Page 149 - 86 human physiology part-2

Chapter 18

• brain damage
• behavioral disturbances
• phenotype blond hair, blue eyes, fair skin

• Sickle cell

• autosomal recessive
• occurs equally in genders
• increased evidence with both parents carriers
• occurs in approximately ¼ of children but may occur more if one parent has the disease
• expression usually seen early in infancy or childhood
• In the punnett square to predict risk P = Phenylketonuria gene / p = normal gene

P p
P PP Pp

p Pp Pp

• 25% chance contracting PKU
• 50% chance of being a carrier of the trait
• 25% chance of having normal genes

• EXAMPLE
• Hemophilia

• X-linked recessive gene
• affects mostly males
• spontaeous hemorrage

• Duschenne's muscular dystrophy

• sex-linked (X-linked) recessive
• usually seen in males
• females are usually carriers
• affected father, yields a carrier daughter
• In the punnett square to predict risk D = Duschenne's gene / d = normal gene

Xd Y
XD
XD XD Xd
Y

Xd Xd Xd Xd Y
• Females = 50% chance of being a carrier/ 50% chance of having normal genes
• Males = 50% chance of having Duschenne's/ 50% chance of having normal genes

364 | Human Physiology