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black one. Why is there only one mother cat here?”
Mr. Wei came up behind them and picked up the large cat with tiger stripes and an orange
face. “This is the mother. She was found near a dumpster last week with all these babies.”
Gabriella looked up. “How could one mother cat have kittens with so many different pat-
terns?”
Mr. Wei smiled at her. “Take a look at them. Are they really that different?” Then he went to
help another customer who was ready to pay.
Jesse and Gabriella turned back to the kittens. “Well, the mother is a tabby cat,” Jesse said.
“Black, orange, and white spots with some brown blotches.”
“Right, and some of the kittens have those same colors,” added Gabriella.
They took a closer look at the kittens. “Actually, they all have small tufts of hair off their ears,
just like their mother,” said Jesse.
“You’re right, Jesse. And the ears are all rounded on top, not pointed like on my cat at home.”
Jesse and Gabriella remembered what they had learned in science class. Organisms display
traits
. Traits include things like eye color in humans, the shape of ears or the color of fur in kit-
tens, and seed shape or stem height in plants. Traits are determined by the
genes
of an individual
organism. Individuals get their genes from their parents. Sometimes individuals display the
same traits as their parents, sometimes they don’t.
Genes are made of two parts called
alleles
[ul-LEELS]. Some alleles are
dominant
—this allele
has the trait that will always appear if it is in the gene. Others are
recessive
—it is hiddenwhen there
is a dominant allele around.
Gabriella turned to her
friend. “Jesse, what color are
your eyes?”
“Brown.”
“What about your parents?”
“Umm. My mom has
brown eyes. And my dad has
blue eyes.”
“And I have brown eyes, as
do both of my parents. Remem-
ber what we learned? Brown
eyes are dominant; the allele
brown always shows through.”
Jesse knew what she was
talking about and piped in,
alleles
different forms of a gene; offspring
inherit one allele from each parent
dominant
the allele that provides a trait that
always appears in the organism
genes
information within the DNA of a
cell that controls a specific trait
recessive
an allele that is masked by a
dominant allele
traits
characteristics of an organism that
are passed to the next generation
Words to Understand