Genetics In corn, colored aleurone (corn seed) is due to the dominant allele R.
ID: 97480 • Letter: G
Question
Genetics
In corn, colored aleurone (corn seed) is due to the dominant allele R. When homozygous, the recessive allele, r, produces colorless aleurone. The plant (leaf) color is controlled by another gene with two alleles, Y and y. The dominant Y produces green plants and the recessive y produces yellow plants. A Dihybrid plant was generated by mating a purebred green plant containing colored aleurone with a yellow plant containing colorless aleurone. The Dihybrid plant was test-crossed by mating it with a double homozygous recessive. The following progeny were generated: a. Use the Chi Square to test whether the plant color gene obeys Mendel's Law of Random Segregation. b. Use the Chi Square to test whether the aleurone gene obeys Mendel's Law of Random Segregation. c. Use the Chi Square to test whether the plant color gene and the aleurone color obey Mendel's Law of Independent Assortment.Explanation / Answer
Points to remember for Mendel’s law of segregation:
-Gregor Mendel studied inheritance of traits in pea plants. He proposed a model where pairs of "heritable elements," or genes, specified traits.
-Genes come in different versions, or alleles. A dominant allele hides a recessive allele and determines the organism's appearance.
-When an organism makes gametes, each gamete receives just one gene copy, which is selected randomly. This is known as the law of segregation.
-A Punnett square can be used to predict genotypes (allele combinations) and phenotypes (observable traits) of offspring from genetic crosses.
-A test cross can be used to determine whether an organism with a dominant phenotype is homozygous or heterozygous.
Punnett Square for the F2 cross.
Female Gametes : GW Gw gW gw
GW GGWW GGWw GgWW GgWw
Male Gw GGWw GGww GgWw Ggww
Gametes gW GgWW GgWw ggWW ggWw
gw GgWw Ggww ggWw ggww
The phenotypes and general genotypes from this cross can be represented in the following manner:
Phenotype General Genotype
88 Green coloured G_W_
12 Yellow coloured G_ww
8 Green, colorless ggW_
92 Yellow colorless ggww
The results of this experiment led Mendel to formulate his second law.
Mendel's Second Law - the law of independent assortment; during gamete formation the segregation of the alleles of one allelic pair is independent of the segregation of the alleles of another allelic pair
As with the monohybrid crosses, Mendel confirmed the results of his second law by performing a backcross - F1 dihybrid x recessive parent.
Punnett Square for the Backcross:
GW Gw gW gw
Male
Gametes gw GgWw Ggww ggWw ggww
The phenotypic ratio of the test cross is:
25 Yellow colored
20 Yellow colored
35 Green colored
15 Green colored.
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