Chromosomes and Genes

Introduction

All humans, with the exception of identical twins, are genetically different. A paternal sperm cell (spermatozoon) combines with a maternal egg cell during fertilisation (ovum). Half of the genetic material in the resultant embryo will have come from the father and half from the mother. As a result, while each child is genetically distinct, they usually exhibit a mix of traits inherited from both parents. The gene is nature’s basic unit of heredity, and genes are passed down through the generations in a predictable manner. Deoxyribonucleic acid (DNA) is used to store information in each gene (DNA).

DNA and cells

The average adult human body contains about 50 trillion cells (50 million). The majority of the DNA in these cells is found in their nuclei; a far lesser percentage is found in their mitochondria, which are tiny bean-shaped organelles found in the cytoplasm of nucleated cells and release the energy they require to exist.

The building blocks of life are nucleic acids, the most prevalent of which is DNA. The genes contain the set of instructions – or genetic blueprint – needed to build the proteins that offer structure to all living organisms. This applies to everything from simple viruses and bacteria to sophisticated multicellular animals like humans.

Chromosomes and DNA

The average human cell is about 20m in diameter (a micron is one-thousandth of a millimetre). The nucleus, which is much smaller: roughly 2-10m in diameter, stores the majority of a cell’s DNA. Each nucleated human cell manages to cram in roughly 3m (10 feet) of DNA despite its modest size.

To make this possible, the DNA is neatly wrapped around histone proteins, which behave like a spool or bobbin.DNA and histone proteins combine to produce chromatin, which is visible as minute granules in the cell nucleus.

The DNA in a cell on the verge of dividing wraps up tighter and tighter and folds into coils. This tightly twisted DNA is denser and thicker, and it appears in the nucleus as chromosomes, which are thread-like structures.

Gender and chromosomes

Human cells (excluding spermatozoa and ova) have 23 pairs of chromosomes, for a total of 46 chromosomes. The diploid number is maintained during cell division (mitosis). In both sexes, the chromosomes in the first 22 pairs – the autosomes – are identical. The 23rd pair defines an individual’s gender; its two chromosomes are known as the sex chromosomes. Most people have one of two sex chromosomal combinations:

XX = female;

XY = male.

As female cells have only X chromosomes, ova will always have only X chromosomes. Male cells, on the other hand, always have both X and Y chromosomes, hence spermatozoa can have either an X or Y chromosome. Because X-bearing and Y-bearing spermatozoa are produced in roughly equal amounts, sex is determined by which kind of spermatozoon unites with the ovum. As a result, approximately half of all children are male and half are female.

When deciding sex, there are just two options (X-bearing spermatozoon creating a girl or Y-bearing spermatozoon producing a boy), thus it’s a bit like flipping a coin: you can see four or five heads (or more) in a row, and parents can have four or five children (or more) of the same sex in a succession. When populations are looked at as a whole, however, the sexes are roughly split 50:50.

Not all males are XY, and not all girls are XX; in fact, the sex chromosomes are affected by some of the most prevalent survivable chromosomal disorders. Part 4 of this series will go over these topics.

Chromosomes and genes definition

Genes are DNA segments that contain the instructions for making a specific protein that operates in one or more types of cells in the body. Chromosomes are cellular structures that house a person’s genes. Chromosomes, which are found in the cell nucleus, contain genes.

Genes are placed in a linear pattern (like beads on a string) along the length of each chromosome, with each gene having its own unique position or locus. One chromosome is always inherited from the mother and the other from the father in a pair of chromosomes. With the exception of genes found on male sex chromosomes, we have two copies of each gene, one inherited from our mother and the other from our father. Alleles are genetic pairings that influence a variety of our features.

The phenotypic and genotype

The genotype refers to the physical traits that arise from having those genes, while the phenotype refers to the physical characteristics that result from having those genes. It is possible to state:

An individual’s genotype is their genetic make-up; their phenotype is their physical appearance, which is mostly dictated by their genes but also influenced by external influences.

Control and structural genes

Structural genes and control (or regulatory) genes are two types of genes.

Structural genes are DNA sequences that code for proteins like:

• Actin and myosin (muscle-building proteins), keratin (found in skin, hair, and nails), and haemoglobin (found in red blood cells) are all examples of proteins.
• Enzymes are responsible for the body’s metabolic activities.
• Hormones that preserve homoeostasis (such as insulin);
• Neurotransmitters are chemical messengers that contribute to physiological process coordination (for example, substance P).

Control of regulatory genes, as the name suggests, govern control of the activity of structural genes, such as when they are turned on or off and how much protein is produced. The pancreas, for example, does not require the genes coding for keratin or haemoglobin to be switched on, but it is critical to have the genes coding for insulin or glucagon switched on. Hormones, growth factors, and neurotransmitters are examples of chemical signals that commonly regulate control genes, either directly or indirectly.

Conclusion

Genes in cells store information in the form of deoxyribonucleic acid (DNA).

When a cell prepares to divide, DNA takes the form of chromosomes, which are thread-like structures. Most human cells have 23 chromosomal pairs, for a total of 46 chromosomes – the diploid number. Aneuploidy is defined as having extra or missing chromosomes, with Down’s syndrome being the most common example. Regulatory genes regulate structural genes, which include DNA sequences that code for proteins.

Genes are passed down through the generations in a predictable fashion, and each parent contributes around half of our genetic material. This page discusses the nature, structure, and function of genes, deoxyribonucleic acid, and chromosomes, as well as how chromosomes determine gender and chromosomal illnesses. It’s the first in a series of four articles about the role of genes and chromosomes in heredity, health, and disease.

FAQ’s

What is the connection between genes and chromosomes?

Genes are DNA segments that contain the instructions for making a specific protein that operates in one or more types of cells in the body. Chromosomes are cellular structures that house a person's genes. Chromosomes, which are found in the cell nucleus, contain genes.

What is the number of genes on a chromosome?

Hundreds to thousands of genes carry the instructions for creating proteins on each chromosome. Each of the estimated 30,000 genes in the human genome produces three proteins on average.

Are genes found on chromosomes?

On a chromosome, proteins and DNA are organised into genes. Each cell normally has 23 pairs of chromosomes.