To determine the phenotypic ratio of the F2 seeds of corn.

4. To understand Mendel’s Law the principle of dominance, segregation and

independent assortment of alleles in corn.

5. To determine the expected number of individuals of each phenotypes in corn.

6. To make comparison between the expected results with the observed/ actual

results.

7. To explain the relationship between environment factor and genes in determining

the traits of organisms.

2. FLOW OF PROCEDURE

1) An ear corn was used, observed and identified the two distinguished traits:

First trait: aluerone colour [Dominant; purple ( R ), Recessive; yellow ( r )]

Second trait : controls the texture of the kernels [smooth kernels (caused by starch production (S) and wrinkled kernels (caused by the production of sugar (s)]

2) The first row of a corn was marked by using a pin.

3) The purple & smooth kernels were counted row by row, followed by the purple & wrinkled kernels, yellow & smooth kernels and lasted for yellow & wrinkled kernels by using a needle.

5) Steps (1), (2) , (3) and (4) were repeated using other three corns.

4) The data was recorded.

7) The expected number of individuals of each phenotypes was calculated by using the expected phenotypic ratio.

6) Dihybrid cross of corn was constructed by using Punnett Square.

3. RESULTS

A. Number of kernels in the different phenotypes:

PHENOTYPES

NUMBER OF

KERNELS EAR 1

NUMBER OF

KERNELS EAR 2

NUMBER OF

KERNELS EAR 3

NUMBER OF

KERNELS EAR 4

TOTAL

Purple, smooth 303 264 396 286 1249

Purple, wrinkled

87 86 83 63 319

Yellow, smooth 102 114 55 75 346

Yellow, wrinkled

36 29 34 35 134

TOTAL528 493 568 459 2048

POST LAB QUESTION

i. Show the inheritance pattern for these traits. Use Punnett square to show your work

P generationPhenotype: purple, smooth yellow, wrinkledGenotype: RRTT X rrtt

Gametes:

F1 generation: RrTt (All purple, smooth)

F1 x F1: RrTt X RrTtGametes:

F2 generation:

Female gamete

RT

Rt rT rt

RT RRTT

Purple, smooth

RRTt

Purple, smooth

RrTT

Purple, smooth

RrTt

Purple, smooth

Rt RRTt RRtt RrTt Rrtt

RT rt

RT

Rt

rT

rt RT

Rt

rT

rt

Male gamete

Purple, smooth

Purple, wrinkled

Purple, smooth

Purple, wrinkled

rT RrTT

Purple, smooth

RrTt

Purple, smooth

rrTT

Yellow, smooth

rrTt

Yellow, smooth

rt RrTt

Purple, smooth

Rrtt

Purple, wrikled

rrTt

yellow, smooth

rrtt

Yellow, wrinkled

Phenotypic ratio: 9 purple, smooth: 3 purple, wrinkled: 3 yellow, smooth: 1 yellow, wrinkled

ii. Complete the table below with the genotypic and phenotypic data derived from F2 generation

Genotype Pheotype Genotypic ratio Phenotypic ratio

RRTT Purple, smooth 1

9RRTt Purple, smooth 2RrTt Purple, smooth 4RrTT Purple, smooth 2RRtt Purple, wrinkled 1 3Rrtt Purple, wrinkled 2rrTT Yellow, smooth 1 3rrTt Yellow, smooth 2rrtt Yellow, wrinkled 1 1

iii. Using the expected phenotypic ratio in Question 1, determine the expected number of individuals of each phenotypes.

Phenotypes Purple, smooth

Purple, wrinkled

Yellow, smooth

Yellow, wrinkled

Total

Observed number of individuals

1249 319 346 134 2048

Expected phenotypic ratio

9 3 3 1 16

Expected number of individuals

1152 384 384 128 2048

iv. What is the expected genotype and phenotype of the offspring for this cross: RrSS X rrSs?

P generation

Phenotype: purple, smooth yellow, smooth

Genotype: RrSS X rrSs

Gametes:

F1 generation:

Female gamete

RS rS

rS RrSS

Purple, smooth

rrSS

Yellow, smooth

rs RrSs

Purple, smooth

rrSs

Yellow, smooth

Genotypic ratio: 1 RrSS: 1 RrSs: 1 rrSS: 1rrSs

Phenotypic ratio: 2 purple, smooth: 2 yellow smooth

Simplest phenotypic ratio: 1 purple, smooth: 1 yellow, smooth.

4. DISCUSSION

RS

rS rS rs

Male gamete

5. CONCLUSION

The dihybrid cross of corn and the Mendel’s Law of segregation &

Independent assortment were studied thereby the contrasting traits in corn were

colour (purple and yellow) and texture (smooth and wrinkled) of kernels. In addition,

the data from F2 ears of corn was collected and the expected phenotypic and

genotypic ratios of F2 seed’s were showed using punnett square. The phenotypic

ratio was 9 purple, smooth: 3 purple, wrinkled: 3 yellow, smooth: 1 yellow, wrinkled.

Moreover, the Mendel’s Law the principle of dominance, segregation and

independent assortment of alleles in corn were understood based on the results of

the dihybrid cross. On top of that, the expected number of individuals of each

phenotypes in corn were determined where purple,smooth was 1152, purple wrinkled

was 384, yellow smooth was 384 and yellow wrinkled was 128. Compared to the

observed number of individuals for purple smooth, purple wrinkled, yellow smooth

and yellow wrinkled were 1249, 319, 346 and 134 respectively. Thus, the expected

results were slightly differences with the actual results. But, the phenotypic ratio

gained was still accepted. Lastly, there was a relationship between environment

factor and genes in order to determine the traits of organisms.

6. REFERENCES

1. Brooker, (4th ed.). (2012). Genetics Analysis and Principles. America,

McGraw-Hill Companies Inc.

2. Klug, W. S., Cummings, M. R., Spencer, C. A., & Palladino, M. A. (10th ed.).

(2012). Concepts of genetics. California, SF: Pearson Education.

3. Teh, L. H., Lee, C., Wong, T. W., & Chan, S. K. (2006). Biology Form 5. Shah

Alam: Arah Pendidikan Sdn. Bhd.