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Most humans have 46 chromosomes (23 pairs) in their body cells.

Most humans have 46 chromosomes (23 pairs) in their body cells. They have only 23 chromsomes in their gametes. Why do you think gametes only have half the number of chromsomes?. Talk to the people around you about what a Punnett square is used for.

vincent-warner
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Most humans have 46 chromosomes (23 pairs) in their body cells.

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  1. Most humans have 46 chromosomes (23 pairs) in their body cells. They have only 23 chromsomes in their gametes. Why do you think gametes only have half the number of chromsomes?

  2. Talk to the people around you about what a Punnett square is used for.

  3. Talk to the people around you about the difference between heterozygous and homozygous.

  4. Talk to the people around you about the Law of Segregation.

  5. Talk to the people around you about the Law of Independent Assortment.

  6. Genes do not exist free in the nucleus of a cell; they are lined up on chromosomes. Section 10.2 Summary – pages 263-273 • Typically, a chromosome can contain a thousand or more genes along its length.

  7. Diploid Cells Section 10.2 Summary – pages 263-273 • A cell with two of each kind of chromosome is called a diploid cell. • Your body cells are diploid, and contain 46 chromosomes.

  8. Section 10.2 Summary – pages 263-273 Homologous Chromosomes • The two chromosomes of each pair in a diploid cell are called homologous chromosomes. • Each pair of homologous chromosomes has genes for the same traits.

  9. Haploid Cells Section 10.2 Summary – pages 263-273 • A cell containing one of each kind of chromosome is called a haploid cell. • Organisms produce gametes (sex cells) that contain one of each kind of chromosome.

  10. Section 10.2 Summary – pages 263-273 Diploid and Haploid Cells Chromosome Numbers of Common Organisms Organism Body Cell (2n) Gamete (n) 4 Fruit fly 8 Garden pea 14 7 10 Corn 20 12 Tomato 24 Leopard Frog 26 13 Apple 34 17 Human 46 23 Chimpanzee 24 48 Dog 78 39 1260 630 Adder’s tongue fern

  11. In Humans, how many chromosomes would each of these cells have….. CHEEK CELL 46 SPERM CELL 23 EGG CELL 23 NERVE CELL 46

  12. Since they have different amounts of chromosomes, the way they are made differ. ● Body cells are made by the division process MITOSIS. ● Sex cells are made by the division process MEIOSIS.

  13. Before a cell can divide by either method, it must first prepare for cell division. The cell cycle (or entire life cycle of the cell) consists of: INTERPHASE: The longest/busiest stage in a cell’s life 1. Chromosomes (DNA) replicates 2. Cell grows bigger CELL DIVISION: Mitosis or Meiosis CYTOKINESIS: When the cytoplasm divides and the cell completely separates.

  14. Mitosis: cell division that makes BODY CELLS. 46 It starts with a DIPLOID cell Chromosomes Replicate 92 46 46 It ends with TWO IDENTICAL DIPLOID cells

  15. PHASES OF MITOSIS (Paul Makes A Taco) PROPHASE • Chromosomes coil up • Nuclear envelope disappears • Spindle fibers form METAPHASE • Chromosomes Line up in the middle • Spindle attaches to chromosomes

  16. PHASES OF MITOSIS (Paul Makes A Taco) ANAPHASE • Chromosomes split and are pulled apart TELOPHASE • Chromosomes uncoil • Nuclear envelopes reappear • Cell is splitting into two

  17. Meiosis: cell division that makes SEX CELLS. 46 It starts with a DIPLOID cell Chromosomes Replicate 92 46 46 23 23 23 23 It ends with FOUR HAPLOID cells (not identical)

  18. Section 10.2 Summary – pages 263-273 Meiosis • These haploid cells are called sex cells— gametes. • Male gametes are called sperm. • Female gametes are called eggs.

  19. Section 10.2 Summary – pages 263-273 Meiosis • When a sperm fertilizes an egg, the resulting zygote once again has the diploid number of chromosomes.

  20. Crossing-Over In Meiosis: When homologous chromosomes actually break and exchange genetic material- is a process known as crossing over.

  21. Crossing-Over Crossing over causes variations in the alleles on each chromosome.

  22. Section 10.2 Summary – pages 263-273 Nondisjunction • The failure of homologous chromosomes to separate properly during meiosis is called nondisjunction. • This would occur when homologous chromosomes are suppose to separate from each other.

  23. Section 12.3 Summary – pages 323 - 329 • This chart of chromosome pairs is called a karyotype, and it is valuable in identifying unusual chromosome numbers in cells.

  24. Down syndrome: Trisomy 21 Section 12.3 Summary – pages 323 - 329 • Down syndrome is the only autosomal trisomy in which affected individuals survive to adulthood.

  25. Section 12.3 Summary – pages 323 - 329 Down syndrome: Trisomy 21 • Extra chromosome on 21 • 1 in every 1100 live births • Range from mild to severe physical and mental disabilities • The incidence of Down syndrome births is higher in older mothers, especially those over 40.

  26. Abnormal numbers of sex chromosomes Section 12.3 Summary – pages 323 - 329 • Many abnormalities in the number of sex chromosomes are known to exist. • Any individual with at least one Y chromosome is a male, and any individual without a Y chromosome is a female.

  27. Turners Syndrome • Absence of one X chromosome • Occurs in 1 out of every 2,500 live female births. • Physical characteristics • No mental disability

  28. Abnormal numbers of sex chromosomes Section 12.3 Summary – pages 323 - 329 • Most of these individuals lead normal lives, but they cannot have children and some have varying degrees of mental retardation. XXX “Trisomy X” XXY “Klinefelter’s” XYY “Jacob’s Syndrome”

  29. Section 2 Check Question 1 A cell with two of each kind of chromosome is __________. A. diploid B. haploid C. biploid D. polyploid

  30. Section 2 Check Homologous Chromosome 4 The answer is A. The two chromosomes of each pair in a diploid cell are called homologous chromosomes. Each has genes for the same traits. a A Terminal Axial Inflated D d Constricted T t Short Tall

  31. Section 2 Check Question 2 Meiosis Haploid gametes (n=23) What is the importance of meiosis in sexual reproduction? Sperm Cell Meiosis Egg Cell Fertilization Diploid zygote (2n=46) Multicellular diploid adults (2n=46) Mitosis and Development

  32. Section 2 Check Meiosis is cell division that produces haploid gametes. If meiosis did not occur, each generation would have twice as many chromosomes as the preceding generation. Meiosis Haploid gametes (n=23) Sperm Cell Meiosis Egg Cell Fertilization Diploid zygote (2n=46) Multicellular diploid adults (2n=46) Mitosis and Development

  33. Section 3 Check Question 2 Trisomy usually results from _______. (TX Obj 2; 6C) A. polygenic inheritance B. incomplete dominance C. nondisjunction D. twenty-two pairs of chromosomes The answer is C.

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