Lecture 1 - Mutations and Disease

Question 1

Locus

Answer 1

Position on a chromosome where a particular gene or genetic marker is located

Question 2

Gene

Answer 2

A section of DNA that codes for a molecule that has a function

Question 3

Allele

Answer 3

A variant form of a locus or gene

Question 4

Genotype

Answer 4

The genetic constitution of an individual at a locus or multiple loci

Question 5

Phenotype

Answer 5

Observable trait or set of traits of an individual. May be a consequence of genetics, the environment, or both.

Question 6

Mutations

Answer 6

Changes in the genetic sequence

Question 7

Substitution mutation

Answer 7

Replace one nucleotide with another

Question 8

SNP

Answer 8

Single nucleotide polymorphyism

Question 9

Synonymous mutation

Answer 9

Nucleotide change in a codon that does not alter the amino acid (aka. silent mutation)

Question 10

Non-synonymous mutation

Answer 10

Nucleotide change in a codon that alters the amino acid

Question 11

Types of non-synonymous mutations

Answer 11

Missense and nonsense

Question 12

Missense mutation

Answer 12

Nucleotide change in a codon that alters the amino acid

Question 13

Nonsense mutation

Answer 13

Nucleotide change that causes substitution for a stop codon, results in a shorter protein due to protein synthesis stopping early

Question 14

Insertion mutation

Answer 14

Addition of one or more nucleotides

Question 15

Deletion mutation

Answer 15

Removal of one or more nucleotides

Question 16

Frameshift mutation

Answer 16

Changes the reading frame, deletion or insertion mutation

Question 17

Slippage

Answer 17

• 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

Question 18

Citrullinaemia in cattle

Answer 18

• 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)

Question 19

Mendelian disorders

Answer 19

Occur when specific mutations in single genes are inherited from either of one’s two parents

Question 20

What mutation causes citrullinaemia

Answer 20

A single base substitution at codon 86 where a C becomes T, creates a stop codon

Question 21

Recessive alleles

Answer 21

The phenotype is observed only in individuals homozygous for the allele (need both copies of the recessive allele to present the trait)

Question 22

Dominant allele

Answer 22

The phenotype is observed in individuals homozygous for the allele and in heterozygotes (only need one or more copies of the allele)

Question 23

Semi-dominant/incomplete allele

Answer 23

The heterozygote exhibits a phenotype intermediate to the two homozygote phenotypes

Question 24

Co-dominant allele

Answer 24

Heterozygote exhibits the phenotypes of both homozygotes

Question 25

Extension gene in horses

Answer 25

• Dominant allele
• Horses with dominant allele copy will be black (EE or Ee)
• Horses homozygous for the recessive gene (ee) will be chestnut

Question 26

Dilution gene in horses

Answer 26

• 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

Question 27

It is easy to eliminate a (dominant/recessive) allele from a population

Answer 27

Dominant, all carriers of the allele express the phenotype

Question 28

Why is it difficult to eliminate a recessive allele from a population?

Answer 28

Heterozygous individuals do not express the unwanted phenotype, helpful to use genetic markers in this case

Question 29

Gene that causes myostatin deficiency

Answer 29

GDF8 - growth differentiation factor 8

This gene normally inhibits muscle growth

Question 30

Myostatin deficiency phenotype

Answer 30

Increased muscle mass

Question 31

Downside of myostatin deficiency

Answer 31

• 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

Question 32

Is myostatin deficiency dominant or recessive?

Answer 32

Recessive

Question 33

Can only one gene cause double muscling?

Answer 33

No, there are different mutations that can lead to the same phenotype

Question 34

Ehlers-Danlos syndrome

Answer 34

Stretchy and fragile skin due to abnormal collagen

Can be caused by any of the 4 genes involved in collagen production