Download what`s in your genes

Gregor Mendel
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Mendelian
Inheritance
Gregor Mendel
Austrian monk
Studied science and mathematics at
University of Vienna
Conducted breeding experiments with the
garden pea Pisum sativum
Carefully gathered and documented
mathematical data from his experiments
Formulated fundamental laws of heredity in
early 1860s
Had no knowledge of cells or chromosomes
Did not have a microscope
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Fruit and Flower of the
Garden Pea
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Garden Pea Traits
Studied by Mendel
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Mendelian
Inheritance
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Blending Inheritance
Theories of inheritance in Mendel’s time:
Based on blending
Parents of contrasting appearance produce
offspring of intermediate appearance
Mendel’s findings were in contrast with this
He formulated the particulate theory of
inheritance
Inheritance involves reshuffling of genes from
generation to generation
Mendel’s Monohybrid Crosses:
An Example
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Mendelian
Inheritance
One-Trait Inheritance
Mendel performed cross-breeding
experiments
Used “true-breeding” (homozygous) plants
Chose varieties that differed in only one trait
(monohybrid cross)
Performed reciprocal crosses
- Parental generation = P
- First filial generation offspring = F1
- Second filial generation offspring = F2
Formulated the Law of Segregation
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Mendel’s Monohybrid Crosses:
Mendelian
Inheritance
An Example
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Mendelian
Inheritance
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Law of Segregation
Each individual has a pair of factors (alleles)
for each trait
The factors (alleles) segregate (separate)
during gamete (sperm & egg) formation
Each gamete contains only one factor (allele)
from each pair
Fertilization gives the offspring two factors for
each trait
Mendelian
Inheritance
Modern Genetics View
Each trait in a pea plant is controlled by two
alleles (alternate forms of a gene)
Dominant allele (capital letter) masks the
expression of the recessive allele (lowercase)
Alleles occur on a homologous pair of
chromosomes at a particular gene locus
Homozygous = identical alleles
Heterozygous = different alleles
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Homologous Chromosomes
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Mendelian
Inheritance
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Genotype Versus Phenotype
Genotype
Refers to the two alleles an individual has for
a specific trait
If identical, genotype is homozygous
If different, genotype is heterozygous
Phenotype
Refers to the physical appearance of the
individual
Mendelian
Inheritance
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Punnett Square
Table listing all possible genotypes resulting
from a cross
All possible sperm genotypes are lined up on
one side
All possible egg genotypes are lined up on the
other side
Every possible zygote genotypes are placed
within the squares
Punnett Square Showing
Earlobe Inheritance Patterns
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Try this one
MONOHYBRID CROSS
Cross a heterozygous tall plant with
a heterozygous tall plant (use T =
tall and t = short) Determine
expected genotype and phenotype
ratios.
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Try these!
Show work
1. Cross a heterozygous red flower with a white
flower. What is the genotype and phenotype
ratio for the offspring? Key: R = red r = white
Mendelian
Inheritance
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Two-Trait Inheritance
Dihybrid cross uses true-breeding plants
differing in two traits
Observed phenotypes among F2 plants
Formulated Law of Independent Assortment
- The pair of factors for one trait segregate
independently of the factors for other traits
- All possible combinations of factors can occur
in the gametes
Mendelian
Inheritance
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Try Mendel’s Classic Dihybrid Cross
Cross two heterozygous tall, heterozygous
green pod producing plants. Use a punnett
square to show expected offspring and
complete a phenotype ratio.
Key:
T = tall
G = green pods
t = short
g = yellow pods
Mendelian
Inheritance
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Two-Trait (Dihybrid) Cross
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Must Know Your Vocab!
Homozygous?
Heterozygous?
Genotype?
Phenotype?
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Try this one – DIHYBRID CROSS
2 traits
Key: T = tall R = red
-
t = short r = white
Cross two heterozygous tall,
heterozygous red flowered plants.
What is the phenotypic ratio of the
offspring?
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Two-Trait (Dihybrid) Cross
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P-square practice
Practice crosses – on a separate
sheet of paper.
• Show parental cross
• Show p-square
• Show phenotype ratio
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WHAT’s IN YOUR GENES?
Mom = 22 autosomes plus X sex
chromosome
Dad = 22 autosomes plus X or Y
chromosome
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Boy or Girl?
Dad determines this – sperm carries
22 autosomes and either an X or Y
sex chromosome
BOYS – your mom gave you the X
and dad gave you the Y – so what?
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Sex-linked – disorders carried on the
X chromosome
- Colorblindness
- Hemophilia
- Baldness (?)
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Analyze Sex-linked traits
Due tom!
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- Albinism ppt
- Huntingtons ppt
- Final concepts
Autosomal Recessive Pedigree Chart
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Autosomal Dominant Pedigree Chart
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INHERITING
A GENE ALBINISM
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This is an
albino
skunk. The
cells are not
able to
produce the
protein that
causes
color.
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Cells in the skin produce a blackbrown pigment called melanin.
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The chemical
melanin is
produced by
specialized cells
in the epidermis
called
melanocytes.
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The melanin leaves the
melanocytes and enters other
cells closer to the surface of
the skin.
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Different
shades of skin
colors is
determined by
the amount of
melanin
deposited in
these
epidermal cells
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Sunlight
causes
melanocytes
to increase
production
of melanin.
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A tan fades because the cells break down the melanin.
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Some
organisms,
such as the
octopus,
can
rapidly
change
from light
to dark.
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They control the color by scattering the
melanin in the cell for a dark color,
and concentrating the melanin in the
center for light color.
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Melanin is made by the melanocytes
by chemically changing the amino
acid, phenylalanin, into tyrosine and
then into melanin.
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An enzyme is required
to change tyrosine into
melanin.
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If the enzyme is not
present, then melanin
cannot be produced by the
melanocytes.
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The result of no melanin is an albino.
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The eyes of an albino appear pink
because there is no dark melanin
in the eye to absorb light.
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The blood in the retina and iris
reflects red light, resulting in pink
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The gene
that
produces
this
enzyme
is on
chromosome 9
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If both the
genes produce
the enzyme
tyrosinase,
there is plenty
to convert
tyrosine to
melanin.
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If neither
gene
produces
tryosinase,
no melanin is
produced
and…
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The
crow is
an
albino
rather
than the
normal
black
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What if one
gene is
normal and
one gene does
not produce
the enzyme?
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The one normal gene produces
enough enzyme to make normal crow
color
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This albino squirrel received one albino gene from
the father and one albino gene from the mother.
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But what if a squirrel
gets a normal gene
from one parent and
an albino gene from
the other parent?
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The one
functioning
gene produces
enough enzyme
to make
melanin for
normal
coloration.
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Is it
possible
for two
normal
colored
cockatiels
to have an
albino
offspring?
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Yes!
Remember
the albino
has two
genes for
albinism.
One gene
from the
father and
one gene
from the
mother.
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To be albino,
both genes
must be
albino genes
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A normal
colored bird
could have
one albino
gene and one
normal gene.
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If the sperm of a normal colored male pigeon
has an albino gene and the ova it fertilizes has
an albino gene than the offspring will be albino.
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The same
happens in
humans. A
normal
pigment
father and
mother can
have an
albino
offspring.
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We can see this in a genetic “family tree”
called a pedigree. The circles are
females, the squares are males. The open
symbols are normal coloration, the black
symbols are albino.
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The parents in the circle have
normal pigment.
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Most of the offspring received
at least one normal gene from
a parent.
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But one female offspring
received an albino gene from
both the mother and the father.
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A Punnett square is a matrix to show
the genetics of a mating.
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What is the probability
of an albino doe giving
birth to a “normal”
fawn if she has mated
with a “normal” male?
The 74
female
must
have two
albino
genes
(use small
“a” for
the albino
gene
- aa
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Since the albino gene is
relatively rare, the male
probably has two normal
genes of color. (Capital
“A” stands for the
normal gene)
- AA
AA X aa
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Next, add the possible sperm and
ova genes.
A
A
a
Aa
Aa
a
Aa
Aa
As long as there is one normal
gene, none of the offsprings will
be albino
A
A
a
Aa
Aa
a
Aa
Aa
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Therefore, all offsprings will have
a normal and an albino gene.
A
A
a
Aa
Aa
a
Aa
Aa
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An albino must get one
albino gene from the
father and one albino
gene from the mother.
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Then how
could an
albino
female
penguin
have an
albino chick.
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The “normal” colored
father must have one
“normal coloration gene
and one albino gene.
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There is only one
way for two normal
colored parents to
produce an albino
offspring.
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Both parents must
have one normal
gene and one albino
gene.
Both
parents
have one
gene for
normal
and one
gene for
albinism.
Aa X Aa
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The
father’s
sperm is
50%
with
normal
gene and
50%
with
albino
gene.
Aa X Aa
A
a
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50% of
the
mother’s
ova have
a normal
gene and
50% of
the ova
have the
albino
gene
Aa X Aa
A
a
A
a
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The ova and
sperm may
combine to
form an
offspring
with two
normal
genes, a
normal gene
and an albino
gene, or two
albino genes.
Aa X Aa
A
a
A AA Aa
a Aa aa
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Only the
offspring
with two
albino
genes will
lack
pigment.
Aa X Aa
A
a
A AA Aa
a Aa aa
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Sometimes an albino is born and
there is no history of albinism in
the colony.
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The color
gene in the
cell that
produced this
white flower
changed to an
albino gene.
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A change in a gene is called a mutation.
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