Mendelian inheritance SDL

why is mendelian inheritance relevant (3)

1. animal breeding

2. genetic disease

3. conservation of species

define gene

• discreet unit of DNA that codes for a protein

define locus

• position of gene on a chromosome

define allele

• alternative form of a gene that produces a distinguishable phenotypic effectdef

define phenotype

• characteristics of an organism determined by its genotype and environment

define homozygous

• organism that has 2 identical alleles of same gene

define heterozygous

• an organism which possesses 2 different alleles of the same gene

define a dominant allele

allele which is always expressed in the phenotype if present in the genotype

define recessive allele

• allele which is only expressed in the phenotype when dominant allele isn’t present

define codominance

when both alleles affect phenotype of a heterozygous individual

define F1

• first filial generation - hybrid offspring of 2 pure breeding parents

define F2

• second filial generation - offspring from interbreeding F1 generation

what is the law of segregation

• 2 alleles for a heritable character separate during gamete formation and end up in different gametes

how do we work out the possible combinations of alleles for an individual?

• punnet square

how did mendel develop law of independent assortment?

• crossed F1 to produce F2 generation

what is teh law of independent assortment

• each pair of alleles segregates independently of each other pair of alleles during gamete formation

to what genes does the law of independent assortment apply?

• genes on non-homologous chromosomes

what law governs mendelian inheritance?

• law of probability

what does the multiplication rule state?

• probability that 2+ independent events occur together is the product of their individual probabilities

when are 3 times that genes deviate from simple mendelian patterns?

1. alleles aren’t completely dominant/recessive - incomplete dominance/codominance

2. gene has 2+ alleles

3. gene produces multiple phenotypes

what is incomplete dominance

• when th ephenotype of F1 hybrids is a mix of the phenotypes of the two parents e.g. pink flower from red and white parent

what is epistasis?

• gene at one locus alters phenotypic expression of a gene at a second locus

what does coat colour depend on in mice and many mammals?

• 2 genes; one for pigment colour and the other for whether the pigment is deposited.

what is linkage

• genes located on teh same chromosome tending to be inherited together

whta can occur between linked genes?

• crossing over → recombinant individuals form

what test can we use tod etermine the genotype of an individual with a dominant phenotype?

• testcross

State some drivers of animal breeding

• profit

• faster production

• better quality production

what are some benefits to be gained from animal breeding?

• income

• faster production

• higher nutritional value

• improve specific animal traits

state 6 traits we may be aiming to improve when animal breeding

1. animal growth rate

2. carcase yield

3. fleece weight

4. fibre diameter

5. variation in birth weights

6. decrease resistance

what is a consequence of breeding animals for more desirable traits?

• genes which cause disease are often linked to them e.g. EPSSM and ERU

what are EPSSM and ERU?

• Equine polysaccharide storage myopathy

• equine recurrent uveitis

• genetic disorders in horses often seen alongisde desireable characteristics

what are 3 sources of genetic variation?

1. mutations

2. gene flow

3. sex

what is gene flow

• movement of genes from one population to another via gametes

what are the 3 results of mutation

1. neutral

2. harmful

3. beneficial

what mutations are we interested in when breeding animals?

• germ-line mutations

why are germ line mutations so important

• they occur in the gametes, therefore will be inherited by offspring and introduced into the population

when a mutation occurs why is it important to determine, especialyl for breeding, whether it affects the germ-line

• if it doesn’t affec the germ-line it cant be passed down generations

• if it affects germ line, it will be present in future generations

what is the purpose of gene flow within a population?

• introduce/reintroduce alleles increasing genetic variation

what is the purpose of gene flow across populations

• make distant populations genetically similar, helping prevent speciation

when does gamete formation occur in:

1. females

2. males

1. in uteru, before she’s even born

2. all the time

what does independent assortment help with?

• genetic variation

what is a gene frequency

• how common an allele is within a population

what is the difference between a gene frequency and genotype

• genotype refers to the genetic makeup of the organism

• gene frequency is the change of an individual containing a particular allele

what is genotype frequency

• the proportion of animals with each genotype

how do we work out gene frequency

• if DD, Dd and dd: 1 - (D genotype proportion x 1) + (D(d) genotype proportion x 0.5)

• you need the % of each genotype within a population to work this out.

what is the hardy-weinberg law?

• genotype frequencies in offspring depend on the gene allele frequency in parents

why don’t genotype frequencies match what is expected by the hardy-weinbery law?

• because this isn’t representative of what actually takes place in nature and random mutation

what are qualitative traits

• traits characterised by segregation in classical ratios - purely genetic influence

• option a or b

what are 3 example conditions which are qualitative

1. susceptibility to scrapie in sheep

2. canine haemophilia B

3. muscular dystrophy in golden retrievers

what are quantitative traits?

• traits that are ‘continuous’ e.g. growth rate/milk yield

how many loci are usually involved in quantitative traits?

• multiple

what are exceptions to quantitative traits in terms of genetic loci?

1. single polymorphic locus with several, differentially expressed alleles → continuous variation

2. expression of quantitative trait is controlled by a mutant allele at a single locus with a high degree of variable expressivity

state 9 environmental factors which influence phenotype

1. temperature

2. light-dark

3. shelter-housing

4. bedding

5. medication

6. hydration

7. nutrition

8. maternal care

9. intrauterine conditions

what does SCNT stand for?

• somatic cell nuclear transfer

what could we use SCNT for?

• to use validated genomes in farm animal breeding

• save endangered species/breeds

state 6 pressures when maing a decision about animalb reeding

1. information available

2. resources - financial and physical

3. current breeds in use

4. local traditions

5. market demand

6. personal preferences

what is a breeding pyramid

• a pyramid which shows the heirarchy of breeding value from commercial flocks → purebred/cross bred breeders → stud/nucleus breeders

• shows the cycle of improvement and development of breeds

why do we want to select between breeds?

• dramatic and rapid genetic changes when there are large genetic differences

• for when the market needs to change breed

what do we call gradual selection in practice?

• grading up/back crossing

is selecting between breeds cheap?

• no it’s very expensive

what is heterosis

• extra performance above mid-parent mean

what else do we call heterosis

• hybrid vigour

what is pig breed example that has been cross bred for efficiency

• meidam

what are 7 benefits to the meidam breed

1. highly prolific

2. more teats

3. increased milk yield

4. calm maternal temperament

5. production durability

6. stress free

7. commercial carcase

what is pedigree selection?

• index combining information on ancestors’ performance, called a pedigree index

what is a performance test

• selection on the animal’s own performance = simplest selection method

what is a progeny test

• looking at an animal based on the performance of their offspring

how do we spot response to selection

• look at the change in mean performance in a population of animals as a result of selection - per year/gestation

for calculating response to selection what do the following stand for:

1. S

2. h²

3. L

1. selection differential

2. heritability

3. generation interval

how do we calculate response to selection?

R = S x h²

Response = selection differential x heritablity

what is the ultimate result of continued inbreeding?

• terminal lack of vigour and possible extinction

what are 4 consequences of inbreeding?

1. reduced fertility

2. contracted geen pool

3. increased abnormalities

4. increased mortality

what are 5 applications of inbreeding?

1. breeding companion animals

2. controlling inheritable diseases

3. managing zoo populations and endangered species

4. estimating heritability

5. artificial selection programmes

define inbreeding

• mating of individuals more closely related than average for the population

why does inbreeding appear to be a logical breeding strategy?

• it will increase the frequency of favourable alleles present in the population

how does inbreeding affect alleles?

• increases favourable and more unfavourable

how does inbreeding affect genotypic frequency?

• fewer heterozygous genotypes

• more homozygous genotypes

what are the consequences of increased homozygosity with inbreeding?

1. reduced genetic variation → reducing response to selection and declining performance traits

what is inbreeding depression?

• reduced response to selection and declining performance in traits associated with fitness due to reduced genetic variation in a population

inbreeding depression and heterosis are functions of what?

• genetic combination, therefore not inherited

how can genes be identical in two different individuals?

• descent - 2 alleles are copies of a single gene from an ancestor common to both parents

what is the inbreeding coefficient?

• the level of inbreeding in an individual = probability both alleles at a single locus are identical by descent

are all homozygous individuals likely caused by descent?

• NO - a homozygous individual will have more homozygous alleles than those identical by descent

what are 5 developing reproductive technologies?

1. AI

2. MOET - multiple ovulation and embryo transfer

3. in vitro embryo producing

4. semen and embryo sexing

5. cloning

what are 4 methods to reduce inbreeding?

1. deliberately choose less related individuals

2. use more than one male from each selected full sib family

3. use selected parents only once

4. use factorial mating designs

state 4 inherited disorders seen in dogs

1. blindness and joint deformaties

2. bleeding disorders

3. deafness

4. range of eye problems

what are single gene disorders and their relevance?

• prerequisite for developing a breeding programme - identifying in potential dams and sires which we can select against if they contain a mutant allele

what are 3 methods for identifying single gene disorders

1. clinical screening

2. biochemical testing

3. DNA testing

what is the purpose of BVA/KC/ISDS schemes? what is a consequence

• identify dogs clinically affected and homozygous so breedrs can choose not to breed these animals

• but increases the chance of carriers in a population, which means they may be undetected and signs may not appear until late in life.

how can we overcome the challenge of not identifying carriers of genetic disease?

• use single gene mutation detection by biochemical analysis - looking at PFK gene

what is the relevance of the PFK gene?

• it’s deficient in a number of dog breeds

• it’s key for metabolism and without → exercise intolerance, muscle disease and anaemia

how can we measure PFK?

• in blood

what result of PFK would we expect for:

1. homozygous normal dog

2. homozygous affected dog

3. heterozygous carrier

1. expected PFK level

2. undetectable PFK levels

3. intermediate levels b/w homozygous normal and affected