Question

Choose one of the following traits (1) Dominant/recessive OR Codominant OR Incomplete dominance OR Sex-linked (2) choose a trait that fits into that category that was not mentioned in the PPT (3) briefly describe the trait and (4) what is the current percentage of people that have this trait in the US.

Answer 1

Complete Dominance

The complete dominance is a type of dominance in which the dominant allele is able to express its phenotype and the phenotype of the recessive allele is masked by the dominant allele.

For example- The character of the height of a pea plant.

The alleles for the tall and dwarf character are shown in the table below-

The genotype of the tall and dwarf phenotypic trait are shown in the table below-

Draw the self-cross between the F1 generation progeny produced after crossing a homozygous dominant tall plant and homozygous recessive dwarf plant to see the genotypic ratio of the F2 generation as shown below-

Therefore, the genotypic ratio of the monohybrid cross when a gene exhibit complete dominance is 1:2:1.

Codominance

The codominance is a type of dominance in which all the dominant alleles are able to express its phenotype and the phenotype of the recessive allele is masked by the dominant allele. For example- ABO blood grouping in humans.

The alleles for different blood groups are shown in the table below-

The genotypes and the phenotypes of different blood groups are shown in the table below-

Draw the cross between male and female each with AB blood type to see the genotypic ratio of the progeny in a monohybrid cross when the gene exhibits codominance as shown below-

Therefore, the genotypic ratio of the monohybrid cross when gene exhibit codominance is 1:2:1.

Incomplete Dominance

Incomplete dominance or semidominance is a type of inheritance in which the dominant allele is not able to dominate completely over the recessive allele. The recessive allele is not completely masked by the dominant allele which results in the intermediate phenotype. For example- The cross between a straight hair person and a curly hair person.

The alleles for the hair type are given in the table below:

The genotypes for the hair type are shown in the table below:

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Draw the self-cross between the F1 generation progeny produced after crossing a straight hair person and a curly hair person to see the genotypic ratio of the F2 generation as shown below-

Therefore, the genotypic ratio of the monohybrid cross when the gene exhibits incomplete dominance is 1:2:1.

Sickle cell anemia is an example of "incomplete dominance". Around 8 percent of African Americans and few Asian Americans carry recessive "sickle-cell" allele and are heterozygous for this attribute.