Genetics and Genetic Diseases Flashcards
What comprises a phenotype?
Genotype + Environment
What are the 3 classes of genetic disease?
Monogenetic - single gene
Multifactorial - multiple genes + environment
Chromosomal - abnormality of chromosome structure or number
What are different versions of genes called?
The most common ___ in a population is known as the
Alleles
Wild type - not usually associated with disease
What 3 things are in Mendel’s Law of Inheritance?
Law of Uniformity - homozygous dominant and recessive = identical offspring
Law of Segregation - gametes carry only one copy of a gene
Law of Independent Assortment - each gene pair segregates independently of other gene pairs
Discuss autosomal dominant inheritance
Expressed when there are one or two copies
Usually involve a gain of function
Vertical pattern of inheritance - affected person must have an affected parent
Low frequency of associated diseases
List some diseases with autosomal dominant inheritance
Familial hypercholesterolaemia
Adult polycystic kidney disease
Huntington disease
Discuss autosomal recessive inheritance
Recessive alleles only expressed when two copies present
Usually involves loss of function
Heterozygous individuals can be carriers and healthy
If both parents are carries there is a 25% chance of affected offspring
What is consanguinity?
‘Sharing of blood’
Mating when partners have one common ancestor great-grandparent level
Higher risk of autosomal recessive disease
List some exceptions to Mendel’s Laws of Inheritance
Co-dominance - gives blend of two phenotypes
ABO blood grouping - A and B are co-dominant, O is recessive
Overdominance - homozygous dominant more severe effect than heterozygotes, often incompatible with life
Incomplete penetrance - not all individuals with genotype exhibit disease
Genomic imprinting - depends from which parent it came from
Sex-linked effects - mostly on X linked genes, males mostly affected
Mitochondrial inheritance
Genetic linkage
Dynamic mutation - increased severity down generations, expansion of repetitive DNA sequence
Give an example of sex-linked recessive diseases
Red/green colour blindness
Duchene muscular dystrophy
Fragile X syndrome
Haemophilia A
What is mosaicism?
Occurs when different cells within the same individual have different genotypes
Seen in very early embryo
If one cell is normal but other is abnormal, effects may be less severe
