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Meiosis and Heredity

Meiosis and Heredity. Honors Biology - rest of Chapter 8. Vocab. Germ cells Somatic cells Gametes Homologous Chromosomes Autosomes Haploid Diploid Meiosis Gametogenesis Polar Bodies. Vocab Continued. Traits Genetics Cross Purebred Law of Segregation Gene Allele Homozygous

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Meiosis and Heredity

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  1. Meiosis and Heredity Honors Biology - rest of Chapter 8

  2. Vocab • Germ cells • Somatic cells • Gametes • Homologous Chromosomes • Autosomes • Haploid • Diploid • Meiosis • Gametogenesis • Polar Bodies

  3. Vocab Continued • Traits • Genetics • Cross • Purebred • Law of Segregation • Gene • Allele • Homozygous • Heterozygous • Dominant Karyotype* • Recessive Carrier • Genome Incomplete Dominance • Crossing Over Codominance

  4. Questions From the Book • P. 92: 1, 2, 3, 4, 5, 6 • P. 95 2, 4 • P. 98: 1, 2, 3, 4 • P. 100 3 (counts as three questions), 4 • P. 106 1, 4 • P. 107: 1, 3

  5. Heredity • Passing along the traits of parents to the offspring • How? Through sexual reproduction (meiosis)

  6. Terms • Chromosome – rod-shaped structures made of DNA and proteins (histones) • Histones – in eukayrotes; helps chromosome keep it’s shape

  7. Chromosomes • Sex chromosomes (X or Y in humans) • Autosomes – all other chromosomes • Humans - 46 total (occur in pairs – 23 pairs) Females - XX Males - XY

  8. Chromosomes • Every cell has 2 copies of each autosome (1 from dad, 1 from mom) • Homologous chromosomes - (or pairs) • Are same size, shape, carry genes for same traits

  9. Karyotype • Used to look at a person’s chromosomes to detect problems • Shows the 46 human chromosomes as 22 homologous pairs of autosomes + 2 sex chromosomes

  10. Cell Types • Diploid cells (2n) - cells with 2 sets of chromosomes (all human cells except...) • Haploid cells (1n) - cells with 1 set (sperm and eggs)

  11. Haploid cells • Have only 23 total chromosomes • Haploid + haploid = a diploid cell results • Haploid cells are the products of meiosis

  12. Cell Division • Mitosis - most body cells (asexual reproduction) • Meiosis - (sexual reproduction) - occurs when gametes form • Gametes - Egg and sperm

  13. Preparing for meiosis • Cells go through interphase just like before mitosis • DNA is duplicated • Only difference - this happens in reproductive cells (ovary and testes)

  14. Meiosis • Diploid cells in ovaries and testes start dividing • Haploid cells (sperm and eggs) are made

  15. Meiosis Stages (pg. 162-163) • Meiosis 1 - similar to mitosis; 1 cell duplicates DNA then goes through 4 phases • Meiosis 2 - Cells continue dividing to make 4 haploid cells

  16. Meiosis 1 • Prophase 1 – duplicated chromosomes line up next to it’s homologue (stage is called synapsis) • Each pair called a tetrad • Mitosis - same things happen here (except pairing up is unique to meiosis) Tetrad 2n

  17. Prophase 1 • During synapsis, chromatids twist around each other and may exchange portions with adjacent chromatids • Results - new combination of genes • Genetic recombination – of maternal and paternal DNA Crossing-over 2n

  18. Metaphase 1 • Tetrads line up along equator • Spindle fibers attach to centromere of one homologous pair 2n

  19. Anaphase 1 • Each homologous pair is pulled toward each pole (pair still attached by centromere) • Independent assortment – random separation of pairs = genetic variation 2n

  20. Telophase 1 & Cytokinesis 1 • Chromosomes reach opposite poles of cell • New cells are now haploid = half total # of original chromosomes • But...chromosomes present still as a pair 1n

  21. Meiosis 2 • Cells from Meiosis 1 continue dividing • Results in formation of gametes

  22. Prophase 2 • Spindle fibers form and nuclear membrane dissolves (in some species it never forms at end of Meiosis 1) • DNA is NOT duplicated again 1n

  23. Metaphase 2 • Chromosome pair moves to equator • Each chromatid faces opposite poles; still attached centromeres 1n

  24. Anaphase 2 • Chromatids now separate and move toward poles 1n

  25. Telophase 2 & Cytokinesis 2 • Each of the two cells now separate, forming 4 new cells • New cells are haploid and chromosomes are no longer in pairs 1n

  26. Meiosis in males • Reproductive cells form four haploid cells called spermatids. • Each spermatid develops into mature sperm cells = spermatogenesis

  27. Meiosis in females • Oogenesis = Cells make only 1 mature cell out of 4 (ovum) • Cytokinesis 1 and 2 - cytoplasm divides unequally; only 1 cell matures to form an egg • Other 3 cells called polar bodies - later dissolve

  28. Sexual reproduction • Union of sperm and egg to form offspring • Offspring - genetically different from parents (as result of crossing over and random separation of chromosome pairs)

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