13. Mendelian Genetics

Incomplete Dominance vs. Codominance

Co-dominance | Genetics

If you look at a blood sample from a person who is heterozygous at the sickle cell locus you will see both normal circular red blood cells and sickle-shaped red blood cells. This is an example of

 No. The Tay-Sachs allele is not dominant at any level. 

 No. Heterozygous individuals produce half the number of functional enzyme molecules. 

 No. The Tay-Sachs allele is recessive at the organismal level. Only children who inherit two copies of the Tay-Sachs allele develop symptoms of the disease. 

 No. Tay-Sachs disease is caused by a mutation in a single gene. 

Remember that a trait may be expressed differently at organismal, biochemical, and molecular levels.

Which choice below describes the expression of Tay-Sachs disease in humans at the biochemical level?

The number of different alleles for ABO blood types is _____ resulting in _____ different blood types.

Animation: Incomplete Dominance in "MendAliens"

 No. Not all progeny plants will be heterozygotes. 

 No. Not all progeny plants will be homozygous for the red allele. 

Draw a Punnett square.

Flower color in snapdragons is an example of incomplete dominance. When a red-flowered plant is crossed with a white-flowered plant, the F1 generation has pink flowers. If a pink-flowered plant is crossed with another pink-flowered plant, the progeny plants will be __________.

Co-dominance and Incomplete Dominance | Biomolecules | MCAT | Khan Academy

 No. There are more possibilities than this. 

Review the inheritance of ABO blood groups, and draw a Punnett square.

Human blood groups are governed by three alleles: IA, IB, and i. IA and IB are codominant and i is recessive to both. A man who has type B blood and a woman who has type A blood could have children of which of the following phenotypes?

Animation: X-Linked Genes

Codominance

A man with type A blood marries a woman with type B blood. Their child has type O blood. What are the genotypes of these three individuals? What genotypes, and in what frequencies, would you expect in future offspring from this marriage?

 No. The red and white alleles are present at equivalent loci on homologous chromosomes. 

 No. There is no indication that a second gene pair is involved. 

 No. There is no indication that more than one gene pair is involved. 

 No. If this were so, there would be only two trait variants&mdash;red and white. 

Both the red and the white alleles are expressed in the roan-colored progeny.

A red bull is crossed with a white cow and all of the offspring are roan, an intermediate color that is caused by the presence of both red and white hairs. This is an example of genes that are __________.

Codominance & Blood Type

Both children are heterozygous for this gene.

A gene for the MN blood group has codominant alleles M and N. If both children in a family are of blood type M, which of the following situations is possible?

 Individuals with two sickle-cell alleles are immune to infection by the malaria parasite. 

 No. Individuals with this allele makeup are homozygous recessive and have sickle-cell anemia; they do not demonstrate codominance of the normal and sickle-cell alleles. 

 The presence of both normal and sickle-shaped hemoglobin in the red blood cells of heterozygous individuals provides immunity to infection by the malaria parasite. 

 No. This is partially correct. The sickle-cell trait in heterozygotes provides selective advantage with regard to malaria but does not confer immunity to infection. 

 Individuals need only one normal allele to have completely normal hemoglobin and reduced densities of malaria parasites in their red blood cells. 

 No. The normal allele is not completely dominant to the sickle-cell allele. In any case, complete dominance would not confer a selective advantage on heterozygotes in the event of malaria infection. 

 None of the listed responses is correct. 

 No. One of the listed responses is correct. 

 Individuals with normal and sickle-cell hemoglobin in their red blood cells are usually healthy and, when infected by the malaria parasite, have lower parasite densities and, thus, reduced malaria symptoms. 

Consider what could be a selective advantage for carriers of the sickle-cell trait.

How does codominance at the molecular level help to explain why evolutionary processes haven't resulted in the elimination of the sickle-cell allele among people of African descent?

No. Both parents could be IAi.

No. One parent could be IAi, and the other parent could be IBi.

 No. These parents can only have children with type O blood. 

 No. One of the other choices is correct. 

Draw Punnett squares using all possible parental genotypes.

Which of the following matings cannot produce a child with blood type O? The letters refer to blood types (phenotypes).

A man with type B blood and a woman who has type A blood could have children of which of the following phenotypes?
a. A or B only
b. AB only
c. AB or O
d. A, B, AB, or O

Incomplete Dominance, Codominance, Polygenic Traits, and Epistasis!

Incomplete Dominance | Genetics

Dominant, Recessive, Incomplete Dominant, Codominant? What The Heterozygous Does This Mean?

Incomplete Dominance

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1. Introduction to Biology

2. Chemistry

3. Water

4. Biomolecules

5. Cell Components

6. The Membrane

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