INHERITING A GENE - ALBINISM
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Transcript of INHERITING A GENE - ALBINISM
INHERITING A GENE - ALBINISM
This is an albino
skunk. The cells are not
able to produce the protein that
causes color.
Cells in the skin produce a black-brown pigment called melanin.
The chemical melanin is
produced by specialized cells in the epidermis
called melanocytes.
The melanin leaves the melanocytes and enters other cells closer to the surface of the skin.
Different shades of skin
colors is determined by the amount of
melanin deposited in
these epidermal cells
Sunlight causes
melanocytes to increase production of melanin.
A tan fades because the cells break down the melanin.
Some organisms, such as the
octopus, can
rapidly change
from light to dark.
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.
Melanin is made by the melanocytes by chemically changing the amino
acid, phenylalanin, into tyrosine and then into melanin.
An enzyme is required to change tyrosine into melanin.
If the enzyme is not present, then melanin
cannot be produced by the melanocytes.
The result of no melanin is an albino.
The eyes of an albino appear pink because there is no dark melanin
in the eye to absorb light.
The blood in the retina and iris reflects red light, resulting in pink
eyes.
The gene that
produces this
enzyme is on
chromo-some 9
If both the genes produce
the enzyme tyrosinase,
there is plenty to convert tyrosine to melanin.
If neither gene
produces tryosinase,
no melanin is produced
and…
The crow is
an albino rather
than the normal black
What if one gene is
normal and one gene does not produce the enzyme?
The one normal gene produces enough enzyme to make normal crow
color
This albino squirrel received one albino gene from the father and one albino gene from the mother.
But what if a squirrel gets a normal gene
from one parent and an albino gene from
the other parent?
The one functioning
gene produces enough enzyme
to make melanin for
normal coloration.
Is it possible for two normal colored
cockatiels to have an
albino offspring?
Yes! Remember the albino
has two genes for albinism. One gene from the
father and one gene from the mother.
To be albino, both genes must be albino
genes
A normal colored bird could have one albino
gene and one normal gene.
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.
The same happens in humans. A
normal pigment
father and mother can
have an albino
offspring.
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.
The parents in the circle have normal pigment.
Most of the offspring received at least one normal gene from
a parent.
But one female offspring received an albino gene from
both the mother and the father.
A Punnett square is a matrix to show the genetics of a mating.
What is the probability of an albino doe giving
birth to a “normal” fawn if she has mated
with a “normal” male?
The female must
have two albino genes
(use small “a” for
the albino gene
- aa
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
Next, add the possible sperm and ova genes.
A A
a
a
Aa Aa
Aa Aa
As long as there is one normal gene, none of the offsprings will be albino A A
a
a
Aa Aa
Aa Aa
Therefore, all offsprings will have a normal and an albino gene.
A A
a
a
Aa Aa
Aa Aa
An albino must get one albino gene from the father and one albino gene from the mother.
Then how could an albino female
penguin have an
albino chick.
The “normal” colored father must have one
“normal coloration gene and one albino gene.
There is only one way for two normal colored parents to produce an albino
offspring.
Both parents must have one normal
gene and one albino gene.
Aa X AaBoth parents have one gene for normal and one gene for albinism.
Aa X Aa
A
a
The father’s sperm is 50% with normal gene and 50% with albino gene.
Aa X Aa
A
a
50% of the mother’s ova have a normal gene and 50% of the ova have the albino gene
A a
Aa X Aa
A
a
A a
AA
aaAa
Aa
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 a
AA
aaAa
Aa
Only the offspring with two albino genes will lack pigment.
Sometimes an albino is born and there is no history of albinism in the colony.
The color gene in the
cell that produced this white flower
changed to an albino gene.
A change in a gene is called a mutation.