CHYS 1F90 Lecture Notes - Ecological Systems Theory, Egg Cell, Prenatal Development
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14 Nov 2011
School
Department
Course
Professor
Child and Youth Studies
CHYS 1F90
Dr. J. McNamara
Fall/Winter 2011
Bronfenbrenner’s Ecological Systems Theory
Ecological Systems Theory
Detailed characterization of various environmental influences on development
–Environment is a series of nested systems
Microsystem
Mesosystem
Exosystem
Macrosystem
Ecological Systems Theory
Contributions
·richest description of environmental influences
·suggests interventions for optimizing development at various levels of society
Criticisms
·generalizability from one environment to next questioned
·not complete; a complement to existing theories
Lecture Overview - Biological Models of Development
–Principles of hereditary transmission
–How are genes expressed?
–Chromosomal and genetic abnormalities
–Behavioural genetics
–Determining heritability
–Interaction of heredity and environment: Nature and Nurture
Conception
– Father’s sperm + Mother’s ovum = Zygote with 46 chromosomes in total
– 23 from each parent
Mitosis
–Mitosis begins after fertilization
–The process by which a cell separates chromosomes in its nucleus into two identical cells
The Chromosomes
–Each chromosome contains genes
–Sections of chromosomes
–Made up of DNA
The chemical code for development
Why Not 50% mom – 50% dad?
Meiosis & Crossing-Over
·Chromosomes within sperm cells divide in half before they fertilize an ovum or egg cell
·Chromosomes with egg cells divide in half before they are fertilized
·The “splitting” is random
·The randomness creates variation in the resulting embryo
·This complicated process is call “Meiosis”
Male or Female?
–23rd pair of chromosomes
–Males have X and Y
–Females have X and X
–Sex of child determined by father’s sperm
Male or Female?
–Note 23rd chromosome:
What Do Genes Do?
–Direct production of amino acids necessary for forming new cells
–Guide cells to develop different parts of body
–Regulate pace and timing of development
–May “turn on” or “turn off” other genes
–Impacted by environmental factors
Gene Expression
–Alleles influence many characteristics
–One pair of genes
–One member from mother, one from father
–Simple dominant – recessive inheritance
–some alleles are stronger than others
Dominant alleles
Recessive alleles
Gene Expression
–If an allele is homozygous…
–Both gene are dominant or both recessive
–To express a trait one must have a homozygous recessive allele
–If an allele is heterozygous…
–One gene is dominant and one is recessive
Dominant Genes
–Dominant genes are almost always stronger than recessive genes