Homozygous vs Heterozygous in Breeding

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Homozygous vs Heterozygous

 

 if T is tobiano coloring and t is not tobiano coloring…

Dominant Trait= this trait will be what you see in the phenotype (or coloring) of the horse, T, tobiano coloring is a dominant trait in horses

Recessive Trait= this trait will be seen in the horse’s pheontype (or coloring) only if there are two recessive traits together, otherwise the dominant trait, T, will be seen and not the recessive, t

Homozygous= both of the traits are the same, both traits can be either dominant (TT, for tobiano coloring) or recessive (tt, for no tobiano coloring)

Heterozygous= the two traits are not the same, one is dominant and one is recessive (Tt), if the donimant trait is present, it will always be the one that is expressed in the phenotype, or coloring, of the horse

Genotype= the genes that the horse has (TT or Tt or tt)

Phenotype= the physical coloring of the horse ( TT would be tobiano coloring, Tt would be tobiano coloring (because the T tobiano trait is dominant over the t no tobiano coloring recessive trait), tt would be no tobiano coloring)

 

Examples:

 

If you are breeding two homozygous dominant horses (TT x TT):

     in this example, both the stallion and the mare would express tobiano coloring

       stallion:               T            T

  mare:               T     T T          T T

                         T     T T          T T

                   genotypes: 4 (TT)                                    

                                   100% chance of TT, homozygous dominat foal                   

                   phenotypes: 4 with tobiano coloring                                     

                                  100 % chance of tobiano coloring in the foal  

If you are breeding one homozygous dominant horse with one heterozygous horse (TT x Tt):     in this example, both the stallion and the mare would express tobiano coloring

       stallion:               T            T

  mare:               T     T T         T T

                         t     T t          T t

                   genotypes: 2 (TT)  2 (Tt)

                                  50% chance of TT, homozygous dominant foal and

                                  50% chance of Tt, heterozygous foal

                    phenotypes: 4 with tobiano coloring

                                      100% of tobiano coloring in foal

 

If you are breeding one homozygous dominant horse with one homozygous recessive horse (TT x tt):

     in this example, the stallion would have tobiano coloring and the mare would

     not have tobiano coloring

       stallion:               T            T

  mare:               t     T t           T t

                        t      T t          T t

                    genotypes: 4 (Tt)

                                    100% chance of Tt, heterozygous foal

                   phenotypes: 4 with tobiano coloring

                                     100% chance of tobiano coloring in foal  

 

If you are breeding two heterozygous horses (Tt x Tt):

     in this example, both the stallion and the mare would express tobiano coloring

       stallion:               T            t

  mare:               T     T T         T t

                         t     T t          t t

                    genotypes: 1 (TT)  2 (Tt)  1 (tt)

                                   25% chance of TT, homozygous dominant foal and

                                   50% chance of Tt, heterozygous foal and

                                   25% chance of tt, homozygous recessive foal

                    phenotypes: 3 with Tobiano coloring, 1 without Tobiano coloring

                                     75% chance of tobiano coloring in foal and

                                     25% chance of no tobiano coloring in foal

 

If you are breeding one heterozygous horse with one homozygous recessive horse (Tt x tt):

     in this example, the stallion would express tobiano coloring and the mare would

     not express tobiano coloring

       stallion:               T            t

  mare:               t     T t          t t

                        t     T t           t t

                    genotypes: 2 (Tt)  2 (tt)

                                    50% chance of Tt, heterozygous and

                                    50% chance of tt, homozygous recessive

                    phenotypes: 2 with tobiano coloring and 2 with no tobiano coloring

                                      50% chance of tobiano coloring in foal and

                                      50% chance of no tobiano coloring in foal

 

If you are breeding two homozygous recessive horses (tt x tt):

     in this example, neither the stallion nor the mare would have tobiano coloring

       stallion:               t            t

  mare:               t     t t          t t

                        t      t t          t t

                    genotypes: 4 (tt)

                                   100% chance of no tobiano coloring in foal

                    phenotypes: 4 without tobiano coloring

                                      100% chance of foal without tobiano coloring