Human Genetics Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lecture Outline

Chromosomal Inheritance oMales and females have 23 pairs of chromosomes Pairs 1-44 are autosomes Chromosomes 45 and 46 are the sex chromosomes  Males have a Y chromosome and an X chromosomes  Females have two X chromosomes

Chromosomal Inheritance oSyndromes can result from: Inheriting of an abnormal chromosome number Inheriting abnormal chromosomes

Chromosomal Inheritance oKaryotyping Will reveal whether an individual has inherited an abnormal number of chromosomes or if a chromosome is an abnormal length or shape Routine blood test for pregnant women measures the levels of:  Alpha-fetoprotein  Estriol  HCG  Inhibin-A

Chromosomal Inheritance Amniocentesis  Amniotic fluid is withdrawn from the uterus of a pregnant woman  Performed after fourteenth week of pregnancy  As many as 400 chromosomal and biochemical problems can be detected  Risk of spontaneous abortion increases by about 0.3% Chorionic villus sampling  Chorionic cells in the region where the placenta will develop are obtained  Can be done as early as the fifth week of pregnancy  Biochemical tests on the amniotic fluid are not possible  Risk of spontaneous abortion increases by about 0.8%  Quicker karyotyping results

Chromosomal Inheritance  Preparing the Karyotype  Obtained cells are stimulated to divide  Mitosis is stopped at metaphase  Cells are prepared on a slide

Chromosomal Inheritance Nondisjunction  Can occur during Meiosis I or Meiosis II  Trisomy  Monosomy  Down syndrome  Trisomy 21 ­Three copies of chromosome 21 ­In most instances, the egg had two copies  Characteristic physical features  Mild to moderate developmental delays  Chance of a woman having a Down syndrome child increases with age

Chromosomal Inheritance Sex chromosome inheritance  Gender of the newborn determined by the father  If a Y-bearing sperm fertilizes the ovum then the child will be male  If an X-bearing sperm fertilizes the ovum the child will be female  Too many/too few sex chromosomes  Turner syndrome – only one sex chromosome  Klinefelter syndrome – two or more X chromosomes in addition to a Y chromosome  Poly-X female – more than two X chromosomes  Jacobs syndrome – male with one X chromosome and two Y chromosomes

Genetic Inheritance oGenes control: Body traits Production of specific proteins oAlleles – alternate forms of a gene having the same locus on a pair of homologous chromosomes Dominant allele Recessive allele

Genetic Inheritance oInheritance of Genes on Autosomal Chromosomes An individual normally has two alleles for an autosomal trait  Homozygous – identical alleles  Heterozygous – non-identical alleles Genotype – genes of the individual Phenotype – physical appearance of the individual

Genetic Inheritance oSex-Linked Inheritance Some sex-linked traits have nothing to do with the gender of an individual  X-linked – control most sex-linked traits  Y-linked Sex chromosomes in males (X and Y) are not truly homologous Males need receive only one recessive allele to have an X-linked disorder

Genetic Inheritance oPunnett Square Aa A a

Genetic Inheritance oGenetic Counseling Help families understand chromosomal and genetic inheritance Help make informed decisions about pregnancy and child bearing If the genotypes of the parents are known, the counselor can predict the chances that any offspring will have a recessive autosomal disorder If the genotypes are not known, a pedigree may be utilized

Genetic Inheritance Preimplantation Genetic Diagnosis  In the past, amniocentesis or chorionic villi sampling were the best methods to test for a genetic disorder  Now, ova can be retrieved from the ovary to test for abnormal alleles

DNA Technology oIncludes working with DNA to: Determine the relatedness of individuals Assist in forensics Develop new treatments for human illnesses

DNA Technology oGene Therapy Insertion of genetic material into human cells for the treatment of a disorder Includes:  Procedures that give a patient healthy genes to make up for faulty genes  The use of genes to treat various other human illnesses

DNA Technology oVectors transport DNA into the cell Modified viruses Four classes of viruses that have been used:  Retroviruses  Adenoviruses  Herpes viruses  Adeno-associated viruses oOther mechanisms used to transport DNA into the cell: Introduce DNA directly into cells Attaching the genes to a liposome Attaching DNA to molecules which have specific receptors on the cell membranes

DNA Technology oGenomics Molecular analysis of a genome Two ways researchers have attempted to map the human chromosomes:  The base sequence map  Human genetic material contains 3.16 billion base pairs  The order of 99.9% of those base pairs is identical in all people  The total number of truly functional genes is estimated to be between 30,000-50,000  The genetic map  Tells the location of genes along each chromosome  Sixteen of the 46 human chromosomes have been mapped