Human Genetics Part 2

Question 1

Types of Genetic Origins of diseases

Answer 1

Allele-related diseases:
-> recessive gene (rarer): needs two copies of the gene to exhibit the disease (e.g., PKU and Tay-Sachs disease)
-> single-dominant inheritance: needs one copy of the gene to exhibit the disease
-> Does not have to happen on the autosomes
(e.g., Huntington’s disease)

Chromosome-related diseases:
-> Sex-linked inheritance: Diseases related to the abnormality of either the sex chromosomes (e.g., Fragile X syndrome)
-> Chromosomal abnormalities: Diseases that are due to an extra of lack of chromosomes (e.g., Down’s, Klienfelter, Turner, XYY)

Polygenic inheritance: diseases that are caused by abnormalities of multiple genes (slight effect of each gene) (e.g., schizophrenia)

Regulator gene inheritance: Diseases cause by the abnormalities of the regulator gene.

Question 2

Describe Tay-Sachs disease

Answer 2

-> fatal autosomal disease
-> defects of the HEXA gene at the chromosome locus 15q23-q24

Question 3

Describe Huntington’s disease

Answer 3

-> autosomal disease
-> defects of the 4p16.3
-> Cause by more tham 40 CAG tri-nucleotide combinations
-> Degeneration of the GABAergic neurons
-> involuntary “dance-like” movement
->Broad cortical and subcortical damage (i.e., atrophy of the basal ganglia (control of movements))

Question 4

Describe Fragile X syndrome

Answer 4

-> caused by the mutation of the CGG trinucleotide on the fMR1 gene of the X (locus Xq 27.3) chromosome
-> leads to the absence of the FMR1 protein that facilitates the development of the brain -> patients have lower IQ

Question 5

What is PKU

Answer 5

-> defects on chromosome 12
-> unable to metabolise phenylalanine
-> however, can be cured with correct diet (how environmental influences can stop/prevent the expression (i.e., phenotype) of the gene)

Question 6

What is the range of reaction

Answer 6

-> Refers to all theoretically possible phenotype outcomes under the given genotype.

Question 7

Explain epigenetics

Answer 7

-> The new-emerging field where believes genes are not “set and locked”. Instead, it can be shaped and altered with the kind of interaction with the environment.
-> For example, a person’s height can be changed from the gene if one’s under the suitable temperature.
-> 3 kinds of mechanisms
Histone modification
DNA methylation
microRNA

Question 8

Some of the deficits that a patient with XXY (Klinefelter) will have

Answer 8

Physical development: fewer muscles and taller
Social development: quieter
Language development: hinder