Alleles, Genotype and Phenotype | Science Primer
Find information, videos, and activities about DNA, genes, chromosomes, the Description: Animations, interactive tutorials, and practice problems that teach a . Experiment with the forces involved and measure the relationship between the Do Some Genes Maintain More Than One Common Allele in a Population?. Genes are the information in DNA that codes for PROTEINS and nothing else. significant problems) and remain in the human genome; for example the allele for blue For instance the insulin gene is located on chromosome 11p which. Genes are part of chromosomes, which are long strands of a chemical Dominant inheritance is when one allele of a gene is dominant within the pair. . likely than unrelated parents to have children with health problems or genetic disorders. The closer the genetic relationship between the parents, the greater the risk of.
DNA is a large and complex polymer, which is made up of two strands forming a double helix. DNA determines the characteristics of a living organism. With the exception of identical twins, each person's DNA is unique. The order of these letters makes up an organism's genetic code. An organism's genome is one copy of all of their DNA. 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. 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.
Genes and Chromosomes - Fundamentals - Merck Manuals Consumer Version
Therefore, genes are made up of DNA. A DNA strand looks like a twisted ladder. The genes are like a series of letters strung along each rung. These letters are used like an instruction book. The letter sequence of each gene contains information on building specific molecules such as proteins or hormones, both essential to the growth and maintenance of the human body.
The working parts of the cell read the RNA to create the protein or hormone according to the instructions. Each gene codes the instruction for a single protein only, but one protein may have many different roles in the human body. Also, one characteristic, such as eye colour, may be influenced by many genes. A variation can occur spontaneously no known cause or it can be inherited. Variations in the coding that make a gene not work properly faulty are called mutations and can directly or indirectly lead to a wide range of conditions.
Chromosomes and sperm and egg cells Humans have 46 paired chromosomes, with about 23, genes. The 46 chromosomes in the human cell are made up of 22 paired chromosomes. These are numbered from 1 to 22 according to size, with chromosome number 1 being the biggest. These numbered chromosomes are called autosomes.
Cells in the body of a woman also contain two sex chromosomes called X chromosomes, in addition to the 44 autosomes. Body cells in men contain an X and a Y chromosome and 44 autosomes. The 23, genes come in pairs.
A sperm and an egg each contain one copy of every gene needed to make up a person one set of 23 chromosomes each. When the sperm fertilises the egg, two copies of each gene are present 46 chromosomesand so a new life can begin. The chromosomes that decide the sex of the baby are called sex chromosomes. 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.
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.