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CHAPTER 11  Introduction to Genetics

CHAPTER 11  Introduction to Genetics. 11.1  The Work of Gregor Mendel Objectives: 1) Outline the garden-pea experiments performed by Gregor Mendel. 2) Distinguish between dominant and recessive traits. 3) State the 2 laws of heredity that were developed by Mendel

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CHAPTER 11  Introduction to Genetics

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  1. CHAPTER 11 Introduction to Genetics • 11.1 The Work of Gregor Mendel • Objectives: 1) Outline the garden-pea experiments performed by Gregor Mendel. • 2) Distinguish between dominant and recessive traits. • 3) State the 2 laws of heredity that were developed by Mendel • 4) Explain the difference between an allele and a gene I. Genetics A. What is genetics? 1. Genetics is the scientific study of heredity B. What is a gene? 1. A gene is a segment of DNA that codes for a trait C. What is a trait 1. A characteristic of an individual 2. A distinguishing feature

  2. II. Gregor Mendel experiment A. Used the common garden pea B. The steps to his experiment 1. Step 1 a. Mendel produced pure-breeding strains of garden peas 1. Organisms that always produce offspring having the same trait as itself 2. Allowed plants to self-fertilize for many generations b. Created offspring that produced only one form of a particular trait a. For example-a “Tall” plant strain only produced offspring that were tall 2. He called these plants the parental generation, P Generation 2. Step 2 a. Crossed 2 different varieties from the P Generation, tall w/ short b. The offspring from this cross only had tall plants, no short plants 1. He called these offspring the F1 generation 3. Step 3 a. He then crossed 2 F1 generation pea plants 1. He called these offspring the F2 generation 2. He found that short plants had returned in the offspring of the F2 generation

  3. P F1 F1 F2

  4. C. Explaining his results 1. Parents transmit info about traits to their offspring in the form of genes 2. Each gene is composed of 2 units called alleles a. The alternative forms of a gene 1. One allele came from mom and one from dad b. Homozygous 1. Individual having 2 of the same alleles for the same trait 2. 2 “Tall” alleles for the trait of plant height

  5. c. Heterozygous 1. Individual having 2 different alleles for the same trait 2. 1 tall allele & 1 short allele for the trait of plant height 3. Alleles a. Genotype 1. All the many alleles an organism has b. Phenotype 1. An organism physical appearance caused by its alleles c. One allele comes from the mother & the other allele comes from the father

  6. 4. Alleles may not always receive equal expression a. In heterozygous individuals the dominant allele receives expression 1. The recessive allele is present but does not receive expression II. Mendel’s conclusions A. The law of segregation 1. Members of each pair of alleles separate when gametes are formed a. A gamete will receive one allele or the other, the other allele will end up in the other gamete B. The law of independent assortment 1. 2 or more pairs of alleles segregate independently of one another during gamete formation 9.2 Genetic Crosses Objectives: 1) Use a Punnett square to predict the results of a monohybrid genetic cross. I. Visualizing Mendel’s experiment A. The punnett square

  7. Perfrom the following crosses. Include the following information: 1. Cross 2. Punnett square filled in 3. Genotype of the F1 generation 4. Phenotype of the F1 generation 1. T stand for tall pea plants and is dominant over t, which stands for short pea plants. TT X Tt 2. B= Black, b= White. Black is dominant over white in guinea pigs. Cross the gametes from a heterozygous black guinea pig with the gametes from a heterozygous black guinea pig

  8. 3/1 Do-Now Activity What is the genotypic RATIO for the following cross? Tt x TT

  9. 11.3 When Heredity Follows Different Rules Objectives: 1) Distinguish between incomplete dominance and codominant alleles 2) Compare multiple allelic and polygenic inheritance 3) Analyze the patterns of sex-linked inheritance 4) Summarize how external and internal environments affect gene expression I. Complex patterns of inheritance A. Intro 1. Mendalian Inheritance Based on experiments a. Inheritance controlled by dominant and recessive paired alleles 2. Most inheritance is more complex a. Most traits are not simply dominant or recessive

  10. B. Incomplete dominance 1. Complete vs. Incomplete Dominance a. Complete Dominance 1. Heterozygous & homozygous dominant individuals a. Both have the same phenotype b. Incomplete dominance 1. Heterozygous Ind. a. Phenotype is intermediate between the 2 homozygotes 2. Red flowers x White flowers = Pink a. Why- Red allele codes for a red pigment, white allele codes for no pigment 1. Flower only gets half the red pigment

  11. C. Codominance: Expression of both alleles 1. Codominant alleles a. Causes the phenotype of both homozygotes to be produced in heterozygous individuals 2. Both alleles receive equal expression in the phenotype 3. White chicken x black chicken = black & white feathers D. Multiple phenotypes from multiple alleles 1. Traits controlled by more than two alleles a. Remember that there can only be 2 alleles per individual

  12. E. Polygenic inheritance 1. Inheritance pattern of a trait that is controlled by 2 or more genes a. May be on the same or different chromosomes b. May have 2 or more alleles 2. Examples a. Eye color, skin color, height F. Sex determination & sex-linked inheritance 1. Sex determination a. XX = Female, XY = male 2. Sex-linked inheritance a. Sex-linked traits 1. Traits controlled by genes located on sex chromosomes 2. Y chromosome has so few genes attached to it you can consider it having none a. This means that a male will only have one allele that gets expressed II. Environmental influences A. External influences 1. May cause mutations in genes that get passed on

  13. B. Internal influences 1. Hormonal factors a. Male pattern baldness 1. Determined by hormonal influences 2. If male & female have same genotype it will only be expressed in the male CHAPTER 14 HUMAN HEREDITY Objectives: 1) Compare codominance, multiple allelic, sex linked, & polygenic patterns of inheritance 2) Distinguish among conditions in which extra chromosomes or sex chromosomes exist I. Codominance in humans A. Sickle-cell Anemia 1. Statistics a. Most common in African Americans 1. 1 in 12 are heterozygous

  14. 2. What is it? a. A condition in which part (heterozygotes) or all (homozygotes) of the red blood cells are shaped like a sickle b. Red blood cells 1. Cells located in your blood that carry oxygen throughout you body 3. What does it cause? a. Slow blood flow, black small vessels, cause tissue damage and pain b. Anemia 1. A low number of red blood cells

  15. 4. Heterozygotes a. Allele for sickle cell and allele for normal cells are codominant b. Individual will have both types II. Multiple alleles A. Blood type 1. 4 different blood types a. A, B, AB, O 2. Controlled by 3 alleles a. A allele is dominant over O b. B allele is dominant over O c. A allele and B allele are codominant

  16. III. Sex-linked traits A. Red-Green color blindness 1. Lack the ability to tell the difference between red and green B. Hemophilia 1. Inability to clot blood IV. Changes in chromosome number A. Down syndrome: Trisomy 21 1. Caused by having one extra number 21 chromosome 2. Only known example of which individuals with an extra autosomal chromosome survive into adulthood B. Sex chromosomes 1. Individual may be XO, XXX, XXY, XYY a. Any individual with a Y chromosome is male and anyone without a Y chromosome is female b. Will lead a normal life but cannot reproduce

  17. I. Making a pedigree A. A family tree 1. Traces a family name and members through successive generations a. You can trace your cousins, aunts, grandparents, etc. B. A pedigree 1. Traces the genes of an individual through successive generations 2. A graphic representation of genetic inheritance a. Utilizes phenotype to trace gene C. Understanding a pedigree 1. Symbols a. Squares and circles 1. Squares = male 2. Circles = female

  18. b. Shaded and unshaded 1. Shaded = Ind. expressing trait being studied 2. Unshaded = Ind. not expressing trait being studied 3. Half shaded = Ind. That is a carrier of the trait being studied but is not expressed(heterozygous) c. Lines 1. Horizontal a. Connecting a square & circle indicates that ind. are parents 2. Vertical a. Connects a set of parents with their offspring d. Horizontal rows represent a generation 1. Most recent generation at the bottom

  19. II. Simple recessive heredity A. Most genetic disorders are caused be recessive alleles 1. Must be homozygous recessive a. A recessive allele from each parent B. Some examples 1. Cystic fibroses a. Most common among white Americans b. Results in the formation and accumulation of thick mucus in the lungs and digestive tract III. Simple dominant heredity A. Dominant traits 1. Only need one dominant allele 2. Can be heterozygous or homozygous dominant

  20. B. Some simple dominant traits 1. Tongue rolling a. If you can roll your tongue you have inherited at least one allele from a parent 2. Ear lobes b. Free hanging ear lobes

  21. C. Huntington’s disease 1. A lethal genetic disorder caused by a dominant allele 2. Results in the breakdown of certain areas of the brain 3. Why rare a. Usually, a dominant allele with such severe effects kills the ind. before they can reproduce b. Huntington’s does not appear until 30-50 years of age 4. No cure but there are DNA tests

  22. 11.4 Meiosis I. Stages of meiosis A. Defined 1. Process of nuclear division that reduces the number of chromosomes in new cells to half the # of diploid chromosomes 2. Cells go through interphase B. Meiosis I 1. 4 phases a. Prophase I 1. Chromatin coils into chromosomes 2. Spindle fibers appear 3. Nuclear membrane disappears

  23. 4. Homologous chromosomes pair up a. Does not happen in mitosis b. Each pair is called a tetrad d. Chromatids line up so corresponding genes line up next to each other e. Crossing-over 1. Portions of broken chromatids attach to adjacent chromatids on homologous chromosomes 2. Results in genetic recombination a. Producing a new mixture of genetic material

  24. b. Metaphase I 1. Tetrads randomly line up along equator of cell 2. Spindle fibers attach to centromeres 3. Spindle fibers from opposite poles attach to different centromeres w/in tetrad

  25. c. Anaphase I 1. Each homologous chromosome moves to opposite ends of cell d. Telophase I 1. Spindle fibers disappear C. Cytokinesis I 1. 2 Diploid cells formed

  26. C. Meiosis II 1. 4 phases a. Prophase II 1. Spindle fibers appear b. Metaphase II 1. Chromosomes line up along the equator of the cell 2. Spindle fibers attach to centromeres

  27. c. Anaphase II 1. Sister chromatids separate & moves to opposite ends of cell d. Telophase II 1. Spindle fibers disappear

  28. C. Cytokinesis II 1. 4 haploid cells formed

  29. II. Spermatogenesis & Oogenesis A. Meiosis is the production of a haploid cell, not a sex cell 1. One more step is needed to create a sex cell B. Spermatogenesis 1. The production of a mature sperm cell a. Occurs only in males 2. The addition of one more steps creates the process called spermatogenesis a. The adding of a head and tail to create a sperm cell

  30. C. Oogenesis 1. The production of a mature unfertilized egg cell a. Occurs only in females 2. Differs from spermatogenesis a. Cytokinesis is unequal in oogenesis

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