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chapter_2_sp13_1.pptxGenetic and Environmental Foundations
Chapter 2
Where do we start? What is inherited from our parents and their ancestors and what role does environment contribute? These are but a few of the questions that this chapter will explore.
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Heredity
DNA
Chromosomes
Genes
Meiosis
Mitosis
Heredity defines one’s nature – which based on the biological transmission of traits and characteristics from one generation to another. The structures we inherit both make our behaviors possible and places limits on them.
Genetic (inherited) influences are fundamental in the transmission of physical traits, such as height, hair texture, and eye color. Genetics also appears to be a factor in intelligence and in the origins of personality traits such as activity level, sociability, shyness, fearfulness etc. Genetic influences are also implicated in psychological problems and disorders such as anxiety and depression, dependence on nicotine and alcohol etc.
Chromosomes and genes – rod shaped structures found in cells. A normal human cell contains 46 chromosomes organized into 23 pairs. Each chromosome contains thousands of segments called genes. Genes carry the biochemical materials that regulate the development of traits. Polygenic – some traits are determined by the combination of pairs of genes.
We begin life as a single cell or zygote. There are 2 types of cell division.
Mitosis – cell division process by which growth occurs and tissues are replaced. Through mitosis, genetic code is carried into new cells in our bodies.
Sperm and ova are produced through meiosis, or reduction division. In meiosis the 46 chromosomes within the cell first line up into 23 pairs. The DNA ladders then unzip, leaving unpaired chromosome halves. As a consequence each new cell only contains 23 chromosomes.
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Fertilization
Union of egg and sperm
Zygote
Union of egg and sperm - please note sperm with y sex chromosomes seem to swim faster then x one of the reason more boys are conceived then girls. Male fetuses suffer higher rate of spontaneous abortion usually during the first month of pregnancy. Boys also higher rate of infant mortality
The resulting fertilized egg is called a zygote.
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Male or Female
Autosomes
Twenty-third pair (sex chromosomes)
XX
XY
When a sperm cell fertilizes an ovum we receive 23 from each which combine for the 23 pairs. Twenty-two of the pairs are autosomes – pair that look alike and possess genetic information concerning the same set of traits.
The 23rd pair consists of the sex chromosomes which look different and determine our sex. Males are XY and females are XX
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Multiple Births
How they occur
Dizygotic twins
Monozygotic twins
Monozygotic or identical twins – one egg fertilized and then the zygote divides into 2.
Dizygotic twins – two eggs fertilized by different sperm.
MZ twins occur with equal frequency in all ethnic groups – but for DZ incidence does vary. European Americans 1in 90 chance; African American 1 in 70 and Asian American 1 in 150.
DZ twins run in families if a woman is a twin, if her mother was a twin or if she has previously borne twin chances rise. Also women who have borne several children have an increased likelihood. Also increases with age – as ovulation becomes less regular will release more then one ovum. Also fertility drugs increases likelihood.
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Patterns of Genetic Inheritance
Homozygous
Heterozygous
Dominant vs. Recessive Inheritance
Modifier genes
Polygenic Inheritance
Phenotype vs. Genotype
Genomic Imprinting
Mutation
Homozygous – two forms of each gene occur at the same place on the chromosome (one from mom and one from dad). Each form is called an allele. If all alleles are the same the child is homozygous.
Heterozygous – when alleles are not the same.
Dominant vs. recessive inheritance – when only 1 allele affect development is it dominant. With heterozygous individuals with one recessive allele they are know as carriers. Modifier genes – enhance or dilute the effects of other genes. Also in some heterozygous circumstances the dominant-recessive relationship does not hold completely. Instead will have incomplete dominance – a pattern of inheritance in which both alleles are expressed in the phenotypes, resulting in a combined trait or one that is intermediate between the two.
Polygenic Inheritance – recognize that many characteristics are made up of a variety of genes
Phenotype is observable characteristics and genotype is the actual genetic pattern
Genomic Imprinting – alleles are imprinted, or chemically marked, in such a way that one pair member ( either the mom’s or the dad’s) is activated regardless of its makeup.
Mutation – is a sudden but permanent change in a segment of DNA. Some occur spontaneously by chance and others are caused by hazardous environmental agents.
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Dominant vs. Recessive Diseases
Ex. PKU (Autosomal)
X-linked inheritance (X-chromosome)
hemophilia
Autosomal- caused by genes locates on the autosomes (PKU). PKU – recessive gene – can not metabolize an amino acid call phenylaline. As a consequence builds up in system and impairs the functioning of the CNS. Results can be mental retardation, psychological disorders, and physical problems. Can be controlled with diet (devoid of meat, poultry, fish, dairy, beans and nuts) Stay on diet at least until teen years.
Others may be sex-linked located on the 23rd pair (Hemophilia – a blood clotting disorder)
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Chromosomal Abnormalities
Ex. Down Syndrome
People normally have 46 but sometimes may have more or fewer. Children with more or fewer experience health problems or behavioral abnormalities. Risk rises with age of parents.
Common – Down’s Syndrome – extra chromosome on the 21st pair. Have characteristic facial features. Shows deficits in cognitive development, encounter frequent disorders of the ear, nose, and throat, which also contribute to academic problems.
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Prenatal Diagnosis
Amniocentesis
Ultrasound
See page 64
Please read on your own about prenatal diagnostic procedures.
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Environmental Contexts
Family
Direct vs. Indirect influences
Socioeconomic Status
Affluence vs. Poverty
Neighborhoods
Schools
Culture
Public Policy
Family – isolation or alienation from the family is often associated with developmental problems.
Direct vs. Indirect influences – one to one interactions vs. third party interactions. Third parties can serve as support for or barriers to development. Example of indirect (and also a potential barrier) is marital conflict.
SES has 3 related variables – years of education, prestige of one’s job and the skill it requires and income. SES is linked to timing of parenthood and to family size. Example people in professional fields tend to marry later and have fewer children. Also parents in higher SES talk to, read to and tend to stimulate their infants and toddlers more. Education also contributes to this!
Affluence – may see too often fail to engage in family interaction and parenting that promotes favorable development.
Poverty – children of poverty more likely to suffer from lifelong poor physical health, persistent deficits in cognitive development and academic achievement, high school dropout, mental illness, impulsivity, aggression, and antisocial behavior.
Neighborhoods offer resources and social ties. With regard to social support – neighborhoods can provide access to valuable information and services, child-rearing controls and role models.
Schools – formal institution designed to transmit knowledge and skills that children need to become productive members of society. Regular parent-school contact supports development at all ages.
Culture – shapes family interactions, school experiences, and community settings.
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Heredity vs. Environment
Range of Reaction
Passive and Evocative Correlation
Active Correlation
Please read on own pages 82-88.
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