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. Image: genetics.thetec.org

Marfan’s Syndrome

Pedigree Example: Image: saburchill.com

Legend Symbols and their meaning: image: uic.org

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 image: torresbioclan.pbworks.com

hemophilia Image: torresbioclan.pbworks.com

Punnett square for hemophilia Father is a carrier. Image: macalester.edu

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 X-linked 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.