Beyond Mendel Genetic changes and Human heredity

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Beyond Mendel Genetic changes and Human heredity

• Last part of Chapter 11 and Chapter 12 for gifted
  book

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• 1879 Walther Flemming German biologist first
  sees the CHROMOSOMES!!!
• also observed and described MITOSIS and noted
  that a full set of chromosomes was being passed
  on to each daughter cell.
• Sixteen years after Mendels death,
  scientists realize that the chromosomes are the
  carriers of heredity Mendels FACTORS are
  ensuring the passing of traits from parents to
  offspring.
• 1902 Walter Sutton American biologist who
  supports idea that factors are located on
  chromosomes

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• 1905 E.B. Wilson and Nettie Stevens Americans
  studying insect chromosomes
• Saw that male insects always showed a
• chromosome that did not seem to have a match
  (females always had a perfect matching set of
  chromosomes.) Thus, they referred to the
  non-matching chromosomes as Sex Chromosomes.
• In females the sex chromosomes do match
• XX
• In males, one of the chromosomes looked as if it
  were missing a part, so called it a Y
• XY

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• 1909 Wilhelm Johannsen Danish biologist who
  coined the term gene to define the physical
  units of heredity
• GENE segment of DNA molecules that carries the
  instructions for producing a specific trait

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• 1912 Thomas Hunt Morgan Showed evidence that
  the presence of white eye color in fruit flies
  was associated with a particular gene on a
  particular chromosome. (Sex Linked traits)

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Inheritance
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What is Sex Determination?
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A. Begins with the differentiation of the sex
chromosomes in males and females
1. These characteristics were observed by Thomas
Hunt Morgan in the early 1900s while studying
fruit flies (Drosophilia)
2. Hypothesized that these chromosomes
determined the organisms sex
B. Sex chromosomes (in pairs) separated during
meiosis I
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Punnett Squares
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C. Sex Linkage
1. The presence of a gene on a sex chromosome
a. Some genes on sex chromosomes play a role in
sex determination, but these chromosomes also
contain genes for other traits (see Linkage
Groups)
2. Morgan hypothesized that more genes could be
carried on the X chromosome than the Y chromosome
a. Genes found on the X chromosome are
considered X-linked genes
b. Genes found on the Y chromosome are
considered Y-linked genes
c. There are more X-linked than Y-linked traits
due to the size of the X chromosome
D. X-Linked Traits
1. A gene located on the X chromosome codes for
that trait
a. Example Red-Green Color Blindness
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E. Sex-Influenced Traits
1. The presence of male or female sex hormones
influences the expression of certain human traits

2. Males and females have different phenotypes
but can have the same genotypes.
a. A trait may only be expressed in one sex
Example Male Pattern Baldness