Page 111 - Zoo Animal Learning and Training

Chapter 6 Introduction to Animals 95

green/blue split (Gg) budgerigar male and female, but
TABLE 6.6
let’s add in a wing tip color. Normal wing tips are homo-
Punnett Square for Breeding a Homozygous zygous dominant black, expressed as (BB), there is also a
Blue Cock (gg) to a Heterozygous Green/ homozygous recessive gray wing tip, expressed as (bb).
Blue Split Hen (Gg) Now we have four possible combinations of alleles from
G female g female each parent. Every combination is used across the top
g Gg gg and the side of the Punnett square.
male The gray winged hen’s phenotype is no match for the
male’s homozygous dominant gene for black wings. Of
g Gg gg
male the 16 possible offspring only 6 of them will be blue with
black wings and 10 will be green with black wings. As can
Because the heterozygous green budgerigar appears like a homozygous green be seen by this chart, the more genetic factors that an
budgerigar, mating a green bird to a blue bird will determine if the parent is individual has the more difficult it becomes to predict
homozygous (GG) or heterozygous (Gg) as in this breeding. Because green is
dominant, a blue offspring can only be obtained from the breeding if the the outcome of the breeding. However, if you took the
green parent is split to blue or heterozygous to the blue color. GgBb offspring (heterozygous green/blue with hetero-
zygous black/gray) and mated that with another of the
same phenotype you would get a different mix of off-
TABLE 6.7 spring again!
Unfortunately, breeding for phenotype over function
Punnett Square for Breeding a Heterozygous and behaviors has developed specific genetic‐based dis-
Green/Blue Cock (Gg) to a Heterozygous eases or conditions, some of which have been passed on
Green/Blue Hen (Gg) to other animals within the species. Examples would be
G female g female the long backs and short legs of the Dachshund. The
G GG gG long back is prone to hyperflexion when the dog jumps
male from the couch or bed to the floor. The jarring impact
g Gg gg causes the disks to become luxated which can cause
male paralysis. When a Dachshund is crossed with a dog with
a normal length back the offspring will have an elon-
Both parents are phenotypically green birds but are split to blue. The
outcome of this breeding would be 25% green homozygous, 50% gated back, telling us that the gene for long backs is
heterozygous green split to blue, and 25% blue homozygous. dominant. Breeding Bulldogs with their brachiocephalic
faces has led to dogs that can’t breathe very well and so
are prone to heat stroke and hypoxia when the weather
is hot and humid. Also, because of the size of their
TABLE 6.8
heads, they cannot give birth easily, if at all, by them-
Punnett Square for Breeding Heterozygous selves. Cesarean sections are how most bulldogs have
Green/Blue, Homozygous Black‐Wing Cock puppies. The big head and chest also prevent them
(GgBB) to a Heterozygous Green/Blue, from swimming well or for very long. This is just a few
Homozygous Gray‐Wing Hen (Ggbb) examples of breeding for a type. There are numerous
Gb female gb female Gb female gb female textbooks that cover genetic conditions in animals that
GB GGbB gGbB GGbB gGbB can be passed on to offspring.
male
gB GgbB ggbB GgbB ggbB
male
gB GgbB ggbB GgbB ggbB
male Learning Exercise
gB GgbB ggbB GgbB ggbB Play around with the Punnett square using your
male
family as an example. Do you have a mom with
Offspring would look like this: brown hair and a dad with black hair? Look at
Homozygous dominant Green, Heterozygous Black wing = 2 your siblings. How many have black hair? Is it a
Homozygous recessive Blue, Heterozygous Black wing = 6 mix? Or use eye color or use height. Can you fig-
Heterozygous Green/Blue, Heterozygous Black wing = 8
ure out the dominant and recessive genes respon-
sible? Plug it into the Punnett square and see what
Another Punnett square shows how more than one the odds were that you would have been born
dominant or recessive trait can be inherited by the off- with a different eye or hair color or height.
spring (Table 6.8). We once again use our heterozygous