L54, L55: Basic Human Genetics + Introduction to Genetic Diseases

Question 1

Human genome

Answer 1

3 billion base pairs x 2 chromosome (2x3x10^9)

Changes in
1. Stability
2. Organisation
3. Expression
4. Inheritance
can cause genetic diseases

Question 2

Structure of chromosome

Answer 2

• short arm
• long arm
• Centromere
• Telomere: 15000bp: decrease 100bp every cell division —> 5000bp: telomere cannot function —> die of old age

Question 3

What is karyotype

Answer 3

Number, Size and Shape of chromosomes arranged in standard manner

Question 4

Structure of gene

Answer 4

1. Regulator
2. Promotor
3. Structure gene: Exon + Intron

Question 5

What is Locus, Allele, Genotype, Phenotype

Answer 5

Locus: location of gene
Allele: versions of locus
Genotype: genetic makeup:
- heterozygous, homozygous, hemizygous
Phenotype: composite of observable traits: affected by Dominant, Recessive, Co-dominant genes

Question 6

Hardy-Weinberg equilibrium

Answer 6

Frequencies of each genotype is stable over successive generations, GIVEN THAT large population + random mating

Random mating: Allele are assigned independently

Genotypic ratio: p^2: 2pq: q^2
(Genotype frequency: Allele frequency x Allele frequency)

For gene frequency <99%, the gene is said to have polymorphism (having other versions of the gene)

Phenotype frequency: frequency of observable traits

Question 7

Types of genetic diseases

Answer 7

1. Chromosomal (spontaneous abortion, birth defect)
   - Structural (deletion, duplication+deletion, insertion, translocation, inversion, isochromosome)
   - Numerical (meiosis: non-segregation of homologous chromosome, fertilisation —> Down’s / trisomy 21, Patau / trisomy 13, Klinefelter 47XXY)
2. Single gene / Mendelian
   - Frame shift (1 nucleotide deleted —> number of nucleotide not divisible by 3, reading frame shift —> totally different translation)
   - Nonsense (premature stop codon —> incomplete/non-functional protein)
   - Missense (single nucleotide change e.g. sickle cell anaemia)
3. Polygenic / Multifactorial
4. Somatic cell genetic