Section 5.3 Patterns of Inheritance pages 219 to 227
Autosomal Inheritance and PEDIGREE CHARTS
The study of human inheritance differs from other kinds of genetic studies in one important way – we can’t do many experiments. When we work with fruit flies, we can mate our subjects any way we want to. We can’t do that with humans. The study of human genetics depends heavily on different kinds of information, the kinds that come from the study of family patterns.
Autosomal inheritance occurs when the traits are found on the autosomes (chromosomes 1 to 22; not the sex chromosomes X and Y).
A pedigree chart is a diagram which shows how a particular trait is transmitted from generation to generation in a family. The conventional symbols used in a pedigree chart are:
Is the pedigree shown a dominant or recessive inheritance? Is it autosomal or on the sex chromosomes?
Autosomal inheritance includes the following diseases:
Huntington disease ______
Cystic fibrosis ______
Sickle cell anemia ______
Phenylketonuria (PKU) ______
Marfan syndrome ______
Tay-Sachs disease ______
PEDIGREE PROBLEMS
1. PKU (phenylketonuria) is a genetic disorder distinguished by the body’s inability to utilize phenylalanine, an essential amino acid. Find the genotypes of the family that has the following family history.
Ø A normal woman marries a normal man.
Ø They have five children
Ø Their first daughter is normal, the second daughter has PKU
Ø Their third child, a boy, also has PKU
Ø Their fourth and fifth children, a girl and a boy, are both normal
Ø The first daughter, marries a man with PKU but all her three daughters are all normal
Ø The second daughter marries a normal man and has a son with PKU
Ø The oldest son marries a normal woman and has three children, two normal sons and a daughter with PKU
Ø The second son marries a normal woman and has a normal son.
? Which family members are carriers of PKU ?
? Is PKU sex-linked or autosomal ?
? Is it recessive or dominant ?
2. Polydactyl is a genetic condition which involves having an extra finger. From the following case study, develop a pedigree chart.
Ø A little girl has polydactyl
Ø None of her three brothers have it.
Ø Her father has polydactyl as does his brother, one of his four sisters and his father
? Is this trait autosomal or sex-linked ?
? Is polydactyl dominant or recessive ?
3. Hairy ear-lobes are genetically determined. From the following case study, develop a pedigree chart.
Ø A man and his two brothers have hairy ear-lobes.
Ø Neither of his sisters have this condition
Ø Their father also had hairy ear-lobes while their mother was normal.
Ø The sons, daughters and husbands of both sisters are normal while all sons of the brothers are afflicted while their daughters and wives are normal.
? Is this trait autosomal or sex-linked ?
? Are hairy ear-lobes dominant or recessive ?
Textbook: Pg. 223 #17 – 22, Pg. 227 # 1,2,3,5,7,8,9,10