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Biology Chapter 11 Introduction to Genetics: Mendel and Meiosis IQ #1 1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis? 2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo? 3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have? Section 11-4: Meiosis I. MEIOSIS A. Meiosis= process of _________________________ in which the number of Reduction Division chromosomes per cell is cut in 1/2 and the homologous chromosomes that exist in a diploid cell are separated. (and produce haploid cells) B. Purpose=Form gametes (egg and sperm) II. DIPLOID AND HAPLOID CHROMOSOME NUMBER A. During ________________ the genetic material fertilization from one parent combines with genetic material from another Example: A fruit fly has 8 chromosomes A set of 4 came from the female fly A set of 4 came from the male fly B. The two sets of chromosomes are said to be homologous = a female chromosome has a corresponding male chromosome. C. Diploid (2n)=contain both sets of homologous chromosomes D. Haploid (n)= contain 1 set only Male gamete Sperm (n) = 23 chromosomes Female gamete Egg (n) = 23 chromosomes Question: If we start with a diploid cell, how do we get an organism that produces haploid gametes? Answer:Meiosis (aka: reduction division) 1 replication; 2 divisions Example: 46 Human what if: 16 92 46 8 Fruit fly Duplicated 8 46 Duplicated chromosomes 8 chromosomes 23 23 23 23 4 4 4 4 III. PROCESS OF MEIOSIS (DIVIDED INTO 2 STAGES: MEIOSIS I & II INTERPHASE: growth, DNA synthesis, protein production, organelle production A. Meiosis I prophase I chromosomes tetrads) 2n 1. homologous pair up (Form 2. nucleoli disappear 3. nucleus disappears 4. crossing-over occurs: portions of chromatids exchange genetic material (diagram 277) Crossing-Over Crossing Over: exchange of genetic material between homologous chromosomes Go to Section: Crossing Over Go to Section: Crossing-Over Crossing Over Go to Section: metaphase I 1. homologous pairs (tetrads) line up at the equator 2. spindles attach to chromosomes independent assortment occurs anaphase I 1. spindles pull the homologous chromosomes toward opposite ends of the cell Key point: homologous pairs separate, cell now haploid Telophase I 1. Nuclear membranes reform n n 2. cell begins to separate into two new haploid cells 3. 2 haploid daughter cells Figure 11-15 Meiosis Meiosis I Section 11-4 Interphase I Prophase I chromosome pairs with Cells undergo Each its corresponding a round of DNAhomologous chromosome to form a tetrad. replication, forming duplicate Chromosomes. Go to Section: Metaphase I Anaphase I Spindle fibers attach to the chromosomes. The fibers pull the homologous chromosomes toward the opposite ends of the cell. Figure 11-15 Meiosis Meiosis I Section 11-4 Interphase I Prophase I Metaphase I Anaphase I Cells undergo a round of DNA replication, forming duplicate Chromosomes. Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. Spindle fibers attach to the chromosomes. The fibers pull the homologous chromosomes toward the opposite ends of the cell. Go to Section: Figure 11-15 Meiosis Meiosis I Section 11-4 Interphase I Prophase I Metaphase I Anaphase I Cells undergo a round of DNA replication, forming duplicate Chromosomes. Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. Spindle fibers attach to the chromosomes. The fibers pull the homologous chromosomes toward the opposite ends of the cell. Go to Section: Figure 11-15 Meiosis Meiosis I Section 11-4 Interphase I Prophase I Metaphase I Anaphase I Cells undergo a round of DNA replication, forming duplicate Chromosomes. Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. Spindle fibers attach to the chromosomes. The fibers pull the homologous chromosomes toward the opposite ends of the cell. Go to Section: B. Meiosis II (similar process as mitosis; no replication) Prophase II Metaphase II Anaphase II Telophase II/ Cytokinesis n n n ***RESULT: 4 haploid daughters that are genetically different!! n Figure 11-17 Meiosis II Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Go to Section: Telophase II Meiosis II results in four haploid (N) daughter cells. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II Go to Section: Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Metaphase II The chromosomes line up in a similar way to the metaphase stage of mitosis. Anaphase II Telophase II The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells. Figure 11-17 Meiosis II Meiosis II Prophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of Go to chromosomes as Section:the original. Metaphase II Anaphase II The chromosomes line up in a The sister chromatids similar way to the metaphase separate and move toward stage of mitosis. opposite ends of the cell. Telophase II Meiosis II results in four haploid (N) daughter cells. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of Go to chromosomes as Section:the original. Metaphase II The chromosomes line up in a similar way to the metaphase stage of mitosis. Anaphase II The sister chromatids separate and move toward opposite ends of the cell. Telophase II Meiosis II results in four haploid (N) daughter cells. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of Go to chromosomes as Section:the original. http://www.sumanasinc.com/webcontent/anisampl es/majorsbiology/meiosis.html Metaphase II The chromosomes line up in a similar way to the metaphase stage of mitosis. Anaphase II The sister chromatids separate and move toward opposite ends of the cell. Telophase II Meiosis II results in four haploid (N) daughter cells. IV. GAMETE FORMATION (refer to page 278) A. Males The 4 haploid cells (gametes) = sperm 1. 2. male gametes produced by a process called _________________ spermatogenesis B. Females 1. 4 haploid cells are produced but only viable egg 1-haploid cell is a 3-producepolar bodies caused by uneven cytoplasmic division 2. female gametes produced by a process called _______________ oogenesis (a) In the male, all four haploid products of meiosis are retained and differentiate into sperm. (b) In the female, both meiotic divisions are asymmetric, forming one large egg cell and three (in some cases, only two) small cells called polar bodies that do not give rise to functional gametes. Although not indicated here, the mature egg cell has usually grown much larger than the oocyte from which it arose. V. COMPARING MITOSIS AND MEIOSIS A. Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells. http://biologyinmotion.com/cell_division/ Mitosis Number of daughter cells Type of cells produced Number of divisions Number of replications Purpose of division 2 diploid cells Body cells Meiosis 4 haploid cells gametes 1 2 1 1 Sexual Growth, replacement, repair, asexual reproduction reproduction Section 11-1 Standards addressed: CA 3.b. Students know the genetic basis for Mendel’s laws of segregation and independent assortment. National 7 2.c. Students know an inherited trait can be determined by one or more genes. 7.2.d. Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining phenotype while the other is recessive. B1. 2.d. Students know new combinations of alleles may be generated in a zygote through the fusion of male and female gametes (fertilization). Key Ideas: What is the principle of dominance? What happens during segregation? INTRODUCTION TO GENETICS I. The work of Gregor Mendel A. Genetics : the scientific study of heredity B. Heredity: Passing genes from generation to generation II. Gregor Mendel's Peas A. In the 1800's, _____________________________ (an Gregor Mendel Austrian Monk) conducted the first scientific study of heredity using pea plants. B. Pea plants contain both male (pollen:sperm) and female (eggs) reproductive parts. Flowering Plant Structures: Pea Plant C. _______________ Fertilization = Joining of male and female reproductive cells D. _________________= a pea plant whose pollen Self-pollination fertilizes the egg cells in the very same flower. 1. Mendel discovered that some plants ___________ “Bred True” for certain traits 2. Trait= Specific Characteristics Example: seed color, plant height 3.True breeding (a.k.a. pure)= Peas that are allowed to self-pollinate produce offspring identical to themselves Example: Short plants that self pollinate for generations always produce offspring that were pure for shortness. Cross Pollination Self pollination E. Cross-pollination _______________= male sex cells from one flower pollinate a female sex cell on a different flower. F. Mendel manually cross pollinated pea plants, removing the male parts to ensure no selfpollination would occur. Through a series of experiments, Mendel was able to make discoveries of basic principles of heredity. 1. principle of Dominance 2. principle of Segregation 3. principle of Independent Assortment III. Experiments Mendel performed A. Mendel studied7 __ different traits in pea plants each with 2 contrasting characters. (refer to page 264) B. Each trait Mendel studied was controlled by one gene. C. Different forms of a gene (trait) Alleles = Example: Gene for plant height has 2 alleles Dominant: T = tall Recessive: t = short Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Mendel’s Seven Crosses on Pea Plants Section 11-1 Go to Section: Seed Coat Color Pod Shape Pod Color Smooth Green Seed Shape Seed Color Round Yellow Gray Wrinkled Green White Constricted Round Yellow Gray Smooth Flower Position Plant Height Axial Tall Yellow Terminal Short Green Axial Tall Mendel Experiment #1: Parent Offspring pure bred tall x pure bred tall TT X TT All plants are TALL pure bred short x pure bred short tt X tt Pure bred tall x pure bred short TT X tt All plants are SHORT All plants are TALL Conclusion: · individual factors (now known as genes _________) · the factors did not blend ________________________________= some alleles Principle of Dominance are dominant (expressed trait;written as a capital letter; ex. T) some are recessive (hidden/masked trait; written as a lower case letter; ex. t) From these conclusions, Mendel wanted to continue his experiments to see what happened to the recessive trait Principles of Dominance Section 11-1 P Generation Tall Go to Section: Short F1 Generation Tall Tall F2 Generation Tall Tall Tall Short Principles of Dominance Section 11-1 P Generation Tall Go to Section: Short F1 Generation Tall Tall F2 Generation Tall Tall Tall Short Principles of Dominance Section 11-1 P Generation Tall Short F1 Generation Tall Tall F2 Generation Tall Tall Tall 3 tall : 1 short Go to Section: Short Conclusion: · ___________________________: The Principle of Segregation reappearance of the recessive allele indicated that at some point the allele for shortness separated from the allele for tallness. Mendel suggested that the alleles separated during the formation of the sex cells (gametes)….During meiosis. IV. PROBABILITY AND PUNNETT SQUARES The likelihood that a particular A. Probability = event will occur # of times a particular event occurs B. Probability= # of opportunities for the event to occur (# of trials) Example #1: If you flip a coin, what is the probability of landing on heads? Probability=1 (side that has a head on it) 2 2( opportunities on a coin; head or tails) Example #2: If you flip a coin 3 times what is the x ½ x ½ = 1/8 probability of landing on heads? ½Probability= A. Each flip is independent of the next. Past outcomes do not affect future ones. Similar to alleles that segregate randomly, like a coin flip. B. Thelarger the number of trials the closer you get to the expected outcomes C. The principles of probability can be used to predict the outcomes of genetic crosses. IV. PUNNETT SQUARES Use of Punnett squares help determine the probable outcomes of genetic crosses. · New vocabulary to help with Punnett squares -Homozygous =Having 2 identical alleles (TT, tt) Having 2 different alleles -Heterozygous= (Tt) Genetic makeup of an organism (TT, tt, -Genotype= Tt) Physical appearance (tall or -Phenotype= short) The offspring resulting from a cross -Hybrids= between parents of contrasting traits Example of a Punnett square: Parent (P) cross homozygous tall( TT) x homozygous short( tt ) · t T Tt T Tt t Tt Tt F1 offspring Probability of producing homozygous tall offspring? 0/4 Probability of producing hybrid? 4/4 IV. PROBABILITY AND SEGREGATION A. For fun, lets cross F1’s to see if Mendel’s assumption about segregation are correct: Tt x Tt T t T TT Tt t Tt tt If the alleles segregate during meiosis, then the probable outcomes will be: TT= 1/4 Tall= 3 Tt= 2/4 Short= 1 tt= 1/4 Ratio tall:short= 3:1 Conclusion: Mendel was correct in his assumptions about Segregration IV. PROBABILITY AND INDEPENDENT ASSORTMENT A. Mendel wondered if one pair of alleles affected the segregation of another pair of alleles. Do round seeds have to be yellow? B.The two factor cross: Mendel crossed RRYY x rryy (P)(aka:two trait cross) All offspring are Hybrid (RrYy) (F1) A. Then he crossed the hybrids (F1): RrYy x RrYy · Punnett square formatting rules for 2 trait crosses 1. Determine the possible gametes produced by the parents. 2 methods: irst two (RY) a. F-utside two RrYy (Ry) (rY) Onside two (ry) I-ast two L- a. Use a punnett square. One trait on top and the other trait on the side. Parent 1: RrYy y Y Parent 2: RrYy Y y R RY Ry R RY Ry r rY ry r rY ry Possible gametes Possible gametes 2. Place one parent’s gametes at the top of a 16Punnett square and the other parent’s gametes on the side of the 16-Punnett square. RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy Section 11-3 Probability: RY (round and yellow)= 9/16 Ry (round and green = 3/16 rY (wrinkled and yellow)= 3/16 ry (wrinkled and green)= 1/16 Phenotype Ratio= 9:3:3:1 Conclusion= Alleles for seed shape independently assort. Go to Section: Independent assortment Genes for different traits can segregate independently during the formation of gametes ****This is true if the traits you are studying are located on different chromosomes Just by chance all 7 of Mendel’s traits were on different chromosomes. **Summary of Mendel’s Principles** 1. The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring. 2. In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. 3. In most sexually reproducing organisms, each adult has two copies of each gene – one from each parent. These genes are segregated from each other when gametes are formed. 4. The alleles for different genes usually segregate Summary of Gregor Mendel’s Work Gregor Mendel concluded that experimented with Pea plants “Factors” determine traits Some alleles are dominant, and some alleles are recessive which is called the Law of Dominance Alleles are separated during gamete formation which is called the Law of Segregation Beyond Dominant and Recessive Alleles Key idea: Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes. Ex. Four O’clock flowers (see next slide) Incomplete Dominance in Four O’clock Flowers Incomplete Dominance: One allele is not completely _______________ dominant over another. Therefore the phenotype in the heterozygous is in between somewhere __________ the two homozygous phenotypes. Incomplete Dominance in Four O’clock Flowers equally Codominance: both alleles contribute _________ to the phenotype. Ex. Cholesterol more than two Mutliple Alleles: Genes that have _____________ alleles. This does not mean an individual can have more than two alleles, but that there are more than two alleles in the _______________ for a given trait. population Ex. Rabbit coat color, blood type Multiple Alleles and Codominance 3 Alleles: iA, iB, I iA and iB are codominant iA, iB both dominate over i Blood Type/Phenotype BO BB Polygenic Inheritance: The interaction of many genes controls one trait. It is usually recognized in traits that show a ____________________ such as skin color, height, range of phenotypes and body weight. Applying Mendel’s Principles. Mendel’s principles do not apply only to plants. Thomas Hunt Morgan 1. In the early 1900’s ________, Morgan (a nobel prize winning geneticist) decided to look for a model organism to advance the study of genetics. 2. He studied the _____________, Drosophila fruit fly melanogaster. 3. This specimen was a good choice because: _______ and can be kept in a small place tiny produce ___________ of offspring hundreds has only _________ of chromosomes 4 pairs they can produce a new _______________ every generation 4 weeks Fruit Flies (Drosophila melanogaster) Genetics and the environment Genes alone ______________________ do not determine the characteristics of an organism. The interaction environment between genes and the ________________are necessary. Ex. Consider the height of a sunflower. Genes provide a plan for the development of a sunflower but the condition of the soil, climate, and water availability will also influence the height of the sunflower. 11-5: Gene Linkage and Gene Maps Standards addressed: CA B1 3.b students know the genetic basis forMendel’s laws of segregation and independent assortment. *B1 3.d. Students know how to use data on frequency of recombination at meiosis to estimate genetic distances between loci and to interpret genetic maps of chromosomes. Key concept: What structures actually assort independently? Actually ________________________ do assort the chromosomes independently just as Mendel had suggested but the _______ linked together genes on the chromosomes can be ____________. A. Linked genes 1. Genes located on the _________ same chromosome together 2. Inherited _____________ 3. Do not undergo independent ___________________; assortment they don't follow Mendel's law (Just by chance all the traits Mendel studied were located on separate chromosomes...none were linked.) B. Linkage group= all the genes on a _____________ chromosome * If there are ___ 4 pairs of chromosomes then there are 4 linkage groups. Humans have ____ 23 pairs of ____ chromosomes therefore ____ 23 linkage groups III. Crossing Over A. If two genes are found on the same chromosome, does it mean that they are linked forever? NO! recombinants. Crossing over produces ___________________ B.new Recombinants= combinations individuals with _________________ of genes IV. Gene Mapping A. Sturtevant stated that: crossing over occurs ________________ along randomly the linkage groups. the _______________ the genes are from each further other the ______________ they will cross over more likely of recombination (how often using thefrequency _______________________ crossing over occurs), a gene _______ can be made map for each chromosome B. Gene map= the __________________ positions of genes on a chromosome Example: gene a and gene b cross over 20% gene a and gene c cross over 5% gene b and gene c cross over 75% chromosome: C A B Figure 11-19 Gene Map of the Fruit Fly Exact location on chromosomes Chromosome 2