Chromosomes (article) | Khan Academy
As a real example, let's consider a gene on chromosome 9 that determines blood type (A, B, AB, or O) 2 ^2 2. Chromosome structure and numbers review. Cells. Cells are the basic units of living organisms. Cells perform several important tasks including: providing structure; extracting nutrients; producing energy. Proteins form the structure of our bodies, as well playing an important role in the processes that keep us alive. Genes are made of a chemical called DNA, which.
In general, when people refer to the human genome, or any other eukaryotic genome, they mean the set of DNA found in the nucleus. Mitochondria and chloroplasts are considered to have their own separate genomes. Chromatin In a cell, DNA does not usually exist by itself, but instead associates with specialized proteins that organize it and give it structure. In addition to organizing DNA and making it more compact, histones play an important role in determining which genes are active.
The complex of DNA plus histones and other structural proteins is called chromatin. Image of a long, double-stranded DNA polymer, which wraps around clusters of histone proteins.
The DNA wrapped around histones is further organized into higher-order structures that give a chromosome its shape. For most of the life of the cell, chromatin is decondensed, meaning that it exists in long, thin strings that look like squiggles under the microscope.
Cell division - AQA
In this state, the DNA can be accessed relatively easily by cellular machinery such as proteins that read and copy DNAwhich is important in allowing the cell to grow and function. Condensation takes place when the cell is about to divide.
When chromatin condenses, you can see that eukaryotic DNA is not just one long string. Bacteria also have chromosomes, but their chromosomes are typically circular. Chromosomes Each species has its own characteristic number of chromosomes. Like many species of animals and plants, humans are diploid 2nmeaning that most of their chromosomes come in matched sets known as homologous pairs.
The 46 chromosomes of a human cell are organized into 23 pairs, and the two members of each pair are said to be homologues of one another with the slight exception of the X and Y chromosomes; see below. Human sperm and eggs, which have only one homologous chromosome from each pair, are said to be haploid 1n. When a sperm and egg fuse, their genetic material combines to form one complete, diploid set of chromosomes.
So, for each homologous pair of chromosomes in your genome, one of the homologues comes from your mom and the other from your dad. Image of the karyotype of a human male, with chromosomes from the mother and father false-colored purple and green, respectively.
Image modified from " Karyotype ," by the National Institutes of Health public domain.
DNA, genes and chromosomes — University of Leicester
The two chromosomes in a homologous pair are very similar to one another and have the same size and shape.
Most importantly, they carry the same type of genetic information: However, they don't necessarily have the same versions of genes. That's because you may have inherited two different gene versions from your mom and your dad.
It's possible for a person to have two identical copies of this gene, one on each homologous chromosome—for example, you may have a double dose of the gene version for type A. On the other hand, you may have two different gene versions on your two homologous chromosomes, such as one for type A and one for type B giving AB blood.
- DNA, genes and chromosomes
The sex chromosomes, X and Y, determine a person's biological sex: XX specifies female and XY specifies male. These chromosomes are not true homologues and are an exception to the rule of the same genes in the same places.
Aside from small regions of similarity needed during meiosis, or sex cell production, the X and Y chromosomes are different and carry different genes. The 44 non-sex chromosomes in humans are called autosomes. Chromosomes and cell division Image of a cell undergoing DNA replication all the chromosomes in the nucleus are copied and chromosome condensation all the chromosomes become compact.
In the first image, there are four decondensed, stringy chromosomes in the nucleus of the cell. After DNA replication, each chromosome now consists of two physically attached sister chromatids. After chromosome condensation, the chromosomes condense to form compact structures still made up of two chromatids. As a cell prepares to divide, it must make a copy of each of its chromosomes. The two copies of a chromosome are called sister chromatids.
The sister chromatids are identical to one another and are attached to each other by proteins called cohesins. The attachment between sister chromatids is tightest at the centromere, a region of DNA that is important for their separation during later stages of cell division. As long as the sister chromatids are connected at the centromere, they are still considered to be one chromosome. For example, have you been told that you have 'your mother's eyes' or 'your grandmother's nose'?
Genes influence what we look like on the outside and how we work on the inside. They contain the information our bodies need to make chemicals called proteins. Proteins form the structure of our bodies, as well playing an important role in the processes that keep us alive. Genes are made of a chemical called DNA, which is short for 'deoxyribonucleic acid'.
The DNA molecule is a double helix: The DNA double helix showing base pairs The sides are sugar and phosphate molecules. The rungs are pairs of chemicals called 'nitrogenous bases', or 'bases' for short.
There are four types of base: These bases link in a very specific way: A always pairs with T, and C always pairs with G. The DNA molecule has two important properties. It can make copies of itself. If you pull the two strands apart, each can be used to make the other one and a new DNA molecule.
Genes and Chromosomes - Fundamentals - MSD Manual Consumer Version
It can carry information. The order of the bases along a strand is a code - a code for making proteins. Genes A gene is a length of DNA that codes for a specific protein. So, for example, one gene will code for the protein insulin, which is important role in helping your body to control the amount of sugar in your blood.