Gene - L07: Heredity and Inherited Disorders

bio

Genetics

study of how traits are passed from parent to child through genes and chromosomes

Female chromos

XX

Male chromos

XY

Inherited disorders

* genes are passed from parent to child
* Two types: Dominant and Recessive

Dominant

a trait that will appear in the offspring if __**one**__ parent donates it

Recessive

* must be contributed by __**both**__ parents
* can be carried in a person’s genes without appearing in that person

Alleles

Two or more alternative forms of a gene that arise by mutation

Simplified earlobe variation

* you inherit one allele for this gene from each parent
* Dominant allele: detached lobes (RR or Rr)
* Recessive allele: attached lobes (rr)

Two types of human variation

* discrete types
* continuous types

Discrete types

* PTC testing
* some genetic disorders

Continuous variation

* height
* weight
* eye colour

PTC and PTU full form

* Phenlythiocarbamide
* Phenylthiourea

PTC test

Tastes very bitter or tasteless depending on the genetic makeup of the taster

What trait do you have if you can taste the PTC test

dominant

Two forms of PTC gene

* tasting allele
* non-tasting allele

Explain the alleles

* each codes for a bitter taste receptor protein with a slightly different shape
* shape determines how strongly the protein binds to the PTC

Examples of recessive disorders

* sickle cell disease
* tay-sachs disease
* cystic fibrosis

Sickle cell disease

* RBC’s are cresent shaped
* causes anemia and pain
* common in african americans

Tay-sach’s disease

* causes mental issues, blindness, seizures
* die by age 5
* eastern european jewish descent, french canadians, cajuns

Cystic fibrosis

* problems in digestion and breathing
* most fatal genetic disease in canada
* common

Dominant disorder

each child of an affected parent has a 50% chance of inheriting the disorder

Example of a dominant disorder

huntington’s disease

Huntington’s Disease

* Neurodegenerative disorder
* cells in the brain die
* loss of control of movement, emotions, recalling event and making decisions
* die 15-25 years after the onset of symptoms

Why are there more X-linked traits

X chromosome is much larger than the Y chromosome

Who are more likely to X chromosome linked disorders

men

Why are X chromosome linked disorders more common in men

* only have one X chromosome
* no dominant gene to cancel out the recessive gene

X-linked recessive disorder

* expressed in all males
* only in females that received both copies of the gene from their parent

Explain passing of X-linked recessive disorders

* all daughters of a female carrier have a 50% chance of becoming carriers
* all daughters of an affected male will be carriers
* All sons of an affected male will not carry the disease since they can only inherit the Y chromosome

Examples of X-linked recessive disorders

* Duchenne muscular dystrophy
* Hemophilia

Duchenne muscular dystrophy

* mostly affects males
* weakness
* muscle wasting
* death around the age of 30

X-linked dominant disorder

* dominant gene for disorder is carried on the X chromosome
* one copy of the gene will cause the disease
* less common than X-linked recessive diseases

Example of X-linked dominant disorder

Fragile X syndrome

Fragile X syndrome

* most common cause of intellectual and developmental disabilities
* piece of X chromosome is not fully attached