1. Chapter 3 – Heredity and Environment
The Developing Person Through the Life Span 8e by Kathleen Stassen Berger
Chapter 3 – Heredity and Environment
PowerPoint Slides developed by
Martin Wolfger and Michael James
Ivy Tech Community College-Bloomington
Reviewed by Raquel Henry
Lone Star College, Kingwood

2. The Genetic Code What Genes Are DNA (deoxyribonucleic acid)
Molecule that contains the chemical instructions for cells to manufacture various proteins
Promotes growth and sustains life

3. What Genes Are Chromosomes: Molecules of DNA
DNA consists of 46 chromosomes arranged in 23 pairs

4. What Genes Are
Genes
Specific sections of a chromosome carry instructions via four chemicals.
Chemicals organized in four pairs (A-T, T-A, C-G, G-C).
Each person has about 3 billion pairs.

5. What Genes Are Allele Genome
A variation that makes a gene different in some way from other genes for the same characteristics
Many genes never vary; others have several possible alleles
Genome
The full set of genes that are the instructions to make an individual member of a certain species

6. The Beginnings of Life Gametes Zygote
Reproductive cells (sperm and ova)
Each consists of 23 chromosomes.
Zygote
Two gametes (sperm and ovum) combine and produce a new individual with 23 chromosomes from each parent.

7. The Beginnings of Life

8. Matching Genes Genes are passed down from generation to generation
Genotype
An organism’s genetic inheritance, or genetic potential
Unique for each organism

9. Matching Genes Homozygous Heterozygous
Two genes of one pair that are exactly the same in every letter of their code.
Heterozygous
Two genes of one pair that differ in some way.
Typically one allele has only a few base pairs that differ from the other member of the pair.

10. Male or Female? Humans usually possess 46 chromosomes.
44 autosomes and 2 sex chromosomes termed the 23rd pair
Females: XX
Males: XY
Sex of offspring depends on whether the father’s Y sperm or X sperm fertilizes the ovum.

11. Male and Female

12. The Beginnings of Life
The zygote begins duplication and division then differentiation and specialization occur.
Cells change from being stem cells, those from which any other specialized type of cell can form, to being only one kind of cell.

13. Twins Monozygotic (identical) twins
Originate from one zygote that splits very early in development
Same genotype
Dizygotic (fraternal) twins
Result from fertilization of two separate ova
by two separate sperm
Incidence is genetic and varies by ethnicity
and age.

14. Assisted Reproduction
Assisted reproductive technology (ART)
a general term for the techniques that help infertile couples conceive and sustain a pregnancy
In vitro fertilization (IVF)
takes place outside a woman’s body
involves mixing sperm with ova surgically removed from the woman’s ovary
if a zygote is produced, it is inserted into a woman’s uterus, where it may implant and develop into a baby.

15. From One Cell to Many Phenotype
The observable characteristics of a person, including appearance personality, intelligence, and all other traits
Intimately connected with genotype
Almost every trait is:
polygenic (affected by many genes)
multifactorial (influenced by many factors)

16. Epigenetics
Referring to environmental factors that affect genes and genetic expression

17. Gene-Gene Interactions
Human Genome Project
International effort to map the complete human genetic code
Essentially completed in 2001; analysis is ongoing
Found “only” about 20,000 genes in humans
Exact number is unknown

18. Additive Heredity Additive genes
Genes that add something to some aspect of the phenotype
Effects of additive genes add up to make the phenotype
Example: Height is affected by the contributions of about 100 genes

19. Dominant-Recessive Heredity
Dominant-recessive pattern - Dominant gene is more influential than the recessive gene (non-additive).
Dominant gene can completely control the phenotype with no noticeable effect of recessive gene.
Genes for blood type B and Rh-positive blood are dominant.

20. Dominant-Recessive Heredity
Carrier: a person whose genotype includes a gene that is not expressed in the phenotype
Unexpressed gene occurs in half of the carrier’s gametes and is passed on to half of the carrier’s offspring
Offspring can be carrier or express the gene in the phenotype (e.g. when unexpressed gene is inherited by both parents)

21. Dominant-Recessive Heredity
X-linked: A gene carried on the x chromosome

22. Alcoholism Alcoholism probably has a genetic basis
Genes can cause an overpowering addictive pull in some people
Environmental conditions can modify the genetic effects
Nature and nurture combine to create an alcoholic

23. Nearsightedness Termed myopia
Low nearsightedness runs in families and is associated with minor variations in the Pax6 gene
Environment also plays a role
Increase in nearsightedness among East Asian schoolchildren
Increased schoolwork may have caused nearsightedness in children with a Pax6 allelle

24. Heritability
Statistical term that indicates what portion of the variation in a particular trait within a particular population is inherited.
Example: 90% of the height differences among children of the same age is genetic.
Environment can affect the expression of inherited genes.

25. Not Exactly 46 Down Syndrome (Trisomy-21)
Three copies of chromosome 21
Specific facial characteristics (thick tongue, round face, slanted eyes)
Hearing losses, heart abnormalities, muscle weakness, short stature
Slow to develop language
Accelerated aging (cataracts, dementia, certain forms of cancer common at age 40)

26. Gene Disorders Dominant-Gene Disorders
Half of the offspring of parents with a dominant disorder will have the disorder.
Most dominant disorders begin in adulthood (fatal dominant childhood conditions cannot be passed on).
Many dominant disorders have relatively mild or variable symptoms.
Tourette syndrome
Some who inherit the dominant gene exhibit uncontrollable tics and explosive outbursts
Most have milder, barely noticeable symptoms

27. Gene Disorders Recessive Disorders Fragile X syndrome
Most common form of inherited mental retardation
Additional symptoms include muscle weakness, shyness, and poor social skills
Sickle-cell trait
Offers some protection against malaria
African carriers are more likely than non-carriers to survive

28. Genetic Problems

29. Genetic Counseling and Testing
Consultation and testing by trained professionals
Enables prospective parents to learn about their genetic heritage, including harmful conditions that may be passed on to their offspring
Ethical Guidelines
Test results are kept confidential
Decisions regarding sterilization, adoption, abortion, or carrying a pregnancy to term are made by the clients

30. Genetic Counseling and Testing
Phenylketonuria (PKU)
Recessive condition
Results in inability to metabolize phenylalanine (amino acid found in many foods)
Buildup of phenylalanine causes brain damage, progressive mental retardation, and other symptoms
Early testing and a special diet usually results in normal development