Genetics - Chromosome Structure and Types - Lesson 18 | Don't Memorise
Summary
TLDRThis video explains how DNA fits into the cell nucleus by coiling into chromatid structures. It introduces chromosomes and describes their classification based on structure: metacentric, submetacentric, acrocentric, and telocentric. It also distinguishes between autosomes (chromosomes 1-22) and sex chromosomes (X and Y), which determine an individual's sex. The video emphasizes the role of the centromere in chromosome classification and explains how chromosomes are categorized in a karyotype. Finally, it hints at the next topic: understanding sex determination in various organisms.
Takeaways
- 🧵 DNA, like a thread, is coiled to fit inside the tiny nucleus of a cell.
- 🧬 The coiling of DNA results in the formation of chromatids, which appear during cell division as chromosomes.
- 📚 There are 46 chromosomes in total, organized into 23 pairs, with each chromosome varying in structure and function.
- 🔬 Chromosomes have two arms: the smaller 'P' arm and the larger 'Q' arm, which helps in their identification.
- 🧷 The centromere is a crucial structure in chromosomes, linking sister chromatids and facilitating attachment to spindle fibers during cell division.
- 🏷️ Chromosomes are categorized into four types based on centromere position: Metacentric, Sub-metacentric, Acrocentric, and Telocentric.
- 🧭 Human cells lack telocentric chromosomes, which have centromeres located at the extreme ends.
- 🧑🤝🧑 Chromosomes are also classified into autosomes (pairs 1 to 22) and sex chromosomes, which determine the sex of an individual.
- 👩🔬 The sex chromosomes are identified as 'XX' for females and 'XY' for males, with the 23rd pair determining the individual's sex.
- 🔍 Karyotyping is a method to visually represent and categorize the chromosomes found in a cell.
Q & A
What analogy is used to describe how DNA is packed inside the cell nucleus?
-The analogy of coiling a one-meter thread to fit inside a small box is used to describe how the long stretch of DNA is coiled to fit inside the tiny nucleus.
What structure does the coiling of DNA give rise to in a metabolically active cell?
-The coiling of DNA gives rise to the chromatid structure in a metabolically active cell.
Why do we say there are 23 pairs of chromosomes in humans?
-We say there are 23 pairs of chromosomes because chromosomes come in pairs, where each pair consists of two chromosomes that are similar in structure but not identical.
What is the primary structural difference between the 'P' arm and the 'Q' arm of a chromosome?
-The 'P' arm is the smaller arm, while the 'Q' arm is the larger arm of the chromosome.
What is the function of the centromere in chromosomes?
-The centromere acts as a link between the two sister chromatids and plays a key role in the attachment of spindle fibers during cell division.
How are chromosomes categorized based on the position of the centromere?
-Chromosomes are categorized into four types based on the position of the centromere: Metacentric, Sub-metacentric, Acrocentric, and Telocentric.
What distinguishes Metacentric chromosomes from other types?
-Metacentric chromosomes have the centromere positioned almost exactly at the center, resulting in two arms of nearly equal length.
What is the significance of Acrocentric chromosomes, and where is the centromere located?
-Acrocentric chromosomes have the centromere positioned near the terminal (end) region, and they play a role in specific cellular functions.
What is the karyotype, and how are chromosomes classified within it?
-A karyotype is a way of representing all the chromosomes found in a cell, and chromosomes are classified into autosomes (chromosomes 1-22) and sex chromosomes (chromosome pair 23).
What determines the sex of an individual according to the script?
-The sex of an individual is determined by the sex chromosomes. If the individual has two 'X' chromosomes, they are female; if they have one 'X' and one 'Y' chromosome, they are male.
Outlines
🧵 Fitting a Meter-Long Thread and DNA Coiling
The paragraph opens with a comparison between fitting a meter-long thread into a small box by coiling it, drawing a parallel to how cells manage to fit long DNA strands inside their nuclei. The process of coiling DNA leads to the formation of chromatids, which exist as thread-like structures within the nucleus of an active cell. During cell division, these chromatids gain a typical shape, known as chromosomes. However, not all chromosomes look the same, leading to the concept of 23 pairs of chromosomes. The paragraph then explains the structural differences in chromosomes and how they are categorized based on their arms—the smaller 'P' arm and the larger 'Q' arm—connected by a centromere. The centromere plays a key role not only in linking sister chromatids but also in spindle fiber attachment during cell division. The classification of chromosomes based on centromere placement includes metacentric, submetacentric, acrocentric, and telocentric types, with the latter not present in humans.
🧬 Human Karyotype: Autosomes vs. Sex Chromosomes
This paragraph introduces the human karyotype, a representation of all the chromosomes in a cell. Chromosomes are classified as either autosomes or sex chromosomes. Autosomes include the first 22 pairs of chromosomes, which have no role in determining an individual's sex. The 23rd pair, however, consists of sex chromosomes, also known as allosomes, which determine the sex of the individual. If the pair consists of two X chromosomes, the individual is female; if the pair consists of one X and one Y chromosome, the individual is male. The paragraph concludes by noting that while both autosomes and sex chromosomes contain genes essential for protein coding, only the latter are involved in sex determination. The teaser at the end hints at further exploration of the concept of sex determination in the next part of the series.
Mindmap
Keywords
💡Chromatid
💡Chromosome
💡Centromere
💡P arm and Q arm
💡Metacentric chromosome
💡Submetacentric chromosome
💡Acrocentric chromosome
💡Telocentric chromosome
💡Karyotype
💡Autosomes
Highlights
Coiling of the long stretch of DNA helps it fit inside the tiny nucleus.
This coiling process leads to the formation of the chromatid structure found in metabolically active cells.
Chromatids form a typical classical structure, visible during cell division, called chromosomes.
There are 23 pairs of chromosomes in humans, not 46 identical ones.
Chromosomes are classified based on shape, structure, and function.
The arms of a chromosome are labeled 'P' for the shorter arm and 'Q' for the longer arm.
The centromere, a knot-like structure, acts as a link between sister chromatids and helps attach spindle fibers during cell division.
The position of the centromere helps categorize chromosomes into four types: metacentric, submetacentric, acrocentric, and telocentric.
Metacentric chromosomes have a centromere near the center, giving them almost equal arm lengths.
Submetacentric chromosomes have a centromere slightly off-center, creating unequal arm lengths.
Acrocentric chromosomes have the centromere near the end region.
Telocentric chromosomes have the centromere at the very end and are not found in humans.
The human karyotype consists of autosomes and sex chromosomes, where the first 22 pairs are autosomes.
Sex chromosomes, or allosomes, determine an individual's sex—XX for females and XY for males.
Autosomes do not determine sex but still contain important genes coding for proteins that make up the human body.
Transcripts
We are asked to fit a thread of one meter
in this small box.
It will be easy if we simply coil the thread
and place it inside.
Did you know that a similar approach is taken
by our cells?
Let’s see how!
We know that the long stretch of DNA
is coiled to a great extent to fit inside the tiny nucleus.
This process of coiling gives rise to the
chromatid structure.
It is a thread like mesh that we find in the nucleus
of a metabolically active cell.
The chromatids gain a typical classical structure
which looks somewhat like this!
It is seen during cell division!
And these are nothing but the chromosomes!
But tell me, do all chromosomes look exactly like this?
Do all the 46 chromosomes look the same?
If yes, then why do we say that there are 23 pairs
of chromosomes?
What helps us categorise these chromosomes as pairs?
Well, all chromosomes are not exactly like one another.
They come in types, depending upon their structures
or shapes and functions!
The first basis for classification is shapes!
We know this is the structure of a typical chromosome.
And is this a single chromosome?
That's right!
The difference is that this
chromosome is not duplicated.
While this one has a duplicated copy attached to itself!
So these are the duplicated sister chromatids
which are attached to the same chromosome.
Now to understand the types, let us first understand
the typical structure.
Here, these two regions are called
the arms of the chromosome.
This arm is named as the “P” arm.
And this is known as the “Q” arm.
So how do we recognise which is the “P”
and which is the “Q” arm?
Is it based on their positions?
Nope!
It depends on the size!
The smaller arm is the “P” arm
while the larger one is the “Q” arm.
So this chromosome has one “P” and one “Q” arm.
While this one has two “P” and two “Q” arms.
Now let us focus on this chromosome structure.
Can you guess what this structure is called
to which the arms are attached?
Well,
this knot like structure is called “Centromere”.
It is the portion of DNA that acts as a link
between the two sister chromatids.
But that is not its sole purpose!
Its major function is the attachment of spindle fibres
during the cell division process!
And let me
tell you one more interesting use of the centromere.
It is the position of the centromere that helps us
categorise the chromosomes into four types.
The four types include Metacentric, Sub-metacentric,
Acrocentric
and Telocentric chromosomes.
Let us have a look at the structures of each type!
Aren’t these simple to understand?
This one is called Metacentric type.
As we can see, the centromere is placed
almost exactly at the centre.
The two arms seem almost of the same length.
We can say that the centromere is placed somewhat
in the middle of the complete structure.
Now the next type is the Submetacentric.
Here, the centromere is placed slightly
away from the centre.
As a result, the two arms of the chromosome
appear unequal.
The next type is the Acrocentric.
In this, the centromere is seen
almost towards the end region.
The term “acro” in Greek relates to “peak”.
Thus the name “acrocentric” refers to the type
where the centromere is near the terminal region.
Lastly, what we see is that the centromere
is present at the extreme end.
That is,
the centromere is placed at the telomeric region.
Hence the name, telocentric!
However,
these chromosomes are not found in humans!
The human karyotype lacks telocentric chromosomes!
But what is karyotype, you may ask!
Well,
it is one way of representing all the chromosomes
found in a cell.
This is how chromosomes are classified
on the basis of their structures or shapes to be precise.
Now let us have a look at the
other type of classification.
This is a much simpler type of classification.
Here,
the chromosomes are classified whether they are
Autosomes or sex chromosomes.
Now what could these be?
This is a representative image
of a typical human karyotype!
The chromosomes that pair from one to twenty two,
are called autosomes.
That is, they are not the sex chromosomes.
To be precise, they have got
no function to deal with the sex of the individual.
The last pair however, determines the sex of the person.
So if the two are identical,
that is both are “X” and “X”,
then the individual is a female.
And what if both are different?
In such a case, when one chromosome is “X”
and the other is “Y”,
the individual is a male.
This pair is the sex chromosomes.
So the chromosomes which help in determining
the sex of an individual
are sex chromosomes
or even called allosomes.
The others which are from first to 22nd pair,
are NOT the sex chromosomes.
This makes them the autosomes.
Both contain genes that code for proteins
which make up our body!
Now that we have understood the various
types of chromosomes,
can you tell me
what helps in determining the sex of an individual?
Is it only the chromosomes?
Or is it some other factor too?
Tune into the next part
to understand the interesting concept of
Sex Determination in various organisms!
Voir Plus de Vidéos Connexes
Substansi Genetika part 1(hubungan antara Kromosom,gen dan DNA)
Video 4 G11S LH En Bio Ch 2 Karyotype1 20 21
Genetics Basics | Chromosomes, Genes, DNA and Traits | Infinity Learn
Multiple Alleles, Sex Chromosomes and Sex-Determination: Knowledge Catalog Grade 9 Biology #9
Chromosome Numbers During Division: Demystified!
GCSE Biology - DNA Part 1 - Genes and the Genome #63
5.0 / 5 (0 votes)