Standard 4 - Genetics

Unit 10 – DNA, RNA, & Protein Synthesis

Objectives

• B4.2C: Describe the structure and function of DNA. • B4.2D: Predict the consequences that changes in the

DNA composition of particular genes may have on an organism (e.g., sickle cell anemia, other).

• B4.2f: Demonstrate how the genetic information in DNA molecules provides instructions for assembling protein molecules and that this is virtually the same mechanism for all life forms.

• B4.2g: Describe the processes of replication, transcription, and translation and how they relate to each other in molecular biology.

The Big PictureMitosis Meiosis

somatic (body) cells sex cells (sperm or egg)

2N

Diploid

2N2N

2N

2N

2N 2N

1N1N 1N 1N

2N = Diploid

1N = Haploid

GENETICS

• PAIRS OF CHROMOSOMES IN LIVESTOCK & HUMANS:• Species # of Chromosomes

Turkeys 41Chickens 39Horses 32Cattle 30Goats 30Sheep 27Humans 23Swine 19

• Homo sapiens (human)46 • Mus musculus (house mouse)40• Drosophila melanogaster (fruit fly)8• Caenorhabditis elegans (microscopic roundworm)12• Saccharomyces cerevisiae (budding yeast)32• Arabidopsis thaliana (plant in the mustard family)10• Xenopus laevis (South African clawed frog)36• Canis familiaris (domestic dog)78• Gallus gallus (chicken)78• Zea mays (corn or maize)20• Muntiacus reevesi (the Chinese muntjac, a deer)23• Muntiacus muntjac (its Indian cousin)6• Myrmecia pilosula (an ant)2• Parascaris equorum var. univalens (parasitic roundworm)2• Cambarus clarkii (a crayfish)200• Equisetum arvense (field horsetail, a plant)216

GENETICS

GENETICS• Chromosomes = Part of a cell that contains genetic information.

• Genes = small bits of heredity information; genes are composed of DNA

and are carried on the chromosomes. • DNA = deoxyribonucleic acid, the molecule that holds genetic information. It

is the biochemical molecule that makes chromosomes and genes. • Relationship between DNA – chromosomes – genes?

– DNA is the concrete, Chromosomes are the wall, Genes are individual blocks.

DNA Molecule: DNA Unzip 1:16

GENETICS

• DNA = deoxyribonucleic acid• Found in the nuclei of cells – there is 46

chromosomes in each human cell nuclei• If the DNA in all 46 human chromosomes

in 1 cell were uncoiled it would stretch out to be more than 6 feet in length

• Crick and Watson worked out the structure of DNA = double helix

• Contains all your traits (genes) and makes up chromosomes

• Thousands of genes are contained on each DNA molecule

DNA: Deoxyribonucleic Acid (02:02)

GENETICS• DNA = deoxyribonucleic acid

• The vertical sides of DNA are made up of sugar and phosphate

• Cross pieces are nucleotide bases: A-T C-G

• Genetic traits are determined by the order of the DNA nucleotide bases A T C G

• DNA makes a copy of itself = replication

• Two different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

• Most organisms are made of DNA, but a few viruses have RNA as their genetic material. The biological information contained in an organism is encoded in its DNA or RNA sequence.

• Interestingly, as much as 98% of human DNA does not code for a specific product.

• Prokaryotic genetic material is organized in a simple circular structure that rests in the cytoplasm.

• Eukaryotic genetic material is more complex and is divided into discrete units called genes.

GENETICS

Genes (02:17)

• The information passed from parents to offspring is transmitted by means of genes that are coded in DNA molecules. These genes contain the information for the production of proteins.

• Genes express their functional effect through the production of proteins, which are complex molecules responsible for most functions in the cell. Proteins are chains of amino acids, and the DNA sequence of a gene (through an RNA intermediate) is used to produce a specific protein sequence.

• Each group of three nucleotides in the sequence, called a codon, corresponds to one of the twenty possibly amino acids in protein — this correspondence is called the genetic code. The specific sequence of amino acids results in a unique three-dimensional structure for that protein, thereby determining its behavior and function.

GENETICS

• The molecular basis for genes is deoxyribonucleic acid (DNA). DNA is composed of a chain of nucleotides, of which there are four types: adenine (A), cytosine (C), guanine (G), and thymine (T). Genetic information exists in the sequence of these nucleotides, and genes exist as stretches of sequence along the DNA chain.

  The genetic code: DNA, through a messenger RNA intermediate, codes for protein with a triplet code.

GENETICS

GENETICS• Nucleotide = Basic building block of DNA and RNA. A nucleotide is

made of a ribose sugar, nitrogenous base, and phosphate group.

• 4 Bases: Adenene, Guanine, Cytosine, Thyamine → A-T C-G

• The nucleotides join together to form a chain. The phosphate end of the chain is referred to as the 5’ end. The opposite end is the 3' end.

GENETICS• Replication = The process of

making an identical copy of a section of duplex (double-stranded) DNA, using existing DNA as a template for the synthesis of new DNA strands

• Transcription = Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. In the case of protein-encoding DNA, transcription is the beginning of the process that ultimately leads to the translation of the genetic code (via the mRNA intermediate) into a functional peptide or protein.

• Translation = The process of turning instructions from mRNA, base by base, into chains of amino acids that then fold into proteins.

Introduction: Transcription of DNA to Messenger RNA (02:24)

GENETICS

• TWINS:• Identical Twins = (monozygotic) result when a single

fertilized egg splits after conception. The resulting twins are the same sex and genetically alike, with similar foot and hand prints, but different fingerprints and teeth marks. The egg then splits into two genetically identical halves. They share 100% of their genes.

• 1 egg and 1 sperm

• Fraternal Twins = (dizygotic) result when two eggs are released by the mother at the same time and each egg is fertilized by a different sperm. Fraternal twins can be of the same or opposite sex. They share up to 50% of their genes, and are no more alike or different than any two siblings would be, but their bond is just as special.

• 2 eggs and 2 sperm

Identical Genes: The Science of Identical Twins (02:13)

• Sex-linked = If a gene is found only on the X chromosome and not the Y chromosome, it is said to be a sex-linked trait. Because the gene controlling the trait is located on the sex chromosome, sex linkage is linked to the gender of the individual. Usually such genes are found on the X chromosome. The Y chromosome is thus missing such genes (See Diagram above.). The result is that females will have two copies of the sex-linked gene while males will only have one copy of this gene. If the gene is recessive, then males only need one such recessive gene to have a sex-linked trait rather than the customary two recessive genes for traits that are not sex-linked. This is why males exhibit some traits more frequently than females.

Examples of Sex-linked Traits: Red-green colorblindnessMale Pattern BaldnessHemophiliaDuchenne Muscular Dystrophy

GENETICS

Genetic Variation• Mendelian Genetics can only account for a majority of the genetic

variations in species seen on earth. Other sources of Genetic Variation include Chromosomes Crossing over, Mutations, and Genetic Drift.

• Crossing Over

• How do you get a chromosome that is totally different from the original chromosomes of both parents? Crossing-Over takes place during Meiosis. During the process, DNA lengths are shared between chromosomes. In the illustration at left, two chromosomes intertwine, and exchange one end of the chromosome with the other. The end Chromosome has a completely different chemical composition from the starting two chromosomes.

• Mutations• Mutation takes place when an organism undergoes a

spontaneous genetic change during replication. During the process of replication, the nucleotides of a chromosome are altered, so rather than creating an identical copy of DNA strands, there are chemical variations in the replicated strands. The alteration on the chemical composition of DNA triggers a chain reaction in the genetic information of an individual. The mutation can be passed to offspring. For example, the mutation toward sickle cell anemia is based upon the production of one different amino acid, which in turn affects the polypeptide strands produced, etc. Mutations are usually non-beneficial to an organism, however, they are almost always recessive and unless two mutations are coupled together the mutation will not be expressed.

• * Predict how mutations may be transferred to progeny (offspring)

Genetic Variation

Genetic Variation

• Mutations …• Gene mutation in a cell

can result in uncontrolled cell division called cancer.

• Also, exposure of cells to certain chemicals and radiation increases mutations and thus increases the chance of cancer.

Basal Cell Carcinoma of the Nose

Mutations (02:03)

• Genetic Drift• Gene flow refers to the passage of traits or genes between

populations. The passage of genes from one population to another prevents high occurrences of mutation, and genetic drift. In genetic drift, random variation occurs because the genetic population is small, leading to the proliferation of specific traits within a population. For example, the population in the colonial history of Martha's Vineyard, settled in Massachusetts in 1642, had an unusually high occurrence of deafness among it's inhabitants. The high occurrence of deafness was a result of genetic drift, in that the population was so small that differing traits from outside populations could not enter in. To prevent genetic drift, genetic material must be shared between differing populations, even so, variations can occur. For example, the trait for sickle cell anemia is beneficial in some climates where there is a high rate of malaria. An individual with a heterozygous genotype for sickle cell anemia is more resistant to malaria. The concept of gene flow consequently ties directly into the concept of adaptation and natural selection.

Genetic Variation

Mutations• A mutation is a permanent change in the DNA sequence of a gene.

Mutations in a gene's DNA sequence can alter the amino acid sequence of the protein encoded by the gene. How does this happen? Like words in a sentence, the DNA sequence of each gene determines the amino acid sequence for the protein it encodes. The DNA sequence is interpreted in groups of three nucleotide bases, called codons. Each codon specifies a single amino acid in a protein.

• Types of mutations:• Original: The fat cat ate the wee rat.• Point Mutation: The fat hat ate the wee rat. • Frame Shift: The fat caa tet hew eer at.• Deletion: The fat ate the wee rat.• Insertion: The fat cat xlw ate the wee rat.• Inversion: The fat tar eew eht eta tac.

• Mutate a sentence!• We can think about the DNA sequence of a gene as a sentence made up

entirely of three-letter words. In the sequence, each three-letter word is a codon, specifying a single amino acid in a protein. Have a look at this sentence:

• Thesunwashotbuttheoldmandidnotgethishat.

• If you were to split this sentence into individual three-letter words, you would probably read it like this:

• The sun was hot but the old man did not get his hat.

• This sentence represents a gene. Each letter corresponds to a nucleotide base, and each word represents a codon. What if you shifted the three-letter "reading frame?" You would end up with this:

• T hes unw ash otb utt heo ldm and idn otg eth ish at.• Or• Th esu nwa sho tbu tth eol dma ndi dno tge thi sha t.

Mutations

• As you can see, only one of these three "reading frames" translates into an understandable sentence. In the same way, only one three-letter reading frame within a gene codes for the correct protein.

• Now, going back to the original sentence:• Thesunwashotbuttheoldmandidnotgethishat.• See how you can mutate the reading frame of this

sentence by inserting or deleting letters within the sentence.

• It's easy to make mutations that create "nonsense" sentences. Can you make mutations that maintain or change the meaning of the sentence without creating such nonsense?

Mutations

Mutations

Mutations

I have been told that due to pestacide use that some tree frogs in the southern US have been having pigment mutation and turning blue.

Mutations

Mutations

Natural Selection and Mutation - The Case of the Peppered Moth

This poor little rascal knows what it's like to have part of his genome deleted

Mutations

Six Legged Calf

Walking Two Legged Dog

Two Headed Turtle

Mutations

Eight Legged Cat

Frog and a Half

• Jumping Genes = Transposons are sequences of DNA that can move around to different positions within the genome of a single cell, a process called Transposition. In the process, they can cause mutations and change the amount of DNA in the genome. Transposons are also called "jumping genes" or "mobile genetic elements". There are a variety of mobile genetic elements, they can be grouped based on their mechanism of transposition.

• Deletion = when a part of a chromosome is missing, or part of the DNA code is missing, in the process of DNA replication, a deletion occurs if a nucleotide or series of nucleotides is not copied. Such deletions may be harmless, may result in disease, or may in rare cases be beneficial.

• Duplication = A double copy of part of a chromosome resulting in an extra (abnormal) dose of the duplicated material, or when a part of a chromosome is present in two copies.

Genetic Variation

• It may be possible to identify genetic defects from a karyotype of a few cells.• Karyotype = A picture of the chromosomes in a cell that is used to check for

abnormalities. A karyotype is created by staining the chromosomes with dye and photographing them through a microscope. The photograph is then cut up and rearranged so that the chromosomes are lined up into corresponding pairs.

Genetic Variation

This is an example of trisomy 21 (47, XY, +21) also known as Down syndrome. Additions or deletions of genetic material are generally lethal in utero, but Trisomy 21 is an example of one form of addition in which the fetus may occasionally survive to term and beyond. The overall incidence is 1 in 1000 livebirths, but the non-dysjunctional event in meiosis that produces this anomaly increases in incidence with increasing maternal age, particularly over age 40.

Genetic Engineering-Genetic engineering techniques provide great potential and responsibilities.

-Genetic engineering, recombinant DNA technology, genetic modification/manipulation (GM) and gene splicing are terms that are applied to the manipulation of genes, implying that the process is outside the organism's natural reproductive process. It involves the isolation, manipulation and reintroduction of DNA into cells or model organisms, to express a protein.-The aim is to introduce new characteristics or attributes physiologically or physically, such as making a crop resistant to herbicide, introducing a novel trait or enhancing existing ones, or producing a new protein or enzyme. -Successful endeavors include the manufacture of human insulin by bacteria, the manufacture of erythropoietin in Chinese hamster ovary cells, the production of new types of experimental mice such as the OncoMouse (cancer mouse) for research, and round up ready crops.

Genetic Engineering

- Roundup Ready Corn and Soybeans - All plants make proteins. Roundup Ready plants produce the same natural proteins as any other plant with one notable exception. These plants make an additional protein which allows them to grow in the presence of Glyphosate, known commercially as “Roundup,” one of the most widely-used herbicides employed by back-yard gardeners, homeowners, golf courses and commercial farms for the past 25 years. The protein is not a toxin to plants, animals, insects, humans or bacteria.

Transgenics: Splicing Genes Across Species (03:19)

Cloning Debate (37-3 / Debate)

Pros of Cloning: + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +• If the vital organs of the human body can be cloned, they can serve as

backup systems for human beings. Cloning body parts can serve as a lifesaver. When a body organ such as a kidney or heart fails to function, it may be possible to replace it with the cloned body organ.

• Cloning in human beings can prove to be a solution to infertility. Cloning has the potential of serving as an option for producing children. Cloning may make it possible to reproduce a certain trait in human beings. We will be able to produce people with certain qualities, human beings with particular desirable traits, thus making human beings a man-made being!

• Cloning technologies can prove helpful for the researchers in genetics. They might be able to understand the composition of genes and the effects of genetic constituents on human traits, in a better manner. They will be able to alter genetic constituents in cloned human beings, thus simplifying their analysis of genes. Cloning may also help us combat a wide range of genetic diseases.

• Cloning can make it possible for us to obtain customized organisms and harness them for health benefits of society. Cloning can serve as the best means to replicate animals that can be used for research purposes.

• Cloning can enable the genetic alteration of plants and animals. If positive changes can be brought about in living beings with the help of cloning, it will indeed be a boon to mankind.

Cloning Debate (37-3 / Debate)

Cons of Cloning: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -• Cloning created identical genes. It is a process of replicating a genetic

constitution, thus hampering the diversity in genes. While lessening the diversity in genes, we weaken our ability of adaptation. Cloning is also detrimental to the beauty that lies in diversity.

• While cloning allows man to tamper with genetics in human beings, it also makes deliberate reproduction of undesirable traits, a probability. Cloning of body organs might invite malpractices in society.

• In cloning human organs and using them for transplant, or in cloning human beings themselves, technical and economic barriers will have to be considered. Will cloned organs be cost-effective? Will cloning techniques really reach the common man?

• Moreover, cloning will put human and animal rights at stake. Will cloning fit into our ethical and moral principles? Cloning will leave man just another man-made being. Won't it devalue mankind? Won't it undermine the value of human life?

• Cloning is equal to emulating God. Is that easy? Is that risk-free? Many are afraid it is not!

Genetic Engineering

• What are the advantages and disadvantages of human manipulation of DNA? …

• Debate

Video Quiz: Genetics: The Molecular Basis of Heredity (01:14)