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Chapter 25 Heredity and Hereditary Diseases Copyright © 2015 Wolters Kluwer Health | Lippincott Williams & Wilkins Key Terms allele genetic pedigree chart amniocentesis genotype phenotype autosome heredity progeny carrier heterozygous recessive chromosome homozygous sex-linked congenital karyotype teratogen dominant meiosis trait familial mutagen gene mutation Copyright © 2015 Wolters Kluwer • All Rights Reserved Genes and Chromosomes Genes • Segments of DNA contained in the chromosomes • Control manufacture of protein synthesis • An allele is a specific version of a given gene Chromosomes • During mitosis, the DNA that makes up the chromosomes is replicated and distributed to daughter cells • 46 chromosomes in humans – 22 autosome pairs – One sex chromosome pair Copyright © 2015 Wolters Kluwer • All Rights Reserved Genes and Chromosomes (cont.) Figure 25-1 Genes and chromosomes. Copyright © 2015 Wolters Kluwer • All Rights Reserved Genes and Chromosomes (cont.) Dominant and Recessive Alleles • Gene pairs – Homozygous—both genes are same – Heterozygous—the 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 © 2015 Wolters Kluwer • 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 person’s genetic makeup – Example: Heterozygous dominant Bb (a carrier) Homozygous dominant BB Homozygous recessive bb Copyright © 2015 Wolters Kluwer • All Rights Reserved Genes and Chromosomes (cont.) Distribution of Chromosomes to Offspring • Reproductive cells produced by meiosis • 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 © 2015 Wolters Kluwer • All Rights Reserved Genes and Chromosomes (cont.) Figure 25-2 Meiosis. How many cells are produced in one complete meiosis? Copyright © 2015 Wolters Kluwer • All Rights Reserved Genes and Chromosomes (cont.) Punnett Squares A grid showing all the combinations of alleles that can result from a given parental cross • Capital letter represents the dominant allele • Lower-case letter represents the recessive allele What percentage of children from this cross will show the recessive phenotype? What percentage will be heterozygous? Copyright © 2015 Wolters Kluwer • All Rights Reserved Genes and Chromosomes (cont.) Sex Determination • Sex chromosomes not matched in size or appearance – Female (X) chromosome larger – Male (Y) chromosome smaller • Sex – Females: Two X chromosomes—XX – Males: An X and a Y chromosome—XY Copyright © 2015 Wolters Kluwer • All Rights Reserved Genes and Chromosomes (cont.) Figure 25-4 Sex determination. What percentage of children from this cross will show the recessive phenotype? What percentage will be heterozygous? Copyright © 2015 Wolters Kluwer • All Rights Reserved Genes and Chromosomes (cont.) Sex-Linked Traits • Traits carried on sex chromosomes (mostly X chromosome) • Most are recessive • Usually males exhibit trait • Heterozygous females are carriers inherited from mother Copyright © 2015 Wolters Kluwer • All Rights Reserved Genes and Chromosomes (cont.) Figure 25-5 Inheritance of sex-linked traits. What is the genotype of a carrier female? Copyright © 2015 Wolters Kluwer • All Rights Reserved Hereditary Traits (cont.) • Observable hereditary traits are skin, eye, and hair color • Less clearly defined traits are weight, body build, life span, and susceptibility to disease • Single-gene inheritance; less common • Multifactorial (multiple gene) inheritance; most common ‒ Produces wide range of variation Copyright © 2015 Wolters Kluwer • All Rights Reserved Hereditary Traits (cont.) Gene Expression • Influenced by: – Sex – Other genes • Codominance • Incomplete dominance – The environment Copyright © 2015 Wolters Kluwer • All Rights Reserved Hereditary Traits (cont.) Genetic Mutation A change in a gene or chromosome • May be caused by: – Chromosomal breakage or loss – Gene fragment rearrangement • May occur during cell division – Spontaneous – Induced by a mutagen Copyright © 2015 Wolters Kluwer • All Rights Reserved Hereditary Traits (cont.) Figure 25-6 Genetic exchange. Copyright © 2015 Wolters Kluwer • All Rights Reserved Hereditary Traits (cont.) Mitochondrial Inheritance • Mitochondria contain some DNA – Multiplies independently – Can mutate, resulting in disease • Passed only from the mother to offspring Copyright © 2015 Wolters Kluwer • All Rights Reserved Genetic Diseases (cont.) 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 © 2015 Wolters Kluwer • All Rights Reserved Genetic Diseases (cont.) Causes of Congenital Disorders (cont.) • Alcohol intake – Fetal alcohol syndrome (FAS) • Cigarette smoking • Poor nutrition – Spina bifida related to inadequate folic acid Copyright © 2015 Wolters Kluwer • All Rights Reserved Genetic Diseases (cont.) Figure 25-7 Congenital and hereditary diseases. Copyright © 2015 Wolters Kluwer • All Rights Reserved Genetic Diseases (cont.) Figure 25-8 Fetal alcohol syndrome. Copyright © 2015 Wolters Kluwer • All Rights Reserved Genetic Diseases (cont.) Figure 25-9 Spina bifida. Copyright © 2015 Wolters Kluwer • All Rights Reserved Genetic Diseases (cont.) Chromosomal Disorders • Down syndrome (trisomy 21) • Klinefelter syndrome • Turner syndrome • Dominant gene disorders – Huntington disease – Marfan syndrome Copyright © 2015 Wolters Kluwer • All Rights Reserved Genetic Diseases (cont.) Chromosomal Disorders (cont.) • Recessive gene disorders – Phenylketonuria (PKU) – Sickle cell anemia – Cystic fibrosis – Tay-Sachs disease – Progressive muscular atrophies – Albinism – Fragile X syndrome – Osteogenesis imperfecta – Neurofibromatosis Copyright © 2015 Wolters Kluwer • All Rights Reserved Genetic Diseases (cont.) Figure 25-10 Chromosomal disorders. Copyright © 2015 Wolters Kluwer • All Rights Reserved Treatment and Prevention of Genetic Diseases (cont.) • More than 4,000 genetic diseases identified • List is growing as science advances Genetic Counseling • Team approach • Those who might consider genetic counseling: – Prospective parents over 35 years of age – Family history of genetic disorders – Considering some form of fertility treatment Copyright © 2015 Wolters Kluwer • All Rights Reserved Treatment and Prevention of Genetic Diseases (cont.) Genetic Counseling (cont.) • Family history – Pedigree chart • Laboratory studies – First-trimester prenatal screening: • Nuchal transparency test • Pregnancy-associated plasma protein test • Human chorionic gonadotropin test Copyright © 2015 Wolters Kluwer • All Rights Reserved Treatment and Prevention of Genetic Diseases (cont.) • Laboratory studies (cont.) – Second-trimester screening • Alpha-fetoprotein (AFP) screening • Estriol test • Inhibin test ‒ Amniocentesis • Chorionic villus sampling • Karyotyping Copyright © 2015 Wolters Kluwer • All Rights Reserved Treatment and Prevention of Genetic Diseases (cont.) Figure 25-11 A pedigree (family history) showing three generations (F1–F3). What are the possible genotypes of the two normal children in the F3 generation? Copyright © 2015 Wolters Kluwer • All Rights Reserved Treatment and Prevention of Genetic Diseases (cont.) Figure 25-12 Prenatal testing. Copyright © 2015 Wolters Kluwer • All Rights Reserved Treatment and Prevention of Genetic Diseases (cont.) Figure 25-13 Karyotype. Look closely at this karyotype. How many chromosomes are present? What is the gender of the baby, and what genetic disorder is represented? Copyright © 2015 Wolters Kluwer • All Rights Reserved Treatment and Prevention of Genetic Diseases (cont.) Counseling Prospective Parents • Counselors have pertinent facts from family history and laboratory studies • Prospective parents may use information to make decisions Copyright © 2015 Wolters Kluwer • All Rights Reserved Treatment and Prevention of Genetic Diseases (cont.) Progress in Medical Treatment • Dietary control for certain diseases – Examples • Maple syrup urine disease • Wilson disease • Phenylketonuria • Vitamins • Hormones • Future: Possible treatment or correction of genetic disorder with genetic engineering Copyright © 2015 Wolters Kluwer • All Rights Reserved Case Study Role of a Genetic Counselor • Works as part of a team along with physicians, nurses, laboratory, and social service professionals • Collects all of the pertinent facts from the family history and laboratory studies • Has knowledge of genetic inheritance patterns • Presents information and discuss with prospective parents/parents the inheritance of their children Copyright © 2015 Wolters Kluwer • All Rights Reserved Word Anatomy (cont.) Word Part Meaning Example Genes and Chromosomes aut/o self Autosomes are all the chromosomes aside from the two that determine sex. chrom/o color Chromosomes color darkly with stains. heter/o other, different Heterozygous paired genes (alleles) are different from each other. homo- same Homozygous paired genes (alleles) are the same. phen/o to show Traits that can be observed or tested for make up a person’s phenotype. Heredity Traits multi- many Multifactorial traits are determined by multiple pairs of genes. Copyright © 2015 Wolters Kluwer • All Rights Reserved Word Anatomy (cont.) Word Part Meaning Example Genetic Diseases -cele swelling In spina bifida, the meninges can protrude through the spine as a meningocele. con- with A congenital defect is present at the time of birth. dacty/o digit (finger or toe) In polydactyly, there is an extra finger on the hand. terat/o malformed fetus A teratogen is an agent that causes birth defects. Treatment and Prevention of Genetic Diseases -centesis tapping, perforation Amniocentesis is a tap of the amniotic fluid. kary/o nucleus A karyotype is an analysis of the chromosomes contained in the nucleus of a cell. Copyright © 2015 Wolters Kluwer • All Rights Reserved