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Unit 6 Notes ¨ ¨ In 1851, Gregor Mendel (a priest from Europe) taught high school and maintained the monastery’s garden In the garden, Mendel grew hundreds of pea plants and began noticing that they had different physical characteristics (traits) ¤ Some pea plants were short, others tall ¤ Some pea plants produced green seeds, others yellow ¨ Mendel observed that the pea plant’s traits were similar to those of their parents ¤ Heredity = the passing of traits from parents to offspring ¤ Genetics = the scientific study of heredity n Mendel is known as the “Father of Genetics” ¨ Mendel’s Peas ¤ A new organism begins to form when egg and sperm are joined in the process of fertilization n When ¤ Mendel plants fertilize themselves, it is called self-pollination developed a method by which he could crosspollinate his pea plants, in order to conduct his experiments ¨ Mendel’s Experiments ¤ Mendel started his experiments with purebred plants n Purebred = plant that always produces offspring with the same form of a trait as the parent ¤ Mendel’s First Experiment n Mendel crossed 1 purebred tall plant with 1 purebred short plant (P1 generation) n The offspring of the P1 cross were called the first filial generation (F1 generation) n The offspring of the F1 cross were called the second filial generation (F2 generation) n See results in Figure 2, p. 78 n Note: the F2 offspring are ¼ short, ¾ tall - Mendel’s Work ¨ Other Traits (see Figure 3, p. 79) ¤ Mendel n Seed observed seven characteristics in total: shape – round or wrinkled n Seed color – yellow or green n Seed coat color – gray or white n Pod shape – smooth or pinched n Pod color – green or yellow n Flower position – side or end n Stem height – tall or short - Mendel’s Work ¨ Dominant and Recessive Alleles ¤ Mendel’s experiments taught him that individual genes must control the inheritance of traits in peas n Alleles n = the different forms of a gene Example: stem height gene has a tall allele and a short allele n The female parent gives one allele, the male parent gives one allele ¤ Mendel also learned that one allele can mask (hide) the other allele n Example: the tall allele masked the short allele in the F1 generation (Figure 2, p. 78) ¤ Individual alleles control the inheritance of traits n Dominant allele = one whose trait always shows up in the organism when the allele is present n Recessive allele = one whose trait is covered up whenever the dominant allele is present n Examples: If we cross two tall P1 plants, can we have a short F1 plant? n If we cross one tall P1 plant and one short P1 plant, can we have a short F1 plant? n Offspring are hybrids (they have two different alleles for the same trait) n If we cross two short P1 plants, can we have a short F1 plant? n ¨ Using Symbols in Genetics ¤ Scientists n A use letters to represent alleles in genetics dominant allele is represented by a capitol letter n Example: dominant tall stem height = T n A recessive allele is represented by the lowercase version of the dominant trait’s letter n Example: recessive short stem height = t two dominant parents produce offspring à TT ¤ When one dominant and one recessive parent produce offspring à Tt (hybrid) ¤ When two recessive parents produce offspring à tt ¤ When Chapter 3-2 Probability = the likelihood that a particular event will occur ¨ Principles of Probability ¨ ¤ If you tossed a coin… n What is the probability that the coin would land heads up? n What is the probability that the coin would land tails up? n In twenty tosses, how many would you predict would land heads up? ¤ The laws of probability predict what is likely to occur – not necessarily what will occur ¨ Probability and Genetics ¤ Mendel was the first scientist to recognize that the principles of probability can be used to predict the results of genetic crosses n Mendel counted the offspring of every cross he carried out n Example: Mendel crossed two plants hybrid for stem height (Tt x Tt) – ¾ of the F1 offspring had tall stems, ¼ had short stems n Therefore, the probability of producing long-stemmed offspring is 3 in 4, and the probability of producing short-stemmed offspring is 1 in 4 ¨ Punnett Squares ¤ Punnett square = chart that shows all the possible combinations of alleles that can result from genetic crosses n Punnett squares can also predict the probability of a particular outcome ¤ Phenotype n Examples: ¤ Genotype is present) = physical appearance (what it looks like) tall, green = genetic makeup (what allele combination n Examples: TT, Gg - Probability and Heredity - Probability and Heredity n Homozygous = an organism that has identical alleles for a trait n Examples: TT, tt, GG, gg n Heterozygous = an organism that has two different alleles for a trait (hybrid) n ¤ For Examples: Tt, Gg the following examples, use these abbreviations: n Homozygous dominant tall = TT n Heterozygous (hybrid) tall = Tt n Homozygous recessive short = tt ¤ Example: n P1: Purebred tall x Purebred tall n F1 result à all tall n 100% chance of being tall T T T TT TT T TT TT ¤ Example: n P1: Purebred tall x hybrid tall n F1 result à all tall n 100 % chance of being tall T T t T TT TT Tt Tt ¤ Example: Purebred tall x short n F1 result à all tall T n P1: n 100% chance of being tall T t Tt Tt t Tt Tt ¤ Example: hybrid tall x hybrid tall n F1 result à 3 tall, 1 short T n P1: 75% chance of being tall n 25% chance of being short n T t t TT Tt Tt $ ¤ Example: hybrid tall x short n F1 result à 2 tall, 2 short T n P1: 50% chance of being tall n 50% chance of being short n t t Tt $ t Tt $ ¤ Example: short x short n F1 result à all short t n P1: n 100% chance of being short t t $ $ t $ $ - Probability and Heredity ¨ Codominance ¤ Sometimes, a dominant allele and a recessive allele do not exist ¤ Codominance = alleles are neither dominant nor recessive n Examples: Chickens in Figure 10, p. 89 n Labrador retrievers (yellow, black, chocolate) n - Probability and Heredity Chapter 3-3 ¨ Chromosomes and Inheritance ¤ In 1903, Walter Sutton studied sex cells in grasshoppers ¤ Chromosome theory of inheritance = genes are carried from parents to their offspring on chromosomes n Sex cells (eggs and sperm) contain half the number of chromosomes of body cells ¤ Meiosis = the process by which the number of chromosomes is reduced by half to form sex cells (eggs and sperm) n See “Meiosis” on p. 94-95 - The Cell and Inheritance ¨ Meiosis and Punnett Squares ¤ See Figure 14, p. 95 ¤ Also, a Punnett square can be used to determine the probability of the gender of offspring n Example: n P1: XY (male) x XX (female) n F1 results à 2 females, 2 males n 50% chance of being male n 50% chance of being female X X X Y - The Cell and Inheritance - The Cell and Inheritance ¨ Chromosomes ¤ Organisms can vary greatly in the number of chromosomes in their body cells n Humans have 46 chromosomes (23 pairs) per body cell n Dogs have 78 chromosomes per body cell n Goldfish have 94 chromosomes per body cell n Note: larger organisms do not necessarily have more chromosomes! ¤ Although your body may only have 23 pairs of chromosomes, your body cells contain between 30,000 and 35,000 genes – each controlling a particular trait n That is why no two people are exactly alike! n See Figure 15, p. 96 Chapter 3-4 ¨ The Genetic Code ¤ The main function of genes is to control the production of proteins in the organism’s cells n Proteins help determine the size, shape, and many other traits of an organism ¤ Chromosomes are composed mostly of DNA ¤ DNA is composed of four different nitrogen bases (adenine, thymine, guanine, cytosine) single “rung” on the DNA “ladder” contains hundreds of millions of nitrogen bases n The nitrogen bases are arranged in a specific order n A n Example: ATGACGTAC ¤ The order of the nitrogen bases along a gene forms a genetic code that specifies what type of protein will be produced n Groups of three nitrogen bases result in the production of a specific amino acid n Amino acids combine to make proteins ¤ Think of the following analogy: n Nitrogen bases = letters n Amino acids = words n Protein = sentence ¨ How Cells Make Proteins ¤ Protein synthesis = the production of proteins n The cell uses information from a gene on a chromosome to produce a specific protein n Takes place on the ribosomes in the cytoplasm of the cell ¨ The Role of RNA ¤ RNA and DNA are similar, but differ in important ways looks like only one side of the “ladder” n RNA contains a different sugar than DNA n RNA has the nitrogen bases adenine, guanine, and cytosine, but has uracil (U) instead of thymine n RNA ¤ Types of RNA n Messenger RNA (mRNA) = copies the coded message from the DNA in the nucleus and carries the message to the cytoplasm n Transfer RNA (tRNA) = carries amino acids and adds them to the growing protein ¨ Translating the Code ¤ See “Protein Synthesis” p. 100-101 n Know steps one through four! ¨ Mutations ¤ Types of Mutations n Single-base substitution (Example: A attaches instead of G) n Chromosomes do not separate evenly during meiosis (resulting in too many or too few chromosomes) ¤ The Effects of Mutations n Helpful mutations – Example: new, better-tasting potatoes n Harmful mutations – Example: cancerous tumor n Neither helpful nor harmful mutations – Example: albino animal in captivity - The DNA Connection - The DNA Connection - The DNA Connection Chapter 4-1 ¨ Traits Controlled by Single Genes ¤ Many traits are controlled by a single gene with two alleles n Often one allele is dominant, and one allele is recessive ¤ Example: n P1 genotype: Ww x Ww n P1 n F1 Figure 2, p. 111 phenotype: widow’s peak x widow’s peak genotype: 1 WW, 2 Ww, 1 ww n F1 phenotype: ¾ widow’s peak, ¼ straight hair line ¨ Multiple Alleles ¤ Some human traits are controlled by a single gene with more than two alleles ¤ Multiple alleles = three or more forms of a gene that code for a single trait ¤ Example: Human blood types (Figure 3, p. 112) n There are four main blood types – A, B, AB, O n Three alleles control the inheritance of blood types The allele for type A and the allele for type B are codominant n The allele for type O is recessive n n Note: People with type O blood are “universal donors” n People with type AB blood are “universal recipients” n ¨ Traits Controlled by Many Genes ¤ Some human traits show a large number of phenotypes because the traits are controlled by many genes n Examples: Height – controlled by at least four genes n Skin color – controlled by at least three genes n ¤ The genes act together as a group to produce a single trait ¨ Male or Female? ¤ The sex of a baby is determined by genes on chromosomes ¤ Each human body cell has 23 pairs of chromosomes n One pair is made of two sex chromosomes The sex chromosomes determine the baby’s gender n The sex chromosomes are the only pair of chromosomes that do not always match n Remember from Chapter 3: XX (Female), XY (Male) n See Figure 5, p. 113 n ¨ Sex-Linked Genes ¤ Sex-linked genes = genes on the X and Y chromosome ¤ Because males have only one X chromosome, males are more likely than females to have a sex-linked trait that is controlled by a recessive allele n Example: red-green colorblindness See Figure 6, p. 114 n See Figure 7, p. 115 n It takes two recessive alleles to have a colorblind female n § Carrier = one who has a recessive allele, but does not have the trait n But, it takes only one recessive allele to have a colorblind male ¨ The Effect of the Environment ¤ The effects of genes are often altered by the environment ¤ Examples: n Diet n Due to better eating habits, the average height of adults in the U.S. has increased by almost 10cm in the last one-hundred years n Medical care n Living conditions Chapter 4-2 ¨ Genetic Disorders ¤ Genetic disorder = an abnormal condition that a person inherits through genes or chromosomes ¤ Genetic disorders are caused by mutations (changes in a person’s DNA) ¤ Examples: n Cystic fibrosis n Sickle-cell disease n Hemophilia n Down syndrome ¨ Cystic Fibrosis ¤ Cystic fibrosis = genetic disorder in which the body produces abnormally thick mucus in the lungs and intestines n Bacteria ¤ The grow in the mucus and cause infections mutation that causes cystic fibrosis is carried on a recessive allele ¤ Currently, there is no cure for cystic fibrosis ¨ Sickle-Cell Disease ¤ Sickle-cell disease = genetic disorder that affects the production of hemoglobin in blood n Hemoglobin = protein in red blood cells that carries oxygen n When oxygen concentrations are low, red blood cells take on an unusual shape n Figure 9, p. 118 n The sickle-shaped cells cannot carry as much oxygen and block blood vessels, resulting in pain and weakness ¤ The mutation that causes sickle-cell disease is codominant with the normal allele ¤ Currently, there is no cure for sickle-cell disease ¨ Hemophilia ¤ Hemophilia = genetic disorder in which a person’s blood clots very slowly or not at all n A person with hemophilia can bleed to death from a minor cut or scrape ¤ The mutation that causes hemophilia is caused by a recessive allele on the X chromosome (sex-linked disorder) ¤ Currently, there is no cure for hemophilia n People with hemophilia can live normal lives – they just have to be careful ¨ Down Syndrome ¤ Down syndrome = results when a person’s cells have an extra copy of chromosome 21 (due to an error in meiosis) ¤ People with Down syndrome have a distinctive physical appearance and some degree of mental retardation n p. 117 ¤ Heart defects are common, but can be treated ¤ Despite limitations, people with Down syndrome can lead full, active lives ¨ Pedigrees = a chart or “family tree” that tracks which members of a family have a particular trait ¤ Pedigree n Geneticists humans ¤ See use pedigrees to trace the inheritance of traits in Figure 10, p. 119 n Circle = female n Square = male n Colored shape = person has trait n Half-colored shape = person is carrier for trait n No color in shape = person does not have trait n Horizontal line = connects two married people n Vertical line & bracket = connects parents to children ¨ Diagnosing Genetic Disorders ¤ Scientists began diagnosing genetic disorders with Punnett squares and pedigrees ¤ Today, scientists use tools such as amniocentesis and karyotypes to help predict genetic disorders n Amniocentesis = procedure done before a baby is born which determines whether the baby will have some genetic disorders n Cells are taken from the fluid surrounding the baby n Karyotype n = picture of all the chromosomes in a cell Made from the cells taken by amniocentesis ¤ Genetic counseling = guidance for couples with family histories of genetic disorders Chapter 4-3 People have developed several ways to create organisms with desirable traits ¨ Selective breeding ¨ ¤ Selective breeding = the process of selecting a few organisms with desired traits to serve as parents for the next generation ¤ Techniques n Inbreeding = involves crossing two genetically similar individuals n Hybridization = involves crossing two genetically different individuals ¨ Cloning ¤ Clone = an organism that is genetically identical to the organism from which it was produced ¤ In plants, scientists grow new plants from cuttings (small parts of the original plant) ¤ In animals, scientists remove an egg, replace the nucleus, and implant the nucleus to develop n This process takes three different animals of the same species n This is controversial, since removing the nucleus can be considered “killing” a life ¨ Genetic Engineering ¤ Genetic engineering = genes from one organism are transferred into the DNA of another organism ¤ Also called “gene splicing” because DNA is cut open and genes are added ¤ Genetic engineering was first successful in bacteria n See n n We “Genetic Engineering” on p. 126 We use genetically engineered bacteria to create insulin (a drug to treat diabetes) also use bacteria to create human growth hormone (a protein controlling growth in children) ¤ Genetic Engineering in Other Organisms n Bacteria have been implanted into tomatoes, wheat, and rice to enable them to: Survive in colder temperatures n Grow in poor soil conditions n Resist insect pests n n Genes have been inserted into animals, which then create medicines for humans n Example: cows can produce a protein that clots blood – helping those with hemophilia ¤ Gene therapy = process of using genetic engineering to try to correct genetic disorders n Working copies of a gene are inserted directly into a person’s cells n Example: “engineered” viruses can be inserted into the lung cells of people with cystic fibrosis, helping them breathe ¨ DNA Fingerprinting ¤ DNA fingerprinting = identifying a person by their own unique DNA n Scientists have found ways gather DNA samples from hair, skin, and blood at crime scenes n These techniques have put many criminals in jail ¨ The Human Genome Project ¤ Genome = all the DNA in one cell of one organism n Researchers estimate that there are 20,000-25,000 genes in one cell’s DNA ¤ The main goal of the Human Genome Project is to identify the DNA sequence of every gene in the human genome n This would help us understand the following: How humans develop n What makes our bodies work n What causes things to go wrong in our bodies n Potential treatments/cures for genetic disorders and disease n