Lecture #31 Human Genetics and Pedigrees Honors Biology Ms. Gaynor

Many human traits follow Mendelian patterns of inheritance  Humans are not convenient subjects for genetic research However, the study of human genetics continues to advance We use pedigrees !

Pedigree Analysis  A pedigree Is a family tree that describes the interrelationships of parents and children across generations

Inheritance patterns of particular traits can be traced and described using pedigrees Figure A, B Ww ww Ww wwWw ww Ww WW or Ww ww First generation (grandparents) Second generation (parents plus aunts and uncles) Third generation (two sisters) Ff ffFf ff Ff Ff or FF Ff FF or Ff ff FF or Ff Widow’s peak No Widow’s peak Attached earlobe Free earlobe (a) Dominant trait (widow’s peak) (b) Recessive trait (attached earlobe)

Pedigrees Can also be used to make predictions about future offspring

Recessively Inherited Disorders  Many genetic disorders are inherited in recessive manner Show up only in individuals homozygous for the alleles  Carriers (only for DOMINANT TRAITS) Are heterozygous individuals, who carry recessive allele but are show “normal” phenotype

Cystic Fibrosis  Example of recessive disorder  Affect mostly people of European descent  Symptoms Mucus buildup in the some internal organs Abnormal absorption of nutrients in the small intestine

Sickle-Cell Disease  Another recessive disorder Affects one out of 400 African-Americans Is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells  Symptoms Physical weakness, pain, organ damage, and even paralysis

Dominantly Inherited Disorders  Some human disorders Are due to dominant alleles  Example is achondroplasia Form of dwarfism  lethal when homozygous for the dominant allele

Another Dominant Disorder  Huntington’s disease (HD) degenerative disease of nervous system No obvious phenotypic effects until about 35 to 40 years of age HD Normal

Figure 15.12a, b Meiosis I Nondisjunction Meiosis II Nondisjunction Gametes n + 1 n  1 n – 1 n + 1n –1 n n Number of chromosomes Nondisjunction of homologous chromosomes in meiosis I Nondisjunction of sister chromatids in meiosis II (a) (b)

Down Syndrome  Down syndrome Is usually the result of an extra chromosome 21  trisomy 21

Genetic Testing and Counseling  Genetic counselors Can provide information to prospective parents concerned about a family history for a specific disease

Tests for Identifying Carriers  For a growing number of diseases Tests are available that identify carriers and help define the odds more accurately Examples  Tay Sachs & CF

Fetal Testing  In amniocentesis The liquid that bathes fetus is removed & tested  In chorionic villus sampling (CVS) A sample of the placenta is removed and tested Can make karyotypes, too!

Newborn Screening  Some genetic disorders can be detected at birth Simple tests are now routinely performed in most hospitals in the United States Example- PKU test