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University of Guelph
Family Relations and Human Development
FRHD 1020
Susan Chuang

Human Development 1 Chapter 2: Genetics and Prenatal Development Genetic Basics  Chromosome: sausage-shaped structure in the nucleus of cells, containing genes, which are paired, except in reproductive cells.  DNA: long strand of cell material that stores and transfers genetic information in all life forms  Gene: segment of DNA containing coded instructions for the growth and functioning of the organism.  Genome: entire store of an organism’s hereditary information  Genotype: organism’s unique genetic inheritance  Phenotype: organism’s actual characteristics, derived from its genotype.  Dominant-recessive inheritance: pattern of inheritance in which a pair of chromosomes contains one dominant and one recessive gene, but only the dominant gene is expressed in the phenotype.  Allele: on a pair of chromosomes, each of two forms of a gene  Incomplete dominance: form of dominant- recessive inheritance in which the phenotype is influenced primarily by the dominant gene but also to some extent by the recessive gene. o Incomplete dominance in sickle cell inheritance: Two recessive genes for the sickle cell trait results in sickle cell anemia, but having one dominant and one recessive gene provides protection against malaria.  Polygenic inheritance: expression of phenotypic characteristics due to the interaction of multiple genes.  Regulator gene: gene that directs the activities of other genes  Gene therapy: method of treating genetic disorders that involves replacing the affected genes with genes that do not have the disorder. The sex chromosomes  Sex chromosomes: chromosomes that determine whether an organism is male (XY) or female (XX).  X-linked inheritance: pattern of inheritance in which a recessive characteristic is expressed because it is carries on the male’s X chromosome. Genes and Environment in Human Development  Nature-nurture debate: debate among scholars as to whether human development is influences mainly by genes(nature) or environment(nurture). Principles of Behaviour Genetics  Behaviour genetics: field in the study of human development that aims to identify the extent to which gened influence behaviour, primarily by comparing persons who share different amounts of their genes/  Monozygotic (MZ) twins: twins who have exactly the same genotype; also called identical twins  Dizygotic(DZ) twins: twins that result when two ova are released by a female instead of one, and both are fertilized by sperm; also called fraternal twins.  Heritability: statistical estimate of the extent to which genes are responsible for the differences among persons within a specific population, with values ranging from 0 to 1.00. o The higher the heritability, the more the characteristic is believed to be influenced. o Heritability estimates have been criticized for giving misleading impression of the influence of genetics on development. o Heritability estimates are estimates based on comparison of persons with different amounts of genetic material in common, not direct measures of the activity of genes.  Concordance rate: percentage that indicated the degree of similarity in phenotype among pairs of family members, expressed as a percentage. Gene-environment Interactions: Epigenesis and Reaction Ranges.  Epigenesis: in development, the continuous bidirectional interactions between genes and environment. o According to epigenetic theory, genetic activity responds constantly to environmental influences. Development is influences by genes but not purely determined by them.  Reaction range: range of possible developmental aths established by genes; environment determines where development takes place within that range.  The theory of genotype  environmental effects: theory proposing that genes influence the kind of environment we experience. The 3 forms of genotype Environment effects  Passive genotype  environment effects: the type that results from the fact that in a biological family, parents provide both genes and environment to their children.  Evocative genotype  environment effects: the type that results occur when a persons inherited characteristics evoke responses from others in the environment.  Active genotype  environment effects: the type that results when people seek out environments that correspond to their genotypic characteristics. Genotype  Environment effects over time  The three types of genotype  environment effects operate throughout childhood, adolescence, and adulthood, but their relative balance changes over time.  In childhood, passive genotype  environment effects are especially pronounced, and active genotype  environment effects are relatively weak. Human Development 3 Chapter 2: Genetics and Prenatal Development  However, the balance changes as children move through adolescence and into adulthood.  Parental control diminishes, so passive genotype  environment effects also diminish.  Autonomy increases, so active genotype  environment effects also increase.  In adulthood, passive genotype  environment effects fade entirely, and active genotype  environment effects move to the forefront.  Evocative genotype  environment effects remain relatively stable from childhood through adulthood.  The theory of genotype environment effects has been the source of vigorous debate. Genes and Individual Development  Gametes: cells, distinctive to each sex, that are involved in reproduction (egg cells in the ovaries of the female and sperm in the testes of the male) Sperm and Egg Formation  Ovum: mature egg that develops in ovaries, about every 28 days in human females.  Meiosis: process by which gametes are generated, through separation and duplication of chromosome 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 the same number of chromosomes as the original cell.  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.  Crossing over: at the outset of meiosis, the exchange of genetic material between paired chromosomes. Conception  Follicle: during the female reproductive cycle, the ovum plus other cells that surround the ovum and provide nutrients.  About 14 days into a womens cycle, the mature follicle cursts and ovulation takes place as the ovum is releaded into the fallopian tube.  The ovum is 2,000 times larger than a sperm because it contains so much cytoplasm.  The cytoplasm will provide 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.  It is only during the first 24 hours after the ovum enters the fallopian tube that fertilization can occur. It takes sperm from afew hours to a whole day to travel up the fallopian tubes, so fertilization is most likely to take place if intercourse occurs on the day of ovulation or the 2 previous days.  When the sperm reaches the ovum they begin to penetrate the surface of the cell, aided by a chemical on the tip of the sperm that dissolves that ovum’s membrane.  Once the sperm penetrates the ovum’s membrane, the head of the sperm detaches from the tail and continues toward the nucleus of the cell while the tail remains outside  When the sperm head eaches the nucleus of the ovum, the final phase of meiosis is triggered in the ovum.  Fertilization takes place as the 23 chromosomes from the ovum pair up with the 23 chromosomes from the sperm.  Zygote: following fertilization, the new cell formed from the union of sperm and ovum.  Twins can also result when a zygote that has just begun the process of cell division splits into 2 separate clusters of cells, creatins MZ twins  MZ twins are less common than DZ twins. SECTION 2 Prenatal Development The Germinal Period (First 2 weeks)  Germinal period: the zygote travels down the fallopian tubes to the uterus and implants in the uterine wall. As it travels, it begins cell division and differentiation.  By week 1 following conception there is a ball of about 100 cells known as a blastocyst which is divided into 2 layers. o Trophoblast: The outer layers of cells which will go on to form structures that provide protection and nourishment to the embryo. o Embryonic disk: the inner layer of cells, which will go on to form the embryo.  During the second week after conception, implantation occurs as the blastocyst becomes firmly embedded into the lining of the uterus.  The trophoblast begins to differentiate into several structures during this 2d week.  Part of it forms a membrane, the amnion, which surrounds the developing organism and fill with fluid, helping to keep a steady temperature for the organism and protect it against the friction of the mother’s movements.  In between the uterine wall and the embryonic disk a round structure, the placenta, begins to develop. The placenta will allow nutrients to pass from the mother to the developing organism and permit wastes to allow nutrients to pass from the mother to the developing organism and permit wastes to be removed. It also protects the developing organism from bacteria and wastes Human Development 5 Chapter 2: Genetics and Prenatal Development in the mother’s blood, and it produces hormones that maintain the blood in the uterine linning and cause the mothers breast’s to produce milk.  An umbilical cord also begins to develop, connecting the plac
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