Question Video: Identifying the Correct Statement About Chromosomes | Nagwa Question Video: Identifying the Correct Statement About Chromosomes | Nagwa

Question Video: Identifying the Correct Statement About Chromosomes Science • Third Year of Preparatory School

Join Nagwa Classes

Attend live Science sessions on Nagwa Classes to learn more about this topic from an expert teacher!

Which statement about chromosomes is true? [A] Chromosomes are always visible in the cell nucleus. [B] Somatic cells are haploid, which means they contain one set of chromosomes. [C] Members of different species usually have the same number of chromosomes. [D] Members of the same species usually have the same number of chromosomes. [E] Reproductive cells are diploid, which means they contain two sets of chromosomes.

06:35

Video Transcript

Which statement about chromosomes is true? (A) Chromosomes are always visible in the cell nucleus. (B) Somatic cells are haploid, which means they contain one set of chromosomes. (C) Members of different species usually have the same number of chromosomes. (D) Members of the same species usually have the same number of chromosomes. Or (E) reproductive cells are diploid, which means they contain two sets of chromosomes.

Let’s review what we know about chromosomes. A chromosome is a long molecule of DNA that is coiled around proteins. The coiling of DNA around proteins is a way of condensing the DNA or packing it up and making it smaller. Chromosomes become particularly visible when they are in the form of highly condensed DNA. DNA is condensed or highly coiled when not in use, but when it is in use, it needs to be loose so that the complementary strands can separate from each other and the DNA base sequence on an individual strand can be used as a template in the process of replication or of building proteins.

When cells are preparing to divide, they first replicate all of their DNA and then all of the DNA is coiled into its most condensed state in preparation for the actual process of cell division, which will include moving the chromosomes around the cell and separating the replicated DNA. When DNA is highly coiled into its most condensed state, we can, with the help of a microscope, visibly see the highly condensed chromosomes inside of a cell. We’re most likely to be able to visibly see the chromosomes like this during the process of cell division when all of the cell’s DNA has been highly coiled into these highly condensed visible chromosomes and the cell’s nuclear membrane is dissolved, allowing the chromosomes to be moved around the cell.

Replicated chromosomes, the kind we usually see at the beginning of cell division, typically look like x’s because they consist of a chromatid or a highly coiled and condensed strand of DNA and its replicated copy sister chromatid. And these chromatids are joined together in the middle by a centromere. In humans and many other organisms, most cells in the body, which we call somatic cells, are diploid, meaning that there are two copies of each chromosome. And the two copies together create what we call a chromosomal set.

Within a set of chromosomes, each chromosome contains the same genes, although there may be different alleles or versions of each gene on each of the chromosomes. Where did these two separate chromosomes with the same genes come from? Well, one came from that individual’s mother, and the other came from that individual’s father. So in order to create a diploid offspring, each parent has to contribute one chromosome from each set. That’s why gametes, or sperm and egg, contain only one chromosome of each set, which is called being haploid. So somatic cells are diploid with two copies of each chromosome, while reproductive cells are haploid with just one copy of each chromosome.

For the purposes of cell division, it’s important that cells have the correct number of chromosomes. For example, if an offspring that is inheriting chromosomes from each parent receives a different number of chromosomes from each parent, that may cause difficulties in cell division in the developing embryo so that it may just essentially stop developing and not survive. For this reason, while different species have different numbers of chromosomes — for example, humans have 46, domestic cats have 38, and goldfish have 50 — within each species, each individual will nearly always have the same number of chromosomes as other individuals of that species.

So let’s look again at the answer choices and determine which of these statements is true. (A) Chromosomes are always visible in the cell nucleus. We know that this is not true because when DNA is in use, it’s loose and not highly coiled and condensed into a visible chromosome. Also during cell division, the nuclear membrane dissolves. So at that point, you could see chromosomes outside of the nucleus.

(B) Somatic cells are haploid, which means they contain one set of chromosomes. Haploid does mean containing one chromosome of each set, but somatic cells or body cells are diploid. So this statement is not correct either.

(C) Members of different species usually have the same number of chromosomes. We just mentioned three different species that have three different numbers of chromosomes. So this statement is not correct either.

(D) Members of the same species usually have the same number of chromosomes. This is correct. For example, humans usually have 46 chromosomes and cats usually have 38.

Let’s look at the last answer choice. (E) Reproductive cells are diploid, which means they contain two sets of chromosomes. Diploid does mean having two chromosomes for each set, but it’s somatic cells that are typically diploid, while reproductive cells are typically haploid. So this last statement is not correct either.

The correct statement and correct answer is that members of the same species usually have the same number of chromosomes.

Join Nagwa Classes

Attend live sessions on Nagwa Classes to boost your learning with guidance and advice from an expert teacher!

  • Interactive Sessions
  • Chat & Messaging
  • Realistic Exam Questions

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy