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Genetics OB1: Explain how characteristics of living things are passed on from generation to generation. Characteristics of living things are passed on from generation to generation by an organism’s genes. Every species has its own characteristic DNA sequence. Of all of the cats in the world, Cinnamon The genetic complement (or genome) of was chosen to be the definitive genetic the pig is comprised of 18 pairs of model for all cats in a project called the chromosomes plus the X and Y (sex) feline genome project. chromosomes. OB5: Students will explain and describe dominant and recessive traits, DNA (genetic material), gene pair, gene combination, and gene sorting. Students will describe how genetic material is passed from parent to young during sexual and asexual reproduction. *Since chromosomes come in pairs (GENE PAIR), there exist two open slots for each gene. (One from each parent) *Sometimes there are two or more forms of the gene, called alleles, for a particular trait. Often there is a dominant and a recessive gene like the tall (TT or Tt) and short (tt) pea plants Mendel studied. (Tt or TT or tt are all GENE COMBINATIONS) *A DOMINANT gene masks or cancels out the effects of a recessive gene, even if the recessive gene is present. *A RECESSIVE gene is only expressed when present with another recessive gene A Punnett square is often used to show how alleles segregate (sort) from an individual when their gametes (sperm & eggs or pollen grains and ova) form. Gametes only have one of the two possible alleles. It is totally random which ones the gamete gets. *The above cross shows the possible combinations by crossing two parents that are HETEROZYGOUS for a particular trait. Note that three of the offspring will show the dominant trait, while only one will show the recessive one. *A co-dominant trait is one where both alleles are expressed on the same organism at the same time. -Human blood type is a co-dominant trait -Speckled feathers in chickens is another -”Rainbow” coloration in boas is another *A polygenic trait is one where more than one gene determines its expression. -Most human traits are polygenic, like skin, hair and eye color, and body height. These traits show a continuous gradation in their expression. *A sex-linked trait is one where the gene is on one of the sex chromosomes, usually the X chromosome. In humans, since males are XY and females are XX, males have only one chance at each of the genes that happen to be on the X chromosome. The Y is not homologous; it does not have the same genes that the X does. If a male gets a bad gene (from his mother), then he’s stuck with it. He doesn’t have a backup like females do. Homologous chromosomes are a pair of chromosomes, one inherited from each parent, that have corresponding gene sequences and that pair during meiosis. OB2: Explain the structure and function of the DNA molecule. DNA is the material that stores and transmits the genetic information from one generation of an organism to the next. *DNA forms a double helix…Its two strands spiral around each other. It resembles a twisted ladder. Sugar-phosphate backbones form the sides of the ladder, and the nitrogenous bases form the rungs. (see figure 12-7) The nitrogenous bases on each strand pair up exactly opposite with each other: BASE PAIRING: *Hydrogen bonds form, holding the strands together *Adenine pairs only with thymine *Cytosine pairs only with guanine A-T T-A C-G G-C OB7: Students will explain and describe DNA replication. *Before a cell can divide, it must duplicate its DNA *Enzymes do the work *The original strand unzips *Base pairs separate at the hydrogen bonds *Each original strand becomes a template *Each complementary strand forms along the template by base pairing *Two identical DNA molecules are the result OB3: Outline and explain the central dogma of genetics. *DNA stays in the nucleus, but protein is made out in the cytoplasm by the ribosomes… *Messenger RNA is made in the nucleus using a section of DNA as a template. This is called TRANSCRIPTION. *The segment of DNA that codes for a needed protein unzips, revealing open bases. Complementary bases of mRNA form on the DNA strand, then are moved off by an enzyme RNA polymerase. *RNA is single stranded, but it obeys the same base pairing rules as DNA (substitute Uracil in place of Thymine) *mRNA goes to the ribosome and acts as a template for protein synthesis. *TRANSFER RNA brings specific amino acids to the ribosome to be hooked on. Every three letters of the mRNA is a code for one of about twenty different amino acids and is therefore called a CODON. *The “feet” of the tRNA that match the CODON are called the ANTI-CODON sequence. Each anticodon carries its own specific amino acid. This process is called TRANSLATION. *There are start and stop sequences built in too. *The new protein then may travel to the Golgi body for further modification and packaging. *Characteristics of living things are called TRAITS. *Since the body is put together with and works chemically by proteins, the action of one or more proteins determines traits in living things. *A GENE is a sequence of DNA that eventually codes for a protein that determines or helps determine a trait. *This process is virtually the same in all living things. OB4: List and give examples of the main types of human proteins. Basic Types of Proteins: 1. Proteins that are structural: -keratins of fingernails, skin, hair -collagens of connective tissue -lipoproteins of cell membrane systems 2. Proteins that are hormones, such as insulin 3. Proteins that transport oxygen (hemoglobin) 4. Proteins that make up chromosomes, such as histones 5. Proteins that are organic catalysts or ENZYMES *Since there are an estimated 22,000+ proteins in the human body alone, it can be said that the functions of proteins are at the very center of life itself! PROTEINS Protein complex from a dinoflagellate…it makes light! (Bioluminescence) *Asexual reproduction involves a cell splitting in half by mitosis (previous chapter). *Other forms of growth can also be considered asexual, like a strawberry plant sending out runners to start new plants, or a starfish or a worm breaking apart to become several new individuals (each genetically identical to the original). *Asexual reproduction results in identical offspring genetically--the only changes come from mutations OB6: Students will explain and describe the purpose of meiosis. Students will explain and describe genetic variation, and the results of new gene combinations. *Meiosis is the special type of cell division that produces gametes (sex cells) *Meiosis takes the maternal and paternal alleles of the individual and gives them a random shuffle. *This means an organism’s gametes are actually a new, totally unique combination of that individual’s own parents! *Chromosomes come in pairs-here parts of each pair are seen swapping pieces during meiosis--this is called CROSSING OVER Here is a diagram of all the possible combinations of gamete chromosomes from crossing over during meiosis with only three chromosomes… With 23 chromosomes in humans, there would be well over 8 million possibilities... OB8: Students will explain and describe the structure and function of chromosomes and how they are duplicated through mitosis. *Coil DNA up around protein (histones) before cell division and you’ve got chromosomes *As you recall, chromosomes are important in cell division Organisms grow not by making their cells bigger, but by making more cells. This process is called cell division, or mitosis. You must know the four phases. Through mitosis cells can specialize. Genetic controls tell stem cells to specialize into different tissues. Family members who have adopted frozen embryo babies applaud President Bush as he makes remarks on embryonic stem cell research in the East Room of the White House in Washington, on 19 July 2006. (Image: AP Photo/Ron Edmonds) And then…. Still going………. And going………….. OB9: Students will explain how new traits may arise in individuals through changes in genetic material (DNA) through mutation. *A mutation is a mistake in duplicating genetic information and/or in transmitting it to the next generation. *Mutations may occur in any cell. *Mutations in reproductive cells (“germ cells”) are GERM MUTATIONS. These may be inherited even if the new trait is not expressed in the parent. *Mutations in all other body cells are called SOMATIC MUTATIONS. Since body cells produce only more body cells, the mutation is not inheritable. Many cancers are caused by somatic mutations. *Mutations can be INSERTIONS or DELETIONS, where a DNA base is inserted into or taken away from a DNA strand. This causes a “frameshift mutation”. Try to read the following: THF ATC ATA TET HER AT Now try it with the missing base put back in: THE FAT CAT ATE THE RAT Since DNA is read three letters at a time, the result of inserting or deleting a base are seen all down the line. A mutation may also be a SUBSTITUTION where one base is accidentally replaced with a different one. This may or may not cause harm to the organism. If the mutation changes the amino acid sequence, it may make the resulting protein inactive and useless. Sickle Cell Anemia is caused by a point mutation in one of the genes that codes for part of the blood protein hemoglobin. OB10: Students will explain and describe natural and human produced sources of mutation. *Mutations may occur naturally and completely at random. *Mutations may also be caused by radiation or by chemical agents. *Mutations are a major source of variation in all speciesthe trick is getting one that is beneficial and not deadly. *Scientists actually try to induce mutations in a variety of plants, animals, and bacteria to obtain, at random, desired traits. *Increasing mutations by any means increases the risk of cancer developing. OB11: Students will explain and describe products of genetic engineering. *Genetic engineering involves cutting useful genes out of one species, and splicing them into the genes of another species. Usually involving bacteria, viruses, and plants, the possibilities of genetic engineering (both good and disastrous) are unlimited. *Disease & drought resistant plants & faster growing *Medicines for animals & humans *Faster growing salmon for fish farms (inserted flounder genes) *Roundup resistant soybeans (produced by Monsanto) *Longer lasting tomatoes & other fruits & veggies *Medical advances using cloning & stem cells