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Genetics Fundamentals
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What is Genetics???
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Genetics is the science and study of heredity
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Whats heredity?
n
Heredity—the passing of traits from one generation to the
next
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So how do we inherit traits from
our parents???
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Hippocrates (ancient father of
medicine) suggested an explanation
called pangensis
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Pangensis—particles called
pangenes travel from each part of an
organism’s body to the eggs or sperm
and are then passed to the next
generation
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Aristotle says Nuh-uh!
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According to Hippocrates, if you
were to start really, and I mean
REALLY pumping iron and getting
buff, then your children would pop
out with biceps and a 6 pack!
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This is so not true!
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By observing inheritance patterns
in ornamental plants, biologists
established that offspring inherit
traits from BOTH parents. This is
called the “blending hypothesis.”
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Blending Hypothesis… not so
much!
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Gregor Mendel
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What up Gregor?!
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An Austrian Monk who studied
physics, mathematics and
chemistry at the University of
Vienna
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Hobbies: Gregor enjoys working in
the garden, cross pollinating plants
and recording the inheritance of
traits from one generation to the
next! He also enjoys long walks on
the beach
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Gregor Mendel
n  He
found—heritable traits (genes)
from the parents maintain their
individuality.
n  Meaning, they don’t blend! Like a
jar of marbles
n  Mendel
chose to study garden peas
n  Garden
peas regularly selfpollinate, which gave Mendel an
advantage to be able to control
cross fertilization
n  Cross
fertilization—fertilization of
one plant by pollen from a different
plant
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Gregor Mendell
He prevented self-fertilization
by cutting off the immature
stamens of a plant before they
produced pollen
He dusted its carpel with
pollen from another plant
After pollination, the carpel
developed into a pod with
seeds
He planted the seeds and the
next generation grew!
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Why pea plants??
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True-breeding
n True-breeding
varieties—varieties
for which self-fertilization produced
offspring all identical to the parent
n Mendel
made sure he had truebreeding lines of pea plants and then
began to cross pollinate them
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What would happen if I crossed
pea plants with purple flowers and
pea plants with white flowers??
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A hybrid-cross—cross fertilization
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Hybrids—the offspring of two different varieties
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How do we keep track of the parents, the offspring, their
offspring… etc to track the inherited traits?
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Generations!
n  P
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generation—The true-breeding parents
(parental generation)
n  F1
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generation—the hybrid offspring of the P generation
(filial generation)
n  F2
generation—the hybrid offspring of organisms from
an F1 generation
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(filial 2 generation)
n  Your
grandparents (on both sides) are the P generation,
your parents are the F1 generation, and you are the F2
generation! (even though humans aren’t truebreeding)
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Mendel
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After developing his truebreeding plants, Mendel crossfertilized specific plants and
kept tract of all generations.
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For example, he chose 1 purple
flowering plant and 1 white
flowering plant as the P
generation.
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He crossed them, and then
planted their seeds (the F1
generation)
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Then allowed the F1 generation
to either self-fertilize, or he
crossed them with an F1
generation from other line
(creating the F2 generation)
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If genes from both parents, how
can only 1 trait be inherited?
n For
example: Mendel crossed one pea plant
with purple flowers and a plant with white
flowers
n This
n  The
is a monohybrid cross
parent plants (P generation) differ in only
one characteristic
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When he performed this
monohybrid cross, all offspring
had purple flowers
n What
happened to the white flower genes
in the F1 generation?
n Mendel
then monohybrid crossed two
purple flower plants from the F1 generation
n He
found about 705 (3/4) had purple
flowers and 224 (1/4) had white flowers.
n A
ratio of 3 to 1!!
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The white flower genes did not
disappear!
n But
somehow the purple gene
was affecting the white gene in
the F1 generation.
n Through
this experiment and
others, Mendel developed four
hypotheses
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Mendel’s 4 hypotheses
n 1. There
are alternative forms of genes
that account for variations in inherited
characteristics
n Alleles—alternative
n Purple
n White
color = P
color = p
versions of a gene
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Mendel’s 4 hypotheses
n  2. For
each characteristic, an organism inherits
two alleles, one from each parent. These alleles
may be the same or different
n  Flowers
with the same two alleles for a trait are
called homozygous
n  Purple flowers PP or white flower pp
n  Flowers
with different alleles for a trait are called
heterozygous
n  Purple flowers Pp
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Mendel’s 4 hypotheses
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3. If the two alleles of an inherited trait differ, then one
determines the organism’s appearance and is called the
dominant allele; the other has no noticeable effect on the
organism’s appearance and is called the recessive allele
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We use uppercase letters to represent dominant alleles and
lowercase letters to represent recessive alleles
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Purple is dominant = P
white is recessive = p
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Mendel’s 4 hypotheses
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4. A sperm or egg carries only one allele for each inherited
trait because allele pairs separate (segregate) from each
other during the production of gametes
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This is known as the law of segregation
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When egg and sperm are reunited at fertilization, each
contributes its allele, restoring the paired condition in the
offspring
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So wait a second…. What are
alleles?
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DNA = genetic material
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A series of bases = a gene
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An allele refers to that specific sequence
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Remember, you get half of your chromosomes from dad and
half from mom. One allele, which is one sequence of DNA that
codes for one gene, is usually dominant over the other.
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Genes and Traits
n The
genetic make up of your
genes (the combination of
your alleles is called a
genotype
n The
physical appearance
you notice as a result of your
alleles is called a phenotype
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Homologous Chromsomes