November 7, 2014
Biology 111-J3
Predicting Patterns of Inheritance Using Monohybrid and Dihybrid Crosses
Introduction
This experiment was on Mendelian Inheritance; which is the inheritance of biological features that are based on the rules proposed my Mendel. The purpose of this experiment was to show how to predict patterns of inheritance by using Punnett Squares to perform monohybrid and dihybrid crosses. Two crosses were performed. Cross one consisted of heterozygous alleles crossed with another set of heterozygous alleles. Cross number two consisted of a set of homozygous dominant and homozygous recessive alleles. Completing the monohybrid and dihybrid crosses using Mendel’s Punnett Square system allows the results for the possible gametes to be viewed by the different alleles being crossed.
Methods and Materials
Blue Beads
Green Beads
Red Beads
Yellow beads
(2) 100 mL Beakers
Permanent Marker
Using the permanent marker, label one 100 mL beaker as “1” and the second beaker as “2”. Count out 50 yellow and 50 blue beads and pour them into “Beaker 1”. Stir the beads to make sure there is an even distribution of both throughout the beaker, or a homogenous mixture. Now pour 50 red and 50 green beads into “Beaker 2” and create another homogeneous mixture. Here are assumptions to be made about the experiment thus far; Beaker 1 contains either yellow or blue beads; Beaker 2 contains either red or green beads; both beakers contain approximately the same number of each colored bead; these colors correspond to the following traits (Y/y is color of kernel color, S/s is for smooth/wrinkled seed). Yellow: (Y) vs. Blue (y). Green (G) vs. Red (g). Without looking pull 2 beads out of Beaker 1. This will be the genotype for the parents of Individual Number 1 for the upcoming generation. Record your results for this in “Table 1: Parent Genotypes: Monohybrid Crosses”. Now repeat this procedure for Individual Number 2 and record the results. Repeat this four more times and return the beads to their corresponding beakers (a total of 5 subsequent generations should be completed at this point). Without looking, remove two beads from Beaker One and two beads from Beaker Two. These beads will be representing the genotype of Individual Number 1. Record the new information into “Table 3: Parent Genotypes: Dihybrid Crosses”. Repeat this step to create the genotype for Individual Number 2 and record the results in Table 3 again. Determine what the possible genotypes could come out to be if each individual had gametes. Record these possibilities in “Table 4: Generation Data Produced by Dihybrid Crosses”. Now, to prove the possibilities, create a Punnett square and determine the genotypes and phenotypes for this type of cross. Repeat this step 4 additional times for a total outcome of 5 subsequent generations
Results
Y-Yellow
y-Blue
G-Green
g-Red
These are the results for the randomly chosen beads for the parent genes.
Table 1:Parent Genotypes: Monohybrid Crosses
Generation
Genotype of Individual 1
Genotype of Individual 2
P
Yy
Yy
P1
YY
Yy
P2
Yy
YY
P3
YY
yy
P4
Yy
Yy
These are the results received once the parent genes were crossed. Yellow was obviously dominant over the blue with only a total of 2 blue and 18 yellow.
Table 2: Generation Data Produced by Monohybrid Crosses
Parents
Possible Offspring Genotypes
Possible Offspring Phenotypes
Genotype Ratio
Phenotype Ratio
P
YY, Yy, Yy, yy
3-Yellow
1-Blue
1:2:1
3:1
P1
YY, YY, Yy, Yy
4-Yellow
2:2
1:0
P2
YY, YY, Yy, Yy
4-Yellow
2:2
1:0
P3
Yy, Yy, Yy, Yy
4-Yellow
1:0
1:0
P4
YY, Yy, Yy, yy
3-Yellow
1-Blue
1:2:1
3:1
These are the results for the possible phenotype and genotypes produced with the monohybrid cross.
Table 3: Parent Generations: Dihybrid Crosses
Generation
Genotype of Individual 1
Genotype of Individual 2
P
YYGg
YyGg
P1
YyGG
YyGg
P2
Yygg
YYGg
P3
YYGg
yyGg
P4
YyGG
Yygg
These are the results for the dihybrid crosses with Yellow/Green being dominant.
Table 4: Generation Data Produced by Dihybrid Crosses
Parents
Possible Offspring Genotypes
Possible Offspring Phenotypes
Genotype Ratio
Phenotype Ratio
P
YYGg, YyGg, YYgg, Yygg
2-Yellow/Green
2-Yellow/Red
1:2:1
2:2
P1
YYGG, YyGG, YyGg, yygG
3-Yellow/Green
1-Blue/Green
1:1:1:1
3:1
P2
YYGg, YyGg, Yygg, Yygg
2_Yellow/Green
2-Yellow/Red
1:1:1:1
2:2
P3
YyGG, YyGg, YyGg, Yygg
3-Yellow/Green
1-Yellow/Red
1:2:1
3:1
P4
YYGg, YyGg, YyGg, yyGg
3-Yellow/Green
1-Blue/Green
1:2:1
3:1
These are the genotypic and phenotypic results for the dihybrid cross with Yellow/Green being dominant.
Monohybrid Crosses
Y y Y Y
Y y Y
YY
Yy
Y
YY
YY
Y YY Yy y Yy
Yy
y
Yy
Yy
Y YY Yy
P
P1
P2
Y
Y
Y y y Yy
Yy
Y YY Yy
y Yy Yy
y Yy yy
P3
P4
Dihybrid Crosses
YG yg YG yG Yg yg YG
YYGG
YyGg
YG
YYGG
YyGG
YG YYGg YyGg yg YyGg
Yygg
yg
YyGg
yyGg
Yg YYgg Yygg
P
P1
P2
YG
Yg
YG yG yG YyGG
YyGg
Yg YYGg YyGg
yg YyGg Yygg
yg YyGg yyGg
P3
P4
Discussion
“Table 1:Parent Genotypes: Monohybrid Crosses” showed the results of when just 2 different alleles were crossed. The dominant trait was Yellow. The ratio of Yellow to Blue was 19:1 in the monohybrid cross. “Table 3: Parent Generations: Dihybrid Crosses” showed the possibility of 4 alleles being crossed. The possible results were Yellow/Green, Yellow/Red, Blue/Green, and Blue/Red with the dominant trait for the dihybrid cross being Yellow/Green. The ratio for all present phenotypes was 14:3:2:1. “Table 2: Generation Data Produced by Monohybrid Crosses” showed the genotype and phenotype ratio of each allele when crossed and all of the possible gene combinations for the monohybrid cross. The dominant trait was Yellow with the ratio of Yellow to Blue being 18:2. “Table 4: Generation Data Produced by Dihybrid Crosses” showed the genotype and phenotype ratio and all of the possible gene combinations for the dihybrid cross. The possible results for this cross were Yellow/Green, Yellow/Red, Blue/Green, and Blue/Red with the dominant trait being Yellow/Green. The phenotypic ratio for this dihybrid cross was 13:5:2:0.
Bibliography
eScience Labs, n.d. November 15, 2014. http://esciencelabs.com
The Josiah Macy, Jr Foundation, Johann Gregor Mendel (1822-1884) Father of Genetics. n.d. Novemeber 15, 2014. http://www.dnaftb.org/1/bio.html
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