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Mendelian Genetics and Meiosis

Mendelian Genetics and Meiosis. Gregor Mendel (1822 – 1884). Father of Genetics Austrian monk who worked with pea plants in monastery garden. Developed first theories on genetic inheritance. http://history.nih.gov/exhibits/nirenberg/images/photos/01_mendel_pu.jpg.

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Mendelian Genetics and Meiosis

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  1. Mendelian Genetics and Meiosis

  2. Gregor Mendel (1822 – 1884) • Father of Genetics • Austrian monk who worked with pea plants in monastery garden. • Developed first theories on genetic inheritance. http://history.nih.gov/exhibits/nirenberg/images/photos/01_mendel_pu.jpg

  3. Why Experiment With Pea Plants? • Grow quickly • Many kinds available • Self-pollinate so they have both male and female reproductive parts on the same flower and can pollinate themselves. They are true-breeding meaning offspring will have same traits as parent. • Can cross-pollinate so one plant can pollinate another plant to produce offspring. http://kentsimmons.uwinnipeg.ca/cm1504/Image215.gif

  4. What was Mendel studying? • Inherited characteristics (features with different forms in a population) that are passed from parents to offspring. • EX: Flower color or seed shape • Studied one characteristic at a time to determine which traits appeared in offspring. http://www.cfkeep.org/html/phpThumb.php?src=/uploads/peas_copy.gif&aoe=1&w=

  5. Mendel's First Experiment • Manually crossed true breeding plants for each characteristic. • Example: crossed purple flower plant & white flower plant. • All offspring displayed the same trait of one parent. In this case, all had purple flowers. White flowers seemed to disappear. http://www.biology.iupui.edu/biocourses/N100/images/10F1.gif

  6. Conclusions: • The trait that showed up most often in the offspring was the DOMINANT trait. • The trait that seemed to disappear or fade away was the RECESSIVE trait. • To determine what happened to the recessive trait, Mendel decided to do another set of experiments. http://www.jbhs.k12.nf.ca/biology/photos/mvc-006f.jpg http://www.windows.ucar.edu/earth/Life/images/earlobes.jpg

  7. Mendel's Second Experiment • Allowed the plants produced by his first experiment to self-pollinate. • All purple flowered plants self pollinated: • 75% of offspring were purple flowered • 25% of offspring were white flowered http://www.biology.iupui.edu/biocourses/N100/images/10f2.gif

  8. Conclusions • Recessive trait did not disappear, it was masked by the dominant trait as it showed up again in the second generation. • Each plant had 2 sets of instructions (one from each parent) for each characteristic. http://upload.wikimedia.org/wikipedia/commons/thumb/1/17/Punnett_square_mendel_flowers.svg/550px-Punnett_square_mendel_flowers.svg.png

  9. Mendel's Principles • Inheritance of traits is predetermined by genes. Genes are passed on from parents. • Some forms of genes are dominant and others are recessive. • Organisms have 2 copies of each gene (one from each parent). • Alleles(different forms for a gene) for different genes segregate independently of one another. (Monohybrid cross) http://www1.umn.edu/ships/updates/9mendels.gif

  10. Alleles • Different forms of a gene • EX: freckles or no freckles • Dominant allele – expressed with an UPPER CASE letter. • Recessive allele – expressed with a lower case letter. • NOTE: The same letter is used to express an allele – variations are expressed with the upper or lower case. http://upload.wikimedia.org/wikipedia/commons/8/83/Punnett_square_(PSF).png

  11. Phenotype vs. Genotype • PHENOTYPE: Physical characteristic – the characteristic that you can see. • EX: Purple flowers • GENOTYPE: The two inherited alleles for a trait. (Cannot be seen) • EX: PP or Pp http://www.bbc.co.uk/schools/gcsebitesize/science/images/25_environmental_variation.gif

  12. Types of Genotypes • Homozygous Dominant: Two dominant alleles • PP or DD or BB • Homozygous Recessive: Two recessive alleles • pp or dd or bb • Heterozygous: One dominant and one recessive allele • Pp or Dd or Bb http://uwadmnweb.uwyo.edu/VetSci/Courses/PATB_4110/4-6/Class_Notes.htm

  13. Punnett Square • Organizes all possible genotype combinations for offspring from particular parents. • How to make a Punnett Square crossing a homozygous recessive white flowering pea plant with a heterozygous purple flowering pea plant.

  14. Exceptions to Mendel's Principles • Incomplete Dominance: One allele is not completely dominant over the other allele. Each allele contributes to the phenotype produced. • EX: Snapdragons (white and red produce pink) • One gene may influence more than one trait. • EX: in white tigers, one gene codes for fur color and eye color. • Several genes may work together to produce a trait. • EX: human skin, hair and eye color http://www.estrellamountain.edu/faculty/farabee/biobk/incomdom.gif

  15. MEIOSIS • Creates the sex cells • It is a copying process that produces cells with ½ the number of chromosomes. • Helped Walter Sutton determine genes are located on chromosomes in the nucleus of the cell. Prior to this no one knew where the genetic traits (genes) were located. http://www2.merriam-webster.com/mw/art/med/meiosis.gif

  16. Steps of Meiosis • Meiosis I • Prophase I • Metaphase I • Anaphase I • Telophase I and Cytokinesis • Meiosis II • Prophase II • Metaphase II • Anaphase II • Telophase II and Cytokinesis

  17. http://www.cps.ci.cambridge.ma.us/CRLS/LC_R/classrooms/AUGUSTINE/Genetics/index_files/frame.html#slide0025.htmlhttp://www.cps.ci.cambridge.ma.us/CRLS/LC_R/classrooms/AUGUSTINE/Genetics/index_files/frame.html#slide0025.html

  18. Prophase I • Homologous chromosomes find each other and pair up (one chromosome from each parent • Crossing over may occur • Centrioles move toward the poles • Nuclear membrane begins to dissolve http://www.sciencecases.org/mitosis_meiosis/images/meiosis_a.gif

  19. Metaphase I • Spindle fibers attach to homologous chromosomes. • Homologous chromosomes line up at the equator http://www.sciencecases.org/mitosis_meiosis/images/meiosis_b.gif

  20. Anaphase I • Homologous chromosomes are separated so each chromosome moves toward opposite poles. http://www.sciencecases.org/mitosis_meiosis/images/meiosis_c.gif

  21. Telophase I • Homologous chromosomes are completely separated with one chromosome at each pole. • Nuclear membrane re-forms • Cytokinesis takes place and cell divides to form two cells. http://www.uic.edu/classes/bios/bios100/lecturesf04am/telophase1m.jpg

  22. Prophase II • Centrioles move to poles • Nuclear membrane dissolves • NOTE: CHROMOSOMES ARE NOT COPIED AGAIN PRIOR TO PROPHASE II http://www.sciencecases.org/mitosis_meiosis/images/meiosis_e.gif

  23. Metaphase II • Spindle fibers form and attach to chromosomes • Chromosomes line up at the equator. http://www.sciencecases.org/mitosis_meiosis/images/meiosis_f.gif

  24. Anaphase II • Chromosomes are pulled apart so each chromatid moves toward opposite poles. http://www.uic.edu/classes/bios/bios100/lecturesf04am/anaphase2m.jpg

  25. Telophase II • Chromatids reach the poles. • Nuclear membrane re-forms • Cytokinesis occurs http://www.sciencecases.org/mitosis_meiosis/images/meiosis_h.gif

  26. MEIOSIS Results • 4 new cells • Each cell has ½ the number of chromosomes as parent cell (haploid – N) • New cells are NOT identical to each other or to the parents as a result of crossing over.

  27. Meosis vs Mitosis Meiosis Mitosis • Sex cells • Two divisions • 4 genetically different cells produced • Cells produced have half the number of chromosomes (haploid) 2n  n • Somatic cells • One division • 2 genetically identical cells produced • Cells produced have the same number of chromosomes as parents 2n  2n

  28. Sex Chromosomes • Chromosomes that carry the genes that determine sex. • In humans: • Females: two X chromosomes (XX) • Males: one X chromosome and one Y chromosome (XY) • Sex of offspring is determined by the male: • Egg fertilized by sperm with X chromosome = FEMALE • Egg fertilized by sperm with Y chromosome = MALE http://howyoudoin.files.wordpress.com/2008/05/male_female_symbol.jpg

  29. Sex-Linked Disorders • Males have an X and Y chromosome. The Y chromosome does not have all the genes found on the X chromosome, so they only have one copy of those genes on the X. If those genes are damaged, they do not have a backup while females do – they have two X chromosomes. Therefore, males are more likely to inherit these disorders. • Examples: • Color blindness • Hemophilia http://www.nlm.nih.gov/MEDLINEPLUS/ency/images/ency/fullsize/9962.jpg http://member.principalhealthnews.com/Imagebank/Articles_images/Hemophilia_02.gif

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