Heredity and Environment

The Developing Person Through Childhood and Adolescence by Kathleen Stassen Berger Seventh Edition Chapter 3 Heredity and Environment Slides prepared by Kate Byerwalter, Ph.D.,Grand Rapids Community College

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. Fertilitytreatments 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: • Schizophrenia • Addiction • Nearsightedness • 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 condition • Couples with a history of infertility or miscarriage • Women 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 Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

Heredity and Environment