1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 19 Lecture Outline See separate PowerPoint slides for all figures and tables pre- inserted into PowerPoint without notes.

Chromosomal inheritance

3 A.Introduction 1.Males and females have 23 pairs of chromosomes a.Chromosomes 1-44 are autosomes b.Chromosomes 45 and 46 are the sex chromosome a.Males have a Y chromosome and an X chromosome b.Females have two X chromosomes

4 2.Syndromes can result from a.Inheriting of an abnormal chromosome number b.Inheriting abnormal chromosomes

5 B.Karyotyping 1.A display of the chromosomes by size, shape, and banding pattern 2.Will reveal whether an individual has inherited an abnormal number of chromosomes or if a chromosome is an abnormal length or shape 3.Routine blood test for pregnant women measures the levels of alpha-fetoprotein, estriol, HCG, and inhibin-A a.Abnormal levels have been linked to certain chromosomal and structural abnormalities

6 4.Amniocentesis a.Amniotic fluid is withdrawn from the uterus of a pregnant woman b.Performed after fourteenth week of pregnancy c.As many as 400 chromosomal and biochemical problems can be detected d.Risk of spontaneous abortion increases by about 0.3%

7 5.Chorionic villus sampling (CVS) 1.A catheter is inserted through the vagina into the uterus 2.Chorionic cells in the region where the placenta will develop are obtained 3.Can be done as early as the fifth week of pregnancy 4.Biochemical tests on the amniotic fluid are not possible because no fluid is collected 5.Risk of spontaneous abortion increases by about 0.8% 6.Quicker karyotyping results

8 Chorionic villus sampling

9 6.Preparing the karyotype 1.Obtained cells are stimulated to divide 2.Mitosis is stopped at metaphase 3.Cells are prepared on a slide – dried and stained

10 C.Nondisjunction 1.Can occur during Meiosis I or Meiosis II when chromosomes do not separate correctly 2.Results in trisomy or monosomy 3.Down syndrome a.Trisomy 21 1)Three copies of chromosome 21 2)In most instances, the egg had two copies b.Characteristic physical features c.Mild to moderate developmental delays d.Chance of a woman having a Down syndrome child increases with age

11 Nondisjunction during oogenesis

12 Down Syndrome

13 D.Sex chromosome inheritance 1.Gender of the newborn determined by the father a.If a Y-bearing sperm fertilizes the ovum then the child will be male (XY) b.If an X-bearing sperm fertilizes the ovum the child will be female (XX)

14 2.Abnormal sex chromosome number a.Turner syndrome – female with only one sex chromosome (XO) b.Klinefelter syndrome – two or more X chromosomes in addition to a Y chromosome (XXY); sterile male c.Poly-X female – more than two X chromosomes (XXX, XXXX) d.Jacobs syndrome – male with one X chromosome and two Y chromosomes (XYY) e.XXY – male f.YO – does not live; one X is needed for survival

15 Turner syndrome Klinefelter syndrome

Genetic inheritance

17 A.Introduction 1.Genes control: a.Body traits b.Production of specific proteins 2.Alleles – alternate forms of a gene having the same locus on a pair of homologous chromosomes a.Dominant allele b.Recessive allele

18 B.Inheritance of genes on autosomal chromosomes 1.An individual normally has two alleles for an autosomal trait a.Homozygous – identical alleles b.Heterozygous – non-identical alleles 2.Genotype – genes of the individual 3.Phenotype – physical appearance of the individual a.Need only one dominant allele to show the dominant phenotype b.Need two recessive alleles to show the recessive phenotype

19 Genetic inheritance

20 C.Sex-linked Inheritance 1.Some sex-linked traits have nothing to do with the gender of an individual a.X-linked – control most sex-linked traits – only on the X chromosome b.Y-linked - only on the Y chromosome 2.Sex chromosomes in males (X and Y) are not truly homologous 3.Males need receive only one recessive allele to have an X-linked disorder 4.Females are usually carriers of the recessive gene and do not have the disorder; unless they receive a recessive gene from each parent

21 Sex-linked inheritance

22 D.Punnett square 1.Used to determine the probability of inheriting a particular trait 2.Use uppercase and lowercase letters to represent the alleles 3.Place father alleles on the top and mother alleles on the left 4.The possible offspring alleles are in the inner blocks

23 Aa AAAAa a aa Punnett Square

24 E.Genetic counseling 1.Helps families understand chromosomal and genetic inheritance 2.Helps make informed decisions about pregnancy and child bearing 3.If the genotypes of the parents are known, the counselor can predict the chances that any offspring will have a recessive autosomal disorder 4.If the genotypes are not known, a pedigree may be utilized

25 Inheritance pattern & pedigree for CF

26 F.Prenatal testing for genetic disorders 1.In the past, amniocentesis or chorionic villi sampling were the best methods to test for a genetic disorder 2.Now, ova can be retrieved from the ovary to test for abnormal alleles

DNA technology

28 A.Includes working with DNA to: 1.Determine the relatedness of individuals 2.Assist in forensics 3.Develop new treatments for human illnesses

29 B.Gene therapy 1.Insertion of genetic material into human cells for the treatment of a disorder 2.Includes: a.Procedures that give a patient healthy genes to make up for faulty genes b.The use of genes to treat various other human illnesses

30 3.Vectors transport DNA into the cell a.Modified viruses b.Four classes of viruses that have been used: 1)Retroviruses 2)Adenoviruses 3)Herpes viruses 4)Adeno-associated viruses

31 Gene therapy, cont 4.Other mechanisms used to transport DNA into the cell: a.Introduce DNA directly into cells b.Attaching the genes to a liposome c.Attaching DNA to molecules which have specific receptors on the cell membranes 5.Genes are being used to treat medical conditions other than genetic disorders 6.Gene therapy is being used as a part of cancer treatment

32 C.Genomics 1.Molecular analysis of a genome – all the genetic information in all the chromosomes of an individual 2.Two ways researchers have attempted to map the human chromosomes: a.The base sequence map 1)Human genetic material contains 3.16 billion base pairs 2)The order of 99.9% of those base pairs is identical in all people 3)The total number of truly functional genes is estimated to be between 30,000-50,000

33 Genomics, cont b.The genetic map 1)Tells the location of genes along each chromosome 2)Sixteen of the 46 human chromosomes have been mapped 3.Still many unanswered questions including ethical considerations dealing with gene therapy and using the information from genomics