You probably can tell by their close resemblance that these two individuals are identical twins. Identical twins develop from the same fertilized egg, so they inherited copies of the same chromosomes and have all the same genes. Unless you have an identical twin, no one else
in the world has exactly the same genes as you. What are genes? How are they related to chromosomes? And how do genes make you the person you are? Chromosomes are coiled structures made of DNA and proteins. Chromosomes are encoded with genetic instructions for making proteins. These instructions are organized into units called genes. Most genes contain the instructions for a single protein. There may be hundreds or even thousands of genes on a single chromosome. Human ChromosomesEach species is characterized by a set number of chromosomes. The human number is 23. Human cells normally have two sets of chromosomes in each of their cells, one set inherited from each parent. There are 23 chromosomes in each set, for a total of 46 chromosomes per cell. Each chromosome in one set is matched by a chromosome of the same type in the other set, so there are actually 23 pairs of chromosomes per cell. Each pair consists of chromosomes of the same size and shape, and they also contain the same genes. The chromosomes in a pair are known as homologous chromosomes. As see in Figure \(\PageIndex{2}\), there are two types of chromosomes, autosomal and sex chromosomes. Read more about this in the genetics chapter. Human GenesHumans have an estimated 25,000 genes. This may sound like a lot, but it really isn’t. Far simpler species have almost as many genes as humans. However, human cells use splicing and other processes to make multiple proteins from the instructions encoded in a single gene. Only about 25 percent of the nitrogen base pairs of DNA in human chromosomes make up genes and their regulatory elements. Out of this 25 percent, only two percent code for genes. The functions of many of the other base pairs are still unclear. The majority of human genes have two or more possible versions, called alleles. Differences in alleles account for the considerable genetic variation among people. In fact, most human genetic variation is the result of differences in individual DNA base pairs within alleles. LinkageGenes that are located on the same chromosome are called linked genes. Linkage explains why certain characteristics are frequently inherited together. For example, genes for hair color and eye color are linked, so certain hair and eye colors tend to be inherited together, such as blonde hair with blue eyes and brown hair with brown eyes. Can you think of other human traits that seem to occur together? Do you think they might be controlled by linked genes? Genes located on the sex chromosomes are called sex-linked genes. Most sex-linked genes are on the X chromosome because the Y chromosome has relatively few genes. Strictly speaking, genes on the X chromosome are X-linked genes, but the term sex-linked is often used to refer to them. Figure \(\PageIndex{3}\) is called a linkage map. A linkage map shows the locations of specific genes on a chromosome. It shows the locations of a few of the genes on the human X chromosome, such as a blood group protein gene, Lethyosis (a skin disease gene), ocular albinism gene, and many more. Chromosomes and genesReview
Explore MoreWatch the video below to learn about sex chromosomal disorders, such as Turner syndrome. Attributions
Which of the following is true of genes that are found very near each other on the same chromosome?Genes that are sufficiently close together on a chromosome will tend to "stick together," and the versions (alleles) of those genes that are together on a chromosome will tend to be inherited as a pair more often than not. This phenomenon is called genetic linkage.
What are genes that are close together called?Final answer: Genes when close together on a chromosome is known as linkage. Q. Q. Assertion :The non-allelic gene for red hair and freckles are usually inherited together.
How do you know if two genes are on the same chromosome?Unlinked genes may be on different chromosomes, or so far apart on the same chromosome that they are often separated by recombination. If two genes are inherited together more than 50% of the time, this is evidence that they are linked on the same chromosome.
What is the term given to genes that are located near each other on the same chromosome tend to travel together during meiosis and fertilization?Linked genes are genes that are likely to be inherited together because they are physically close to one another on the same chromosome. During meiosis, chromosomes are recombined, resulting in gene swaps between homologous chromosomes.
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