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Autosomal Dominant Gene Disease
- Abnormal Gene comes from one parent
- Parent with the condition has 50% chance of an affected child
- Abnormal gene of one of he first 22 genes
- children who do not inherit the disease will not develop or pass down the disease
- can occur when

HUNTINGTON'S DISEASE
- Causes breakdown of nerve cells in the brain
- main symptoms are cognitive and movement problems (muscle problems, slow eye movement, balance issues, speech difficulty, difficultly with thought process)

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Inheritance
- two inherited genes that are changed or mutated (one from each parent)
- 25% unaffected, child 50% carrier (unaffected) child and 25% affected child
- Because the parents only have one, they are likely unaffected.
Example
- Cystic Fibrosis (CF)
- symptoms included: severe damage to the digestive system, lungs, and other organs in the body
- the cells that produce sweat, mucus, and digestive fluids are affected
- Debilitating to live with, often times they can't go to work or school

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Inheritance pattern: sex-linked
- passed down through families through one of the X or Y chromosomes
- sex-linked traits usually refer to traits due to genes on the X chromosome
- also are disorders associated with the Y chromosome, but these are inherited less frequently because they often associate with infertility
- Dominant inheritance is when one parent causes the disease, even though gene from other parent is normal
- recessive inheritance is when both genes are abnormal
- many sex-linked traits are inherited in a recessive manner
- X-linked recessive diseases most often occur in males - a single recessive gene on that chromosome will cause disease
- Y chromosome doesn't contain most of the genes of the X chromosome, so doesn't protect the male
- females can get an X-linked recessive disorder, but it is very rare because an abnormal gene would be required from both parents
- if male as one abnormal gene, than disease is prevalent, if females have one abnormal gene, than they are carriers

Colour blindness:
- recessive gene on X chromosome
- males need one copy of the abnormal recessive gene to be colourblind, females need two copies to be colourblind
Symptoms:
- red-green colour blindness: cannot tell the difference between red and green, appear as shades of brown

Hemophilia:
- occurs from a recessive gene on the X chromosome
- affects the blood's ability to clot
Symptoms:
- people with hemophilia do not have as many clotting factors as they should have in their blood - they will bleed for longer than usual
- ie nosebleeds that take a long time to stop, bleeding gums

Duchenne Muscular Dystrophy (DMD)
- fatal neuromuscular disorder caused by a recessive mutation on the X chromosome
- DMD gene encodes dystrophin, a huge muscle protein that helps maintain structural integrity of muscle cells
- cells with mutated DMD genes cannot make dystrophin
Symptoms
- most babies do not start showing signs of disease until 3-5 years old
- first symptom is muscle weakness - cannot climb stairs or finds it challenging to run
- people often have to use a wheelchair when muscle weakness worsens
- often is a fatal disease when people reach 20s or 30s, results in heart or respiratory problems

Sources:
https://medlineplus.gov/ency/article/002051.htm#:~:text=Sex%2Dlinked%20diseases%20are%20passed,The%20abnormal%20gene%20dominates.
https://flexbooks.ck12.org/cbook/ck-12-middle-school-life-science-2.0/section/3.13/primary/lesson/sex-linked-inheritance-ms-ls/
https://www.nhs.uk/conditions/haemophilia/
https://www.nature.com/scitable/topicpage/sex-linked-diseases-the-case-of-duchenne-800/