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

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 family tree  describes relationships & inheritance btw parents & children across generations Can also be used to make predictions about future offspring

Inheritance patterns of particular traits can be traced and described using pedigrees Ww ww WW or First generation (grandparents) Second generation (parents plus aunts and uncles) Third generation (two sisters) Ff ff FF or Ff FF Widow’s peak No Widow’s peak Attached earlobe Free earlobe (a) Dominant trait (widow’s peak) (b) Recessive trait (attached earlobe) Figure 14.14 A, B

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

Cystic Fibrosis Example of recessive autosomal disorder Affect mostly Caucasian people of (European descent) Deletion of codon  mutated NaCl channel protein in membrane Symptoms Mucus buildup in internal organs (lungs) Abnormal absorption of nutrients in small intestine

Sickle-Cell Disease Another recessive autosomal disorder Affects mostly African-Americans caused by point mutation in hemoglobin gene  protein in red blood cells Symptoms Physical weakness, pain, organ damage and even paralysis

Achondroplasia Autosomal dominant disorder Form of dwarfism lethal when homozygous for the dominant allele AA= die Aa= dwarf aa= normal height

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

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

Disorders from Nondisjunction Down syndrome Results with an extra chromosome 21 trisomy 21 Other disorders: Klinefelter’s XXY Turner’s XO Edward’s 18th Patau Syndrome 13th

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

Tests for Identifying Carriers For many diseases Tests are available that identify carriers and help define the odds (probabilities) more accurately Examples Tay Sachs, HD & CF

Can make karyotypes, too! 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