HBHD 13e Ch25

Copyright © 2015 Wolters Kluwer Health | Lippincott Williams & Wilkins
Chapter 25
Heredity and
Hereditary Diseases

Copyright © 2015 Wolters Kluwer • All Rights Reserved
Overview

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
Learning Objectives
1. Define a gene, and briefly
describe how genes function.
2. Explain the relationship
between genotype and phenotype for
dominant and recessive alleles.
3. Explain how chromosomes are
distributed in meiosis.
4.Perform a genetic cross using a
Punnett square.
5.Explain how sex is determined
in humans and how sex-linked traits
are inherited.

Hereditary Traits
Learning Objectives
6.List three factors that may influence
the expression of a gene.
7.Define mutation.
8.Explain the pattern of mitochondrial
inheritance.

Genetic Diseases
Learning Objectives
9. Differentiate among congenital,
genetic, and hereditary disorders, and
give several examples of each.
10. Give several examples of
teratogens, and describe their effects.
11. Describe the symptoms and
inheritance patterns of some common
genetic diseases.
12. Describe four methods for
diagnosing fetal disorders.

Treatment and Prevention of Genetic
Diseases
Learning Objective
13. Give examples of methods
currently used to treat certain genetic
disorders.

Case Study
Learning Objective
14. Using the case study and
information in the text, describe the
role of a genetic counselor.

Word Anatomy
Learning Objective
15. Show how word parts are used to build words related
to heredity.

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.
How many chromosomes are present in a human
gamete?
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

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

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

Figure 25-2 Meiosis.
How many cells are produced in one complete meiosis?

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

Figure 25-3 A Punnett square.
What percentage of children from this cross will show the
recessive phenotype? What percentage will be
heterozygous?

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.
What percentage of children from this cross will show the
recessive phenotype? What percentage will be
heterozygous?

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.
What is the genotype of a carrier female?

✓
Checkpoints
25-1 What is a gene? What is a gene made of?
25-2 What term describes a gene that always expresses its
effect?
25-3 What is the difference between a genotype and a
phenotype?
25-4 What is the process of cell division that forms the
gametes?
25-5 Human body cells have 46 chromosomes. How many
chromosomes are in each gamete?
25-6 What sex chromosome combination determines a
female? A male?
25-7 What term describes a trait carried on a sex
chromosome?

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

Gene Expression
•Influenced by:
– Sex
– Other genes
• Codominance
• Incomplete dominance
– The environment

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.

Mitochondrial Inheritance
•Mitochondria contain some DNA
– Multiplies independently
– Can mutate, resulting in disease
•Passed only from the mother to offspring

✓
Checkpoints
25-8 What is a mutagen?
25-9 From which parent does a child get mitochondrial
genes?

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

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.

Figure 25-8 Fetal alcohol syndrome.

Figure 25-9 Spina bifida.

Chromosomal Disorders
•Down syndrome (trisomy 21)
•Klinefelter syndrome
•Turner syndrome
•Dominant gene disorders
– Huntington disease
– Marfan syndrome

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.

✓
Checkpoints
25-10 What does the term congenital mean?
25-11 What is a teratogen?
25-12 What is the scientific name for Down syndrome?
25-13 Is fragile X syndrome more common in males or
females?

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

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

Diseases (cont.)
• Laboratory studies (cont.)
– Second-trimester screening
• Alpha-fetoprotein (AFP) screening
• Estriol test
• Inhibin test
‒ Amniocentesis
• Chorionic villus sampling
• Karyotyping

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?
Treatment and Prevention of Genetic Diseases
(cont.)

Figure 25-12 Prenatal testing.
(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?
(cont.)

Diseases (cont.)
Counseling Prospective Parents
•Counselors have pertinent facts from family history and
laboratory studies
•Prospective parents may use information to make
decisions

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

Diseases (cont.)
✓
Checkpoints
25-14 What kind of chart can show the inheritance pattern
of a gene within a family?
25-15 What are two procedures for removing fetal
samples for study?
25-16 What is a karyotype?

Case Study (cont.)
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.)

HBHD 13e Ch25

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