Unit 3: Introduction to animal genetics (Lecture 1-2) Flashcards
What is a gene ?
Part of the DNA sequencing that encodes a protein
What is an allele ?
Different forms of the same gene
What is the genotype ?
The combination of alleles for a gene locus
What is Mendel’s first principle ?
The principle of segregation
What is the principle of segregation ?
That for any particular trait during gamete formation the two alleles in each parent separate and only one allele is passed to the offspring
What is a monohybrid cross ?
A genetic cross that examines the inheritance of a single trait
What statistical test can be used to confirm the principle of segregation ?
Chi squared
What is Mendels second principle ?
The principle of independent assortment
What is the principle of independent assortment ?
- That when a parent is segregating two or more gene loci, alleles for each gene are passed to the offspring independently of each other
- Combinations of phenotypes present in neither parent will be produced
What is a dihybrid cross ?
A cross that examines the inheritance of 2 genes simultaneously
What is the F2 ratio for a dihybrid cross ?
9:3:3:1
What is a wild type allele ?
A normal, unaltered allele
What is the predominant allele at the gene locus in the population ?
The wild type allele
What are the 3 types of alleles ?
1) Loss of function alleles
2) Gain of function alleles
3) Isoalleles
What is a loss of function allele ?
- Where the gene product has reduced activity compared to the wild type
- Tend to be recessive to wild type
- Has no overall effect on the phenotype
- Seen in lactose intolerance
What is a gain of function allele ?
- Where the gene product has increased activity with respect to wild type
- Generally dominant to wild type
- Involved in cancer
What is a isoallele ?
- Neutral allele
- Mutant allele has same action as wild type allele
What are the 5 modes of inheritance leading to genetic disease in domestic animals ?
1) Autosomal dominant
2) Autosomal recessive
3) X linked recessive
4) Sex limited inheritance
5) Polygenic or complex
What is an autosome ?
Anything that is not a sex chromosome
What is autosomal dominance ?
- Gene on autosome
- Only one copy of mutated allele needed for phenotype
- Passes from one generation to the next without skipping a generation
Give an example of autosomal dominance in cats
Lack of tail in Manx cats
What is autosomal recessive ?
- Gene on autosome
- Two copies of mutated allele required for phenotype
- Commonest mode of inheritance of single gene disorders in domestic animals
- Can skip many generations
- Frequency increases with inbreeding
Give an example of autosomal recessive in bulls
Double muscling, extreme muscularity in proximal fore and hindquarters
What is incomplete penetrance ?
When offspring has the genotype but does not express the phenotype
What is X-linked recessive ?
- Where the gene is on the X chromosome
- Usually males are affected and females are the carriers
Give 2 examples of X-linked recessive in dogs
- Haemophilia A in dogs- Failure of blood clotting
- Von Hillebrands disease- blood clotting disorder
What is sex linked inheritance ?
When the gene is on an autosome but the condition is only expressed in one sex
What is polygenic inheritance ?
Genotype and environment interaction
What does it mean when a trait is said to be multifactorial ?
When a large number of factors, both genetic and environmental are involved
What are the 2 Hardy Weinberg equations ?
p^2 + 2pq + q^2 = 1
p + Q = 1
What letter can be used to represent affected individuals ?
q^2
What letter can be used to represent the frequency of carriers ?
2pq
If allele frequencies deviate from hardy Weinberg equilibrium than what 4 things need to be considered ?
1) If one allele is advantageous
2) Genetic drift
3) Denovo mutations
4) Non random mating
What is a mutation ?
An error in the replication of DNA or in the separation of chromosomes during cell division
What are the two categories of mutation ?
1) Point mutations
2) Chromosome mutations
What is a point mutation ?
Altered nucleotide sequence of a gene such as substitutions, insertions or deletions. Uncorrected mistakes during DNA replication
What is a chromosome mutation ?
Errors during cell division such as translocations, deletions and alterations in chromosome number
What are the 5 types of chromosome mutation ?
1) Translocation
2) Inversion
3) Deletion
4) Duplication
5) Chromsome disjunction
What is translocation ?
Where one piece of chromosome is moved to another, often reciprocal with swapping of material
What is an inversion ?
Where segments of the chromosome flips its orientation with respect to the rest of the chromosome
What is a deletion ?
Where a large segment of chromosome is deleted resulting in the loss of a number of genes
What is a duplication ?
Where some genes are duplicated on the same chromosome
What is chromosome non-disjunction ?
Where chromosomes fail to separate during cell division resulting in one daughter cell having an extra chromosome and the other daughter cell lacking one
What are the 6 types of single base mutations ?
1) Silent mutation
2) Nonsense mutation
3) Missense mutation
4) Splice site mutation
5) Insertion
6) Deletion
What is a single nucleotide polymorphism ?
- A point mutation
- Represents the rare allele (frequency of at least 1%)
