Question

Mendelian Genetics 98 Exercise D: Mendel’s Dihybrid Cross But wait... there’s more! Mendel’s monohybrid crosses established that inheritance of phenotypes happened by the interactions of discrete ’particles’ (we now call alleles). Further, he discovered that these alleles segregate during the process of meiosis in the production of gametes, which recombine during fertilization. The result of these two insights can easily be predicted by a technique developed by R. C. Punnett. Once these principles were established, Mendel sought to understand how multiple phenotypes were related to each other during inheritance. He developed two alternate hypotheses: Dependent assortment hypothesis The dependent assortment hypothesis predicts that phenotypes are linked to each other. For example, a purple-flowered plant would always have green seeds (but never yellow seeds). Independent assortment hypothesis Alternatively, flower color and seed color could be independently assorted, in which purple-flowered plants could have green or yellow seeds, and a white-flowered plant could also have green or yellow seeds. In other words, flower color is independent of seed color. Mendel’s dihybrid crosses To test these alternate hypotheses, Mendel used the same approach as he did in his monohybrid crosses, except this time he analyzed two phenotypes at the same time. For example, we will analyze the results of flower and seed color. He began his experiment by conducting several controlled crosses of plants with known dominant alleles generating a pure line: homozygote purple-flowered (FF) and yellow-seeded (SS). Collectively this is represented as FFSS. He conducted another controlled cross of another plant with two known recessive alleles, ffss. 14. Refer to table 1, what was the phenotype of the ffss genotype of the P generation in Mendel’s dihybrid cross? and 15. From what Mendel understood about dominant and recessive phenotypes from his monohybrid crosses, he expected all of the offspring in the F1 generation to have the following phenotypes: and Results of Mendel’s dihybrid F1 generation The results of the F1 generation provided the evidence to reject one of his alternate hypotheses, while supporting the other. The dependent assortment hypothesis predicted that the allele of one gene was linked to the allele of another gene. For example, dominant alleles expressing flower color (F) would always be linked with the dominant alleles expressing seed color (S). Alternatively, recessive alleles would also link: would always be associated with s. In other words, gametes would either have the allele combination FS or fs, but never F s or fS. Expected genotypic results supporting the dependent assortment (which wasn’t supported) for the F2 generation are shown in Fig. 3. Results of Mendel’s dihybrid F2 generation FS fs FS FFSS FfSs fs FfSs ffss Fig. 3. Expected genotypic results of the F2 supporting the dependent assortment hypothesis www.thebiologyprint.com

Mendelian Genetics 98
Exercise D: Mendel’s Dihybrid Cross
But wait... there’s more! Mendel’s monohybrid crosses established that inheritance of phenotypes
happened by the interactions of discrete ’particles’ (we now call alleles). Further, he discovered that
these alleles segregate during the process of meiosis in the production of gametes, which recombine
during fertilization. The result of these two insights can easily be predicted by a technique developed
by R. C. Punnett. Once these principles were established, Mendel sought to understand how multiple
phenotypes were related to each other during inheritance. He developed two alternate hypotheses:

Dependent assortment hypothesis
The dependent assortment hypothesis predicts that phenotypes are linked to each other. For example, a
purple-flowered plant would always have green seeds (but never yellow seeds).

Independent assortment hypothesis
Alternatively, flower color and seed color could be independently assorted, in which purple-flowered
plants could have green or yellow seeds, and a white-flowered plant could also have green or yellow
seeds. In other words, flower color is independent of seed color.

Mendel’s dihybrid crosses
To test these alternate hypotheses, Mendel used the same approach as he did in his monohybrid crosses,
except this time he analyzed two phenotypes at the same time. For example, we will analyze the
results of flower and seed color. He began his experiment by conducting several controlled crosses of
plants with known dominant alleles generating a pure line: homozygote purple-flowered (FF) and
yellow-seeded (SS). Collectively this is represented as FFSS. He conducted another controlled cross of
another plant with two known recessive alleles, ffss.

14. Refer to table 1, what was the phenotype of the ffss genotype of the P generation in Mendel’s
dihybrid cross?
______________________ and ______________________

15. From what Mendel understood about dominant and recessive phenotypes from his monohybrid
crosses, he expected all of the offspring in the F1 generation to have the following phenotypes:
______________________ and ______________________

Results of Mendel’s dihybrid F1 generation
The results of the F1 generation provided the evidence to reject one of his alternate hypotheses, while supporting the
other. The dependent assortment hypothesis predicted that
the allele of one gene was linked to the allele of another gene.
For example, dominant alleles expressing flower color (F)
would always be linked with the dominant alleles expressing
seed color (S). Alternatively, recessive alleles would also link:
would always be associated with s. In other words, gametes
would either have the allele combination FS or fs, but never F s
or fS. Expected genotypic results supporting the dependent
assortment (which wasn’t supported) for the F2 generation are
shown in Fig. 3.

Results of Mendel’s dihybrid F2 generation
FS fs
FS FFSS FfSs
fs FfSs ffss

Fig. 3. Expected genotypic results of the F2 supporting the dependent
assortment hypothesis
www.thebiologyprint.com

Mendelian Genetics 98
Exercise D: Mendel’s Dihybrid Cross
But wait... there’s more! Mendel’s monohybrid crosses established that inheritance of phenotypes
happened by the interactions of discrete ’particles’ (we now call alleles). Further, he discovered that
these alleles segregate during the process of meiosis in the production of gametes, which recombine
during fertilization. The result of these two insights can easily be predicted by a technique developed
by R. C. Punnett. Once these principles were established, Mendel sought to understand how multiple
phenotypes were related to each other during inheritance. He developed two alternate hypotheses:

Dependent assortment hypothesis
The dependent assortment hypothesis predicts that phenotypes are linked to each other. For example, a
purple-flowered plant would always have green seeds (but never yellow seeds).

Independent assortment hypothesis
Alternatively, flower color and seed color could be independently assorted, in which purple-flowered
plants could have green or yellow seeds, and a white-flowered plant could also have green or yellow
seeds. In other words, flower color is independent of seed color.

Mendel’s dihybrid crosses
To test these alternate hypotheses, Mendel used the same approach as he did in his monohybrid crosses,
except this time he analyzed two phenotypes at the same time. For example, we will analyze the
results of flower and seed color. He began his experiment by conducting several controlled crosses of
plants with known dominant alleles generating a pure line: homozygote purple-flowered (FF) and
yellow-seeded (SS). Collectively this is represented as FFSS. He conducted another controlled cross of
another plant with two known recessive alleles, ffss.

14. Refer to table 1, what was the phenotype of the ffss genotype of the P generation in Mendel’s
dihybrid cross?
and

15. From what Mendel understood about dominant and recessive phenotypes from his monohybrid
crosses, he expected all of the offspring in the F1 generation to have the following phenotypes:
and

Results of Mendel’s dihybrid F1 generation
The results of the F1 generation provided the evidence to reject one of his alternate hypotheses, while supporting the
other. The dependent assortment hypothesis predicted that
the allele of one gene was linked to the allele of another gene.
For example, dominant alleles expressing flower color (F)
would always be linked with the dominant alleles expressing
seed color (S). Alternatively, recessive alleles would also link:
would always be associated with s. In other words, gametes
would either have the allele combination FS or fs, but never F s
or fS. Expected genotypic results supporting the dependent
assortment (which wasn’t supported) for the F2 generation are
shown in Fig. 3.

Results of Mendel’s dihybrid F2 generation
FS fs
FS FFSS FfSs
fs FfSs ffss

Fig. 3. Expected genotypic results of the F2 supporting the dependent
assortment hypothesis
www.thebiologyprint.com

Added by Alison P.

Question

Please give Ace some feedback