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Genetics.notebook Unit 3: Genetics October 26, 2012 1. Explain the significance of Mendel`s experiments and observations and the laws derived from them. a. Explain the concept of independent events. b. Understand that the probability of an independent event is not altered by the outcomes of previous events. Jun 241:36 PM Oct 232:58 PM Heredity • All organisms pass on their characteristics from generation to generation through INHERITANCE. • 2 kinds of characteristics inherited: 1. Species characteristics: each species always passes on their own traits. 2. Individual Characteristics: even though we inherit things equally from both parents, offspring is always different from their parents because we are a combination of both parents (i.e. mother's hair colour, father's build, mother's nose, etc.) Environment • Even though we inherit traits from our parents, our environment will affect the full potential of what we inherit. • Example: Food: people in Canada are bigger and taller than 100 years ago > Exercise: stronger, healthier bodies > Sunlight: lightens hair, darkens freckles Independent Events • Heredity is controlled by a chemical code in our DNA. • Another factor that will affect what we inherit are independent events. • This genetic code is present in the chromosomes of the gametes (egg and sperm). • An event that takes place that no previous event has an effect on. Oct 232:58 PM • Example: you broke your finger when you were six and it is now crooked. You will not pass this crooked finger on to any of your offspring, it is an independent event. Oct 233:03 PM 1 Genetics.notebook October 26, 2012 Probability InClass Discussion How does heredity affect you? • In genetics, we use a mathematical process called probability. Probability is the chance that an event will occur (i.e. the chance that you will have curly hair or blue eyes). • When determining probability, we do not consider items like the environment or independent events. What traits have you received that are NOT affected by the environment or independent events? What traits have you received that have been affected by the environment or independent events Instructions: 1. In groups of 2 or 3, discuss the 3 questions above, make a list of traits that have been inherited, and a list of traits that have been affected/altered. 2. Look at the list of traits that your group has made and decide which ones are most common and which ones are not as common....decide what this might have to do with the terms "dominant" and "recessive". Oct 233:07 PM List of Traits: Dominant or Recessive: Oct 233:09 PM Dominant and Recessive Genes Dominant Gene: determine the expression of the genetic trait in offspring. Dominant gene is given an upper case (capital) letter. Recessive Gene: genes that are overruled by dominant genes. Recessive gene is designated by a lower case letter. Other Examples: To determine some other examples of traits that are dominant or recessive, we will conduct a class survey. http://www.uni.edu/walsh/genetics.html Oct 249:13 AM Oct 249:28 AM 2 Genetics.notebook Review... 1. What does the term "heredity" mean? 2. What is the difference between a dominant and a recessive trait? Provide an example of each. October 26, 2012 1. Explain the significance of Mendel`s experiments and observations and the laws derived from them. c. Describe Mendel`s experiments and observations. d. Describe the relationship between genotype and phenotype. e. Use the concept of the gene to explain Mendel`s Laws. f. Describe the ideas of dominant and recessive traits with examples. h. Explain the law of segregation. Oct 249:14 AM GENETICS GENETICS: the branch of biology that studies the ways in which hereditary information is passed on from parents to offspring. GREGOR MENDEL: • (18221884) first to study heredity (monk). • studied pea plants (traits) and came up with some basic principles. • Peas: easy to grow, mature quickly, show sharply contrasting traits (tall vs. short, yellow vs. green, wrinkled vs. smooth). • Easy to cross pollinate for humans. • Kept careful records. Oct 249:14 AM Mendel and His Experiments • Gregor Mendel: Austrian monk 18221884 studied garden peas • Mendel studied peas and crossfertilized them by hand. Peas had specific traits that he studied. Crosses: Round seeds X Wrinkled(parents) Round Seeds(offspring) Tall plants X Short plants(parents) Tall Plants(offspring) Yellow seed coats X Green seed coats(parents) Yellow seed coats(offspring) Jun 241:36 PM Jun 241:36 PM 3 Genetics.notebook October 26, 2012 • Mendel discovered that genes control the traits of a plant. Genes are located on chromosomes. • Mendel also discovered that some genes are dominant over others (recessive). Ex) round seeds dominant over wrinkled seed tall plants dominant over short plants yellow seed coat dominant over green seed coats Dominant Gene: determine the expression of the genetic trait in offspring. Dominant gene is given an upper case (capital) letter. Recessive Gene: genes that are overruled by dominant genes. Recessive geneis designated by a lower case letter. Mendel's Laws of Heredity: 1. Inherited characteristics are controlled by genes. Genes happen in pairs. During fertilization 2 genes come together to form a pair. 2. Principle of Dominance one gene masks the effect of another. The gene for round seed coats masks the effect of the gene for wrinkled seed coats. Round is dominant over wrinkled. 3. Law of Segregation: Genes separate during the formation of sex cells. Organisms get one gene from each parent for a particular trait. During the formation of gametes (sex cells), alleles (form of a gene) separate randomly so that each gamete receives one or the other. The Law of Segregation deals with meiosis, which will be talked about later. • For each trait, an organism gets one gene form the mother and one gene from the father. Jun 241:36 PM Jun 241:36 PM Genotype: refers to the genes that an organism has for a particular trait. Ex) RR, Rr, rr; a round seed coat can have genotype RR or Rr, a wrinkled seed coat has only one genotype rr. YOU CAN'T TELL THE GENOTYPE BY JUST LOOKING AT AN ORGANISM Review.... Phenotype: refers to the observable traits of an organism, the traits that you see, Ex) there are only 2 phenotype for seed coat, wrinkled and smooth. 1. List and explain one of the new terms learned last day. Homozygous: an organism contains 2 genes for one trait that are the same, Ex) RR or rr : the organism is pure for the trait. 2. What was one of Gregor Mendal's laws? Heterozygous: an organism contains 2 genes for one trait that are different. Ex) Rr Alleles: two or more alternate forms of a gene. Ex) seed coat alleles Dominant R (smooth) Recessive r (wrinkled) Oct 249:35 AM Oct 249:41 AM 4 Genetics.notebook October 26, 2012 Monohybrid Cross 1. Explain the significance of Mendel`s experiments and observations and the laws derived from them. • Mono (one) • Hybrid (result from crosses between parents that are genetically not alike) g. Consider the value of the punnett square by creating examples of mono and dihybrid crosses. • Monohybrid Cross: a cross that involved one pair of contrasting genes for one trait. Oct 249:41 AM Jun 241:36 PM Ex) Dealing with the trait of Seed Coat Punnet Square for Monohybrid Cross Punnet Square: chart used by geneticists to show the possible combinations of alleles in offspring. Round seed coat X Wrinkled seed coat (parent) rr Crossed Again Hybrid Offspring X RR (F1 generation) Round Seed Coat (F = filial) Rr Wrinkled Parent (homozygous) r r Rr RR (F2 generation) Rr Rr rr R Round Parent (homozygous) R (F1 generation) all _ Rr, heterozygous Jun 241:36 PM Jun 241:36 PM 5 Genetics.notebook October 26, 2012 Monohybrid Cross Genotypic Ratio 1 RR (homozygous dominant) : 2Rr (heterozygous) : 1rr (homozygous recessive) Round Parent (heterozygous) r R Monohybrid Cross Phenotypic Ratio R 3 round : 1 wrinkled Round Parent (heterozygous) 3 with the dominant trait showing : 1 with the recessive trait showing r 3/4 or 75% : 1/4 or 25% (F2 generation) _ RR homozygous dominant, _ Rr heterozygous and _ rr homozygous (recessive) Jun 241:36 PM Jun 241:36 PM Lets look at this in more detail. Examples: X RR rr (parents) sex cells R R 1. Brown eyes (B) are dominant over blue eyes. If a parent homozygous for blue eyes produce offspring. What are the chances that the offspring has brown eyes? blue eyes? sex cells r r Rr (F1 generation) X Rr Parent A = BB Parent B = bb RR (F2 generation) Rr Rr round Jun 241:36 PM sex cells R r rr wrinkled Oct 241:03 PM 6 Genetics.notebook 2. In plants, tall (T) is dominant over short (t). Two plants, that are tall, are crossed and produce a plant that is short. Determine the genotype of the parents. October 26, 2012 3. In guinea pigs, curly hair (C) is dominant over straight hair (c). If two guinea pigs that have curly hair and are straight hair carriers mate, what is the chance they have a straight haired offspring? Genotype of parents = short plant = tt Oct 241:06 PM 1. Explain the significance of Mendel`s experiments and observations and the laws derived from them. g. Consider the value of the punnett square by creating examples of mono and dihybrid crosses. Oct 242:24 PM Oct 241:18 PM Review Question.... 1. Both a hen and a rooster are heterozygous trait carriers. They both have a trait to be black (B) and a trait to be white (b). Black is the dominant colour, what will the phenotypes and genotypes of their offspring be? Oct 241:00 PM 7 Genetics.notebook October 26, 2012 Example of a dihybrid cross: Yellow Round Dihybrid Cross X Green Wrinkled (parent) Di = 2 Hybrid: result from crosses between parents that are genetically not alike. Dihybrid cross: a cross that involves 2 traits. (gametes YR) yyrr YYRR (gametes yr) Crossed Again (F1 generation) X Yellow Round YyRr (gametes = YR, Yr, yR, yr) YyRr (gametes = YR, Yr, yR, yr) (F2 generation) 1 YYRR, 2 YyRR, 2 YYRr, 4 YyRr, 1 YYRR, 2 yyRr, 1 yyrr, 1 YYrr Jun 241:36 PM Jun 241:36 PM Punnet Square for Dihybrid Cross YyRr yyrr Green and Wrinkled Parent (homozygous) YYRR Parent Yellow & Round (homozygous) yr yr YR YR (F1 Generation) _ YyRr (yellow & round, heterozygous) YR YyRr Yellow & Round Parent (heterozygous) Yr yr yR YR Yellow & Round Yr Parent (heterozygous) yR yr • Dihybrid Cross Phenotypic Ratio 9/16 Yellow & Round : 3/16 Yellow & Wrinkled : 3/16 Green & Round : 1/16 Green & Wrinkled **Remember** Dihybrid Cross = 9 : 3 : 3 : 1 Jun 241:36 PM Jun 241:36 PM 8 Genetics.notebook October 26, 2012 2. In guinea pigs, black coat colour (B) is dominant to white (b), and short hair length (S) is dominant to long (s). Indicate the genotypes and phenotypes from the following crosses: Examples.... 1. Black coat colour (B) in cocker spaniels is dominant to white coat colour (b). Solid coat pattern (S) is dominant to spotted pattern (s). A male that is black with a solid pattern mates with two females. The mating with female A which is white, solid, produces four pups: 2 black, solid, and two white, solid. The mating with female B, which is black, solid, produces a single pup, which is white, spotted. Indicate the genotypes of the parents. a) Homozygous for black, heterozygous for shorthair guinea pig crossed with a white, longhaired guinea pig. b) Heterozygous for black and shorthair guinea pig crossed with a white, longhair guinea pig. Oct 241:20 PM c) Homozygous for black and longhair crossed with a heterozygous black and shorthair guinea pig. Oct 241:26 PM 2. Discuss the relationship among chromosomes, genes, and DNA. h. Examine incomplete dominance, alleles, sex determination, and sex linked traits in the context of human genetics. i. Discuss several human genetic disorders such as hemophilia, sicklecell anemia, Down`s syndrome, and TaySach`s disease. Oct 241:29 PM Oct 242:27 PM 9 Genetics.notebook October 26, 2012 Test Cross There is an organism showing the dominant trait but it is unknown if the organism is homozygous or heterozygous, it's genotype is unknown. To figure out the genotype you cross the unknown genotype and a homozygous recessive genotype. If the offspring all show the dominant trait, the unknown genotype is homozygous dominant. If any of the offspring show the recessive trait, the unknown genotype was heterozygous dominant. Jun 241:36 PM Jun 241:36 PM Incomplete Dominance Determine the genotype of the parent plants by looking at the phenotypes of the offspring from the following cross. The lack of a dominant gene. Both alleles contribute to the phenotype of a heterozygote. Produces an offspring with traits unlike either parent. Round, yellow X Wrinkled, green Ex) 1/4 round, yellow, 1/4 round, green, 1/4 wrinkled, yellow, 1/4 wrinkled, green Red snapdragon (RR) X White snapdragon (WW) F1Generation All Pink Snapdragons (RW) RW F2Generation X RW R W R W 1 RR (red) : 2RW (pink) : 1 WW (white) Jun 241:36 PM Jun 241:36 PM 10 Genetics.notebook October 26, 2012 Codominance • Two dominant genes are expressed at the same time in the heterozygous organism. Ex) Shorthorn Cattle Red (H RHR) X White (HW HW ) Roan Calf it has intermingling of white and red hair Multiple Alleles • The problem we have dealt with so far only have dealt with 2 alleles the dominant allele and the recessive allele. The dominant allele controlled the trait. • Multiple Alleles when more than 2 different alleles exist for a trait. Ex) the fruit fly Drosophilz many different eye colors are possible. Red (wild type) eyes : most common F1 Generation (all) HRHW X HRHW Dominant Hierarchy Apricot Honey F2 Generation HR HW HR White Note: a drosophila can only have 2 different genes at one time, but many alleles are possible. Hw 1 HRHR : 2HRHW : 1HW HW Jun 241:36 PM • When using multiple alleles we no longer use upper and lower case letters. Capital letters with subscript numbers are used. Jun 241:36 PM Ex) Human Blood Typing: example of codominance and multiple alleles • The ABO blood typing system in humans is determined by a set of 3 alleles multiple alleles. IA, IB , i • Different combinations of these alleles in people produce 4 different blood types. Type A, Type B, Type AB, Type O Red (wild type) eyes E1E1 OR E1E2, E1E3, E1E4 Apricot E2E2, E2E3, E2E4 Honey E3E3, E3E4 White E4E4 Genotype Phenotype IAIA or IAi Type A Blood IB IB or IB i Type B Blood IAI B Type AB Blood * ii Type O Blood * This is codominance different alleles expressing their full phenotype in a heterozygote, giving a new phenotype. Jun 241:36 PM Jun 241:36 PM 11 Genetics.notebook October 26, 2012 Exceptions to Mendel's Laws Example Questions... 1. For ABO blood groups, the A and B genes are codominant, but both A and B are dominant over type O. Indicate the blood types possible from the mating of a male who is blood type O with a female of blood type AB. Exceptions to Mendel's Laws Example Questions... 3. Thalassemia is a serious human genetic disorder that causes severe anemia. The homozygous condition (TmTm) leads to sever anemia. People with thalassemia die before sexual maturity. The heterozygous condition (TmTn) causes a less serious form of anemia. The genotype TnTn causes no symptoms of the disease. Indicate the possible genotypes and phenotypes of the offspring if a male with the genotype TmTn marries a female of the same genotype. 2. Could a female with blood type AB ever produce a child with blood type AB? Could she ever have a child with blood type O? Oct 241:39 PM Review... 1. What is incomplete dominance? Provide an example. 2. What is meant by the term "multiple alleles?" Provide an example. Oct 241:40 PM 2. Discuss the relationship among chromosomes, genes, and DNA. h. Examine incomplete dominance, alleles, sex determination, and sex linked traits in the context of human genetics. i. Discuss several human genetic disorders such as hemophilia, sicklecell anemia, Down`s syndrome, and TaySach`s disease. 3. What is codominance? Oct 241:41 PM Oct 241:41 PM 12 Genetics.notebook Incomplete Dominance Examples... A cross between a blue blahblah bird and a white blahblah bird produces offspring that are sliver. The color of blahblah birds is determined by just two alleles. a) What are the genotypes of the parent blahblah birds in the original cross? October 26, 2012 Incomplete Dominance Examples... 1. The color of fruit for Golgi plants is determined by two alleles. When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit. What are the genotypes of the parent orange-fruited plants? b) What is/are the genotyp(s) of the silver offspring? c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds? Oct 241:41 PM Co-dominance Example Problem... 1. Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull? Oct 241:42 PM Multiple Alleles Example Problem... 1. Remembering what you learned about blood types, what are the possible phenotypes of children in the following families? a) Heterozygous type A mother, Homozygous type A father? b) Homozygous type B mother, type AB father? 2. What should the genotypes and phenotypes for parent cattle be if a farmer wanted only cattle with red fur? c) type AB mother, type AB father? Oct 241:42 PM Oct 241:42 PM 13 Genetics.notebook October 26, 2012 Sex - Linked Traits 2. Discuss the relationship among chromosomes, genes, and DNA. h. Examine incomplete dominance, alleles, sex determination, and sex linked traits in the contexts of human genetics. i. Discuss several human genetic disorders such as hemophilia, sicklecell anemia, Down`s syndrome, and TaySach`s disease. • Sexlinked traits : controlled by genes located on the sex chromosomes. • In humans the sex chromosomes go as follows: Female = XXMale = XY • The X chromosomes are relatively the same size. In a female you have two homologous X chromosomes. Locus: the actual site of the gene on a chromosome. j. Discuss the similarities and differences between sex chromosomes and somatic chromosomes. X Oct 241:43 PM In a male you have one large X chromosome and a smaller Y chromosome. The Y chromosome is shorter than the X chromosome. Some of the genes on the X chromosome may be missing on the Y chromosome. There is nothing to match. X Y X Jun 241:36 PM Sexlinked disorders in Humans: 1. ColorBlindness: person can't perceive certain colors, usually red and green. : more common in males than females. : Females may be carriers for it, because they have the recessive allele for colorblindness on one X chromosome and the normal dominant allele on the other X chromosome. Female Carrier Normal Female Colorblind Female XX' XXX'X' • Most sexlinked traits are determined by genes found on the X chromosome but not on the Y chromosome. Jun 241:36 PM Jun 241:36 PM 14 Genetics.notebook October 26, 2012 • Every male gets an X chromosome from its mother and a Y chromosome from his father. Mother = XX Father = XY Male Offspring Male Offspring • In order for a female to be color blind, she must inherit the color blind allele from both parents and this is a rare event. XY Mother a Carrier XX' • Since the Y chromosome is smaller than the X, the Y chromosome has no spot for color vision. When a son gets the defective color blind allele from his mother the color blindness is expressed and the son is color blind. Father XY Mother XX' Father X'Y ColorBlind Female Offspring X'X' XY or X'Y Remember: colorblindness is transmitted only through the female. There is a 50% chance that the male son will have color blindness. Jun 241:36 PM Jun 241:36 PM Somatic Cells: are all the cells of an organism except the sex cells. 2. Hemophilia: sexlinked disorder in which the blood is unable to clot because it lacks a certain bloodclotting protein. : the recessive gene for hemophilia is carried on the X chromosome. What is a somatic chromosome based on what you know about somatic cells? : Most affected individuals are male. : Females with one recessive genes are carriers but show no sign of the illness. : Smallest cut or bruise can cause the person to bleed severely. Jun 241:36 PM What is the difference between sex chromosomes and somatic chromosomes? Oct 269:43 AM 15 Genetics.notebook October 26, 2012 Pedigree Pedigree means of tracing sexlinked traits in family trees through a pictorial representation females are represented by circles, males are represented as squares. matings are shown by horizontal lines connecting two individuals offsprings are connected by vertical lines to the mating line different shades or colors added to the symbols represent carious phenotypes each generation is listed on a separate row labeled with Roman Numerals Oct 241:45 PM Review... 1. Explain why it is more likely for a male child to be born colorblind if his father is normal, but his mother is a carrier for colorblindness. Jun 241:36 PM 2. Discuss the relationship among chromosomes, genes, and DNA. a. Describe how the genetic code is carried on the DNA. i. Discuss several human genetic disorders such as hemophilia, sicklecell anemia, Down`s syndrome, and TaySach`s disease. Oct 241:46 PM Oct 241:46 PM 16 Genetics.notebook Chromosomes Chromosomes: long threads of genetic material found in the nucleus of cells : made up of nucleic acids and proteins : humans have 46 chromosomes (23 pairs) Genes: located on the chromosomes made up of DNA units of instruction, located on chromosomes that produce or influence a specific trait in offspring. October 26, 2012 Diploid Chromosome Number: (2n) the full compliment of chromosomes. Everyday cells in the body, except sex cells have a diploid chromosome number (ex Humans = 46) Haploid Chromosome Number: (n) one half of the full compliment of chromosomes. Sex cells have haploid chromosome number (ex Humans=23) Homologous Pairs/Homologous Chromosomes: are similar in size, shape, and gene arrangement. Get one from each parent (ex 23 pairs in humans). DNAdeoxyribonucleic acid: carries the genetic code, carries genetic information. Jun 241:36 PM Karyotype: pictures of chromosomes arranged in homologous pairs. Jun 241:36 PM Sex Chromosomes: chromosomes that determine the sex of an individual. Ex) Human pair #23 XY = male XX = female Somatic Chromosome/Autosomes: chromosomes not involved with sex determination. Ex) Human pairs #'s 122. Monosomy: is the presence of a single chromosome in place of a homologous pair. Ex) Turner's Syndrome: a female that has a single X chromosome (pair #28). Only females, do not develop sexually, tend to be short and have thick wide necks. Jun 241:36 PM Jun 241:36 PM 17 Genetics.notebook Trisomy: the presence of three homologous chromosomes in place of homologous pair. Ex) Down's Syndrome: an extra chromosome for pair #21. Often called trisomy 21. Characteristics include round full face, enlarged creased tongue, short height, large forehead and decreased mental capabilities. October 26, 2012 2. Discuss the relationship among chromosomes, genes, and DNA. b. Outline the process of replication. d. Describe the process of transcription. e. Describe the functions of mRNA, tRNA, amino acids, and ribosomes in protein synthesis. Ex) Klinefelter Syndrome: 3 sex chromosomes (XXY). Appears to be male, @ puberty produces large amounts of female hormones. Sterile. Jun 241:36 PM Protein Synthesis 1. Transcription Oct 242:41 PM 2. Discuss the relationship among chromosomes, genes, and DNA. f. Describe the causes and effects of both chromosomes and gene mutations. 2. Translation Jun 241:36 PM Oct 242:51 PM 18 Genetics.notebook October 26, 2012 2. Discuss the relationship among chromosomes, genes, and DNA. Mutations Handout k. Using examples from living organisms discuss the importance of asexual and sexual reproduction to their growth and survival. Jun 241:36 PM Asexual vs. Sexual Reproduction a. Asexual Reproduction • Asexual cell division = mitosis producing 2 daughter cells identical to the parent cell. • Asexual reproduction in organisms involves one parent with the offspring looking identical to nearly identical to the parent. • Cloning is a type of asexual reproduction. • Budding is a type of asexual reproduction (ex. hydra, strawberries). • There is no variation in traits with asexual reproduction, this is dangerous because what happens if there is a change in environment. Jun 241:36 PM Oct 242:42 PM b. Sexual Reproduction: • Sexual cell reproduction = meiosis producing gametes that have genetic variation. • Animals that reproduce sexually have male and female sexes. They produce gametes through the process of meiosis. • Humans reproduce sexually. • In sexual reproduction there is diversity and genetic variation. • An advantage of sexual reproduction is that there is variety in the population and some organisms may be better able to survive (survival of the fittest); or if there is an environmental change some organisms may survive while others may not. Jun 241:36 PM 19 Genetics.notebook October 26, 2012 Mitosis... • The process in which the cell triggers itself to asexually reproduce forming 2 identical daughter cells from 1 parent cell • Necessary for growth and to replace injured cells • Before the mother cell splits, the chromosomes in it have duplicated into 2 sets. • When the mother cell splits, 1 set of chromosomes goes to each of the 2 daughter cells. • The process a cell goes through to duplicate itself is called the cell cycle, and looks like this: 2. Discuss the relationship among chromosomes, genes, and DNA. c. Compare mitosis and meiosis. Oct 242:40 PM Mitosis 1st INTERPHASE Oct 241:47 PM Cell division occurs in a series of stages, or phases. 3rd: METAPHASE • Chromatids (or pairs of chromosomes) attach to the spindle fibers. • Chromosomes are copied (# doubles). • Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy (sister chromosome) change to sister chromatids at end of this phase. sister chromatids centromere 4th: ANAPHASE 2nd: PROPHASE • Mitosis begins (cell begins to divide) • Centrioles (or poles) appear and begin to move to opposite ends of cell. • Spindle fibers form between the poles. Jun 241:36 PM • Chromatids (or pairs of chromosomes) separate and begin to move to opposite ends of the cell. sister chromatids split Jul 282:05 PM 20 Genetics.notebook October 26, 2012 5th: TELOPHASE • Two new nuclei form • Chromosomes appear as chromatin (threads rather than rods) • Mitosis ends One final note... During telophase in plant cells, a cell plate forms in the center and grows outward creating a cell wall (rather than the cell membrane pinching inward). 6th: CYTOKINESIS • Cell membrane moves inward to create two daughter cells each with its own nucleus with identical chromosomes. Jul 282:05 PM Review... 1. What happens, most importantly, during interphase? cell plate Oct 241:48 PM 2. Discuss the relationship among chromosomes, genes, and DNA. c. Compare mitosis and meiosis. 2. What is the end result of mitosis? Oct 241:49 PM Oct 241:50 PM 21 Genetics.notebook October 26, 2012 Meiosis... • Is the process that takes place in the sex organs of all living organisms in order to produce haploid sex cells (also known as gametes). • This process is absolutely essential, otherwise at fertilization, when two gametes unite together, there would be too many chromosomes! • In humans, meiosis reduces the number of chromosomes from 46 to 23, so that every sperm or egg cell has 23 chromosomes. At fertilization, 23 chromosomes from the sperm unite with 23 chromosomes from the egg to produce the original 46 chromosomes. Meiosis : two divisions of chromosomes a. MEIOSIS I = first round of divisions; stage where the chromosome # is reduced by half i) INTERPHASE I: as in interphase of mitosis, it is the period during which the cell grows and replicates its chromosomes ii) PROPHASE I Oct 241:50 PM each tetrad moves onto a spindle and attaches to a single fibril at the equator iv) ANAPHASE I Oct 241:52 PM v) TELOPHASE I iii) METAPHASE I Early Prophase I: chromosomes appear as long, thin threads nucleoli starts to disappear and centrioles move to opposite ends of the cell Middle Prophase I: the chromosomes come together in homologous pairs through the process of synapsis (intertwining) each homologous pair is composed of chromatids and is referred to as a tetrad intertwined chromatids may break and exchange segments = crossing over tetrads become shorter and thicker Late Prophase I: centrioles are at opposite poles spindle formation is complete nucleus begins to dissolve the two sets of double stranded chromosomes become enclosed in new nuclei chromosomes remain double stranded and disappear cytokinesis occurs creating two haploid daughter cells that are NOT identical centromeres do not divide and homologous chromosomes move apart to opposite poles in a process called segregation now, half the number of double stranded chromosomes at each pole Oct 241:52 PM Oct 241:52 PM 22 Genetics.notebook October 26, 2012 b) MEISOSIS II: occurs in both haploid daughter cells at the same time iii) ANAPHASE II Interkinosis: basically interphase, except there is no replication of chromosomes the centromere holding each pair of sister chromatids together dissolves sister chromatids move to opposite poles i) PROPHASE II nuclear membrane dissolves centrioles move and spindles form doublestranded chromosomes shorten and thicken iv) TELOPHASE II ii) METAPHASE II doublestranded chromosomes attach the spindle and line up at the equator Oct 241:53 PM Review... nuclear membranes are restored, spindles disappear, and cytokinesis occurs results in 4 haploid daughter cells that are different from each other and the parent cell Oct 241:55 PM 2. Discuss the relationship among chromosomes, genes, and DNA. 1. What is the end result of meiosis? 2. Why must our sex cells be produced through meiosis and not mitosis? Oct 241:56 PM g. Consider the purposes and techniques of gene mapping. Oct 242:53 PM 23 Genetics.notebook October 26, 2012 Genetic Engineering Activities Gene Mapping • there are approximately 100 thousand genes in the nucleus of each human cell among the 46 chromosomes. Human Genome • all the genes that make up the 'master blue print' • 3 billion base pairs of nucleotide bases that make up DNA Jul 282:05 PM Human Genome Project • to identify the full set of genetic instructions contained in our cells and to read the complete text written in DNA. • Worked on by 100's of biologists, chemists, engineers, mathematicians, etc. all over the world. • Will revolutionize our understanding of how genes control the function of the human body. • Provide new strategies to diagnose, treat, prevent human diseases. • Estimate to take 15 years. 1) complete maps of the 46 chromosomes 2) sequence the DNA in chromosomes • it's like shedding an encyclopedia and trying to put it back together again so it can be read. Consider: • Body made of several trillion body cells. • Each cell has 46 chromosomes in nucleus. • Each chromosome is made of DNA with thousands genes. • 3 billion base pairs make of DNA. Jul 282:05 PM 3. Delineate the impact of biotechnology on our society. a. Describe the basic processes involved in the production of recombinant DNA. b. Discuss examples of current uses of recombinant DNA technology in the agricultural and pharmaceutical industries. Research Project c. Discuss techniques of genetic screening. d. Consider the implications of genetic screening of adults, children, and fetuses. Oct 242:44 PM Oct 242:54 PM 24 Genetics.notebook October 26, 2012 4. Discuss the application of population genetics to the study of evolution. a. Describe the concepts of the deme and gene pool. b. Consider the HardyWeinberg principle. c. Describe the factors which influence genetic drift. Population Genetics Activities d. Consider the relevance of the gene pool and the idea of mutations to the concept of evolution. Oct 242:46 PM Jul 282:05 PM 25