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Section Outline Section 11-1 11–1 A. B. C. 1. 2. The Work of Gregor Mendel Gregor Mendel’s Peas Genes and Dominance Segregation The F1 Cross Explaining the F1 Cross Genetics • This is the branch of biology which studies heredity. White Tiger - This type of tiger can have yellow parents. How can that happen? Daschuand, Collie, Great Dane, Poodle, Greyhound, Labrador, Terrier, Pit-bull What are some inherited traits for some dog breeds? (Physical and behavior) How do you keep producing a pure breed? Terms -alleles, hybrid, genes, purebred, traits 11-1 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? What is the F1 generation? What else did Mendel do? This generation showed only one trait from the parents that were crossed ( green pod, no yellow pod). He allowed these to self-pollinate. This is called the F2 generation. Results of this pollination showed 3/4 were green and only 1/4 were yellow. The yellow 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? GREGOR MENDEL 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. Mendel’s experiments: 1. He studied each characteristic individually. He took “pure” plants for a trait and allowed them to go through self-pollination. What are pure plants? What is self-pollination? The offspring which resulted from this cross in known at the parental generation or P1 generation. ( parent self-pollinated) 2. Mendel then crossed the P1 generation of opposite traits by crosspollinating them (yellow pods with green pods). 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 an 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) 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 Go to Section: C. Probability and Segregation D. Probabilities Predict Averages Tt X Tt Cross Section 11-2 Tt X Tt Cross Section 11-2 Go to Section: Section 11-3 Interest Grabber 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 *Gene interactions(Recessive vs. Dominant) recessive genes do not produce the enzyme for a trait to be demonstrated. 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) 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 xR’) Polygenic Inheritance - traits are controlled by two or more genes. (Ex Lab retrievers have two separate genes which determine coat color) Multiple alleles - numerous versions of a gene are possible. (eye color, blood type, etc.)diagram Section 11-3 Concept Map Gregor Mendel concluded that experimente d with Pea plants “Factors” determine traits Some alleles are dominant, and some alleles are recessive which is called the Law of Dominance Go to Section: Alleles are separated during gamete formation which is called the Law of Segregation Figure 11-11 Incomplete Dominance in Four O’Clock Flowers Section 11-3 Go to Section: Figure 11-10 Independent Assortment in Peas Section 11-3 Go to Section: 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. *A human cell has about 100 000 different genes attached in a single line on each chromosome. 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. Punnett Square - name after Reginald Punnett who studied genetics in the 1900’s. Sutton - (1902) His Chromosome theory of heredity states that genes are located on chromosomes and each occupies a certain place. Each chromosome contains a form of the gene called an allele. There can be two or more alleles for each gene. (see diagram) Linked genes - they are found on the same chromosome and do not undergo independent assortment. Discovered in fruit flies by Thomas Hunt Morgan. What if there was no crossing-over in any organism? 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. Sex linkage - There is an exception to the rule that all chromosomes has a matching homolog. This was discovered by Nettie Stevens (1905) in her study of meal worm chromosomes. The Y chrom is much smaller and a different shape than the X chrom. Her promising scientific career was cut short by cancer at age 41. (FYI) Genes located on one of the sex chromosomes is said to be sex linked. How is the sex of offspring determined? (Review) Crossing-Over Go to Section: Crossing-Over Go to Section: Crossing-Over Go to Section: 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