ABO Blood Group Locus Function
The ABO blood group locus, located on human chromosome 9, contains the gene responsible for determining the ABO blood group system.
Gene Product Identification
The gene at the ABO locus codes for a specific type of enzyme. This enzyme's primary function is crucial for defining an individual's blood type.
Enzyme Activity in ABO System
The enzyme produced by the ABO gene is a glycosyltransferase. Its role is to attach specific sugar residues to a precursor substance called the H antigen.
- If the enzyme adds N-acetylgalactosamine, the A antigen is formed.
- If the enzyme adds galactose, the B antigen is formed.
- Individuals with type O blood have a non-functional allele, meaning the enzyme does not attach any sugar, leaving the H antigen unmodified.
Analysis of Options
Evaluating the given options:
- (A) Acyl transferase: Enzymes that transfer acyl groups; not involved in ABO blood group synthesis.
- (B) Galactosyltransferase: This enzyme adds galactose, a key step in forming the B antigen. The ABO gene product is a transferase responsible for forming either A or B antigens, making this the correct function.
- (C) Transposase: An enzyme involved in DNA transposition; unrelated to blood groups.
- (D) $\beta$-Galactosidase: An enzyme that hydrolyzes lactose; unrelated to ABO blood group determination. The LaTeX notation is correctly rendered as $\beta$-Galactosidase.
Therefore, the ABO blood group locus codes for a transferase enzyme, specifically Galactosyltransferase (or N-acetylgalactosaminyltransferase), responsible for ABO antigen formation.
Important Questions from Mendelian Inheritance
The allele associated with albinism in humans is recessive ($c$). The probability that an albino male ($cc$) and a carrier female ($Cc$) will have an offspring with normal skin pigmentation is _________.
(Round off to one decimal place)
- The blood group of the mother is A⁺ and that of the father is AB⁺. Which of the following statements is/are correct?
- Fabry disease in humans is a X-linked disease. The probability (in percentage) for a phenotypically normal father and a carrier mother to have a son with Fabry disease is ________.
A pedigree of an inheritable disease is shown below.
- In tomato plant, red (R) is dominant over yellow (r) for fruit color and purple (P) is dominant over green (p) for stem color. Fruit color and stem color assort independently. The number of progeny plants of different fruit/stem colors obtained from a mating are as follows:
Red fruit, purple stem - 145
Red fruit, green stem – 184
Yellow fruit, purple stem - 66
Yellow fruit, green stem - 47
What are the genotypes of the parent plants in this mating?
