CHYS 1F90 Lecture Notes - Ecological Systems Theory, Egg Cell, Prenatal Development

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Child and Youth Studies
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
Ecological Systems Theory
·richest description of environmental influences
·suggests interventions for optimizing development at various levels of society
·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
Father’s sperm + Mothers ovum = Zygote with 46 chromosomes in total
23 from each parent
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?
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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
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