Chapter 7 Body Systems

Chapter 7 Body Systems

Chapter 25 Genetics and Genetic Diseases Copyright 2014 by Elsevier Inc. All rights reserved. Lesson 25.1 Mechanisms of Genetics and Mutations 1. Explain how genes can cause disease. 2. Distinguish between dominant and recessive

genetic traits. 3. Describe sex-linked inheritance and explain how genetic mutations may occur. Copyright 2014 by Elsevier Inc. All rights reserved. 2 Genetics and Human Disease Genetics, begun by Mendel more than 140 years ago, is the scientific study of

inheritance Inherited traits can produce disease Copyright 2014 by Elsevier Inc. All rights reserved. 3 Mechanisms of Gene Function Geneindependent genetic units (DNA segments) that carry the genetic code Genes dictate the production of enzymes

and other molecules, which in turn dictate the structure and function of a cell Genes are active in the chromatin (strand) form and inactive when DNA is in the chromosome (compact) form Copyright 2014 by Elsevier Inc. All rights reserved. 4 Human Genome

Copyright 2014 by Elsevier Inc. All rights reserved. 5 The Human Genome Genomeentire set of human chromosomes (46 in nucleus of each cell, 1 mitochondrial chromosome) Rough draft of entire human genome

(nearly all nucleotides in sequence) published in 2001 Contains about 30,000 genes and pseudogenes which are large amounts of noncoding DNA Copyright 2014 by Elsevier Inc. All rights reserved. 6 Terms Genomicsanalysis of the sequence

contained in the genome Proteomicsanalysis of the entire group of proteins encoded by the genome, called the human proteome Copyright 2014 by Elsevier Inc. All rights reserved. 7 Expression of Genomic Information Genomic information can be expressed

in various ways Ideogramcartoon of a chromosome showing the centromere as a constriction and the short segment (parm) and long segment (q-arm) Genes are often represented as their actual sequence of nucleotide bases expressed by the letters a, c, g, and t Copyright 2014 by Elsevier Inc. All rights reserved. 8

Distribution of Chromosomes to Offspring Meiotic cell division produces gametes with 23 chromosomes each At conception, two gametes join and produce a zygote with 46 chromosomesthe complete human genome Two meiotic divisions First meiotic division distributes the chromosome pair into separate cells

Second meiotic division separates the strands of the duplicated chromosome and distributes to an individual gamete Copyright 2014 by Elsevier Inc. All rights reserved. 9 Meiosis Copyright 2014 by Elsevier Inc. All rights reserved. 10

Chromosomes Twenty-two pairs of chromosomes are called autosomes; each member of a pair resembles its partner The chromosomes in the remaining pair of chromosomes (pair 23) are called sex chromosomes Copyright 2014 by Elsevier Inc. All rights reserved.

11 Genetic Variation Genetic variation among offspring is increased by: Independent assortment of chromosomes during gamete formation Crossing-over of genes or linked groups of genes between chromosome partners

during meiosis Copyright 2014 by Elsevier Inc. All rights reserved. 12 Crossing-Over Copyright 2014 by Elsevier Inc. All rights reserved. 13 Hereditary Traits

Dominant genes have effects that appear in the offspring (dominant forms of a gene are often represented by uppercase letters) A genetic carrier is a person who carries a recessive gene but does not show its effects because of masking effect of a dominant gene Codominant genes are two or more genes that are all dominant and when

they appear together produce a combined effect in offspring Copyright 2014 by Elsevier Inc. All rights reserved. 14 Recessive Genes Recessive genes have effects that do not appear in the offspring when they are masked by a dominant gene (recessive forms of a gene are

represented by lowercase letters) Copyright 2014 by Elsevier Inc. All rights reserved. 15 Genes and Chromosomes Dominant and Recessive Alleles Gene pairs Homozygousboth genes are same Heterozygousthe two genes differ

Dominant allele Express effect whether homozygous or heterozygous Need to inherit from one parent only Recessive allele Only expressed if homozygous Need to inherit from both parents Copyright 2014 by Elsevier Inc. All rights reserved. Genes and Chromosomes (cont.)

Dominant and Recessive Alleles (cont.) Phenotype: Any characteristic that can be observed or tested for Example: Eye color, blood type Genotype: A persons genetic makeup Example: Heterozygous dominant Bb (a carrier)

Homozygous dominant BB Homozygous recessive bb Copyright 2014 by Elsevier Inc. All rights reserved. Inheritance of Albinism Copyright 2014 by Elsevier Inc. All rights reserved. 18 Sex-Linked Traits

The large X chromosome (female chromosome) contains genes for female sexual characteristics and many other traits The small Y chromosome (male chromosome) contains only genes for male sexual characteristics Normal males have XY as pair 23; normal females have XX as pair 23 Nonsexual traits carried on sex chromosomes are sex-linked traits; most are X-linked traits

Copyright 2014 by Elsevier Inc. All rights reserved. 19 Sex Determination Copyright 2014 by Elsevier Inc. All rights reserved. 20 Sex-Linked Inheritance Copyright 2014 by Elsevier Inc. All rights reserved.

21 Genetic Mutations Mutation means change; genetic mutation is a change in the genetic code Can result in abnormalities in the genetic code that cause disease Most mutations are believed to be caused by substances or agents called mutagens

Copyright 2014 by Elsevier Inc. All rights reserved. 22 Lesson 25.2 Genetic Diseases, Prevention, and Treatment 4. Explain the mechanisms of genetic disease and list some important inherited diseases. 5. Describe how nondisjunction can result in

trisomy or monosomy and list some disorders that result from it. 6. List some tools used in genetic counseling and explain how they are used to help clients. 7. Describe how genetic disorders can be treated. Copyright 2014 by Elsevier Inc. All rights reserved. 23 Genetic Diseases

Congenital versus Hereditary Diseases Congenital means present at the time of birth Hereditary means genetically transmitted May not manifest until later in life Causes of Congenital Disorders Often not known Certain infections and toxins transmitted from mother (e.g., German measles)

Teratogen (agent, i.e., drug) Ionizing radiation Copyright 2014 by Elsevier Inc. All rights reserved. Congenital Disorders Causes of Congenital Disorders Alcohol intake Fetal alcohol syndrome (FAS) Cigarette smoking

Poor nutrition Spina bifida related to inadequate folic acid Copyright 2014 by Elsevier Inc. All rights reserved. Mechanisms of Genetic Disease Single-gene diseases result from individual mutant genes (or groups of genes) that are passed from generation to generation Some diseases result from the combination

of inheritance and environmental factors Epigenetics (imprinting) is the science that describes how environmental factors may result in offspring with genetic traits that cannot be explained by genes alone Copyright 2014 by Elsevier Inc. All rights reserved. 26

Chromosomal Diseases Chromosomal diseases result from chromosome breakage or from nondisjunction (failure of a chromosome pair to separate during gamete formation) Trisomya chromosome triplet (instead of the usual pair), caused by nondisjunction

Monosomya single chromosome (instead of a pair) Copyright 2014 by Elsevier Inc. All rights reserved. 27 Location of Genes Involved in Genetic Diseases Copyright 2014 by Elsevier Inc. All rights reserved. 28

Effects of Nondisjunction Copyright 2014 by Elsevier Inc. All rights reserved. 29 Examples of Single-Gene Diseases Cystic fibrosisrecessive autosomal condition characterized by excessive secretion of mucus and sweat, often

causing obstruction of the gastrointestinal or respiratory tracts Phenylketonuria (PKU) recessive autosomal condition characterized by excess phenylketone in urine, caused by accumulation of phenylalanine in tissues; may cause brain injury and death Copyright 2014 by Elsevier Inc. All rights reserved. 30 Examples of Single-Gene Diseases

Tay-Sachs disease (TSD) is a recessive condition involving failure to make a subunit of an essential lipid-processing enzyme, hexosaminidase Causes abnormal lipid accumulation in brain tissue, leading to retardation and death by age 4 Copyright 2014 by Elsevier Inc. All rights reserved.

31 Epigenetic Conditions Some diseases thought to result from epigenetic DNA changes that alter gene activity Some cancers are associated with methylation (abnormal levels of methyl groups) Fragile X syndrome (FXS) is associated with over methylation of part of the X chromosome, causing mental retardation

Copyright 2014 by Elsevier Inc. All rights reserved. 32 Examples of Chromosomal Diseases Down syndromeusually caused by trisomy of chromosome 21; characterized by mental retardation and multiple structural defects Klinefelter syndrome caused by the

presence of two or more X chromosomes in a male (usually trisomy XXY); characterized by long legs, enlarged breasts, low intelligence, small testes, sterility, chronic pulmonary disease Copyright 2014 by Elsevier Inc. All rights reserved. 33 Down Syndrome

Copyright 2014 by Elsevier Inc. All rights reserved. 34 Klinefelter Syndrome Copyright 2014 by Elsevier Inc. All rights reserved. 35 Turner Syndrome Turner syndromecaused by monosomy

of the X chromosome (XO); characterized by immaturity of sex organs (resulting in sterility), short stature, webbed neck, cardiovascular defects, and learning disorders Copyright 2014 by Elsevier Inc. All rights reserved. 36 Turner

Syndrome Copyright 2014 by Elsevier Inc. All rights reserved. 37 Genetic Counseling Professional consultations with families regarding genetic diseases Pedigreechart illustrating genetic

relationships over several generations Punnett squaregrid used to determine the probability of inheriting genetic traits Copyright 2014 by Elsevier Inc. All rights reserved. 38 Pedigree Copyright 2014 by Elsevier Inc. All rights reserved.

39 Punnett Square Copyright 2014 by Elsevier Inc. All rights reserved. 40 Inheritance of sex-linked traits What is the genotype of a carrier female? Copyright 2014 by Elsevier Inc. All rights reserved.

Hereditary Traits Mitochondrial Inheritance Mitochondria contain some DNA Multiplies independently Can mutate, resulting in disease Passed only from the mother to offspring Copyright 2014 by Elsevier Inc. All rights reserved. Karyotype

Arrangement of chromosome photographs used to detect abnormalities Amniocentesisinvolves collection of fetal cells floating in the amniotic fluid (via a syringe needle through the uterine wall) Chorionic villus samplinginvolves collection of embryonic cells from outside of chorionic tissue (via tube through cervical opening)

Copyright 2014 by Elsevier Inc. All rights reserved. 43 Amniocentesis Copyright 2014 by Elsevier Inc. All rights reserved. 44 Prenatal testing

Copyright 2014 by Elsevier Inc. All rights reserved. Treating Genetic Diseases Most current treatments for genetic diseases are based on relieving or avoiding symptoms rather than attempting a cure Gene therapymanipulates genes to cure genetic problems; most forms of gene therapy have just

begun in humans Copyright 2014 by Elsevier Inc. All rights reserved. 46 Types of Gene Therapy Gene replacement therapyabnormal genes in existing body cells are replaced by therapeutic genes Gene augmentation therapycells carrying normal genes are introduced into

the body to augment production of a needed protein Copyright 2014 by Elsevier Inc. All rights reserved. 47 Gene Therapy Copyright 2014 by Elsevier Inc. All rights reserved. 48

Leber Congenital Amaurosis and Cystic Fibrosis Treatment Leber congenital amaurosis (LCA) is a form of blindness due to defective chromosome Using viruses with the therapeutic gene added and compounds to manufacture the missing proteins in the eye have shown early promise

Cystic fibrosis (CF) therapies include putting therapeutic genes in cold viruses or sending plasmids with the therapeutic gene into the respiratory tract Copyright 2014 by Elsevier Inc. All rights reserved. 49 RNA Interference RNAi therapyRNA interferencesilences

individual genes that cause disease In laboratory studies, RNAi can turn off one gene at a time Copyright 2014 by Elsevier Inc. All rights reserved. 50

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