Inquiry into Life Twelfth Edition Chapter 26 Lecture PowerPoint to accompany Sylvia S. Mader...

Inquiry into LifeTwelfth Edition

Chapter 26

Lecture PowerPoint to accompany

Sylvia S. Mader

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

26.1 Counseling for Chromosomal Disorders

• Genetic Counselors

– Help individuals understand modes of inheritance

– Medical consequences of genetic disorders

– Inform individuals of possible decisions they may

need to make


• Karyotyping– A karyotype is a visual

display of individual’s chromosomes

– Can be performed on any babies, children, teens, adults and on a fetus


• Amniocentesis– A prenatal test– A sample of amniotic

fluid is collected– Fetal cells can be

isolated and analyzed– Risk of spontaneous

abortion is 0.25 - 0.5%


• Chorionic Villi Sampling– A prenatal test– Chorionic cells can be

collected and analyzed– Can be performed

earlier than amniocentesis

– Risk of spontaneous abortion is 0.5 - 1.0%


Normal Karyotype (male) Down Syndrome Karyotype


• Changes in Chromosome Number

– Too many or too few chromosomes

– Due to a process called nondisjunction

– Trisomy: An extra chromosome is carried

by an egg or sperm

– Monosomy: An egg or sperm lacks a

chromosome

Nondisjunction of Chromosomes During Oogenesis

Abnormal Autosomal Chromosome Number

Abnormal SexChromosome Number


• Changes in Chromosomal Structure– Chromosomal Mutations

– Radiation, certain chemicals, and some viruses can causes chromosomes to break apart

• Deletions• Duplications• Translocations• Inversions


• Chromosomal Mutations– Deletions

• Williams Syndrome– Chromosome 7 loses an end piece

» Individuals have a turned up nose and a wide mouth with small chin

» Poor academic skills but well-developed verbal and musical skills

• Cri Du Chat Syndrome– Chromosome 5 loses an end piece– Small head, mental retardation, cat-like cry

A Deletion


• Chromosomal Mutations– Duplication

• This example is characterized by poor muscle tone and autistic traits


• Chromosomal Mutations– Translocations

• The exchange of chromosomal segments between two nonhomologous segments

– A translocation of pieces of chromosomes 14 and 21 is another phenomena that results in Down syndrome (5% of all cases)

A Translocation

• Alagille Syndrome– Translocation of chromosomes 2 and 20


• Inversion– Segment is turned 180

degrees– Leads to altered gene

activity

26.2 Counseling for Genetic Disorders

• Family Pedigrees– Chart of Family’s History

• Key– Males are indicated by squares

– Females are indicated by circles

– Shaded means individual is affected by disorder

Pedigrees for Autosomal Disorders

Autosomal Recessive Autosomal Dominant

Autosomal Recessive Pedigree

Autosomal Dominant Pedigree


• Pedigrees for Sex-linked Disorders– X-linked disorders

• X-linked recessive disorders– To be affected, daughters must inherit it from both parents

– Sons can only inherit it from mother, therefore more males affected than females

• X-linked dominant disorders– Affected males pass the trait only to daughters

– Females can pass trait to both daughters and sons

– Y-linked disorders• Present only in males• Fathers pass trait to all sons

X-linked Recessive Pedigree


• Genetic Disorders of Interest– Autosomal Recessive Disorders

• Tay-Sachs Disease• Cystic Fibrosis (CF)• Phenylketonuria (PKU)• Sickle-Cell Disease


• Tay-Sachs Disease– Lack of Hex A enzyme– Results in defective

lysosomes (especially in the brain)

– Symptoms appear in the first year of life

– Disease is progressive and fatal


• Cystic Fibrosis– Most common genetic

disorder in Caucasians in U.S.

– Defect in chloride channel proteins in cells

– Thick, abnormal mucus production

• Lungs, bronchial tubes, pancreatic ducts affected


• Autosomal Recessive Disorders– Phenylketonuria

• Lack enzyme for phenylalanine metabolism• Affects nervous system development• Can usually be controlled with diet

– Sickle-cell anemia• Irregular red blood cells caused by abnormal hemoglobin

– Clog vessels- poor circulation

– Internal hemorrhaging

• Heterozygous individuals are normal unless dehydrated or experience mild oxygen deprivation


• Autosomal Dominant Disorders– Marfan Syndrome

• Defect in fibrillin-protein in elastic connective tissue– Long limbs and fingers, weakened arteries, dislocated lenses in

the eyes

– Huntington Disease• Progressive degeneration of brain cells• Gene for defective protein called Huntington

– Too many copies of the amino acid glutamine


• Incompletely Dominant Disorders– Familial hypercholesterolemia

• Affects the number of LDL-cholesterol receptors on cells– Homozygous for defective gene- has no receptors and develops

cardiovascular disease in teenage years– Heterozygous individual has half the normal number of receptors


• X-linked Recessive Disorders– Color Blindness

• About 8% of Caucasian males have red-green color blindness

– Duchene's Muscular Dystrophy• Absence of a protein called dystrophin

– Causes calcium to leak into muscle cells which actives enzymes that break down the cells

– Hemophilia• Hemophilia A is due to a lack of clotting factor VIII• Hemophilia B is due to a lack of clotting factor IX• Blood clots slowly or not at all


• Testing for Genetic Disorders– Testing for a Protein

• Some mutations lead to disorders caused by a missing enzyme

– Tay-sachs disease-test for quantity of hex A enzyme present in a sample of cells

» can determine if individual is homozygous normal, a carrier, or has Tay-sachs

– PKU-blood test done on all newborns to detect the presence of phenyalanine

Use of a Genetic Marker to Test for a Genetic Mutation


• Testing for Genetic Disorders – Testing the DNA

– Testing for genetic markers-similar to DNA fingerprinting

» Restriction enzymes cleave DNA

» Used to test for Huntington disease

– Testing with DNA probes

» DNA probe-single stranded piece of DNA that binds to complementary DNA

» For genetic testing, the probe has a mutation of interest

– DNA chip can test for many abnormalities at once

» Has many DNA segments

» mutated genes bind if present and are detected by laser scanner

Use of a DNA Chip


• Testing the Fetus– Ultrasound

• The fetus is exposed to high frequency sound waves to produce a picture


• Testing Fetal Cells– Amniocentesis

• Performed at 15 weeks of gestation • Can also test for alpha fetoprotein (AFP) which can indicate

neural tube defects

– Chorionic Villi Sampling• Performed earlier than amniocentesis • no amniotic fluid taken so cannot test for AFP

– Fetal Cells in Mother’s Blood• A small number of fetal cells enters the mother’s blood• These can be isolated and analyzed


• Testing the Embryo– Following in vitro fertilization, the embryo is allowed to

develop. At the 8-cell stage, a cell can be removed and tested.

– Only “normal” embryos are implanted

• Testing the Egg– Test the polar bodies of women who are

heterozygous prior to in vitro fertilization• If the polar body has the defect, then the ovum is normal

Counseling for genetic disorders: the present cont’d.

• Testing for genetic disorders cont’d.– Testing the embryo

• If both parents are carrier, they may want assurance that embryo is normal

– Following in vitro fertilization, can remove a cell at 6-cell stage and test for defect, then implant only those embryos that are normal

– Testing the egg• Test the polar bodies of women who are

heterozygous prior to in vitro fertilization– If the polar body has the defect, then the ovum is normal

26.3 Genomics

• Genomics is the Study of Genomes.– Humans have 20,000 - 25,000 genes that code for

proteins– Many other organisms have more genes than do

humans

26.3 Genomics

• Sequencing the Bases– The Human Genome project was a project to

sequence all of the base pairs in all of the DNA of human chromosomes.

• Genome Comparisons– Scientists can compare the genomes of different

species of organisms to gather data regarding the cause of many diseases.

26.3 Genomics

• The HapMap Project

– The objective is to catalog common sequence

differences that occur in human beings.

– People have been found to inherit patterns of

sequence differences, these are called haplotypes.

– Information gained from this project will allow

scientists to link haplotypes to the risk of specific

illnesses.

26.3 Genomics

• Proteomics and Bioinformatics– Proteomics

• Study of structure, function, and interaction of cellular proteins

• Translation of all human genes results in a collection of proteins called the proteome

• Computer modeling provides information about the three-dimensional shape of protein molecules

– May be possible to correlate drug treatment to genetic profiles

26.3 Genomics

• Proteomics and Bioinformatics– Bioinformatics

• Application of computer technologies to the study of the genome

• Analysis of data produced by genomics and proteomics• Cause and effect relationships between various genetic

profiles and genetic disorders caused by multifactor genes• Current genome includes gene “deserts” with no known

function– Bioinformatics may discover functions of these regions

26.3 Genomics

• Expanding Present-Day Genomics– The Human Genome is described as three-

dimensional• One dimension is the sections of DNA that encode proteins

– This accounts for less than 2% of the DNA

• A second dimension is what used to be called “junk” DNA– This “junk” DNA may code for RNA, researchers are trying to

determine what this RNA does

• A third layer of our genome lies outside DNA.– It consists of proteins and other chemicals that surround and

adhere to DNA. These may provide clues to the inheritance of certain diseases.

26.3 Genomics

• Gene Therapy– Insertion of genetic material into human cells for

treatment of a disorder– Ex vivo gene therapy

• Cells are removed from the patient– Treated outside the body and then returned to the patient

• Ex: SCID (Severe Combined Immunodeficiency)

– In vivo gene therapy• Patient is given a foreign gene directly• Gene is incorporated into the genome within the body• Ex: Cystic fibrosis

Ex Vivo Gene Therapy in Humans

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Inquiry into Life Twelfth Edition Chapter 26 Lecture PowerPoint to accompany Sylvia S. Mader...

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