A chromosome is made up a coiled up DNA with thousands of genes.
Pea plants provide a model of how genes work in a very simple way. However, things get more complex in larger organisms.
Mendel’s work may have been initially ignored because it was missing the molecular basis of genetics.
In 1902, two scientists, Boveri, and Sutton, who had never seen Mendel’s work, began their own research. Studying sea urchins and grasshoppers, they each noticed that chromosomes seemed to behave to Mendel’s Three Laws of Inheritance.
They were the first to deduce that chromosomes were the cells that contain genes. It would allow them to identify a physical cell that was parents passed to offspring and was described by Mendel.
It was called the Boveri-Sutton chromosomal theory.
What is a chromosome simple definition?
In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
Scientists carefully documented the behavior of chromosomes during cell division (mitosis), using dyes to make them visible.
A chromosome is the 3D shape of a coiled DNA. Source
Chromosome divisions, mitosis & meiosis.
Mitosis is a type of cell division where two identical daughter cells are created.
In complex life, (eukaryote cells) chromosomes use a form of replication called meiosis.
What happens to chromosomes during meiosis?
Meiosis is a type of cell division that results in four daughter cells. Each with half the number of chromosomes of the parent cell (a gamete).
The three steps of meiosis are:
- Each chromosome copies itself and the duplicates line up at the “equator” of the cell.
- Duplicate copies of each chromosome are then pulled toward opposite poles.
- Finally, the cell splits at the equator, producing two new cells with identical sets of chromosomes.
During mitosis, two identical daughter cells are made. During meiosis, chromosomes split to create four daughter cells. Source
How many human chromosomes are there during meiosis?
Human DNA contains 46 chromosomes (23 pairs).
During meiosis, a cell splits its chromosomes splits to reduce from 46 to 23 chromosomes.
Humans have 23 pairs of chromosomes or a total of 46. Source
How is sex determined and inherited?
Out of the 23 human chromosomes, there are two sex chromosomes X & Y.
Unlike the other chromosomes, they are different sizes.
X is female, Y is male. Sex is determined in humans by the XX/XY system. It is found in most mammals.
Male sperm (gametes) contain two types of sex chromosomes (XY).
Female eggs (gametes) contain two of the X sex chromosomes (XX).
How sex is determined in human genetics. Source
Human sex is determined by the presence or absence of a Y chromosome. However, it also depends on a gene, called the SRY gene found on the Y chromosome.
Once the SRY gene is activated, cells create testosterone that builds the male reproductive system.
In normal XX embryos, cells secrete estrogen, which drives the body in a female cell pathway.
What is a gamete?
A gamete is a sex cell (sperm or egg in humans) that contains only one set of different chromosomes. It equates to half the genes necessary to reproduce an offspring.
They join with other gametes (egg joins with sperm) to form a full set of genetic material.
Conclusion:
Chromosomes are the molecule that carry your DNA code.
Do you have any questions about chromosome structure and function? Leave them it comment section below.
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