The "Father" of GENETICS" - Mendel

What is the Human Karyotype?

Karyotype is a term in genetics. It refers to the complement of chromosomes either at the species level, or of indivduals. The normal human karyotype comprises 23 pairs of chromosomes, making 46 in total. In humans - and indeed in mammals, the final pair varies between males (XY) and females (XX) as explained below.
At an individual level the complement of chromosome may vary from the standard. Some of these genetic abnormalities may result in observable symptoms; some may be invisible.
The poster illustrates the standard human karyotype really well. You can see 22 matched pairs. The final, 23rd, pair can be made up of either two X chromosomes or one X chromosome and one Y chromosome. Typically women have two X chromosomes; men have one X an one Y. Since we all acquired 23 chromosomes (ie one of each pair) from our mothers and another 23 from out fathers, every child will inherit an X chormosome from his/her mother but may inherit either an X or a Y chromosome from his/her father.

If the child inherits an X chromosome from her father she will have a typical human female karyotype - 46,XX. The number shows she has 46 chromosomes in total and the XX shows that the final pair is two Xs.

If a child inherits a Y chromosome from his father he will have a typical male karyotype - 47,XY.

How many chromosomes do people have?

In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. Twenty-two of these pairs, called autosomes, look the same in both males and females. The 23rd pair, the sex chromosomes, differ between males and females. Females have two copies of the X chromosome, while males have one X and one Y chromosome. normalkaryotype.jpg so, a MALE (a man's or a boy's) Karyotype will look like this: karyotype_male.gif

What is a gene?

A gene is the basic physical and functional unit of heredity. Genes, which are made up of DNA, act as instructions to make molecules called proteins. In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases. The Human Genome Project has estimated that humans have between 20,000 and 25,000 genes.
Every person has two copies of each gene, one inherited from each parent. Most genes are the same in all people, but a small number of genes (less than 1 percent of the total) are slightly different between people. Alleles are forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each person’s unique physical features.

What is mitochondrial DNA?

Although most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA. This genetic material is known as mitochondrial DNA or mtDNA.
Mitochondria (illustration) are structures within cells that convert the energy from food into a form that cells can use. Each cell contains hundreds to thousands of mitochondria, which are located in the fluid that surrounds the nucleus (the cytoplasm).
Mitochondria produce energy through a process called oxidative phosphorylation. This process uses oxygen and simple sugars to create adenosine triphosphate (ATP), the cell’s main energy source. A set of enzyme complexes, designated as complexes I-V, carry out oxidative phosphorylation within mitochondria.
In addition to energy production, mitochondria play a role in several other cellular activities. For example, mitochondria help regulate the self-destruction of cells (apoptosis). They are also necessary for the production of substances such as cholesterol and heme (a component of hemoglobin, the molecule that carries oxygen in the blood).
Mitochondrial DNA contains 37 genes, all of which are essential for normal mitochondrial function. Thirteen of these genes provide instructions for making enzymes involved in oxidative phosphorylation. The remaining genes provide instructions for making molecules called transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), which are chemical cousins of DNA. These types of RNA help assemble protein building blocks (amino acids) into functioning proteins.