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From Mendel to DNA

From Mendel to DNA. Recap from previous lessons. Mitosis produces daughter cells with: fewer chromosomes than the parent cell more chromosomes than the parent cell the same number of chromosomes as the parent cell. -C. 2. As a result of mitosis, how many cells are produced? One Two

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From Mendel to DNA

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  1. From Mendel to DNA

  2. Recap from previous lessons • Mitosis produces daughter cells with: • fewer chromosomes than the parent cell • more chromosomes than the parent cell • the same number of chromosomes as the parent cell

  3. -C

  4. 2. As a result of mitosis, how many cells are produced? • One • Two • Four

  5. -B

  6. 3. How many pairs of chromosomes does a human body cell contain? • 4 • 23 • 46

  7. -B

  8. 4. Which statement about sex chromosomes is correct? • Females are XY and males are XX. • Females and males are XX. • Females are XX and males are XY.

  9. -C

  10. 5. Where are the cell's chromosomes found? • In its nucleus. • In its cytoplasm. • In its mitochondria.

  11. -A

  12. 6. Compared to a body cell, a gamete contains: • Half the genetic information. • The same amount of genetic information. • Twice the genetic information.

  13. -A

  14. Higher Questions • During meiosis: • No copies of the chromosomes are made. • Gametes are formed, each with a single set of chromosomes. • The cell divides five times to form four gametes.

  15. -B

  16. 8. As a result of meiosis, how many sex cells are produced? • One • Two • Four

  17. -C

  18. Learning Objectives • To understand the work Mendel carried out and why its importance was not recognised until after his death. • To know why DNA fingerprinting is possible.

  19. Early Beliefs and Mendel

  20. Pioneer of Genetics: Gregor Mendel One of the classic scientific experiments on inheritance was performed by an Austrian monk named Gregor Mendel (1822–1884)

  21. Mendel’s work with garden peas….. Why did Mendel choose the garden pea on which to perform his work?

  22. Chromosomes • The 2 chromosomes in each pair carry information for the same characteristic • Examples of characteristic include eye colour, hair colour etc... • So each body cell has 2 sets of information for all of your characteristics • One set is inherited from your mother the other from your • father One set of information for eye colour from father One set of information for eye colour from mother

  23. Inheritance of Characteristics • Just like us, the pea plants chromosomes also come in pairs • And just like us, each pair carries genes for the same characteristic • Sometimes the form of these genes are different and sometimes they are the same • Different forms of genes are • called alleles One set of information from ‘mother’ One set of information from ‘father’

  24. Inheritance of Characteristics White and Purple pea plant bred together All the offspring (F1 generation) are Purple

  25. Inheritance of Characteristics 2 purple pea plants from the F1 generation crossed The offspring (F2 generation) are purple and white. Mendel wondered how white flowers could disappear for a generation but then come back

  26. Inheritance of Characteristics • The combination of alleles determines what our characteristics will be • Alleles can be either Dominant or Recessive • You will always see the effect of the dominant allele over the recessive one.

  27. Allele Example • In pea plants Purple flowers are dominant and white flowers are recessive For a flower to be white it must have 2 white alleles. Since the white colour is recessive For a flower to be purple it could have 2 purple alleles or one white and one purple allele. Since purple is the dominate colour

  28. We can show inheritance of flower colour using a genetic diagram. We use capital letters to represent the dominant allele and the same lower case letter to represent the recessive allele. PP pp Pp

  29. Pp Pp P p PP Pp P Pp pp p

  30. Mendel Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel, • When a tall pea plant was crossed with a dwarf pea plant – all offspring were tall pea plants (i.e. 100% identical) • When the two offspring (tall pea plants), three of the offspring were tall and one was a dwarf (i.e. 3:1)– why?

  31. Genetic Crosses Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel, Tall x Dwarf TALL plants (TT) 100 ‘Tt’ As ‘T’ is DOMINANT and ‘t’ is RECESSIVE, All plants are TALL carriers. T T DWARF plants (tt) t Tt Tf t Tt Tt

  32. Genetic Crosses Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel, Tall Carrier x Tall Carrier TALL CARRIER plants (Tt) TT = Tall Tt = Tall tt = dwarf So 3:1 T t T TT Tf t Tt tt

  33. Genetic Crosses Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel, Alleles are different forms of the same gene. Normal Boring Hamster All Bb So, all are normal and boring hamsters. B B Wild Scatty Hamster b Bb Bb b Bb Bb

  34. Genetic Crosses Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel, Bb x Bb – What are their offspring like? BB = Tall Bb = Tall bb = dwarf So 3:1 B b B BB Bb b Bb bb

  35. Homozygous Dominant Homozygous Recessive Heterozygous

  36. Recessive

  37. He published a book of his findings in 1866, when he was 44 years old. • People did not understand his theories as no one had seen chromosomes. • He died 20 years later with no one taking notice of his work.

  38. 16 years after his death people could finally see chromosomes through a microscope and he was given the recognition for his findings.

  39. Cystic Fibrosis Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel, This is a genetic disorder of the cell membranes. It results in a thick sticky mucus in the air passages and in the pancreas.

  40. Huntington’s Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel, This is a genetic disorder of the nervous system which results in shaking, erratic body movements and eventually severe mental deterioration.

  41. Genetic Disorders Keywords: Chromosomes, Alleles, Genetic Crosses, Mendel, • Cystic Fibrosis is caused by a recessive allele. For a child to have Cystic Fibrosis, but its parents not to have the condition, what must the parent genetic code be? Draw a genetic diagram to explain your answer. • Huntington’s is a disease that is caused by a dominant allele. What is the chance of offspring having Huntington’s when one parent is normal and the other is a carrier/sufferer? • Before embryos are inserted back into the female in IVF, the embryo are screened for genetic disorders. Is the screening of embryo’s right or wrong? Cc x Cc 50% (Nn x nn)

  42. Single-Trait Inheritance 1. Since one allele is inherited from each parent, various genotypes are possible. 2. The dominant phenotype is expressed if the offspring is either heterozygous or homozygous for the dominant allele.

  43. 3. The recessive phenotype is expressed only if the offspring is homozygous for the recessive allele. 4. When there are multiple alleles for a given characteristic, the alleles have a dominance hierarchy.

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