Chromosomes Genes Alleles And Mutations Worksheet Pdf

chromosomes genes alleles and mutations worksheet pdf

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Genes and Chromosomes

Genes are segments of deoxyribonucleic acid DNA that contain the code for a specific protein that functions in one or more types of cells in the body.

Chromosomes are structures within cells that contain a person's genes. Some traits are caused by mutated genes that are inherited or that are the result of a new gene mutation. Proteins are probably the most important class of material in the body.

Proteins are not just building blocks for muscles, connective tissues, skin, and other structures. They also are needed to make enzymes. Enzymes are complex proteins that control and carry out nearly all chemical processes and reactions within the body.

The body produces thousands of different enzymes. Thus, the entire structure and function of the body is governed by the types and amounts of proteins the body synthesizes. Protein synthesis is controlled by genes, which are contained on chromosomes. The phenotype is how the genotype manifests in a person—not all the instructions in the genotype may be carried out or expressed. Whether and how a gene is expressed is determined not only by the genotype but also by the environment including illnesses and diet and other factors, some of which are unknown.

Genes consist of deoxyribonucleic acid DNA. DNA contains the code, or blueprint, used to synthesize a protein. Genes vary in size, depending on the sizes of the proteins for which they code. Each DNA molecule is a long double helix that resembles a spiral staircase containing millions of steps. The steps of the staircase consist of pairs of four types of molecules called bases nucleotides. In each step, the base adenine A is paired with the base thymine T , or the base guanine G is paired with the base cytosine C.

Each extremely long DNA molecule is coiled up inside one of the chromosomes. Except for certain cells for example, sperm and egg cells and red blood cells , the cell nucleus normally contains 23 pairs of chromosomes.

A chromosome contains many genes. A gene is a segment of DNA that provides the code to construct a protein. The DNA molecule is a long, coiled double helix that resembles a spiral staircase. In it, two strands, composed of sugar deoxyribose and phosphate molecules, are connected by pairs of four molecules called bases, which form the steps of the staircase.

In the steps, adenine is paired with thymine and guanine is paired with cytosine. Each pair of bases is held together by a hydrogen bond. A gene consists of a sequence of bases. Sequences of three bases code for an amino acid amino acids are the building blocks of proteins or other information. Proteins are composed of a long chain of amino acids linked together one after another. There are 20 different amino acids that can be used in protein synthesis—some must come from the diet essential amino acids , and some are made by enzymes in the body.

As a chain of amino acids is put together, it folds upon itself to create a complex three-dimensional structure. It is the shape of the folded structure that determines its function in the body.

Because the folding is determined by the precise sequence of amino acids, each different sequence results in a different protein. Some proteins such as hemoglobin contain several different folded chains. Instructions for synthesizing proteins are coded within the DNA. The code is written in triplets. That is, the bases are arranged in groups of three. Particular sequences of three bases in DNA code for specific instructions, such as the addition of one amino acid to a chain. For example, GCT guanine, cytosine, thymine codes for the addition of the amino acid alanine, and GTT guanine, thymine, thymine codes for the addition of the amino acid valine.

Thus, the sequence of amino acids in a protein is determined by the order of triplet base pairs in the gene for that protein on the DNA molecule. The process of turning coded genetic information into a protein involves transcription and translation. When transcription is initiated, part of the DNA double helix opens and unwinds.

There, the mRNA attaches to a ribosome, which is a tiny structure in the cell where protein synthesis occurs. Each molecule of tRNA brings one amino acid to be incorporated into the growing chain of protein, which is folded into a complex three-dimensional structure under the influence of nearby molecules called chaperone molecules. These cells look and act differently and produce very different chemical substances. However, every cell is the descendant of a single fertilized egg cell and as such contains essentially the same DNA.

Cells acquire their very different appearances and functions because different genes are expressed in different cells and at different times in the same cell.

The information about when a gene should be expressed is also coded in the DNA. Gene expression depends on the type of tissue, the age of the person, the presence of specific chemical signals, and numerous other factors and mechanisms. Knowledge of these other factors and mechanisms that control gene expression is growing rapidly, but many of these factors and mechanisms are still poorly understood. The mechanisms by which genes control each other are very complicated.

Genes have chemical markers to indicate where transcription should begin and end. Various chemical substances such as histones in and around the DNA block or permit transcription. Cells reproduce by dividing in two.

Because each new cell requires a complete set of DNA molecules, the DNA molecules in the original cell must reproduce replicate themselves during cell division. Replication happens in a manner similar to transcription, except that the entire double-strand DNA molecule unwinds and splits in two. After splitting, bases on each strand bind to complementary bases A with T, and G with C floating nearby.

When this process is complete, two identical double-strand DNA molecules exist. There are also chemical mechanisms to repair DNA that was not copied properly. However, because of the billions of base pairs involved in, and the complexity of, the protein synthesis process, mistakes may happen. Such mistakes may occur for numerous reasons including exposure to radiation, drugs, or viruses or for no apparent reason. Minor variations in DNA are very common and occur in most people.

Most variations do not affect subsequent copies of the gene. Mistakes that are duplicated in subsequent copies are called mutations. Inherited mutations are those that may be passed on to offspring. Mutations can be inherited only when they affect the reproductive cells sperm or egg.

Mutations that do not affect reproductive cells affect the descendants of the mutated cell for example, becoming a cancer but are not passed on to offspring. Mutations may be unique to an individual or family, and most harmful mutations are rare. Mutations may involve small or large segments of DNA. Depending on its size and location, the mutation may have no apparent effect or it may alter the amino acid sequence in a protein or decrease the amount of protein produced.

If the protein has a different amino acid sequence, it may function differently or not at all. An absent or nonfunctioning protein is often harmful or fatal. For example, in phenylketonuria , a mutation results in the deficiency or absence of the enzyme phenylalanine hydroxylase.

This deficiency allows the amino acid phenylalanine absorbed from the diet to accumulate in the body, ultimately causing severe intellectual disability. In rare cases, a mutation introduces a change that is advantageous.

For example, in the case of the sickle cell gene, when a person inherits two copies of the abnormal gene, the person will develop sickle cell disease. However, when a person inherits only one copy of the sickle cell gene called a carrier , the person develops some protection against malaria a blood infection. Although the protection against malaria can help a carrier survive, sickle cell disease in a person who has two copies of the gene causes symptoms and complications that may shorten life span.

Natural selection refers to the concept that mutations that impair survival in a given environment are less likely to be passed on to offspring and thus become less common in the population , whereas mutations that improve survival progressively become more common.

Thus, beneficial mutations, although initially rare, eventually become common. The slow changes that occur over time caused by mutations and natural selection in an interbreeding population collectively are called evolution.

Not all gene abnormalities are harmful. For example, the gene that causes sickle cell disease also provides protection against malaria. A chromosome is made of a very long strand of DNA and contains many genes hundreds to thousands. The genes on each chromosome are arranged in a particular sequence, and each gene has a particular location on the chromosome called its locus. In addition to DNA, chromosomes contain other chemical components that influence gene function. Except for certain cells for example, sperm and egg cells or red blood cells , the nucleus of every normal 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 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.

The Roles of DNA, Genes, Alleles, and Chromosomes in Inheritance

They code for the proteins that determine virtually all of a person's characteristics. Most genes come in pairs and are made of strands of genetic material called deoxyribonucleic acid , or DNA. Genetic disorders are caused by one or more changes, or mutations , in the instruction code of a particular gene s , preventing the gene s from functioning properly. The physical location of a gene is its locus. Different versions of genes are called alleles. For example, an eye color gene may have a blue allele and a brown allele. Genes are organized in structures called chromosomes.

Explain that the information passed from parents to offspring is transmitted by means of genes which are coded in DNA molecules. Explain how crossing over, jumping genes, and deletion and duplication of genes results in genetic variation. Explain how mutations can alter genetic information and the possible consequences on resultant cells. Use molecular models to demonstrate gene mutation and recombination at the molecular level. Describe how the process of meiosis results in the formation of haploid gametes and analyze the importance of meiosis in sexual reproduction. Explain how the process of DNA replication results in the transmission and conservation of the genetic code.


DNA Mutations Practice Worksheet You will need a Genetic Code Chart. Which type of mutation is responsible for new variations (alleles) of a trait? mutations affecting a single gene, there can be large scale alterations in chromosome.


chromosomes genes allele

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Genes are segments of deoxyribonucleic acid DNA that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are structures within cells that contain a person's genes. Some traits are caused by mutated genes that are inherited or that are the result of a new gene mutation.

Genetic variation is a measure of the variation that exists in the genetic makeup of individuals within population. Genetic variation is a measure of the genetic differences that exist within a population. The genetic variation of an entire species is often called genetic diversity. Genetic variations are the differences in DNA segments or genes between individuals and each variation of a gene is called an allele. For example, a population with many different alleles at a single chromosome locus has a high amount of genetic variation.

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During gamete formation, the alleles for each gene segregate from each other so that each A. A gene mutation affects the DNA of more genes than a chromosomal mutation. B. A gene mutation One twin exercises and eats well. They do.

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