Biological Foundations

Phenotype:

• Observable characteristics, actual appearance and behavior (outward expression of the genotype)

• Genotype + Environment = Phenotype

• Phenotype depends on relationship between alleles

Genotype

Your unique combination of genes and alleles

Chromosomes

• molecules made up of DNA that store and transmits genetic information

DNA (deoxyribonucleic acid)

• long, double stranded molecule, each rung contains pairs of bases

Genes

• segments of DNA located along chromosomes; how they are expressed influences development

Human Chromosomes

• 22 pairs of autosomes

• 1 pair of sex chromosomes

Twins

• Monozygotic

• Dizygotic

Monozygotic (Identical)

• One zygote that divides into two individuals

• Share 100% genes

• 1 in every 350-400 births

Dizygotic (Fraternal)

• 2 sperm + 2 ova

• Two zygotes, or fertilized ova

• Share 50% genes

• 1 in every 33 births in US

Allele

• Homozygous Alleles

  • Inherited alleles from mom = dad

• Heterozygous Alleles

  • inherited from mom = / = dad

  • Influence of one gene in the allele > than other gene

Examples of Dominant and Recessive Charachteristics

Dominant-Recessive Disorders

• PKU: Phenylketonuria

  • Infants born with PKU lack enzyme that converts phenylalanine (amino acid) in tyrosine essential for body functioning

Chromosomal Abnormalities

• Numerical abnormalities

Numerical Abnormalities

• Extra chromosome

  • Trisomy 21 (Down syndrome)

  • Sex chromosomes

    • Trisomy X (xxx)

    • Klinefelter’s syndrome (xxy)

    • XXY Syndrome

• Missing chromosomes

  • sex chromosomes

    • Turner’s syndrome (xo)

Down Syndrome

• Zygote has 3 copies of chromosome 21

• Intellectual disability, delayed motor development, faster aging

• Social support, early intervention, and a positive attitude help

• Risk of giving birth to a Down syndrome child increases with maternal age

Myth or Fact?

• Down syndrome is a very rare genetic disorder? Myth

• Most people with Down syndrome are institutionalized? Myth

• Adults with Down syndrome are unemployable? Myth

• People with Down syndrome have a short life span? Myth

• Children with Down syndrome must be placed in segregated special education programs? Myth

Prenatal Diagnostic Methods

• Amniocentesis

• Chorionic Villus

• Sampling (CVS)

• Fetoscopy

• Ultrasound

• Maternal Blood Analysis

• Ultrafast fetal MRI

• Preimplantation

• Genetic Diagnosis

Tay-Sachs Disease

• What type of genetic inheritance best describes Tay-Sachs disease

  • Homozygous recessive trait

• Imagine that you and your partner have a history of Tay-Sachs in your extended families. You would like to have a baby. Before you try to get pregnant, what should you do?

  • Human genome test allows you to see early if your a carrier of genetic diseases