Lecture 1 - Mutations and Disease Flashcards
Locus
Position on a chromosome where a particular gene or genetic marker is located
Gene
A section of DNA that codes for a molecule that has a function
Allele
A variant form of a locus or gene
Genotype
The genetic constitution of an individual at a locus or multiple loci
Phenotype
Observable trait or set of traits of an individual. May be a consequence of genetics, the environment, or both.
Mutations
Changes in the genetic sequence
Substitution mutation
Replace one nucleotide with another
SNP
Single nucleotide polymorphyism
Synonymous mutation
Nucleotide change in a codon that does not alter the amino acid (aka. silent mutation)
Non-synonymous mutation
Nucleotide change in a codon that alters the amino acid
Types of non-synonymous mutations
Missense and nonsense
Missense mutation
Nucleotide change in a codon that alters the amino acid
Nonsense mutation
Nucleotide change that causes substitution for a stop codon, results in a shorter protein due to protein synthesis stopping early
Insertion mutation
Addition of one or more nucleotides
Deletion mutation
Removal of one or more nucleotides
Frameshift mutation
Changes the reading frame, deletion or insertion mutation
Slippage
- Mechanism for frameshift mutations
- New strand or template strand loops out causing an insertion or deletion of a nucleotide
Template strand loops = deletion
New strand loops = insertion
Citrullinaemia in cattle
- Inborn error of metabolism leads to ammonia poisoning
- Recessive condition
- Calf dies 3-5 days after birth
- Loss of the enzyme argininosuccinate synthetase means urea cycle cannot be completed, causes buildup of upstream molecules (ammonia)
Mendelian disorders
Occur when specific mutations in single genes are inherited from either of one’s two parents
What mutation causes citrullinaemia
A single base substitution at codon 86 where a C becomes T, creates a stop codon
Recessive alleles
The phenotype is observed only in individuals homozygous for the allele (need both copies of the recessive allele to present the trait)
Dominant allele
The phenotype is observed in individuals homozygous for the allele and in heterozygotes (only need one or more copies of the allele)
Semi-dominant/incomplete allele
The heterozygote exhibits a phenotype intermediate to the two homozygote phenotypes
Co-dominant allele
Heterozygote exhibits the phenotypes of both homozygotes
Extension gene in horses
- Dominant allele
- Horses with dominant allele copy will be black (EE or Ee)
- Horses homozygous for the recessive gene (ee) will be chestnut
Dilution gene in horses
- Incomplete dominance
- Causes dilution of base color
- N/N : black base
- N/Cr : smoky black
- Cr/Cr : smoky cream
- N/N : chestnut
- N/Cr : palomino
- Cr/Cr : cremello
It is easy to eliminate a (dominant/recessive) allele from a population
Dominant, all carriers of the allele express the phenotype
Why is it difficult to eliminate a recessive allele from a population?
Heterozygous individuals do not express the unwanted phenotype, helpful to use genetic markers in this case
Gene that causes myostatin deficiency
GDF8 - growth differentiation factor 8
This gene normally inhibits muscle growth
Myostatin deficiency phenotype
Increased muscle mass
Downside of myostatin deficiency
- Neonatal calves are large, more c-sections required
- Require more nutrient dense feed
- More susceptible to a number of conditions including heat stress and dystocia
Is myostatin deficiency dominant or recessive?
Recessive
Can only one gene cause double muscling?
No, there are different mutations that can lead to the same phenotype
Ehlers-Danlos syndrome
Stretchy and fragile skin due to abnormal collagen
Can be caused by any of the 4 genes involved in collagen production
