5.3 Tracking Inheritance
Pages 197-201
Pedigree
A diagram of an individual’s ancestors
used in human genetics to analyze the
Mendelian inheritance of a certain
trait; also used for selective breeding
of plants and animals.
Freckles
The allele for freckles, F, is dominant.
Marfan’s Syndrome
Pedigree
Example:
Legend
Symbols and their meaning:
Guidelines:
Roman numerals signify generations
Arabic numerals identify individuals within
generations.
Birth order is left to right
Sex Linkage-Following the X and Y
chromosome
Autosomal inheritance is found on the
autosome
Sex-linked genes are found on the X
chromosome
X-linked
Females must inherit 2 recessive alleles on the
X-chromosomes to express the trait.
Males only need to inherit one X chromosome
from their mothers to express the trait. The Y
chromosome cannot mask the trait.
hemophilia
Carried on the X chromosome
Punnett square for hemophilia
Father is a carrier.
Red-green colour blindness
X-linked traits
 The sexes exhibit different phenotypic ratios.
 More males than females will express the
recessive phenotype.
 More females are carriers of the recessive Xlinked alleles.
Examples: red-green colour blindness,
hemophilia, and male-pattern baldness
Y-linked traits
Traits are controlled by a single allele passed on
from fathers to sons on the Y chromosome.