Dog Days of Science ■ 131Figure 7.11
Gordon Lark and Mopsa
involved in an eye disease that causes blindness
in both humans and dogs. Her lab also identi-
fied a gene involved in kidney cancer in dogs that
causes a similar syndrome in humans.
Today, Lark and Ostrander both continue their
canine research, and the Georgie Project lives on.
In one investigation, the team is collecting data
from tissues of deceased PWDs to determine the
dogs’ state of health at time of death. From data
gleaned, they hope to learn how the health of
aging dogs (and maybe people) is associated with
their genetic makeup. “I’m really happy with the
growth of the field,” says Ostrander, “and there’s a
lot of research coming down the pike.”
Mopsa, the puppy that Karen Miller gave Lark
in 1996 in return for studying PWDs, died in April
2012, just a week short of her sixteenth birthday
(Figure 7.11). But Lark has a new best friend, a
PWD puppy he named Chou (pronounced “shoo”),
for the French petit chou, meaning “little cabbage.”
“We often make a mistake and call Chou
‘Mopsa,’ because Chou looks so similar,” says
Lark. After all, he adds, PWDs share similar
genotypes and thus similar phenotypes. And
these genetic traits make them the cuddly,
devoted pets that they are.
REVIEWING THE SCIENCE
● (^) A genetic trait is any characteristic that is inherited
and may be physical, biochemical, or behavioral. All
of these types of traits are either invariant (the same
in all members of a species) or variable (different in
different members of a species).
● (^) A gene is a stretch of DNA that affects one or more
genetic traits. Genes are formed on chromosomes,
threadlike molecules made of DNA and proteins.
● (^) The genotype is an individual’s genetic makeup or,
more specifically, the pair of different versions of
a given gene (alleles) that determine a given trait.
The phenotype is the physical expression of an
individual’s genetic makeup or, more specifically, the
expression of a version of the given trait.
● (^) An allele is dominant when it prevents a second allele
from affecting the phenotype. This second allele is
said to be recessive because it has no effect on the
phenotype when paired with a dominant allele.
● (^) When a genotype consists of two copies of the
same allele, it is homozygous for that gene. A
genotype that consists of two different alleles is
heterozygous for that gene.
● (^) A grid-like diagram called a Punnett square helps
predict the probability of genotypes and phenotypes
resulting from a genetic cross.
● (^) Mendel’s experiments enabled him to deduce
two laws of inheritance: The law of segregation
states that two alleles of a gene are separated
during meiosis and end up in different gametes.
The law of independent assortment states that
during meiosis, the two alleles of any given gene
segregate independently of any two alleles of any
other gene.
● (^) Mendelian traits are genetic traits controlled by
a single gene and unaffected by environmental
conditions.
● (^) The chromosome theory of inheritance explains
how Mendel’s laws arise: genes occupy
specific locations on chromosomes, and those
chromosomes are randomly shuffled and
recombined during meiosis.
● (^) When a heterozygote displays an intermediate
phenotype, neither allele is dominant—a condition
known as incomplete dominance, in which neither