Genetic Diseases

Genetic Diseases

Understanding how mutations are inherited

Mutations

Genetic diseases are a result of mutations. Deletions, additions (insertions and duplications) and substitutions can all happen at the point level, but can also happen to entire segments and entire chromosomes.

Multiple Choice

What is a "point mutation?"

• A mutation that is silent.

• A mutation that occurs only as a recessive trait.

• A mutation that occurs at one singe nucleotide in a gene.

How are they inherited?

• The answer- it depends on the location of the mutation

• AND if it resides on a recessive or dominant allele

• Some mutations are not hereditary although they happen at the germ line, such as Down's syndrome. These just happen spontaneously: De Novo.

• Let's look at some examples of various disorders and how they are inherited.

Autosomal Recessive Disorders

"Autosomal" means on any chromosome besides the sex chromosome. These disorders need 2 copies of the damaged gene to show up in a phenotype, because they are recessive.

EXAMPLE: Cystic Fibrosis

Sickle Cell Anemia

Sickle cell is another Autosomal Recessive disease. However, it is strange in that those who are just carriers still express some sickle-shape, but do not have the disease. (Incomplete dominance!)

More about Sickle Cell

Carriers (Ss) don't have the disease, but their blood cells slightly sickle in, which actually protects these individuals from Malaria. (An example of good mutation?)

Autosomal Dominant

Autosomal dominant disorders are disorders on non-sex chromosomes, located on dominant alleles.

An example: Huntington's Disease

Huntington's Disease

• Caused by a repeat of C-A-G codons on the huntingtin gene- HTTT, which is on the short arm of Chromosome 4. (Normal is 20 repeats, those with Huntington's have 35 or more.)

• Onset of the disease is ages 30-50, so often those who have have already passed it on to their children.

Multiple Choice

A genetic disorder that is NOT found on a sex chromosome.

• Sex-linked

• Autosomal

• De Novo

Multiple Choice

How many autosomal recessive alleles need to be inherited for a person to show the trait (or disease) in their phenotype?

• 1

• 2

• 4

• 0

Multiple Select

How many autosomal dominant alleles need to be inherited in order for a trait or disease to appear in the phenotype? (check all that apply.)

• 0

• 1

• 2

• 3

Multiple Choice

What is the autosomal recessive disorder that causes build-up of mucus in pathways of the body?

• Huntington's Disease

• Sickle-Cell Disease

• Cystic Fibrosis

• Cancer

Multiple Select

Check all that apply. Sickle-Cell Disease:

• Damages tissue due to reduced oxygen levels and poor blood circulation.

• Only effects females

• shortens the lifespan of those who have it.

• is autosomal recessive.

Multiple Choice

Why does Huntington's disease lead to cognitive decline, among other things?

• It causes cancer.

• It causes loss in volume of brain tissue.

• It damages the brain from a young age.

Sex-Linked Disorders

• Sex-linked disorders arise from mutations that reside on the X and Y chromosomes.

• They can be dominant or recessive, but for males, sex-linked disorders always show up in the phenotype. Why do you think that is?

Hemophilia

Hemophilia is a sex-linked recessive disorder that keeps blood from clotting. This can be deadly.

Because it is recessive, females are usually just carriers. But males only inherit 1 allele for this trait. If born from a female carrier, they will have 50% of having hemophilia.

A little unfair for our XY males.

• Other disorders follow this same inheritance, such as...

• Color blindness

• Baldness

• Duchenne Muscular Dystrophy

Multiple Choice

Genes located on the X and Y chromosome are called

• Sex-linked

• autosomal

• de novo

Multiple Choice

How many alleles to males inherit from genes located on the X chromosome?

• 1

• 2

• 3

• 4

Non-disjunction of Sex Chromosome disorders

• De Novo disorders: Error happens in gamete formation

• Klienfelter's Syndrome (XXY Males)

• Turner's Syndrome X Females (or Xx with a damaged second X.)

• Jacob's Syndrome XYY males (also called super-male)

• Triple X Syndrome, (also called super-female)

Klinefelter's Syndrome XXY

• Males have an extra X chromosome

• Leads to female characteristics

• Slightly lower IQ but not to the level of disability

• Small testes

• fertility issues (ranges)

Turner's Syndrome

• Females only inherit 1 X, or the second is damaged

• Small stature and webbed-neck

• Other physical abnormalities

• Infertile

• Kidney malformation

• Mental delays, lower IQ

Jacob's Syndrome

• Taller than average male

• Aggression and lack of inhibition

• No physical deformities

• Low sperm count

• estimated that over half of violent offenders in prisons have XYY

• Lower than average IQ

Triple X Syndrome

• Female with an extra X chromosome

• Taller than average

• Struggles with emotional regulation

• Developmental delays and lower than average IQ

• Ovarian Failure

• Weak muscle tone

• Adults: higher fat storage percentage