Select the correct option of haploid cells from the
following groups:
Explanation:
In meiosis, cells become haploid (n) after the first division or as gametes. Secondary spermatocyte is haploid (produced after meiosis I in spermatogenesis). The first polar body is also a haploid product of meiosis I. The ovum (egg) is a haploid gamete after meiosis. Thus all three in option 2 are haploid. Other options mix diploid and haploid cells (e.g., primary oocyte and spermatogonia are diploid; spermatid is haploid but not with the others in that group). Therefore option 2 is correct according to NCERT concepts of haploid cells in human gametogenesis.
🧠 Did You Know?
During oogenesis, the first polar body divides or may not; in humans, the secondary oocyte completes meiosis II only after fertilization, producing the ovum and a second polar body.
💡 NCERT Memory Line:
Haploid cells contain a single set of chromosomes (n). In human gametogenesis, meiosis I and II produce haploid products such as secondary spermatocytes, polar bodies, and ova.
The best example of pleiotropy is Phenylketonuria (PKU). In pleiotropy, a single gene affects many traits. The PKU gene causes a deficiency of the enzyme phenylalanine hydroxylase, leading to accumulation of phenylalanine and affecting multiple body processes. This results in various problems such as intellectual disability, growth issues, and other metabolic effects, illustrating one gene influencing several traits.
🧠 Did You Know?
NCERT discusses pleiotropy with examples like PKU to show how a single gene mutation can impact more than one phenotype.
E.coli has only 4.6 × 106 base pairs and completes the process of replication within 18 minutes; then the average rate of polymerisation is approximately:
In NCERT biology, the term kinetin was coined by F. Skoog and Miller. They introduced and named this cytokinin when studying plant growth regulators from extracts (e.g., coconut milk) in the 1950s.
🧠 Did You Know?
Went contributed to early work on plant growth regulation and auxins; Darwin’s studies are foundational in tropisms; Kurosawa is associated with research on cytokinins, but the term “kinetin” was coined by Skoog and Miller.
💡 NCERT Memory Line:
Kinetin term coined by Skoog and Miller (not by Went, Darwin, or Kurosawa).
