GENETIC DISEASES & DISORDERS

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)

	Mother
Father		F	f
	F	FF	Ff
	F	Ff	ff

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 21^st 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)

	Mother
Father		h	h
	H	Hh	Hh
	h	hh	hh

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