basic genetics in dexters

Gregor Mendel, a 19th century Monk, was born in 1822 in Austria.  Mendel conducted experiments with pea plants that led to some of the founding principles of genetics and theories of heredity. 

One of his methods, known as Mendel’s Square, can be applied to some of the basic characteristics we often come across in our Dexters. Below we will be dealing with colour. This can quite easily be determined by making use of Mendel’s Square by placing one parent’s genes on the vertical axis and the other parent’s genes on the horizontal axis. 

Colour
Dexters come in three colours, black, red and dun. For this exercise, we will be dealing with black and red only. 

Black (B) is dominant and red (r) is recessive. This means that whenever a black gene is present, your Dexter will be phenotypically black, even though a red gene may be present in the animal. An animal can thus be black if it inherits a black gene from both its parents (BB) or when it inherits a black gene from one and a red gene from the other parent (Br). Black can thus carry red in the background and pass this red gene to its progeny. Two black parents can thus produce a red calf provided both parents carry red.

Red (rr) occurs when a red gene is passed to the calf by both parents. Red cannot carry black. If a black gene had been present in the animal, the animal would have been black due to the dominance of black over red. Red is thus the only colour in Dexters that breeds true. In other words, two red parents cannot produce a black calf.

Firstly, we will be using a red cow (rr, she carries two red genes) with three different bulls, BB (double black), Br (black carrying red) and rr (red):

Figure 1:  Using a homozygous black bull (BB), all the progeny will be black but they will all carry red (from the mother) in the background. When in turn they are bred, they will pass either black or red to their own calves.

Figure 2:  Using a heterozygous black bull (Black carrying red (Br)), there will be a 50% chance for a black calf, carrying red. The other 50% of the progeny will be red.

Figure 3:  Using a red bull, 100% of these calves will be red. Remember red is the only colour that breeds true to itself.

Next, we will use a heterozygous black cow (black carrying red (Br)):

Figure 4: With a BB bull, all the progeny will be black. Half of them will be homozygous black (double black) the other half will be heterozygous black (black carrying red).

Figure 5: With a Br bull, 25% of the calves will be homo black (BB). 50% will be hetero black (Br) and 25% will be red (rr).

Figure 6: With a red bull, 50% of the calves will be black carrying red. The other 50% will be red.

Thirdly, we will be using a homozygous black cow, a cow carrying two black genes, no red:

Figure 7: With a BB bull, 100% black BB calves.

Figure 8: With a Br bull, 50% chance for BB and 50% chance for Br. Still all phenotypically black though.

Figure 9: With a red bull, still 100% chance for black calves. They will however all carry red from their father which was all he had to give.