Chapter 3 Sections 3

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Chapter 3 Sections 3 4

• General Science 7

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INTRODUCTION

• Gregor Mendel provided many early solutions to
  the riddle of genetics however, he did not have
  all of the answers.
• Mendel did not know where the hereditary factors,
  or genes, are located in the cell.
• 1882 German biologist Walter Flemming discovered
  chromosomes.

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INTRODUCTION

• Chromosomes rod-shaped structures that are
  found in the nucleus of every cell in an
  organism.
• 1902 Walter Sutton, an American graduate student
  who in was doing research on grasshopper
  chromosomes.
• Sutton concluded that chromosomes carried
  Mendels hereditary factors, or genes, from one
  generation to the next.

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Grasshoppers have 24 chromosomes, arranged in 12
pairs.
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Each of a grasshopper's sex cells contains 12
chromosomes, or half the number in body cells.
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Chromosome Theory of Inheritance

• Meaning genes are located on chromosomes.
• Suttons idea is known as the chromosome theory
  of heredity.
• According to the chromosome theory
• genes are carried from parents to their
  offspring on chromosomes.

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Chromosomes and Genes

• Chromosomes control all the traits of an
  organism.
• The main function of genes on chromosomes is to
  control the production of substances called
  proteins.
• Proteins help to determine the size, shape, and
  other physical characteristics of an organism.

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Chromosomes and Genes

• The kind and number of proteins in an organism
  determine the traits of that organism.
• So by controlling the kind and number of proteins
  produced in an organism, chromosomes are able to
  determine the traits of that organism.

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Chromosomes and Genes

• Chromosomes are found in pairs within the nucleus
  of a cell.
• For any particular trait, the gene contributed by
  one parent is on one of the paired chromosomes.
• The other gene for that trait, contributed by the
  other parent, is on the second chromosome of the
  pair.
• Each genes major role is to control the
  production of a specific protein.

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Meiosis

• The process of meiosis produces the sex cells,
  the sperm or egg cells.
• As a result of meiosis, the number of chromosomes
  (and genes that they carry) in each sex cell is
  half the normal number of chromosomes found in
  the parent
• Called haploid number
• When the sex cells combine to form the offspring,
  each sex cell contributes half the normal number
  of chromosomes.
• Thus, the offspring gets the normal number of
  chromosomes half from each parent.

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Sex Chromosomes

• In 1907, the American zoologist Thomas Hunt
  Morgan began his own studies in genetics.
• He experimented with insects called fruit flies.
• Morgan quickly discovered something strange about
  the fruit flies four pairs of chromosomes.
• In female fruit flies, the chromosomes of each
  pair were the same shape.
• In males, however, the chromosomes of one pair
  were not the same shape.

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Sex Chromosomes

• One chromosome of the pair was shaped like a rod,
  and the other chromosome was shaped like a hook.
• Morgan called the rod-shaped chromosome the X
  chromosome and the hook-shaped chromosome the Y
  chromosome.
• After performing a number of experiments and
  analyzing his results, Morgan discovered that the
  X and Y chromosomes determine the sex of an
  organism.

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Sex Chromosomes

• For this reason, the X and Y chromosomes are
  called the sex chromosomes.
• In general, an organism that has two X
  chromosomes (XX) is a FEMALE.
• An organism that has one X chromosome and one Y
  chromosome (XY) is a male.
• An exception female birds are (XY).

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How Cells Make Proteins

• Cell uses info from a gene to make a specific
  chromosome
• Takes place on ribosomes
• mRNA (messenger RNA)
• copies genetic code from DNA and carries to
  cytoplasm
• tRNA (transfer RNA)
• Carries amino acid and adds to growing protein

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Protein Synthesis
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DNA versus RNA
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Mutations

• any change that occurs in in a gene or
  chromosome
• -can cause an incorrect protein to form
• this will alter the genotype and
• phenotype of an organism
• TYPES
• Substitution of base pair
• Error during meiosis

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Effects of Mutation

• Some harmful
• Some helpful
• Some neither harmful nor helpful
• Mutations can cause
• Some forms of cancer
• Antibiotic resistance

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End of Chapter 3

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