inheritance patters Flashcards
homogametic
XX, ZZ
heterogametic
XY, ZW (determines gender)
how many alleles does an animals have/gene
two
what is an allele
a version of a gene
why is an example of an ethical mate choice for a dominant mutation in manx
-in manx cats to breed mm X Mm because you will result in 50% Mn (show quality) and 50% mm (tails)
-same precent will be show quality in Mm X Mm except 1/4 will be MM and die, with 1/4 long tail
breeding Oo X Oo ovaro in horses
-1 oo (solid)
-2 Oo (ovaro)
- OO (white, lethal, intestinal issues)
what happens if you breed Pp X Pp Chinese crested dog
1/4 lethal 1/2 show quality 1/4 powder puff
dominance higharchy
-discovering which of more then two genes are more dominant
-because sometimes have more then 2 alleles at a locus
melanocytes
produce pigment for hair follicle
what are the two melanin pigments
phaeomelanin and eumelanin
phaeomelanin
-melanin pigment
-red, yellow, cream
eumelanin
-melanin pigment
-black, brown, grey
melanocortin receptor 1 gene MC1R ED
ED=eumelanin=black
melanocortin receptor 1 gene MC1R e
e/e=phaeomelanin=red
melanocortin receptor 1 gene MC1R E+
-“wild type”
-colour depends on other genes
-i.e. brown
heterozygote phenotypes
-heterozygots are different from either homozygotes
-codominant (both phenotypes expressed together but observed separately)
-incomplete dominant (both phenotypes expresses as a blend appearance
codominance in merle dogs
-MM= deaf, some microphthalmic (small eyes)
-Mm= merle, heterochromic irides, some black patches and some white
-mm= not merle
SLC45A2 or MATP gene in horses (codominance)
-CC=chestnut
-Cc=palomino
-cc=cremello
-if horses are e/e at MC1R, so no black (eumelanin) will be present
autosomal recessive generalizations
-most are enzyme deficiencies (inborn errors of metabolism)
-phenotype is generally consistent, exspecially within a family
-symptoms often severe
-consanguinity common (linebred)
why are many diseases called autosomal recessive
-because neither parents looks affected
-however not always autosomal recessive because you cant see it (can have reduced penetrance or be “dimmed”)
-but recessive X recessive=100% recessive offspring
-but such breeding is often not possible
symptoms for autosomal recessive (generlizations)
-often severe
-many such disorders are present at birth=congenital
-if untreated, they are often lethal
autosomal recessive (generlizations) consanguinity
-offten disorders show up when linebred is lised
implications of autosomal recessives
-cull the homozygote affected
-both parents are “obligate” carriers…cull?
what are the statistics if you were to breed two autosomal recessive carriers
-1 AA: 2 Aa: 1aa
-1/3 of unaffected not carriers
-2/3 of unaffected are carriers
-because 2/3 unaffected are carriers its important to have access to a carrier direction kit
carrier detection tests
-breeding test
-direct tests (biochemical, DNA test for mutation)
-indirect test (DNA linkage test)
carrier detection breeder tests
-mate a sire of interest to either affected dams of heterozygous carrier dams and see if any affected offspring are born
-if so sire is a carrier
spider syndrome in sheep
-mate with carriers
-Ss ewes (s/s do not survive to breeding age)
-16 off spring all ok=99% chance sire is S/S
-if S/s X S/s
-1/4 of lambs will have spider syndrome
testing if a polled sire carries horns
-mate sire to horned cows (homozygous p/p)
-polled in cattle is dominant to horned
-7 offspring have no horns= 99% chance sire PP
-(1/2)^7=0.0078
how many times do you have to breed test something matted to aa (recessive)
7x
ho many times do you need to mate to Aa (carrier)
16x
mechanisms of a direct biochemical test
-measures specific range (level) of enzymes or protein
-Beta-mannosidosis or deficency of beta mannosidase
-homozygous normal=100% active (BB)
-heterozygote=50% active (Bb)
-affected=0% active (bb)
-gene dosage=affect
-not all samples give definitive results
mechanisms of direct test DNA test for the mutation
-most tests now based on PCR
-method to amplify small amounts of DNA
-samples: hair roots, buccal swab, blood, semen
indirect tests: DNA linkage test
-used when the causative gene is not known
-location of gene, or biochemical pathway, etc. is known
-less accurate then direct test i.e. depends on distance of marker to gene
DNA linkage test mechanism
-use a marker “linked” to the causative gene
-DNA variation within an intron or other noncoding segment
-markers do not affect any phenotype so have “accumulated” in animals
-which allele segrates with the allele of interest is pedigree specific
-therefore must sample the family ot test for carriers
when does recombination occur
during meiosis between homologous chromosomes
why would a carrier detection test be used for a dominant disorder
-if dominant dis order is late onset, so genotype is know prior to breeding
