1.What genetic phenomenon occurs when a dominant allele (H for hair texture) has
ID: 211688 • Letter: 1
Question
1.What genetic phenomenon occurs when a dominant allele (H for hair texture) has different appearances between heterozygous individuals (Hh have wavy hair) and homozygous individuals (HH have curly hair)?
2.
The MN blood group in humans is under the control of a pair of alleles, M and N. Each allele causes the red blood cell to express a specific glycoprotein (identifying markers) on the cell surface. M/M individuals express the M-type glycoprotein on their blood cells, N/N individuals express the N-type glycoprotein on their blood cells, M/N individuals express both types of glycoprotein on their blood cells. This is an example of:
incomplete dominance
3.
High cholesterol, and the cardiovascular disease the it causes, can have a genetic basis in some people. There is a incompletely dominant gene (L) that produces a protein called low density lipoprotein receptor (LDL-R). This protein is needed to remove cholesterol from the bloodstream and transport it into cells. People who are homozygous dominant produce the normal level of LDL-receptors and have normal cholesterol levels. People who are heterozygous for the gene (Ll) produce half the normal number of LDL-receptors which results in high cholesterol; they are likely to develop cardiovascular disease prematurely in their 30s and 40s. People who are homozygous recessive for the gene (ll) develop severe cardiovascular disease during childhood.
Identify all possible genotypes of the children from parents who are each heterozygous for the cholesterol receptor. (Select all that apply.)
continuous variation codominance polygenic inheritance incomplete dominanceExplanation / Answer
Answer to the 1st question:
INCOMPLETE DOMINANCE
Explanation:
Incomplete dominance is a special type of genetical phenomena where the dominant gene exerts partial dominance over the recessive gene. Homozygous individual with dominant genes (HH) will exhibit phenotype of curly hair. Person with homozygous recessive gene (hh) will show straight hair. The person with the blend of these two genes i.e., heterozygous form (Hh) will exhibit wavy hair. Hence, the heterozygous form will be intermediate between the dominant and recessive types with incomplete control of the dominant gene.
One more example for this phenomenon is mirabilis flower, in which the plant with homozygous dominant gene for flower colour will be red, homozygous recessive will be exhibit white and the heterozygous form will exhibit intermediate colour of pink.
Answer to the 2nd question:
CODOMINANCE
Explanation:
Codominance is commonly seen in the blood grouping. In codominanace, heterozygous individual with both the dominant and recessive genes will coexpress, producing mixed phenotype.
Red blood cells (RBC) express glycoproteins/antigens on their cell surface, based on which blood grouping will be done. Coming to the ABO blood group, A group will express homozygous (AA) antigens on RBC cell surface and the person will have B antibodies in the plasma. B blood group person will have RBC expressing homozygous B (BB) antigens on their cell surface and A antibodies in the plasma. AB blood group person will express both A and B antigens on their cell surface (AB – heterozygous) and no antibodies in the plasma. O-blood group person will express no antigens and with A and B antibodies in the plasma. Here, in the AB blood group, both A and B exhibit equal dominance on each other and hence both will coexpress together.
Similarly in MN blood group, person with homozygous MM genes will possess M blood group, NN genes containing individual express N blood group where as M and N genes expressing persons will show MN blood group with both the genes coexpressing together.
Answer to the 3rd question:
The progeny will express all the three phenotypes in 1:2:1 ratio - one dominant (LL) : two incomplete dominant (Ll) : one recessive (ll)
L
l
L
LL
Ll
l
Ll
ll
In this condition, both genotypic and phenotypic ratios will be same i.e., 1:2:1.
L
l
L
LL
Ll
l
Ll
ll
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