The human body is made up of cells. For example, when you have a sunburn and your skin peels, then you are shedding skin cells. In the center of each cell is an area called the nucleus. Human chromosomes are located inside the nucleus of the cell. A chromosome is a structure that holds your genes. You may have heard that is the magic number , but if you ask a geneticist, they'll tell you the real magic is in Why 46?
Because that's the total number of chromosomes found in almost every human cell — 23 pairs to be exact — and those little thread-like structures pack all the information about who you are and what makes you unique.
To understand what chromosomes are, you first have to understand what DNA is. Formally known as deoxyribonucleic acid, DNA is a complex molecule found in all plants and animals.
It's found in almost every cell of an organism's body, and it contains all the information necessary to keep that organism up and running and developing and reproducing. DNA also is the primary way organisms pass on hereditary information. In the process of reproduction, a portion of DNA is passed along from parent to offspring.
In short, DNA is what tells the story of your totally unique biology. As you can probably imagine, DNA has to be pretty long to hold all that important info.
And it is — if you stretched the DNA in just one cell all the way to its full length, it would be about 6. Luckily, cells are pretty smart and have an ingenious way of packaging all that info into space-efficient parcels. Enter: the chromosome. With its name rooted in the Greek words for color chroma and body soma , the chromosome is a cell structure or body that scientists can spot under a microscope by staining it with colored dyes get it?
Each chromosome is made up of protein and — you guessed it — DNA. Every chromosome contains exactly one molecule of DNA, to be exact, and that long string of genetic info is tightly wrapped around the protein called a histone , which acts like a spool, efficiently bundling the lengthy, info-rich molecule into the perfect size and shape to fit inside the nucleus of a cell.
Every human cell has 23 pairs of chromosomes for a total of 46 aside from sperm and egg cells , which each contain only 23 chromosomes. The magic number of 46 23 pairs per cell isn't universal among living things.
First, though, humans also happen to be a "diploid" species, which means that most of our chromosomes come in matched sets called homologous pairs the two members of each pair are called homologues. A lot of animals and plants are diploid, but not all of them have a total number of Mosquitoes, for example have a diploid chromosome number of six, frogs have 26 and shrimp have a whopping chromosomes! But why do humans have 23 pairs? It happened during evolution. In many types of cells, telomeres lose a bit of their DNA every time a cell divides.
Eventually, when all of the telomere DNA is gone, the cell cannot replicate and dies. White blood cells and other cell types with the capacity to divide very frequently have a special enzyme that prevents their chromosomes from losing their telomeres.
Because they retain their telomeres, such cells generally live longer than other cells. Telomeres also play a role in cancer. The chromosomes of malignant cells usually do not lose their telomeres, helping to fuel the uncontrolled growth that makes cancer so devastating. In fact, each species of plants and animals has a set number of chromosomes.
A fruit fly, for example, has four pairs of chromosomes, while a rice plant has 12 and a dog, In humans and most other complex organisms, one copy of each chromosome is inherited from the female parent and the other from the male parent.
This explains why children inherit some of their traits from their mother and others from their father. The pattern of inheritance is different for the small circular chromosome found in mitochondria. Only egg cells - and not sperm cells - keep their mitochondria during fertilization.
So, mitochondrial DNA is always inherited from the female parent. In humans, a few conditions, including some forms of hearing impairment and diabetes, have been associated with DNA found in the mitochondria. Yes, they differ in a pair of chromosomes known as the sex chromosomes. Females have two X chromosomes in their cells, while males have one X and one Y chromosome. Inheriting too many or not enough copies of sex chromosomes can lead to serious problems.
For example, females who have extra copies of the X chromosome are usually taller than average and some have mental retardation. Males with more than one X chromosome have Klinefelter syndrome, which is a condition characterized by tall stature and, often, impaired fertility. Another syndrome caused by imbalance in the number of sex chromosomes is Turner syndrome. Women with Turner have one X chromosome only.
They are very short, usually do not undergo puberty and some may have kidney or heart problems. Scientists looking at cells under the microscope first observed chromosomes in the late s.
However, at the time, the nature and function of these cell structures were unclear.
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