Biological Foundations of

Child Development

Chapter 2

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 non-identical alleles at a particular position

Genotype and Phenotype

Genotype—a person’s genetic makeup as determined at the moment of fertilization

Phenotype—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.

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.

Dominant and X-Linked Patterns

Color BlindnessDeuteranopia

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.