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Meiosis and Genetics: Organization of Genetic Material, Cell Cycles, and Chromosome Structure

This article provides an overview of meiosis and genetics, including the organization of genetic material, the stages of mitosis, and the process of meiosis. It also discusses the importance of meiosis in sexual reproduction and the role of genetic recombination. Additionally, it explores the relationship between meiosis and genetics, including the inheritance of traits and the occurrence of chromosomal diseases.

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Meiosis and Genetics: Organization of Genetic Material, Cell Cycles, and Chromosome Structure

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  1. Meiosis and Genetics

  2. Organization of genetic material Prokaryotes: DNA is circular, not associated with proteins Eukaryotes: DNA is linear, associated with proteins

  3. Somatic Cell Cycles • Somatic (body) cells have a distinct cell cycle with four phases: • G1: growth • S : DNA is replicated • G2: growth • M phase: cells divide by mitosis

  4. Chromosome Structure Has two chromatids (replicated chromosomes) Chromatids held together by a region of DNA called a centromere

  5. Stages of Mitosis

  6. Most eukaryotic cells are diploid: --two sets of chromosomes, one from each parent --chromosomes from parents are similar, but not identical: homologous chromosomes --Humans have 46 chromosomes, or 23 pairs of chromosomes Karyotype

  7. Mitosis summary • Daughter cells have the same number of chromosomes as parental cells • Daughter cells have the same DNA content as parental cells • Daughter cells have identical DNA structure as the parental cells • Mitosis starts with diploid cells and produces diploid cells

  8. Meiosis Occurs only in organisms that use sexual reproduction Specialized cell division that only occurs in germ cells. The product cells of meiosis are the gametes (egg, sperm).

  9. Overview of Meiosis • Germ cells duplicate their DNA ONCE--prior to meiosis • Two stages of meiosis, each with cell division • Germ cells are diploid; gametes are haploid From GlaxoSmithKline:http://genetics.gsk.com/graphics/meiosis-big.gif

  10. Prophase I • During meiosis I (prophase I), there is exchange of genetic material between chromosomes: geneticrecombination. • Genetic recombination may allow for a competitive advantage by rearranging genetic material from generation to generation.

  11. Meiosis I

  12. Key points about Meiosis I • Germ cells start out diploid • Germ cells duplicate their DNA • Homologous chromosomes exchange genetic material during prophase I • Meiosis I ends with the separation of thehomologs and the physical division of the cells • Products of meiosis I are not diploid because they do not have homologous chromosome pairs • Products of meiosis I are not haploid (yet)

  13. Key points about Meiosis II • No DNA duplication prior to meiosis II • Separation of the attached chromatids (replicated chromosomes) • Four products (gametes) are genetically NOT identical to each other! • Four products (gametes) are haploid—no homologous chromosome pairs

  14. Mitosis/Meiosis

  15. Meiosis to Genetics.... • Meiosis produces gametes with a haploid chromosome number. • During fertilization, these gametes unite to form a diploid zygote, which then develops by successive cell divisions into an organism. • Thus, organisms inherit two sets of genetic information: one from each gamete (parent).

  16. Chromosomal Diseases • Gametes have abnormal chromosome numbers and mutations • Offspring inherit extra chromosome or are missing a chromosome • Caused by problems with meiosis

  17. Nondisjunction of chromosomes during meiosis Based on: Brooks/Cole – Thomson Learning

  18. Nondisjunction and Trisomy 21

  19. Some Characteristics of Trisomy 21 (Down Syndrome)

  20. Genetics: Introduction Each organism displays certain traits which are inherited from previous generations. The monk Gregor Mendel, through his studies of pea plants, discovered a mechanism for the inheritance of specific traits.

  21. Genes and Alleles • Gene: unit of information about a specific trait, passed from parent to offspring • Allele: all of the different forms of the gene, in diploid organisms, each gene has at least two alleles.

  22. Alleles Continued • Allele combinations • homozygous: when both alleles are identical • heterozygous: when each allele is different • Types of alleles • Dominant alleles: capital letter (D) • Recessive alleles: lowercase letter (d) When paired, the dominant allele will mask the effect of the recessive allele

  23. Examples of Inheritance

  24. Dominant and Recessive Traits Brown eyes are dominant Tongue rolling ability is recessive

  25. Mendel's Law of Segregation For a given trait (gene), the pair of alleles in each parent separate such that the offspring only inherits one allele. Separation of alleles occurs during the meiotic divisions that produce the gametes.

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