1. Chapter 3: Genetic Bases of Child Development
MODULES
3.1 Mechanisms of Heredity
3.2 Genetic Disorders
3.3 Heredity Is Not Destiny
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2. Module 3.1 Mechanisms of Heredity
LEARNING OBJECTIVES
Define chromosomes and genes.
Explain the mechanism of heredity for dominant and recessive traits.
Understand how heredity influences behavioral and psychological development.
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3. The Biology of Heredity
Father’s sperm +
Mother’s egg
46 chromosomes total
23 from each parent
(gamete)
Meiosis: the biological process of cell division resulting in gametes that have 23 chromosomes, which is half the amount of genetic material normally seen in a human cell.
Mitosis: the biological process of cell division resulting in bodily cells that are exact copies of their parent cells and have a full set of 46 chromosomes.
In-vitro fertilization: an artificial form of egg fertilization in which sperm and egg are united in a laboratory dish.
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4. The Biology of Heredity
The first 22 pairs of chromosomes are autosomes and the 23rd pair are sex chromosomes.
Chromosomes consist of Deoxyribonucleic acid (DNA) which codes for proteins and enzymes.
Genotype is one’s complete set of genes and phenotype is one’s physical, behavioural, and psychological features.
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5. Single Gene Inheritance
Pairs of alleles can be either homozygous or heterozygous.
Dominant allele: its chemical instructions are followed.
Recessive allele: its chemical instructions are ignored.
Incomplete dominance: one allele doesn’t dominate the other completely.
Single nucleotide polymorphism (SNP): a change in the normal nucleotide base at a particular location within a strand of DNA.
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6. Sickle Cell Trait: An Example of Incomplete Dominance
Endogamy: a preference for mating with people from one’s own social or cultural group.
Clinical variation: continuous genetic variation observed.
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Behavioural Genetics
The study of the inheritance of behavioral and psychological traits.
Many behavioural genotypes reflect polygenic inheritance, which involves many genes.
Behavioural geneticists rely upon twin studies (monozygotic and dizygotic) and adoption studies.
Intelligence, psychological disorders (i.e. depression and schizophrenia),and personality (introversion/extroversion) are all strongly affected by heredity.
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8. An Example of Polygenic Inheritance
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The Nature of Nurture
Parents don’t provide exactly the same environments for all of their children (non-shared environmental influences).
Non-shared environmental influences
Experiences unique to individual, not shared by other members of family in same environment.
Shared environmental influences
Experiences common to all family members in same environment.
Parents provide the child’s genes and environment, but the child also influences her own environment.
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The Nature of Nurture
The family environment is important, but it usually affects each child in unique ways, which makes siblings differ.
Families create multiple, unique environments for each child in the household.
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11. Module 3.2 Genetic Disorders
LEARNING OBJECTIVES
List a number of disorders that are inherited.
State what disorders are caused by too many or too few chromosomes.
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Inherited Disorders
Inherited disorders that affect development are usually triggered when a child inherits two recessive alleles.
Examples include Albinism, Cystic fibrosis, PKU, and Tay-Sachs disease.
Most inherited disorders are very rare.
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Abnormal Chromosomes
Some people are born with too many, too few, or damaged chromosomes.
People with Down Syndrome usually have an extra 21st chromosome.
Damaged autosomes always affect development because autosomes contain so much genetic material.
A number of disorders are caused by missing or extra sex chromosomes (see Table 3-5).
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14. Module 3.3 Heredity Is Not Destiny
LEARNING OBJECTIVES
Describe how genes affect behaviour.
Explain whether one genotype always leads to the same phenotype.
Understand how the relationship between heredity and environment changes as children develop.
Trace how family environments influence children’s development.
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15. Paths from Genes to Behaviour
Genes never cause behaviour directly.
The behavioural consequences of genetic instructions depends on the environment.
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Reaction Range
A genotype can lead to a range of phenotypes depending on the environment.
People with PKU genotype: those who eat normal diet will be cognitively delayed, but those who eat special diet will have normal intelligence.
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17. Reaction Range of Intelligence
Source: Gottesman, 1963
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18. Changing Relations between Nature and Nurture
Passive gene-environment relation: parents pass on genotype and environment.
Evocative gene-environment relation: different genotypes evoke different responses from the environment.
Active gene-environment relation: actively seek environments related to their genes.
Niche-picking: the process of deliberately selecting an environment suitable to one’s genotype.
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19. The Relation Between Genes and Environment
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Conclusions
Parents are the source of children’s genes and the primary source of young children’s experiences both shared and non-shared environments.
Intricate link between nature, nurture and all aspects of child development.
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