Genes and Chromosomes - Fundamentals - MSD Manual Consumer Version
Revise genetic inheritance for Edexcel with BBC Bitesize. A gene is a small section of DNA on a chromosome, that codes for a shows the relationship between the cell, its nucleus, chromosomes in the nucleus, and genes. The genotype. Find information, videos, and activities about DNA, genes, chromosomes, the Experiment with the forces involved and measure the relationship between the. DNA is the most basic level of organization of genetic material. All it is is a double stranded helical molecule with base pairs. But because DNA is such a long.
An XX pairing means a girl, while an XY pairing means a boy. As well as determining sex, these chromosomes carry genes that control other body functions. There are many genes located on the X chromosome, but only a few on the Y chromosome.
How we inherit characteristics We can inherit characteristics in many different ways. Variations in the gene for that characteristic cause these different forms.
We can inherit different alleles of the gene pair one from each parent in different ways. Dominant and recessive genes The two copies of the genes contained in each set of chromosomes both send coded messages to influence the way the cell works. Generally, for example, the coded message from the genes that tells the eye cells to make brown colour is dominant over blue eye colour.
However, a number of different genes together determine eye colour and so blue-eyed parents can have a child with brown eyes. Dominant and recessive blood-group inheritance Dominant inheritance is when one allele of a gene is dominant within the pair.
For blood groups, the A allele is dominant over the O allele, so a person with one A allele and one O allele has the blood group AO. Another way of saying this is that the O group is recessive — a person needs two O alleles to have the blood group O. So a child may have blood group A because the blood group A gene inherited from their mother is dominant over the blood group O gene inherited from their father.
The father has two O alleles OOso he has the blood group O. Each one of their children has a 50 per cent chance of having blood group A AO and a 50 per cent chance of having blood group O OOdepending on which alleles they inherit. Co-dominant genes Not all genes are either dominant or recessive. Sometimes, each allele in the gene pair carries equal weight and will show up as a combined physical characteristic.
So someone with one copy of A and one copy of B has the blood group AB. Continuing the example of blood groups, a person with the alleles AO will have the blood group A. The observable trait — blood group — is known as the phenotype. The genotype is the genes that produce the observable trait.
Chemical communication Although every cell has two copies of the 23, genes, each cell needs only some specific genes to be switched on in order to perform its particular functions. The unnecessary genes are switched off.
What is the Relationship Between a Chromosome and an Allele?
Genes communicate with the cell in chemical code, known as the genetic code. The cell carries out its instructions to the letter. A cell reproduces by copying its genetic information then splitting in half, forming two individual cells.
Occasionally, a mistake is made, causing a variation genetic mutation and the wrong chemical message is sent to the cell. Genetic mutations are permanent. Some of the causes of a spontaneous genetic mutation include exposure to radiation, chemicals and cigarette smoke. Genetic mutations also build up in our cells as we age. For example, skin cancer can be caused by a build-up of spontaneous mutations in genes in the skin cells caused by damage from UV radiation.
Sometimes, a parent may have one copy of a gene that is faulty and the other copy containing the correct information. The correct copy of a gene overrides the faulty copy. For example, the gene controlling red—green colour recognition is located on the X chromosome.
A mother who carries the faulty gene causing red—green colour blindness on one of her X chromosome copies will have perfectly normal vision, as she still has a functioning gene copy for red—green colour recognition on her other X chromosome. However, her sons have a 50 per cent chance of being colourblind. This is because there is a 50 per cent chance that they will inherit the X chromosome from their mother that contains the faulty gene.
There is also a 50 per cent chance that they will inherit the X chromosome containing the correct copy of the gene and so will have normal vision. Genetic conditions To date, scientists have identified around 1, conditions caused directly or indirectly by changes in the genes. Around half of all miscarriages are caused by changes in the total number of genes in the developing baby. Similarly, about half of the Australian population will be affected at some point in their life by an illness that is at least partly genetic in origin.
The three ways in which genetic conditions can happen are: The variation in the gene that makes it faulty a mutation happens spontaneously in the formation of the egg or sperm, or at conception. The faulty gene is passed from parent to child and may directly cause a problem that affects the child at birth or later in life. The faulty gene is passed from parent to child and may cause a genetic susceptibility.
Environmental factors, such as diet and exposure to chemicals, combine with this susceptibility to trigger the onset of the disorder.
It simply means you are at increased risk of developing the condition. Many conditions involving genetic susceptibility, such as some types of cancer, need to be triggered by environmental factors such as diet and lifestyle.
For example, prolonged exposure to the sun is linked to melanoma.
Avoiding such triggers means significantly reducing the risks. Genes and genetics — related parents Many cultures approve of marriage between relatives such as first cousins. The aims of intermarrying are often to bolster family unity and keep wealth within the family. Consanguinity is often associated with factors such as: Related parents are more likely than unrelated parents to have children with health problems or genetic disorders.
This is because the two parents share one or more common ancestors and so carry some of the same genetic material.
- Genetic inheritance
- Genes and genetics explained
With the exception of identical twins, no two people's genomes are the same. Some characteristics are controlled by a single gene, such as fur in animals and red-green colour blindness in humans.
Each gene might have different forms, and these are called alleles. The diagram shows the relationship between the cell, its nucleus, chromosomes in the nucleus, and genes. Chromosomes are made from genes which are made from the DNA double helix Chromosomes are found in the nucleus of a body cell in pairs. One chromosome of each pair is inherited from the mother and the other one is inherited from the father.
What Is the Relationship Between a Chromosome & an Allele? | Sciencing
The chromosome in each pair carries the same gene in the same location. These genes could be the same, or different versions: Alleles are different versions of the same gene. For example, the gene for eye colour has an allele for blue eye colour and an allele for brown eye colour.
For any gene, a person may have the same two alleles, known as homozygous or two different ones, known as heterozygous. A dominant allele is always expressed, even if one copy is present.
Dominant alleles are represented by a capital letter, for example you could use a B. The allele for brown eyes, B, is dominant. You only need one copy of this allele to have brown eyes. Two copies will still give you brown eyes.