Download Test Cross

Test Cross
• If you have to determine if something is
homozygous or heterozygous, you take
the test animal and mate it with a double
recessive (this is called a test cross)
• TT – pure tall (homozygous tall)
• Tt – hybrid tall (heterozygous tall)
• E.g. The bull has a red coat (red is
dominant), it is heterozygous or
homozygous?
• The bull could be Rr or RR. Breed with a
cow, rr (white)
Possibilities:
F1
r
r
R
r
Rr
Rr
F1
R
rr
rr
r
Rr
Rr
r
Rr
Rr
100% red
50% red
50% white
R
• If the results (from breeding) are 50% red
and 50% white, then you conclude that the
bull is heterozygous.
• If the results are 100% red, then it is
homozygous.
Selective Breeding
• Farmers and ranchers have been using
selective breeding for plants and animals.
• Selective breeding is the crossing of
desired traits from plants or animals to
produce offspring that have one of several
favoured characteristics
• Have you ever heard of a purebred?
• Dogs and horses are considered
purebreds if they came from a gene line
that was closely regulated by inbreeding
• Inbreeding is a process by which
breeding is limited to a number of
desirable traits
• New varieties of plants and animals are
made by hybridization. The process of
mating two different parents to produce
offspring with desirable traits of both
parents.
Pedigree Charts
• See handouts