Gene Involvement in Corn Seedlings

• November 16, 1999
• James Skemp
• article

Objective

In the 1860s, Gregor Mendel followed the pattern of inheritance in plants, hoping to understand the transmission of characteristics by heredity. A few important terms in inheritance are;

• Segregation: Inherited pairs of genes for traits segregate/separate into separate gametes.
• Phenotype: In these experiments, the observable trait of a plant. Whether it is tall or short, or green or white.
• Genotype: The genetic makeup of the plants. Whether it is GG, Gg, or gg, in this experiment.

The hypothesis for experiment one is: That there will be a 9 to 3 to 3 to 1 ratio.

The hypothesis for experiment two is: That there will be a 3 to 1 ratio in green to white corn seedlings.

Materials and Methods

2 week corn seedlings that were under growing lights and were in vermiculite, were counted for:

• In experiment one; whether they were short or tall, and whether they were green or white in color. Tray number 4 was used in this experiment.
• In experiment two; whether they were green or white. Tray number 5 was used in this experiment.

In both experiments, the seedlings were the F2's of two true-breeding parents, GG and gg, with G representing green and g representing white. The white color in some seedlings was caused by a lack of chlorophyll in the seedlings.

Results for Experiment One

From the parents (GGTT and ggtt), the first generation was

F1	GT	GT	GT	GT		F2	GT	Gt	gT	gt
gt	GgTt	GgTt	GgTt	GgTt		GT	GGTT	GGTt	GgTT	GgTt
gt	GgTt	GgTt	GgTt	GgTt		Gt	GGTt	GGtt	GgTt	Ggtt
gt	GgTt	GgTt	GgTt	GgTt		gT	GgTT	GgTt	ggTT	ggTt
gt	GgTt	GgTt	GgTt	GgTt		gt	GgTt	Ggtt	ggTt	ggtt

Table 1: Punnett square showing potential offspring from a dihybrid cross between true-breeding green/tall and white/short corn seedlings. According the Punnett square, it should be a 9:3:3:1 ratio.

Phenotype	Observed	Expected	(obs-exp)2/exp
Green and Short	32	15.9375	16.1884803922
Green and Tall	31	47.8125	5.91184640523
White and Short	14	5.3125	14.2066176471
White and Tall	8	15.9375	3.95318627451
Total	85	85	Accepted if <7.82

Table 2: Results of a Chi-square analysis of a dihybrid cross between true-breeding green/tall and white/short corn seedlings. Chi-square accepted at . Degrees of Freedom = 3.

Results for Experiment Two

From the parents (GG and gg), the first generation was four Gg. The second generation was one GG, two Gg, and one gg (see table 3).

F1	G	G		F2	G	g
g	Gg-green-100%	Gg-green-100%		G	GG-green-75%	Gg-green-75%
g	Gg-green-100%	Gg-green-100%		g	Gg-green-75%	gg-white-25%

Table 3: Punnett square showing potential offspring from a dihybrid cross between true-breeding green (genotype=GG) and white (genotype=gg) corn seedlings. Green color in corn seedlings is completely dominant over white color. According the Punnett square, it should be a 3:1 ratio.

Phenotype	Observed	Expected	(obs-exp)2/exp
Green	97	92.25	0.2445799458
White	26	30.75	0.7337398374
Total	123	123	all are <3.84

Table 4: Results of a Chi-square analysis of a dihybrid cross between true-breeding regular/green (genotype=GG) and chlorophyll-lacking/white (genotype=gg) corn seedlings. Corn seedlings with Chlorophyll (G) is completely dominant over chlorophyll-lacking (g). Chi-square accepted at 0.245 and 0.734. Degrees of freedom = 1.

Discussion for Experiment One

Based on the results for experiment one, the hypothesis of a 9:3:3:1 ratio, is not correct. The possible reason for this, is because if the plants are white, that means that they are lacking chlorophyll. Plants that lack chlorophyll usually do not grow very much. Therefore, the chances of a having a tall white corn seedling is lower than having a short white corn seedling. In other words, short white should be a three and tall white should be a one. If these ratios were used, the Chi-square values would be much closer to zero.

Discussion for Experiment Two

Based on the results for experiment two, the hypothesis of a 3:1 ratio, has been confirmed by the values of the Punnett square. You would expect to see more green seedlings than white ones, because chlorophyll-lacking plants are caused by a recessive gene.

Bibliography

Biology with Cells; Charles A. Ihrke and Thomas B. Mowbray; Copyright 1986

Notes

Created: November 16th 1999
Modified: March 5th 2005
Notes: Report for a Principles of Biology I course during college, freshman year.