Chapter 2 Notes Human Development

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Family Relations and Human Development
FRHD 1010
Susan Chuang

Chapter 2 Notes: Genetic Influences on Development Genetic Basics Genotype and Phenotype  Nearly all cells in humans have 46 chromosomes in 23 pairs.  Chromosome: sausage shaped structure in the nucleus of cells, containing genes, which are paired, except in reproductive cells  Dna (DEOXYTIBOYNUCLEIC ACID) long strand of cell material that stores and transfers genetic information  Genes: segment of DNA containing coded instructions for the growth and functioning of the organism  There are about 23,000 genes in our 46 chromosome, the total human genome is about 3 billion nucleotide pairs  Genome: entire store of organism’s hereditary information  Genotype: organism’s unique genetic inheritance  Phenotype: organism’s actual characteristics, derived from genotype  Allele: on a pair of chromosomes, each of two forms of a gene  Only the dominant gene influences the phenotype  Incomplete dominance: phenotype is influenced by both dominant and recessive gene  Polygenic inheritance: expression of phenotypic characteristics due to the interaction of multiple genes The Human Genome Project  Beginning in 1990, project engaged a team in the goal of describing the chemical features of every gene in the human genome  Goal reached in 2000  Findings: o There are only 23,000 protein coding genes in the human genome, far fewer than expected to find o The 23,000 protein-coding genes are only 3% of human genome, other 97% which does not code is dismissed as junk o Many genes can make multiple proteins o Regulator gene: directs the activities of other genes o Most human characteristics are polygenic (due to the collaboration of multiple genes not just a single gene) o Gene therapy: method of treating genetic disorders that involves replacing the affected genes with genes that do not have the disorder The Sex Chromosomes o Sex chromosomes: determine whether you’re a male(XY) or female (XX) o Having one X chromosome makes males more vulnerable than females to a variety of recessive disorders that are linked to the X chromosomes  If a female has one X that contains recessive genes for a disorder, the dominant X will prevent it from being expressed Genetics and Environment in Human Development  Nature-nurture debate: whether human development is influenced mainly by genes(nature) or environment(nurture)  Behavior genetics: filed in study of human development that aims to identify the extent to which genes influence behavior by comparing persons who share different amounts of their genes  Monozygotic (MZ) twins: twins who have exactly same genotype (identical)  Dizygotic (DZ) twins: twins that result when two ova are released by a female and are both fertilized  Heritability: statistical estimate of the extent to which genes are responsible for the differences among persons within a specific population, values from 0-1.00 o Higher score, the more characteristic is believed to be influenced by genes o For intelligence, heritability estimates have been found to be about .50 o For personality, heritability estimates range from .40 to .50 o Heritability estimates are a measure not just of genetic influence but of how much the environment allows the genes to be expressed  Heritability measures phenotype not genotype  Concordance rate: degree of similarity in phenotype among pairs of family members, expressed as a percentage  Epigenesis: in development, the continuous bidirectional interactions between genes and environment  Reaction range: range of possible developmental paths established by genes; environment determines where development takes place within that range o Genes for height establish the reaction range’s upper and lower boundaries and where a person’s actual height ends up (phenotype) is determined by environmental influences such as nutrition and disease Theory of Genotype  Environment Effects  Theory of genotype  environment effects: proposing that genes influence the kind of environment we experience o The relative strengths of genetics and the environment are difficult to unravel because our genes actually influence the kind of environment we experience  Based on our genetics, we create our own environments to an extent  Three forms of genotype  environment effects: o Passive genotype  environment effects: the type that results from the fact in a biological family, parents provide both genes and environment to their children  In a biological family its hard to separate genetic influences from environment because parents provide both and they are likely to provide an environment that reinforces the tendencies they have provided to their children through their genes  Just because there is a correlation between the behavior of parents and the characteristics of their children, doesn’t mean the parents behavior caused the children to have those characteristics o Evocative genotype  environment effects: the type that results occur when a persons inherited characteristics evoke responses from other in the environment  Easier for you to be warm and supportive to kids who are cheerful and cooperative than disobedient and disruptive o Active genotype  environment effects: the type that results when people seek out environments that correspond to their genotypic characteristics  Niche-picking  People are drawn to environments that match their inherited abilities  Genotype  environment effects over time o The three types effects operate throughout childhood, adolescence and adulthood but their relative balance changes over time o In childhood, passive genotype  environment effects are highest because the younger child is more controlled by parents and has less autonomy o As child becomes young adult, autonomy increases so active genotype  environment effects also increase o By adulthood, passive genotype effects fade completely in most cultures o Evocative genotype effects remain relatively stable Genes and Individual Development Sperm and Egg Formation  Sperm and eggs themselves go through a process of development  Only cells in human body that do not contain 46 chromosomes are the reproductive cells (gametes) o Gametes: cells, distinctive to each sex, that are involve in reproduction (egg cells in the ovaries of female and sperm in the testes of males) o Ovum: mature eggs that develops in ovaries, about every 28 days  Meiosis: process by which gametes are generated, through separation and duplication of chromosomes pairs, ending in four new gametes from the original cell, each with half the number of chromosomes of the original cell  Mitosis: process of cell replication in which the chromosomes duplicate themselves and the cell divides into two cells, each with same number of chromosomes as the original cell  In males, the outcome of meiosis is four viable sperm, whereas in females meiosis produces only one viable ovum, along with 3 not functioning polar bodies  Cytoplasm: in an ovum, fluid that provides nutrients for the first 2 weeks of growth if the ovum is fertilized, until it reaches the uterus and begins drawing nutrients from the mother  At puberty, males produce millions of sperm each day o There are 100-300 million sperm in the typical male cumshot  Females are born with all their ovum o Females are born with about 1 million ova, but it diminishes to 40,000 by puberty o About 400 of these will mature during a womans child bearing years Conception - Only a few hundred sperm make it up the fallopian tubes - Follicle: ovum produces other cells that surround the ovum and provide nutrients - About 14 days into a women’s cycle, the mature follicle bursts and ovulation takes place as the ovum is released into the fallopian tube - Ovum is 2,000 times larger than a sperm due to al the cytoplasm - It is only during the first 24 hours after the ovum enters the fallopian tube that fertilization can occur o Fertilization will take place if intercourse occurs on the day of ovulation or 2 the two previous days - When sperm head reaches nucleus of ovum, final stage of meiosis is triggered o Fertilization takes place as the 23 chromosomes from the ovum pair up with the 23 chromosomes from the sperm and a new cell (zygote)  Zygote: following fertilization, it’s the new cell formed from union of sperm and ova Prenatal Development  Germinal Period: week 1-2, zygote divides and forms blastocyst, which implants in uterus and begins forming the amnion, placenta and umbilical cord o Cell division begins 30 hours after conception o Blastocyst: ball of about 100 cells formed by about one week following conception  Blastocyst becomes firmly embedded in uterine lining  Over half of blastocysts never implant successfully, usually due to chromosomal problems that have caused cell division to slow down or stop o Trophoblast: in the blastocyst, the outer layer of cells, which will go on to form structures that provide protection and nourishment to the embryo o Embryonic disk: in the blastocyst, the inner layer of cell, will go on to form embryo o Amnion: fluid filled membrane that surrounds and protects the developing organism in the womb o Gestation: elapsed time since conception  Embryonic stage: week 3-4, three layers form, the ectoderm, the mesoderm and the endoderm; neural tube develops and produces neurons; heart begins beating; ribs, muscles and digestive tract form. 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