Heredity
Goals:
1. Explain how traits are
inherited.
2. Identify Mendel’s role in the
history of Genetics.
3. Use a Punnett square to predict
the results of crosses.
4. Compare and contrast the
difference between an
individual’s genotype and
phenotype.
5. Explain how traits are inherited
by incomplete dominance.
6. Compare multiple alleles and
polygenic inheritance, and give
examples of each.
7. Describe two human genetic
disorders and how they are
inherited.
8. Explain how sex-linked traits
are passed to offspring.
Summarize what alleles are and how
they are inherited.
The different forms of a trait that
a gene can have are called alleles.
An organism usually has 2 alleles
Black Dog
for each trait, one from each
parent.
B
b
Blond Dog
Bb
bb
bb
b Bb
The black dog carries heterozygous
black-fur traits. The blond dog
carries homozygous blond-fur traits.
The chance that the offspring will
have black fur is ____%, or one in
two.
b
Summarize Mendel’s three principles of
heredity:
1. Traits are controlled by alleles
on chromosomes.
2. An allele’s effect is dominant or
recessive.
3. When a pair of chromosomes
separates during meiosis, the
different alleles for a trait move
into separate sex cells.
Neither allele is dominant in
incomplete dominance. The offspring
have a phenotype intermediate to that
of the parents.
A chromosome disorder occurs as a
result of a mistake in the process of
meiosis. It causes an organisms to
have more or fewer chromosomes.
Sex-linked disorders usually result
from recessive alleles on the X
chromosome. A man will have the
disorder when his only X chromosome
has the recessive allele. A woman
will have the disorder when both of
her X chromosomes have the recessive
allele.