Genetics

[Kenren]

Well, genetics seems to be one of the hardest things for people to pick up, and I'm not saying that this will make it any easier, but I'm gonna copy and paste the notes I take in my horse management class that pertain to genetics (Taught by Dr. John Shelle at Michigan State University). Sorry for how unorganized it looks, Proboards doesn't allow tabbing D:

DAY ONE

Definitions
-Chromosome
----- threadlike structure that carries genetic information
-Gene
----- located on chromosome
----- regulate body functions by regulating protein production
-Locus
----- where a gene is located on a chromosome (loci - plural)
-Allele
----- member of a gene series
----- may be several alleles of a given gene thatppear on the same locus
-Meiosis
----- reduction of chromosome numbers to 1/2 during sperm and egg production
----- only one allele of a pair is passed to the next generation
-Dominant
----- the dominant allele masks the effect of the other present allele
-Recessive
----- if present with dominant, it will not be expressed
-Homozygous
----- identical alleles
-Heterozygous
----- different alleles
-Incomplete Dominanace
----- when one allele is present, partial masking of other allele
----- both alleles are present, more extreme effect is noted
-Phenotype
----- outward characteristics
-Genotype
----- genetic make-up
-Environment - affects the expression of genes present, therefore genotype and phenotype may differ

LOCI

-C locus
----- the color gene
----- there are 3 alleles that occur at this locus
---------C dominant
---------C^Cr - dilution gene, co-dominance
--------- c recessive
--------- cc (both recessive) no pigment is true albino, does not exist in horses (die in-utero)
---------C^Cr is thought to be a mutation of the c allele has an additional effect which will be discussed with other dilutions
-B locus
----- only two alleles possible
----- B/E - dominant, produces black
----- b/e - recessive, chestnut
----- only two base colors
-A locus
----- the agouti or wild pattern gene, affects distribution of black pigment (has no affect on chestnut)
----- A, A⁺, A^t, a (in order of dominance)


DAY TWO

- aa creates fading black on B

E Locus
- these alleles work jointly with the alleles present at the B and C loci to control intensity of the pigment present
- Three alleles E^D, E, and e (in order of dominance)
-----E^D increases intensity of dark pigment (mahogany bay, dark bay, liver chestnut, etc.)
-----E allows normal pigment expression
-----e increases the intensity of light
---------pigment (yellow-red/sorrel) suppresses dark pigment
-E^DED will mask the actions of the A locus, i.e. bay horse will be black
-----E^DE^D on black is non-fading black
-----ee produces light bays and sorrels

Dilution genes
D Locus, dilution of base color
-D dilutes base color
-d base color unaltered
-Dd or DD black to grulla, mouse, or smoky blacks
-Bay to yellow dun with brown to redden manes
-Chestnuts to yellow dun with dun manes and tails

C^Cr at the C Locus
-has one effect in the heterozygous state (co-dominance), more complete effect in the homozygous state
-CC^Cr
-----Chestnut - palominos
-----Bay - buckskins
-----Seal browns or black - little change, may appear bay
-C^CrC^Cr, or C^Crc
-----chestnuts - cremello
-----bay, black, and seal brown - perlino

Modifying Genes
G Locus - produces grey from any base color
-G dominant, produces grey
-g recessive, base color unchanged

Rn Locus - produces roaning
-Rn dominant, produces roan pattern
-rn recessive, base color unchanged
-RnRn thought to be lethal in-utero as this horse does not exist in the population

W Locus - produces white horses
-W dominant, white
-w recessive, base color stays the same
-WW lethal in-utero
-Brown eyes


Once we've completed the genetics portion of my class, I'll arrange this into a more comprehensive guide. For now, you get typos ;D