The Developing Person Through Childhood and Adolescence by

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 n Chromosomes: a molecule of DNA that contains the instructions to make proteins n The instructions are organized into genes, the basic unit for transmitting heredity. n Humans have 46 chromosomes (23 pairs), and about 25, 000 genes. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Karyotype (Map of Chromosomes) Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

The Genetic Code (cont. ) n Human genome: the code for making a human being n 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, 7 th Edition, Chapter 3

The Beginnings of Life n Development begins at conception, when the sperm penetrates the ovum. n The organism is first called a zygote, and is the fused nuclei of sperm and egg. n The genotype of the zygote is the genetic information on the 23 chromosome pairs. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Gene Pairs n Gene pairs are closely matched on 22 of the 23 chromosomes. n In some cases, an allele occurs: an alternate version of variable genes. n On the 23 rd pair, XX = female, XY = male. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Determining a Zygote’s Sex Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

From One Cell to Many n The phenotype is the actual appearance and behavior of a person, and occurs because some instructions on the genotype are ignored, and others amplified. n This occurs through cell differentiation, gene-gene (polygenic), and geneenvironment interactions. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Human Genome Project n The Human Genome Project is an international effort to map the entire human genome. n It has already revealed a great deal about the nature of genes and genetic variations. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Additive Heredity n 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, 7 th Edition, Chapter 3

Dominant-Recessive Heredity n 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. n 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, 7 th Edition, Chapter 3

Twins and Clones n Dizygotic (fraternal) twins result from two sperm penetrating two ova, and share 50% of their genes. n Monozygotic (identical) twins originate from one zygote, and share 100% genes. n A clone originates from a live organism. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Dizygotic or monozygotic? DAVID YOUNG-WOLFF / PHOTOEDIT BRUCE ROBERTS / PHOTO RESEARCHERS, INC. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Multiple Births n The likelihood of multiple births vary by age and ethnicity. Fertility treatments may also cause them. n Hazards of multiples include birth complications, death, disease, and disabilities. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Research on the Effects of Genes n 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. n The results may surprise you! Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Findings from Genetic Research n Genes affect every aspect of human behavior. n The non-shared environment of families is powerful. n Genes elicit responses from other people that shape development (an indirect effect). Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Psychopathology n Genes have been found to influence several disorders, including: ¨ Schizophrenia ¨ Addiction ¨ Nearsightedness ¨ Diabetes n However, the environment ALSO plays a key role in these disorders. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Chromosomal Abnormalities n Chromosomal abnormalities when the zygote’s cells have fewer or more chromosomes than 46. n Maternal age is the most common correlate of chromosomal abnormalities. n Many zygotes with chromosomal abnormalities are spontaneously aborted. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Down Syndrome (Trisomy 21) n Down syndrome occurs when a zygote has 3 copies of chromosome 21. n Sufferers experience mental slowness, faster aging, and physical problems. n Social support and a positive attitude help. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Abnormalities of the 23 rd pair n About 1 in 500 infants have either one too many or too few chromosomes on the 23 rd pair. n This can lead to underdeveloped sexual organs (girls), breast development (boys), or other anomalies. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Dominant Disorders n Huntington’s disease is a fatal CNS disorder caused by a genetic miscode. It is inactive until middle adulthood. n Tourette syndrome, a dominant disorder, can lead to uncontrollable tics and obscenities. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Fragile X Syndrome n Fragile X syndrome is caused by a single gene that has 200 repetitions of a triplet. n The effects of Fragile X include cognitive deficits and poor social skills. n Males are at greater risk of developing this syndrome. Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3

Genetic Counseling n 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, 7 th Edition, Chapter 3

Genetic Counseling (cont. ) n Genetic counseling raises a number of ethical and complicated issues. ¨ Example: What if a couple decides to abort a child of abnormal height? n 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, 7 th Edition, Chapter 3

Genetic Counseling Decision Tree for High-Risk Couples Berger: The Developing Person Through Childhood and Adolescence, 7 th Edition, Chapter 3