Heredity and Environment

Slides prepared by Kate Byerwalter, Ph.D.,Grand Rapids Community College

The Developing Person Through Childhood and Adolescence by Kathleen Stassen Berger

Chapter 3

Seventh Edition

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

The Genetic Code

Chromosomes: a molecule of DNA that contains the instructions to make proteins

The instructions are organized into genes, the basic unit for transmitting heredity.

Humans have 46 chromosomes (23 pairs), and about 25,000 genes.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Karyotype (Map of Chromosomes)

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

The Genetic Code (cont.)

Human genome: the code for making a human being

Every person has a slightly different code, but the human genome is 99.5% the same for any 2 people.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

The Beginnings of Life

Development begins at conception, when the sperm penetrates the ovum.

The organism is first called a zygote, and is the fused nuclei of sperm and egg.

The genotype of the zygote is the genetic information on the 23 chromosome pairs.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Gene Pairs

Gene pairs are closely matched on 22 of the 23 chromosomes.

In some cases, an allele occurs: an alternate version of variable genes.

On the 23rd pair, XX = female, XY = male.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Determining a Zygote’s Sex

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

From One Cell to Many

The phenotype is the actual appearance and behavior of a person, and occurs because some instructions on the genotype are ignored, and others amplified.

This occurs through cell differentiation, gene-gene (polygenic), and gene-environment interactions.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Human Genome Project

The Human Genome Project is an international effort to map the entire human genome.

It has already revealed a great deal about the nature of genes and genetic variations.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Additive Heredity

Additive genes combine to make a phenotype.

Example: HEIGHT. The inherited genes from mother and from father are added together. However, some additive genes get enhanced by other genes, making their input greater.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Dominant-Recessive Heredity A dominant-recessive pattern occurs

when the influence of one gene in the allele is greater than the other gene.

Example: Blood types A and B and brown eyes result from dominant genes.

This pattern may be X-linked (on the X chromosome), in which case males are more affected (e.g., color-blindness).

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Twins and Clones

Dizygotic (fraternal) twins result from two sperm penetrating two ova, and share 50% of their genes.

Monozygotic (identical) twins originate from one zygote, and share 100% genes.

A clone originates from a live organism.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Dizygotic or monozygotic?

DAVID YOUNG-WOLFF / PHOTOEDIT BRUCE ROBERTS / PHOTO RESEARCHERS, INC.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Multiple Births

The likelihood of multiple births vary by age and ethnicity. Fertility treatments may also cause them.

Hazards of multiples include birth complications, death, disease, and disabilities.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Research on the Effects of Genes

Researchers have employed several methods (e.g., twin studies, adoption studies) to investigate the relative influence and interaction of genes and environment in shaping human behavior and traits.

The results may surprise you!

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Findings from Genetic Research

Genes affect every aspect of human behavior.

The non-shared environment of families is powerful.

Genes elicit responses from other people that shape development (an indirect effect).

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Psychopathology Genes have been found to influence

several disorders, including:

SchizophreniaAddictionNearsightedness Diabetes

However, the environment ALSO plays a key role in these disorders.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Chromosomal Abnormalities

Chromosomal abnormalities when the zygote’s cells have fewer or more chromosomes than 46.

Maternal age is the most common correlate of chromosomal abnormalities.

Many zygotes with chromosomal abnormalities are spontaneously aborted.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Down Syndrome (Trisomy 21)

Down syndrome occurs when a zygote has 3 copies of chromosome 21.

Sufferers experience mental slowness, faster aging, and physical problems.

Social support and a positive attitude help.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Abnormalities of the 23rd pair

About 1 in 500 infants have either one too many or too few chromosomes on the 23rd pair.

This can lead to underdeveloped sexual organs (girls), breast development (boys), or other anomalies.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Dominant Disorders

Huntington’s disease is a fatal CNS disorder caused by a genetic miscode. It is inactive until middle adulthood.

Tourette syndrome, a dominant disorder, can lead to uncontrollable tics and obscenities.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Fragile X Syndrome

Fragile X syndrome is caused by a single gene that has 200 repetitions of a triplet.

The effects of Fragile X include cognitive deficits and poor social skills.

Males are at greater risk of developing this syndrome.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Genetic Counseling Genetic counseling provides facts. It is

recommended for:

Couples from the same ethnic group Individuals with a close relative with a genetic

conditionCouples with a history of infertility or miscarriageWomen 35 or older, men 40 or older

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Genetic Counseling (cont.)

Genetic counseling raises a number of ethical and complicated issues.

Example: What if a couple decides to abort a child of abnormal height?

Results are an estimate of risk, not a guarantee that a disorder will or won’t occur.

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Genetic Counseling Decision Tree for High-Risk Couples