1. Heredity and Hereditary Diseases
Chapter 25
Heredity and Hereditary Diseases

2. 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

3. 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

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

5. 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

6. 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

7. 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

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

9. 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?

10. 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

11. 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?

12. 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

13. 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?

14. 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

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

16. 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

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

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

19. 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

20. 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

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

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

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

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

25. 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

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

27. 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

28. 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

29. 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

30. Treatment and Prevention of Genetic Diseases (cont.)
Figure A pedigree (family history) showing three generations (F1–F3).
What are the possible genotypes of the two normal children in the F3 generation? 30

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

32. Treatment and Prevention of Genetic Diseases (cont.)
Figure 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

33. 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

34. 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

35. 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

36. 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.

37. 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.