Genes and Chromosomes II: Human Genetic Disease

Question 1

Incomplete Dominance

(red and white snapdragons produce what)

Answer 1

Incomplete Dominance is when both alleles contribute to the phenotype

Crossing a white and red snapdragon can produce pink snapdragons

HETEROZYGOTES HAVE THEIR OWN PHENOTYPE

Question 2

How is hypercholesterolemia in humans related to Incomplete Dominance?

Answer 2

Homozygous dominant: Normal ability to make LDL receptors
Heterozygous: Mild disease, less LDL receptors
Homozygous recessive: unable to make LDL receptors, atherosclerosis

Question 3

Co-Dominance

Explain how this works in blood type

Answer 3

Both alleles affect the phenotype in separate, distinguishable ways
In blood –>
IA and IB are co-dominant over i.
Type A Blood: Ia,i or Ia,Ia
Type B Blood: Ib,i or Ib,Ib
Type AB Blood: Ia,Ib
Type O Blood: ii

Question 4

Pleiotropy

How is this related to sickle-cell anemia?

Answer 4

Pleiotropy is when a gene affects more than one phenotypic character

In sickle cell anemia, the mutation causes a cascade of symptoms (pain, stroke, kidney problems, etc.)

Question 5

Crispr Gene Editing

How is this used to treat sickle cell anemia?

Answer 5

A guide RNA is injected, leading a CAS9 (nuclease) to the damaged DNA, cutting it open and activating DNA repair mechanisms to repair it
- Stem cells are taken from the patient and are repaired through the CRISPR-Cas9 system, and are transplanted back into the patient to produce correct blood cells

Question 6

Epistasis

(ee in dogs)

Answer 6

Epistasis is when a gene at one locus alters the phenotyhpic expression of a gene at a second locus.

In dogs, a gene for pigment deposition (E/e) is epistatic to gene that codes for black (B) or brown (b) pigment.
If a dog is homozygous recessive for pigment deposition (ee) , it will be neither black nor brown

Question 7

Polygenetic Inheritance

How does this work for skin color? What kind of distribution is formed?

Answer 7

Basically, there are just an enormous amount of phenotypes that can occur. For example, in skin a cross between AaBbCc individuals would produce a LOT of phenotypes. The range of phenotypes forms a normal distribution.

Question 8

Environmental effect on multifactorial characters

Answer 8

For multifactorial characters, environment contributes to their quantitative nature.
- Humans can be effected by nutrition, activity, and sun-tanning

Question 9

Histone Acetylation

This is an EPIGENETIC MECHANISM

Answer 9

The process of adding an acetyl group to a histone tail, promoting transcription of the gene by opening up the chromatin structure tightly packing it, making it more accessible.

epi=above

Question 10

Why do twins become different as they grow up?

What is the epigenome?

Answer 10

The epigenome is a collection of epigenetic tags, which regulate gene expression by controlling gene access using histone proteins. These ‘tags’ change with experiences, environmental interaction, and even out diet, explaining changes to twins as they grow up.

Question 11

DNA Methylation

This is an epigenetic mechanism

What happens if you feed pregnant yellow mice folic acid (DNA Methyl donor)? Bisphenol A (pulls DNA methyl away)?

Answer 11

DNA Methylation is the process by which a methyl group is added to a histone tail, condensing the chromatin around the gene and preventing gene expression.

If you feed a pregnant yellow mice folic acid, the methyl will prevent gene expression and the pups will be born normal. If you feed them BPA, the gene will be expressed and will make the births of the pups abnormal.

Question 12

Are these traits/diseases recessive or dominantly inherited?

1. Albinism
2. Polydactyly (6 toes)
3. Huntington’s disease

Answer 12

1. Albinism = recessive
2. Polydactyly = dominant
3. Huntington’s = dominant