How are DNA chromosomes and genes related? | Socratic
Every cell in the human body contains a nucleus, with the exception of red blood cells, which lose this structure as they mature. Within the nucleus are tightly . Genes are part of chromosomes, which are long strands of a chemical substance called deoxyribonucleic acid (DNA). Therefore, genes are made up of DNA. A DNA . A couple who suspect they may be related can seek genetic counselling. Your genes are part of what makes you the person you are. You are different from everyone alive now and everyone who has ever lived. DNA. But your genes.
How are DNA chromosomes and genes related?
Within the nucleus are tightly coiled threadlike structures known as chromosomes see Figure 1. Humans normally have 23 pairs of chromosomes, one member of each pair derived from the mother and one from the father see Figure 2.
One those pairs consists of the sex chromosomes—with two X chromosomes determining femaleness, and one X and one Y determining maleness. Some chromosomes are significantly larger than others, and some are more densely packed with genes. Under the standard system of identification, scientists have numbered these autosomes from 1—22 in size order that is, the number of base pairs with chromosome 1 being the largest million base pairs, and an estimated genes.
Sometimes a polypeptide can form a complete protein on its own as in the case of insulinbut in most cases a number of polypeptides combine to create a single functional protein as in the case of collagen and globin. These nucleotides link together to form long polynucleotide chains see Figure 4. Pairing Except for certain cells for example, sperm and egg cells or red blood cellsthe nucleus of every human cell contains 23 pairs of chromosomes, for a total of 46 chromosomes.
Normally, each pair consists of one chromosome from the mother and one from the father. There are 22 pairs of nonsex autosomal chromosomes and one pair of sex chromosomes. Paired nonsex chromosomes are, for practical purposes, identical in size, shape, and position and number of genes. Because each member of a pair of nonsex chromosomes contains one of each corresponding gene, there is in a sense a backup for the genes on those chromosomes. The 23rd pair is the sex chromosomes X and Y. Sex chromosomes The pair of sex chromosomes determines whether a fetus becomes male or female.
Males have one X and one Y chromosome. Females have two X chromosomes, one from the mother and one from the father. In certain ways, sex chromosomes function differently than nonsex chromosomes. The smaller Y chromosome carries the genes that determine male sex as well as a few other genes.
The X chromosome contains many more genes than the Y chromosome, many of which have functions besides determining sex and have no counterpart on the Y chromosome. In males, because there is no second X chromosome, these extra genes on the X chromosome are not paired and virtually all of them are expressed.
Genes on the X chromosome are referred to as sex-linked, or X-linked, genes. Normally, in the nonsex chromosomes, the genes on both of the pairs of chromosomes are capable of being fully expressed.
However, in females, most of the genes on one of the two X chromosomes are turned off through a process called X inactivation except in the eggs in the ovaries. X inactivation occurs early in the life of the fetus. In some cells, the X from the father becomes inactive, and in other cells, the X from the mother becomes inactive. Because of X inactivation, the absence of one X chromosome usually results in relatively minor abnormalities such as Turner syndrome.
Thus, missing an X chromosome is far less harmful than missing a nonsex chromosome see Overview of Sex Chromosome Abnormalities.The relationship between nucleus, chromosome, dna, genes, and alleles
If a female has a disorder in which she has more than two X chromosomes, the extra chromosomes tend to be inactive. Thus, having one or more extra X chromosomes causes far fewer developmental abnormalities than having one or more extra nonsex chromosomes. For example, women with three X chromosomes triple X syndrome are often physically and mentally normal.
Males who have more than one Y chromosome see XYY Syndrome may have physical and mental abnormalities. Chromosome abnormalities There are several types of chromosome abnormalities.
DNA, genes and chromosomes — University of Leicester
A person may have an abnormal number of chromosomes or have abnormal areas on one or more chromosomes.
Many such abnormalities can be diagnosed before birth see Testing for chromosome and gene abnormalities.
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Abnormal numbers of nonsex chromosomes usually result in severe abnormalities. For example, receiving an extra nonsex chromosome can be fatal to a fetus or can lead to abnormalities such as Down syndromewhich commonly results from a person having three copies of chromosome Absence of a nonsex chromosome is fatal to the fetus. Large areas on a chromosome may be abnormal, usually because a whole section was left out called a deletion or mistakenly placed in another chromosome called translocation.
For example, chronic myelogenous leukemia is sometimes caused by translocation of part of chromosome 9 onto chromosome This abnormality can be inherited or be the result of a new mutation. Mitochondrial chromosomes Mitochondria are tiny structures inside cells that synthesize molecules used for energy.
Unlike other structures inside cells, each mitochondrion contains its own circular chromosome.
DNA, RNA, genes and chromosomes | ALRC
This chromosome contains DNA mitochondrial DNA that codes for some, but not all, of the proteins that make up that mitochondrion. Mitochondria from the sperm usually do not become part of the developing embryo.
Traits A trait is any gene-determined characteristic. Many traits are determined by the function of more than one gene. For example, a person's height is likely to be determined by many genes, including those affecting growth, appetite, muscle mass, and activity level. However, some traits are determined by the function of a single gene. Variation in some traits, such as eye color or blood type, is considered normal.
Other variations, such as albinismMarfan syndromeand Huntington diseaseharm body structure or function and are considered disorders. However, not all such gene abnormalities are uniformly harmful. For example, one copy of the sickle cell gene can provide protection against malaria, but two copies of the gene cause sickle cell anemia. Genetic Disorders A genetic disorder is a detrimental trait caused by an abnormal gene.
The abnormal gene may be inherited or may arise spontaneously as a result of a mutation. Gene abnormalities are fairly common. 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.