Chromosomes are tightly packed DNA. Organisms can have any number of chromosomes in their cells. The number of chromosomes does not represented how evolved or intelligent an organism is, for example:
Humans have 46 chromosomes
turkeys have 80 chromosomes
rats have 42 chromosomes
Although the turkey has more chromosomes than us, we more complex organisms.
Bellow is an karyogram of a human male. The way we can tell that this person is male is by the Y chromosome. Females have XX, while males have XY. Notice the size of the Y chromosome compared to the X.
Humans have 23 pairs of chromosomes, of those 23 pairs, 22 are Autosomal.
Autosomal refers to chromosomes which do not determine sex in the organism. In humans, only the X and Y determine our sex. The other 22 pairs do not (Autosomal).
Depending on the sex of the person, they can either have 22 or 23 Homologous chromosomes. Homologous means the chromosomes are the same size. As you can see from the Karyogram above, all the chromosomes, except the X and Y are the same size, meaning they are homologous.
The picture to the right is a karyogram of a females XX chromosomes. Notice they are the same size, meaning females have 23 homologous chromosomes.
All the cells in the human body except sex cells (i.e. sperm cells) contain 23 pairs of chromosomes. This means they are Diploid (2n) in chromosomal number.
Sex cells, such as sperm cell or the egg cells, contains half of the amount of other cells. A sperm cell will only contain 23 chromosomes, one of each pair. This means they are Haploid (n).
The image to the left are sperm cells trying to enter the egg.
The reason for these cells being haploid is because when the sperm and egg meet each other, they form a full set of chromosomes. Creating a diploid cell. This is also called a Zygote
Sperm + Egg = full cell
23 chromosomes + 23 chromosomes = 46 chromosomes
An interesting thing is, your sex is determined by your farther. Your mother only supplies and X chromosome, while your father gives you either an X or Y chromosome.
Basics of Chromosome Structure
During every day life, cells chromosomes are a single linear shape. However when the chromosome begins to replicate it multiples, giving it an X shaped appearance. Notice the image on the right. Each chromosome is an X shape, as opposed to when it is at rest.
Parts of a chromosome
The image to the left is a chromosome after it has replicated.
There are some key parts of the chromosome you must know.
All organisms will under go some form of cellular division during their development. The reason for cell replication is for growth, development, maintenance are repair.
During early human development, stem cells replicate and begin to specialise. This is seen in the video to the left. These cells will eventually develop into blood, bone, muscle and other cells.
Other times your body will de vide its cells in order to replace dyeing or damaged cells. An example of this are cells on your skin or lining the gut.
However prokaryotes and eukaryotes undergo very different processes.
Prokaryotes (such as bacteria) divide viaBinary Fission. This is because their DNA is much
simpler, lacking a nucleus and only a single chromosome with no Centromere.
