Note (Phenotype = The visible characteristic as a result of their genes)
(Genotype = The alleles that an organism has. usually written as a specific letter)
Cystic
Fibrosis-
Symptoms:
Build up of
sticky mucus in the lungs, can cause breathing problems and increase risk of
lung infections. Mucus also clogs the pancreas (digestion), this stops enzymes (protease, carbohydrase,
lipase) reaching food in the gut and helping with digestion. This means people
with cystic fibrosis don’t absorb nutrients from food as well so need to eat
more food. This is why they have an increased hunger with not as much growth.
It is caused by
a recessive allele, this means only homozygous recessive individuals will be
affected
Treatments:
No cure, but
some treatments to control symptoms e.g bronchodilators to widen airways and
make breathing easier
Punnet Square:
“f” is the
cystic fibrosis allele
Homozygous =
(ff-will develop cystic fibrosis)
Heterozygous =(Ff-will
not develop cystic fibrosis)
Homozygous =
(FF-will not develop cystic fibrosis)
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Mother
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Father
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F
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f
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F
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FF
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Ff
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F
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Ff
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ff
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Pedigree
Diagram:
Test Cross:
Down
Syndrome-
Symptoms:
Floppiness, flat
back of head and delayed development (Not always set characteristic of a down
syndrome). Could be problems with the heart and bowel and difficulties with
hearing and vision.
It is caused by
the presence of an extra chromosome. So a sperm cell with 23 chromosomes fertilises
with an egg cell with 24 chromosomes. So they will have 47 chromosomes rather
than the normal 46. They have three copies of the 21st chromosome
rather than 2.
Treatments:
Nothing medical
like medicine. Just therapies and special education.
Haemophilia-
Symptoms:
Ability for the
blood to clot is severely reduced, causing the sufferer to bleed severely from
even the smallest cut.
Caused by a
recessive allele on the X chromosome
Treatments:
There are
genetically engineered clotting factor medicines that are used to prevent and
treat prolonged bleeding. These are given as an injection.
Huntington’s
disease-
Symptoms:
Causes damage
to certain brain cells and is caused by a dominant allele. It’s a progressive brain
disorder that causes uncontrolled movements, emotional problems and loss of cognition.
Caused by the
presence of one dominant allele.
Treatments:
Specific medicines
for antidepressants or medicines to reduce involuntary movements
Genetic Diagram:
Dominant allele
= H (and is the one that causes Huntington’s disease)
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Mother
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Father
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h
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h
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H
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Hh
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Hh
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h
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hh
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hh
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Here, the mother is
homozygous and the father is heterozygous. So the chance of them producing a child
with Huntington’s disease is 50%
Polydactyls-
Symptoms:
Could be an
extra finger or toe.
Caused by a
dominant allele. (so 50/50 for offspring to have polydactyls)
Treatments:
Usually treated
in early childhood, with the removal of the extra digit
Colour
Blindness-
Symptoms:
Difficulty distinguishing
between colours. The inability to see shades or tones of the same colour.
This one is
more complicated. It is “ X-linked recessive” meaning that the gene causing the
trait or the disorder is located on the X chromosome. Females have two X
chromosomes; males have one X and one Y. There is a 50% chance that the
daughter will carry the gene and pass it onto the next generation. And a 50% chance
that the daughter will not carry the gene, so won’t be able to carry it on.
There is a 50% chance the son will not have the gene and will not be able to
pass it on. However there is 50% chance that the son will have inherited the
gene and will express the colour blindness.
“Their expression in females and
males is not the same. Genes on the Y chromosome do not exactly pair up
with the genes on the X chromosome. X-linked recessive genes are expressed in
females only if there are two copies of the gene (one on each X chromosome).
However, for males, there needs to be only one copy of an X-linked
recessive gene in order for the trait or disorder to be expressed. For example,
a woman can carry a recessive gene on one of the X chromosomes unknowingly, and
pass it on to a son, who will express the trait”
Treatments:
No cure, but contact
lenses and glasses are available with filters.
https://www.chop.edu/conditions-diseases/x-linked-recessive-red-green-color-blindness-hemophilia
