What involves two cell divisions during which the chromosome number is halved?
Meiosis
Understanding Cell Division and Chromosome Number
The question asks about a specific type of cell division process. This process is characterized by having two cell divisions and resulting in the halving of the chromosome number in the daughter cells compared to the parent cell.
Let's look at the options provided:
- Heterozygous: This term relates to genetics and describes an organism that has two different alleles for a specific gene. It is not a cell division process.
- Genes: These are the basic units of heredity. While genes are involved in cell division (as they are part of chromosomes), 'genes' itself is not a process of cell division.
- Meiosis: This is a type of cell division that occurs in sexually reproducing organisms. It involves two successive nuclear divisions, called Meiosis I and Meiosis II. The key outcome of meiosis is the production of four daughter cells, each containing half the number of chromosomes as the parent cell. For example, a diploid cell (\(2n\)) undergoes meiosis to produce haploid cells (\(n\)). This process is essential for forming gametes (sperm and egg cells).
- Homozygous: Like heterozygous, this term relates to genetics and describes an organism that has two identical alleles for a specific gene. It is not a cell division process.
Based on the description given in the question – two cell divisions and halving of the chromosome number – the process being referred to is Meiosis.
In summary:
- Meiosis I separates homologous chromosomes, reducing the chromosome number by half.
- Meiosis II separates sister chromatids, similar to mitosis, resulting in four haploid cells.
This two-step division process is exactly what leads to the halving of the chromosome number.
Important Questions from Nature and Structure of Science
Under which organisation's aided project did NCERT develop an instructional material titled "Science is Doing"?
In which year did E. L. Thorndike develop the theory of trial and error learning?
In which stage, science should be introduced as separate disciplines with emphasis on experiments / technology and problem solving?
- Read the excerpt given below and answer the question.
French scientist Henri Becquerel was working on phosphorescent materials, which glow in the
dark after exposure to light. He believed that sunlight was the reason that the crystal would burn
its image on a photographic plate. On a stormy day in $1896$, he decided to leave it for few days
and resume his experiments later. A few days later, he took his crystal out of a darkened drawer.
He noticed that the image burned on the plate was 'fogged' which meant that the crystal had still
emitted rays, despite the lack of sunlight.
What does the above excerpt illustrate about science ? - Which of the following attributes would you associate with 'Scientific temper'?
(A) Perseverance in carrying out scientific investigations.
(B) Creativity in coming up with big problems to be investigated and breaking them down into
smaller 'solvable' parts.
(C) Scepticism towards non-scientific beliefs.
(D) Commitment towards cultural preservation.
