intro to genetics

type of genetic diseases

genetic disease - caused by changes in genome

hereditary disease - caused by genes inherited from parents

congential disease - present from birth - can be due to genetic or environmental factors

selective breeding

change the appearance of animals

reduce or eradicate hereditary diseases

improve productivity and fitness

improve resilience of populations to stresses/ diseases 

adapt animals to their current environment or function 

breeding insemination

AI

semen sexing

multiple ovulation and embryo transfer

in-vitro embryo transfer

cloning

gene editing

genes

DNA segment at specific position on the genome that encodes a functional product

alleles

different forms of same gene

genotype

genetic makeup of an animal at one or more loci

for a single gene, genotype = combination of alleles 

phenotype

the end result - what we can see/ measure

the form that shows e.g. - coat colour, milk production, mastitis resistance 

qualitative traits

discrete

typically strong genetic component

often controled by single gene

coat colour 

quantitative traits

counted or measured

typically influenced by non-genetic components

often controlled by manhy genes

e.g litter size, milk production and disease resistance

homozygous and heterozygous

diploid organisms have 2 copies of same gene

form of gene = allele

pair of alleles  genotype for that gene 

2 copies of same alleles  = homozygous

different allels = heterozygous 

mendels law of inheritance

law of dominance - some alleles are dominant others recessive

law of segregation - parents pass one allele to their offspring 

law of independant assortment - genes of different traits are inherited independantly of each 

complete dominance

homozygoys dominant phenotype is same as heterozygous phenotype

e.g aberdeen angus coat colour 

incomplete dominance

heterozygous phenotype closer to homozygous dominant phenotype

e.g double muscling 

co dominance

additive gene action

gene action

non-additive - phenotype doesnt equal genotype, alleles are either dominant or recessive

additive - phenotype=genotype, alleles have equal dominance

sex-linked = gene on sex chromosome

sex-limited = autosomal gene but phenotype only present in one sex

sex- influenced = phenotype more common in one sex

genomic imprinting = phenotype depends on sex of parent that contributes gene

sex-linked gene

usually X-linked - more genes on X chromosome than Y

females - sex linked traits similar to autosomal

males - single x-traits can affect phenotype even if recessive allele - no paired allele to override

X-activation 

females don’t need twice as many products as males 

one copy of x chromosome becomes inactive in each cell in embryo development = x-activation 

specific x chromosome turned off in each cell is random 

pleiotropy

phenotpye variability

incomplete penetrance - only proportion of animals with genotype display phenotype

variable expressibity - different degrees of same phenotype

mitchondrial genes

mini-genome - 37 genes

equally affects males and females

mitochondrial DNA only passed from mother so affected males can’t pass on condition