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Unit 8 – Part 1 Notes Meiosis and Mutations

Unit 8 – Part 1 Notes Meiosis and Mutations. How does sexual reproduction lead to the production of genetically different cells?. Vocabulary. genes Sex Chromosome Autosome Homologous chromosome Karyotype Diploid Haploid synapsis tetrad. gametes zygote Crossing-over meiosis

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Unit 8 – Part 1 Notes Meiosis and Mutations

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  1. Unit 8 – Part 1 Notes Meiosis and Mutations How does sexual reproduction lead to the production of genetically different cells? Unit 8 notes - part 1 - meiosis

  2. Vocabulary • genes • Sex Chromosome • Autosome • Homologous chromosome • Karyotype • Diploid • Haploid • synapsis • tetrad • gametes • zygote • Crossing-over • meiosis • Genetic recombination • Independent assortment • Spermatogenesis • Oogenesis • Polar body • Sexual reproduction Unit 8 notes - part 1 - meiosis

  3. Review • Chromosomes are rod-shaped structure made of DNA and proteins. • Genes are segments of DNA that control traits • DNA replicates (S phase of cell cycle) before cell division takes place • Replicated chromosomes are made up of two identical chromatids (sister) joined by a centromere. • DNA in its less tightly coiled form is called chromatin. Unit 8 notes - part 1 - meiosis

  4. Chromosome Numbers XY - male • Chromosomes are categorized as either sex chromosomes or autosomes. • Sex chromosomes are the chromosomes that have genes that determine the sex of an organism. (23rd chromosome) • Autosomes are chromosomes with genes that determine traits other than sex. (1-22) XX - female Unit 8 notes - part 1 - meiosis

  5. eye color locus eye color locus hair color locus hair color locus • Every cell in an organisms produced by sexual reproduction has two copies of chromosomes – one from each parent. • Two copies of each chromosome from a parent are called homologous chromosomes. • Homologous chromosomes or homologues are the same size and shape and carry genes for the same traits. Unit 8 notes - part 1 - meiosis

  6. A karyotype is a photomicrograph of the chromosomes in a normal dividing cell. • Humans have 46 chromosomes – 22 pairs of autosomes and 1 pair of sex chromosomes • Males are XY • Females are XX Unit 8 notes - part 1 - meiosis

  7. Karyotype Unit 8 notes - part 1 - meiosis Female - XX

  8. Karyotype Down Syndrome – Trisomy 21 Unit 8 notes - part 1 - meiosis Female - XX

  9. Diploid and Haploid • Cells having two sets of chromosomes are diploid. Called 2n (n is haploid chromosome) • All body (somatic)cells are diploid. • Cells with one set of chromosomes are haploid or n. • Haploid cells have ½ the number of chromosomes present in diploid cells. • Diploid 46 • Haploid 23 Unit 8 notes - part 1 - meiosis

  10. sperm n=23 n=23 egg 2n=46 zygote Fertilization • The fusion of a sperm and egg to form a zygote. • A zygote is a FERTILIZED EGG Unit 8 notes - part 1 - meiosis

  11. Meiosis • The form of cell divisionby which GAMETES (sex cells), with HALF the number of CHROMOSOMES, are produced. • DIPLOID (2n)  HAPLOID (n) • Meiosis is SEXUALreproduction (combining of sex cells with different characteristics of parents). • TWO divisions (MEIOSIS Iand MEIOSIS II). Unit 8 notes - part 1 - meiosis

  12. Meiosis • Sex cells divide to produce GAMETES(sperm or egg). • Gametes have HALF the normal number of chromosomes. • Occurs only in GONADS (testes or ovaries). • Male: SPERMATOGENESIS-production of sperm cells • Female: OOGENESIS - production of egg or ova Unit 8 notes - part 1 - meiosis

  13. n=23 human sex cell sperm n=23 n=23 2n=46 n=23 n=23 diploid (2n) haploid (n) n=23 Meiosis I Meiosis II Spermatogenesis Unit 8 notes - part 1 - meiosis

  14. Haploid (1n) n=23 human sex cell egg n=23 2n=46 n=23 diploid (2n) Meiosis I Meiosis II Oogenesis Polar Bodies (die) Unit 8 notes - part 1 - meiosis

  15. Meiosis Animation Unit 8 notes - part 1 - meiosis

  16. Interphase I • Similar to mitosis interphase. • CHROMOSOMES(DNA)replicate in the S phase • Each duplicated chromosome consist of twoidenticalSISTER CHROMATIDS attached at their CENTROMERES. • CENTRIOLE pairs also replicate. Unit 8 notes - part 1 - meiosis

  17. Interphase I • Nucleus and nucleolus visible. Nucleus chromatin cell membrane nucleolus Unit 8 notes - part 1 - meiosis

  18. Meiosis I (four phases) • Cell division that reduces the chromosome number by one-half. • Four phases: a. Prophase I b. Metaphase I c. Anaphase I d. Telophase I Prophase I Unit 8 notes - part 1 - meiosis

  19. Prophase I • Longest and most complex phase (90%). • Chromosomes condense. • Synapsis occurs - Homologous chromosomescome togetherto form a tetrad. • Tetrad is two chromosomesor four chromatids (sister and non-sister chromatids). Unit 8 notes - part 1 - meiosis

  20. Non-Sister Chromatids-HOMOLOGS • Homologs contain DNA that codes for the same genes , but different versions of those genes • Genes occur at the same loci Unit 8 notes - part 1 - meiosis

  21. Homologous chromosomes sister chromatids sister chromatids Tetrad Prophase I - Synapsis Unit 8 notes - part 1 - meiosis

  22. Homologous Chromosomes • Pair of chromosomes (maternal and paternal) that are similar in shape and size. • Homologous pairs (tetrads) carry GENES controlling the SAME inherited traits. • Each locus(position of a gene) is in the same position on homologues. • Humans have 23 pairs of homologous chromosomes: a. First 22 pairs of autosomes b. Last pair of sex chromosomes LOCI Unit 8 notes - part 1 - meiosis

  23. eye color locus eye color locus hair color locus hair color locus Paternal Maternal Homologous Chromosomes Unit 8 notes - part 1 - meiosis

  24. Crossing Over • Crossing over may occur between non-sister chromatids at sites called chiasmata. • Crossing over: segments of nonsister chromatids break and reattach to the other chromatid. • Chiasmata (chiasma) are where chromosomes touch each other and exchange genes (crossing over.) • Causes Genetic Recombination – new mixture of genetic material Unit 8 notes - part 1 - meiosis

  25. Tetrad nonsister chromatids chiasmata: site of crossing over Genetic Recombination Unit 8 notes - part 1 - meiosis variation

  26. Unit 8 notes - part 1 - meiosis

  27. spindle fiber centrioles aster fibers Prophase I • Nucleus & Nucleolus disappear • Spindle forms • Chromosomes coil & Synapsis (pairing of homologues) occurs • Tetrads form & Crossing over Occurs Unit 8 notes - part 1 - meiosis TETRAD

  28. Metaphase I • Shortest phase • Tetrads align on the equator. • Independent assortment occurs – chromosomes separate randomly causing GENETIC RECOMBINATION Unit 8 notes - part 1 - meiosis

  29. OR Homologs line up at equator or metaphase plate Metaphase I Unit 8 notes - part 1 - meiosis

  30. Anaphase I • Homologous chromosomes separate and move towards the poles. • Sister chromatids remain attached at their centromeres. Unit 8 notes - part 1 - meiosis

  31. Telophase I • Each pole now has haploid (1n) set of chromosomes. • Cytokinesis occurs and two haploid daughter cells are formed. Unit 8 notes - part 1 - meiosis

  32. Telophase I cytokinesis Unit 8 notes - part 1 - meiosis

  33. Meiosis II • No Interphase II or very short • No DNA Replication • Remember: Meiosis II is similar to mitosis Unit 8 notes - part 1 - meiosis

  34. Prophase II • Same as Prophase in mitosis • Nucleus & nucleolus disappear • Chromosomes condense • Spindle forms Unit 8 notes - part 1 - meiosis

  35. Chromosomes (not homologs) line up at equator Metaphase II • Same as Metaphase in mitosis Unit 8 notes - part 1 - meiosis

  36. Anaphase II • Same as Anaphase in mitosis • SISTER CHROMATIDS separate Unit 8 notes - part 1 - meiosis

  37. Telophase II • Same as Telophase in mitosis. • Nuclei and Nucleoli reform, spindle disappears • CYTOKINESIS occurs. • Remember: FOUR HAPLOID DAUGHTER cells are produced. • Called GAMETES (eggs and sperm) 1n Sperm cell fertilizes 1n egg to form 2n zygote Unit 8 notes - part 1 - meiosis

  38. Telophase II Unit 8 notes - part 1 - meiosis

  39. Variation • Also known as GENETIC RECOMBINATION • Important to population as the raw material for NATURAL SELECTION. • All organisms are NOT alike • Strongest “most fit” survive to reproduce & pass on traits Unit 8 notes - part 1 - meiosis

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