Heredity and Hereditary Diseases Chapter 25 Heredity and Hereditary Diseases

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

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

Figure 25-1 Genes and chromosomes. Genes and Chromosomes (cont.) Figure 25-1 Genes and chromosomes.

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

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

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

Genes and Chromosomes (cont.) Figure 25-2 Meiosis. How many cells are produced in one complete meiosis?

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?

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

Figure 25-4 Sex determination. 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?

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

Figure 25-5 Inheritance of sex-linked traits. Genes and Chromosomes (cont.) Figure 25-5 Inheritance of sex-linked traits. What is the genotype of a carrier female?

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

Hereditary Traits (cont.) Gene Expression Influenced by: Sex Other genes Codominance Incomplete dominance The environment

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

Figure 25-6 Genetic exchange. Hereditary Traits (cont.) Figure 25-6 Genetic exchange. 17

Hereditary Traits (cont.) Mitochondrial Inheritance Mitochondria contain some DNA Multiplies independently Can mutate, resulting in disease Passed only from the mother to offspring

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

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

Figure 25-7 Congenital and hereditary diseases. Genetic Diseases (cont.) Figure 25-7 Congenital and hereditary diseases. 21

Figure 25-8 Fetal alcohol syndrome. Genetic Diseases (cont.) Figure 25-8 Fetal alcohol syndrome. 22

Genetic Diseases (cont.) Figure 25-9 Spina bifida. 23

Genetic Diseases (cont.) Chromosomal Disorders Down syndrome (trisomy 21) Klinefelter syndrome Turner syndrome Dominant gene disorders Huntington disease Marfan syndrome

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

Figure 25-10 Chromosomal disorders. Genetic Diseases (cont.) Figure 25-10 Chromosomal disorders. 26

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

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

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

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? 30

Figure 25-12 Prenatal testing. Treatment and Prevention of Genetic Diseases (cont.) Figure 25-12 Prenatal testing. 31

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? 32

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

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

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

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.

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.