Basic body color for horses is influenced by several genes, one of which has several different alleles. Two of these alleles— the chestnut (dark brown) allele and a diluting (pale cream) allele (often incorrectly called albino)—display incomplete dominance. A horse heterozygous for these two alleles is a palomino (golden body color with flaxen mane and tail). Is it possible to produce a herd of pure-breeding palomino horses? Why or why not? Work the Punnett square for mating a palomino to a palomino and predict the phenotypic ratio among their offspring.

The chestnut (dark brown) allele and a diluting (pale cream) alleles show incomplete dominance, means that both the alleles in heterozygous condition show their effect. So the heterozygous show the phenotype which is intermediate of both the parents, here a horse heterozygous for these two alleles is a palomino.

There is in fact, no particular allele present for palomino, this phenotype only results due to having two different alleles for a gene. So, palominos can never be pure-breeding because they can never be homozygous.

Let P1 chestnut and P2 dilute,

Palomino is P1P2

The Punnett’s Square for palomino mated to palomino:

P1P2× P1P2

Gametes are: parent-1 P1 and P2 , parent-2: P 1 and P2

Progeny are: P1P1, P1P 2, P 2 P1, P2 P2

Genotypic Ratio: 1 P1P 1 : 2 P1P 2 : 1 P2P 2

Phenotypic Ratio: 1 Chestnut : 2 Palomino : 1 Dilute

marianaegarciaperedo marianaegarciaperedo · Answer 2 · 2025-04-14T01:23:52-04:00

In incomplete dominance, three phenotypes can be expressed, the dominant, the recessive, and the intermediate one. 1) No / 2) Phenotypic Ratio 1:2:1

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Available data:

Two alleles in a gene express incomplete dominance
In h0m0zyg0us state one of them codes for chestnut (dark brown)
In h0m0zyg0us state other allele codes for diluting (pale cream)
Heter0zygous individuals exhibit the phenotype palomino (golden body color with flaxen mane and tail)

In incomplete dominance cases, three phenotypes are expressed.

One of them is expressed by h0m0zyg0us dominant individuals.

Another phenotype is expressed by h0m0zygous recessive individuals.

And a third phenotype, which is intermediate between the other two, is expressed by heterozyg0us individuals.

In these cases, the dominant alleles do not completely dominate over the other one.

1) Is it possible to produce a herd of pure-breeding palomino horses?

Only when crossing a chestnut individual with a diluting individual, the whole progeny is expected to be Palomino. In these cases, there is a probability of 100% of getting the intermediate phenotype.

However, when crossing two palomino individuals, there is only a 50% chances of getting a palomino individual.

So, when crossing two palomino individuals it is not possible to produce a herd of pure-breeding palomino horses. Only 50% of their progeny is expected to be palomino.

2) Work the Punnett square for mating a palomino to a palomino and predict the phenotypic ratio among their offspring.

Cross: Palomino x Palomino

Parentals) Pp x Pp

Gametes) P p P p

Punnett square) P p

P PP Pp

p Pp pp

F1)

1/4 of the progeny is expected to be h0m0zyg0us dominant expressing the chestnut phenotype

2/4 = 1/2 of the progeny is expected to be heter0zygous expressing the Palomino phenotype

1/4 of the progeny is expected to be h0m0zyg0us recessive expressing the diluting phenotype.

Phenotypic ratio ⇒ 1:2:1

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