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Section Outline • 11–1 The Work of Gregor Mendel A. Gregor Mendel’s Peas B. Genes and Dominance C. Segregation 1. The F1 Cross 2. Explaining the F1 Cross Gregor Mendel history Bill Nye 11-1 Quiz? 1. Discuss who Gregor Mendel was and discuss his contribution to biology. 2. What characteristics did he study? 3. What is the P1, F1, F2 generation? 4. What are pure plants? Give one example of self-pollination and cross pollination. 5. How did Mendel determine which of each pair of traits was the dominant trait and which was recessive? 6. Although Tall plants appear to be tall, could they be considered “pure” for the tall trait? Why or why not? GREGOR MENDEL prezi Mendel was a monk who lived during the mid 1800’s in Austria. He was great in math and was a gardener at the monastery. He noticed various things about pea plants and their characteristics. He studied seven characteristics of pea plants and noticed what we today call inheritance or the passing of traits by heredity. P1- pure parent cross contrasting traits F1 generation This generation showed only one trait from the parents showed up. (dominant) Mendel allowed these to self-pollinate. This is called the F2 generation. Results of this pollination showed 3/4 were yellow and only 1/4 were green. The green pod trait had appeared to be lost in the F1 generation, actually reappeared in the F2 generation. • How did Mendel determine which of each pair of traits was the dominant trait and which was recessive? • Although Tall plants appear to be tall, could they be considered “pure” for the tall trait? Why or why not? Principles of Dominance Section 11-1 P Generation Tall Short F1 Generation Tall Tall F2 Generation Tall Tall Tall Short Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Section 11-1 Seed Coat Color Pod Shape Pod Color Flower Position Smooth Green Axial Tall Yellow Terminal Short Green Axial Seed Shape Seed Color Round Yellow Gray Wrinkled Green White Constricted Round Yellow Gray Smooth Plant Height Tall Conclusions of Mendel 1. Principle of dominance and Recessiveness One factor of a pair of alleles may mask the appearance of another. (Ex: blond hair is recessive to dark hair) 2. Principle of Segregation The two factors for a characteristic separate, during the formation of eggs and sperm. (B - Brown, b - blue) Which allele did you get? 3. Principle of Independent Assortment- Factors for different characteristics are distributed independently to sex cells. (curly fur /size of dog or tall plant /wrinkled seeds) These principles will make more sense at the end of the chapter. • Mendel’s most important decision was to study just a few isolated traits of the pea plants. Section 11-1 Parents First Generation Second Generation Long stems short stems All long 787 long: 277 short Red flowers white flowers All red 705 red: 224 white Green pods yellow pods All green 428 green: 152 yellow Round seeds wrinkled seeds All round 5474 round: 1850 wrinkled Yellow seeds green seeds All yellow 6022 yellow: 2001 green What do the numbers mean? What is the ratio of dominant to recessive? Section Outline Section 11-2 • 11–2 Probability and Punnett Squares A. Genetics and Probability B. Punnett Squares C. Probability and Segregation D. Probabilities Predict Averages Go to Section: Punnett squares 1-factor Punnett squares 2-factor Tt X Tt Cross Section 11-2 Tt X Tt Cross Section 11-2 Go to Section: Figure 11-10 Independent Assortment in Peas Section 11-3 Go to Section: Section 11-3 Height in Humans • Height in pea plants is controlled by one of two alleles; the allele for a tall plant is the dominant allele, while the allele for a short plant is the recessive one. • What about people? • Are the factors that determine height more complicated in humans? • Can you only be tall or short? Go to Section: 11–3 Exploring Mendelian Genetics A. Independent Assortment 1. The Two-Factor Cross: F1 2. The Two-Factor Cross: F2 B. A Summary of Mendel’s Principles C. Beyond Dominant and Recessive Alleles 1. Incomplete Dominance 2. Codominance 3. Multiple Alleles 4. Polygenic Traits D. Applying Mendel’s Principles Polygenic Inheritance - traits are controlled by two or more genes. (Ex Lab retrievers have two separate genes which determine coat color) Human skin color link Multiple alleles - numerous versions of a gene are possible. (Hair color, eye color, blood type, etc.) eye link Codominance - both differing alleles of a gene are expressed at the same time. There is no dominance of one over the other. (Ex: roan cattle are a hybrid of a Red and White cross R x R1) Charlais (R1 R1) Red (RR) X Roan hybrid (R R1 ) Incomplete dominance - hybrids are intermediates of the parents. (Ex red x white = pink). The recessive allele can not make any pigment at all so less pigment shows up (diagram) Go to Section: Section 11-3 Concept Map Gregor Mendel concluded that experimented with Pea plants Different traits separate randomly “Factors” determine traits Some alleles are dominant, and some alleles are recessive which is called the Law of Dominance Go to Section: which is called the Law of Independent assortment Alleles are separated during gamete formation which is called the Law of Segregation Section 11-4 Interest Grabber continued 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? Go to Section: Section Outline 11–4 Meiosis Prezi link Use instead A. Chromosome Number B. Phases of Meiosis 1.Meiosis I 2.Meiosis II C. Gamete Formation D. Comparing Mitosis and Meiosis Meiosis • This is the division of chromosomes that creates new cells with half the number of chromosomes (haploid) • This type of cell division occurs in sex cells egg, sperm, pollen, spores,etc. • They have the chromosome number of 1n • (1n + 1n = 2n) (Diploid) • Two main parts of Meiosis: Meiosis I - Homologous Chromosomes separate into separate cells Meiosis II - Chromatids of each chromosome are segregated into separate cells. Figure 11-15 Meiosis Meiosis I Section 11-4 Interphase I Prophase I Metaphase 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 The fibers pull the homologous chromosomes chromosomes. toward the opposite ends of the cell. Go to Section: Anaphase I Figure 11-17 Meiosis II Section 11-4 Prophase II Meiosis II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up The sister chromatids haploid (N) daughter cells, in a similar way to the separate and move toward each with half the number metaphase stage of mitosis. opposite ends of the cell. of chromosomes as the original. Go to Section: Telophase II Meiosis II results in four haploid (N) daughter cells. Meiosis I Prophase I DNA replication has already happened. Metaphase I DNA condenses into Tetrads chromosomes. (Homologue) Nuclear move to the membrane middle of the disappears Each cell chromosome lines up next to its homologue These homologues twist around each other to form a tetrad and genetic material can be exchanged (crossing- over) Anaphase I Telophase I The cytoplasm The divides, Homologous forming two pairs of new daughter chromosomes cells. Each separate. cell has one of One the chromosome homologues. of each hom. Pair moves to each side. The sister chromotids did not separate. Meiosis II No DNA replication has happened. Prophase II Metaphase II Anaphase II Telophase Recoiling may Chromosomes Centromeres are moved to occur to form joining the the middle of chromosomes chromatids the cell from divide chromatin Sister Spindles form chromatids are now separate Each chromatid is moved to the opposite pole Spindles disappear Nuclear membrane forms Chromatids unwind into chromatin Cytokinesis occurs separate from meiosis Egg and Sperm Formation Gametes - sex cells that have half the number of chromosomes as somatic cells (body) p. 278 • Sperm are formed in the male sex organs through the process of meiosis. Four (4) new sperm are produced from this process from every “mother cell”. • Eggs are formed in the female sex organs through meiosis. One egg cell or ootid and three (3) polar bodies are produced from every “mother cell”. Genetic Variation Sexual reproduction - fusion of gametes with different genetic material. Offspring are genetically different than parents. Asexual reproduction - there is no exchange of genetic material. Organism is identical to parent. Binary fission, budding, cloning. How does genetic variety help organisms survive? (Think of long-term populations, not individuals) Section 11-4 Crossing-Over of tetrads FYI Reduction Division reduces the number of chromosomes per daughter cell by half. Prophase I – can last years. Human females have potential eggs which have entered prophase I by birth. Eggs remain “stuck” in this stage for decades. Oocytes – germ cells with potential to form eggs are in follicles, found in the ovary tissue. Each follicle has a single oocyte. All germ cells are in prophase I of meiosis by birth. Oocyte grows and is packed full of nutrients for a developing embryo. Oogensis – egg forms and follicle ruptures releases the egg. Ovulation occurs. Meiosis II is completed after the fertilization of the 1 egg. 3 polar bodies are produced and disintegrate. Synapsis – process of chromosome alignment in Prophase I. Synapsed pair of homologous chromosomes are called a tetrad. Crossing over can occur. Sperm – produced in seminiferous tubules from stages of cells. Spermatogonia primary spermatocytes spermatidsimmature sperm Janssens (1909) predicted crossing over leads to genetic recombination/ which increases diversity of all life. Chiasmata- the points where two homologous chromosomes are in contact. Site where crossing over takes place. Crossing over does not require the breakage an reunion of thick, compact chromosome pieces, but of individual DNA molecules (nucleotides+nucleotides). There are 223 combination possible in humans for to independent assort (8million possibilities) 1 in 70 million chance of having identical siblings in different pregnancies. Pleiotrophy – product of one gene can cause many problems. (Ex: cystic fibrosis) Epistasis – one pair of alleles (recessive) effect the genes or alleles at another loc (part of chromosome). Ex: Albinism Section Outline Section 11-5 • 11–5 Linkage and Gene Maps A. Gene Linkage B. Gene Maps Go to Section: What are some products that often come in packages containing several different colors and flavors? What happens if you want only one flavor? What else do you get besides the color or flavor you want? Linkage groups- these are “packages” of genes that tend to be inherited together. There is one linkage groups for every homologous pair of chromosomes. *Crossing Over If genes for body color and wing size are linked, why aren’t they linked all the time? Sections of the chromosomes can cross, break and reattach during Meiosis I. (see diagram) Recombinants - individuals with new combinations of genes. It is believed that 2-3 cross-overs occurs on each pair of human homologs in sex cells. Linked genes - they are found on the same chromosome and do not undergo independent assortment. Discovered in fruit flies by Thomas Hunt Morgan. Chromosomes assort, not individual genes. http://www.biologycorner.com/fruitflygenetics/index.html Why are fruit flies used in genetics? Gene Mapping Distance between genes (alleles) determines how often crossing over occurs. The farther apart- the more likely genes are to cross-over. This distance helps to “map” a chromosome and tell the probable place to find a certain gene on the chromosome. Genes located on one of the sex chromosomes is said to be sex linked. Crossing-Over Go to Section: Crossing-Over Go to Section: Crossing-Over Go to Section: 5% recombination 1% recombination 8 9 17 Figure 11-19 Gene Map of the Fruit Fly Section 11-5 Exact location on chromosomes Go to Section: Chromosome 2 Comparative Scale of a Gene Map Section 11-5 Mapping of Earth’s Features Mapping of Cells, Chromosomes, and Genes Cell Earth Country Chromosome State Chromosome fragment City People Go to Section: Gene Nucleotide base pairs