Chapter 4 Pedigree Analysis in Human Genetics

Fig. 3.14

Fig. 3.15

Difficulties • Long generation time • Data must be obtained from offspring produced • Experimental matings are not possible • Limited sample size

• Pedigree is an orderly presentation of family information • First step in studying the inheritance of traits • Important in predicting genetic risk • May be incomplete due to difficulties collecting information

Chapter 4 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning Pedigree Analysis • Construct pedigree using available information • Rule out all patterns of inheritance that are inconsistent with the data • May not have enough information to identify the mode of inheritance • Some genetic disorders may have more than one pattern of inheritance

Figure 4.4

Fig. 4.4

• For rare traits most affected individuals have unaffected parents • Offspring of two affected individuals are affected • Expressed in males and females equally • In rare traits unaffected parents with affected offspring may be related to each other

Fig. 3.16

• First affected family member who seeks medical attention for a genetic disorder

Fig. 4.5

aa I 1 2 1 2

II 1 2 3

III aa aa 2 3 5

aa I 1 2 1 2

II Aa Aa 1 2 3

III aa aa 2 3 5

AA? aa Aa? Aa? I 1 2 1 2

II Aa Aa Aa 1 2 3

III aa aa 2 3 5

Chapter 4 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning Chapter 4 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning Cystic Fibrosis Is an Example of an Autosomal Recessive Trait • Disabling and fatal disorder

• Affects sweat glands and glands that produce mucus and digestive enzymes

• Gene located on chromosome 7 • Cloned in 1989 • (Tsui & Collins)

Fig. 4.8

• CFTR regulates flow of chloride ions across the plasma membrane

• Reduces fluid in glandular secretions Fig. 4.9

• Hemoglobin is an oxygen transport molecule in red blood cells (RBC) • Sickle cell hemoglobin is abnormal and causes RBCs to become crescent or sickle shaped • RBCs are fragile • It is difficult to maintain normal oxygen carrying capacity

Fig. 4.11 • Many systems are affected • Lethal as homozygous recessive • Heterozygotes generally unaffected • Confers resistance to malaria parasite • High frequency in populations where malaria is found

•Hbα gene β α •Hb gene β α β •Wild-type Hbβ = A allele •Sickle-cell allele Hbβ = S allele

α αAA α αAS α αSS Wild type Carrier Affected

Α α Three kinds S α α Α of hemoglobins α S

Polypeptides: α, A and S

Α α S α α Α α Α S α α S

Hb production AA AS SS Codominant

RBC shape Normal Normal Sickle A -dominant S - recessive

S - dominant Malaria resistance Normal Resistant Resistant A - recessive

• Heterozygotes and homozygous dominant individuals are affected

• Affected offspring have at least one affected parent

• Equal number of males and females

Fig. 4.12