Lec. 21 Genes and Chromsomes II: Human Genetic Disease

Question 1

What are some inheritance patterns that are more complex than Mendalian genetics

Answer 1

1. incomplete dominance
2. multiple alleles on one chromosome (co-dominance
3. Pleiotropy
4. Epistasis
5. Polygenic inheritance
6. Environmental impact

Question 2

Incomplete Dominance

Answer 2

Both alleles of a gene are partially expressed resulting in a “mixture” or different phenotypes from the parents
- 1:2:1 F2 ratio for genotype AND phenotype
- Neither genotype is recessive (C^R and C^W cross for a red and white plant)

Red and white plants result in a pink plant

Question 3

What is an example of incomplete dominance in hypercholesterolemia? (H)

Answer 3

H is the ability to make LDL receptors
- HH=lots of LDL receptors=NO DISEASE (low blood pressure)
- Hh= mild amounts of LDL receptors=MILD DISEASE (mild blood pressure
- hh=no LDL receptors=SEVERE DISEASE (high blood pressure)

Question 4

Co-Dominance

Answer 4

Both alleles affect the phenotype, in seperate, distinguisable ways

In blood, I^AI^A or I^Ai=Type A blood

I^A and I^B are co-dominant, both dominant over i

Question 5

Pleiotropy

Example

Answer 5

When a gene affects more than one phenotypic character

Symptoms (pain, stroke, kidney problems) of sick-cell anemia are due to a single gene. ie a base change in DNA

Question 6

CRISPR/Cas9 Gene editing

Answer 6

Editing of the human genome
- Sickle cell anemia mutation reversed by CRISPR-Cas9 gene editing
- Cas 9 Protein is a nuclease that cuts out DNA (causing sickle cell) and replaces it with guide RNA that is complementary to the DNA

Question 7

Epistasis

Answer 7

When a gene at one locus alters the phenotypic expression of a gene at a second locus
- (E/e) (NO PIGMENT DEPOSITED) is epistatic to the gene that codes for color (B/b)
- Controls whether or not pigment of any color will be desposited

9:3:4 rather than 9:3:3:1- both follow the law of indepdent ass.

Question 8

Polygenic Inheritance

Example

Answer 8

• ## A cross between two AaBbCc individuals (intermiediate shade) produce offspring covering a wide range of shades

Skin color

Question 9

Epigenetics

Answer 9

Changing chromatin structure (unravelling) to turn on gene expression or off (tightening chromatin) is an epigenetic mechanism

“beyond your genes”

Epigenetic tags change with experiences, environment, diet

Question 10

What types of inheritance display Mendalian patterns of inheritance?

Answer 10

1. pedigree analysis
2. recessively inherited disorders (sickle cell, albinism)
3. dominantly inherited disorders (polydactyly, Huntingtons)

Huntingtons is the loss of neurons over time