Genetics: An Introduction
BIOLOGY 12
A little motivational video:
 http://www.youtube.com/watch?v=B_PQ8qYtUL0
What is Genetics?
 The science that studies heredity
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Heredity is the passing of traits from parents to offspring
Joke of the day:
Variation:
 Genetic variation describes naturally occurring
genetic differences among individuals of the same
species
 Why?
 Recombination of chromosomes that occurs during sexual
reproduction (called independent assortment)
 Crossing over during meiosis
Some vocabulary:
 Genes
 Humans have ~21,500
 Chemical instructions for building proteins
 Locus/loci: specific location on a chromosome
 Diploid cells contain two copies of each gene on pairs
of homologous chromosomes
 Allele: each version of a gene
Video: ABC News: All in the family: Mixed race twins
 http://abcnews.go.com/Health/twins-white-black-born-biracial-
parents-stirs-issues/story?id=12984334
The color of skin is genetically very complicated!
 Skin color comes from the
pigment melanin
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Produced by melanocytes in skin
cells
More than 100 genes directly or
indirectly influence amount of
melanin in an individual’s skin
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Lead to many variations in skin color
History of Genetics
 People have known about inheritance for a long
time.
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children resemble their parents
domestication of animals and plants, selective breeding for
good characteristics
Sumerian horse breeding records
Egyptian data palm breeding
Mid 1800’s Discoveries
 Major events in the mid-1800’s
led directly to the development
of modern genetics.
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1859: Charles Darwin publishes The
Origin of Species, which describes
the theory of evolution by natural
selection. This theory requires
heredity to work.
1866: Gregor Mendel publishes
Experiments in Plant Hybridization,
which lays out the basic theory of
genetics. It is widely ignored until
1900.
History of Genetics:
 Pioneer of Genetics: Gregor Mendel
 Born in 1822 in Czechoslovakia.
 Became a monk at a monastery in
1843.
 Taught biology and had interests in
statistics.
 Also studied at the University of
Vienna
Major Events in the 20th Century
 1900: rediscovery of Mendel’s work by Robert Correns, Hugo de
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Vries, and Erich von Tschermak .
1904: Gregory Bateson discovers linkage between genes. Also
coins the word “genetics”.
1910: Thomas Hunt Morgan proves that genes are located on the
chromosomes (using Drosophila).
1944: Oswald Avery, Colin MacLeod and Maclyn McCarty show
that DNA can transform bacteria, demonstrating that DNA is the
hereditary material.
1953: James Watson and Francis Crick determine the structure
of the DNA molecule, which leads directly to knowledge of how it
replicates
1966: Marshall Nirenberg solves the genetic code, showing that 3
DNA bases code for one amino acid.
1972: Stanley Cohen and Herbert Boyer combine DNA from two
different species in vitro, then transform it into bacterial cells:
first DNA cloning.
2001: Sequence of the entire human genome is announced.
To do :
 Read pages 130 and 131.
 Read Mendel biography articles and answer the
questions at the bottom based on both readings!