Chapter Two

Biological Foundations of Child Development

Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

Chapter 2

Key Chapter Questions

How does the biology of life at the cellular level affect human development?

How are traits passed from generation to generation?

What are some explanations for how genes and the environment interact?

What are the main components of the nervous system and the brain?

How does health care policy affect children’s well-being?

DNA, RNA, and Protein

Deoxyribonucleic acid (DNA) The genetic material of cells; made of chemical building blocks called nucleotides arranged in a double-stranded helix. DNA contains all of the instructions needed to direct the activities of cells.

Genes and Heredity

Gene—a segment of a DNA molecule; genes are the basic building blocks of inheritance

Chromosome—a strand of DNA containing a number of genes

Mitosis—the process by which somatic cells duplicate themselves, resulting in genetically identical cells with 46 chromosomes

Base Pairs

• Adenine

• Guanine

• Cytosine

• Thymine

• The combination and sequence of these base pairs is the basic code of life on planet earth

Genes and Heredity continued

Karotype —photographic representation of human chromosomes

Patterns of Heredity

Alleles —pairs of corresponding genes located at specific positions on specific chromosomes

Homozygous—a condition in which an individual has a pair of identical alleles at a particular position

Heterozygous—a condition in which an individual has a pair of nonidentical alleles at a particular position

Genotype and Phenotype

Genotype—a person’s genetic makeup as determined at the moment of fertilizationPhenotype—the observable expression of a person’s genotype

Recessive Diseases

Polygenic Inheritance

• Many traits such as height, shape, weight, color, and metabolic rate are governed by the cumulative effects of many genes.

• Polygenic traits are not expressed as absolute or discrete characters,

• Polygenic traits are recognizable by their expression as a gradation of small differences

Skin Color

• Human skin color is a good example of polygenic (multiple gene) inheritance.

• Capital letter genes (A, B and C) control dark pigmentation.

• Lower case (a, b & c) control light pigmentation

• All "dominant" genes (AABBCC) has the maximum amount of melanin and very dark skin.

• All "recessive" small case genes (aabbcc) has the lowest amount of melanin and very light skin.

Dominant and X-Linked Patterns

The Genetic Difference Between Males and

Females

Sex Linked Traits

• Some genes that cause certain phenotypes are located on the X and Y chromosome

• These chromosomes are not identical so there are some interesting inheritance patterns for these sex linked traits

• Mothers are XX so they can only give an X

• Fathers are XY so if they give an X the child will be a girl; a Y and the child is a boy.

• If the child is a Boy we can be certain he got his X from his mother.

Color BlindnessDeuteranopia

Did you see a difference?

A. True

B. False

Chromosomal Abnormalities

Chromosomal Disorders

Down Syndrome—Trisomy 21 an extra chromosome exists on the 21st pair

Turner Syndrome—females with Turner Syndrome and missing an X chromosome

Fragile X Syndrome—the most common cause of intellectual disability in males

Fragile X

• It is the most common cause of genetically-inherited mental impairment.

• Abnormality on the X chromosome which is restricted or broken

• Retardation, Autism, Hyperactivity, Tactile Sensitivity

X Y Abnormalities• Klinefelter’s Syndrome

• An extra X chromosome in a male.

• At puberty the body does not know whether to mature as a male or female.

• Breasts may form, underdevelopment of male genitals and marked weight gain can be some of the symptoms.

Genetic Counseling

Provides guidance for parents about the possibility of genetic disorders in their future children based on an extensive health history of both parents’ families over as many generations as possible

Genetic (Genomic) Imprinting

• The phenomenon of parent-of-origin gene expression. The expression of a gene depends upon the parent who passed on the gene.

• They are due to deletion of the same part of chromosome 15.

• Father = Prader-Willi

• Mother = Angelman Syndrome.

Neurogenesis —the process of developing new neurons

Myelination—the process of laying down myelin sheaths to insulate the axons of neurons; it begins before birth and occurs in spurts throughout childhood

The Brain

Anatomy of a Neuron

Neuron Communication

Action potential—electrochemical communication of neurons

Synapse—a tiny space between neurons, across which the neurons communicate

Neurotransmitters—chemicals released into the synapse by neurons to enhance communication between neurons

Communication Across Synapses

Neurotransmitters

Brain Parts

Cerebrum—largest part of the brain, has two hemispheres and four lobes, responsible for higher thought processes

Cerebral cortex—the thin layer of gray matter (neuronal cell bodies) that covers the cerebrum and cerebellum

Corpus collosum—large band of white matter that allows sensory and motor information to be communicated between the hemispheres

Lateralization—the extent to which certain brain functions are associated with either the right or left hemisphere of the brain

The Lobes of the Cerebrum