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Family Relations and Human Development
FRHD 1010
Susan Chuang

Chapter 2 Genetics and Prenatal Development Section 1: Genetic Influences on Development 1. Genetic Basics Genotype and Phenotype  Nearly all cells In the human body contain 46 chromosomes (sausage shaped structure in nucleus of cells, containing genes which are paired, except in reproductive cells) in 23 pairs o Each pair has one from mother and one from father o They are composed of DNA (deoxyribonucleic acid)  DNA composed into segments called genes (basic unites of hereditary information) genes contain sequences of chemicals called nucleotides  There are 23,000 genes in out 46 chromosomes, the total human genome (entire store of human organism’s hereditary information)  genotype – the totality of an individuals genes/ organisms unique individual features  phenotype – The persons actual characteristics derived from genotype Example – born with exceptional musical ability is your genotype, but with no access to musical instruments this genotype might not be apparent in your phenotype.  allele – pair of chromosomes, each of two forms of a gene (can have dominant and recessive forms)  dominant-recessive inheritance – influences the relationship of genotype and phenotype o Pattern of inheritance in which a pair of chromosomes contains one dominate and one recessive gene, but one the dominate gene is expressed in the phenotype (example: curly/straight hair, curly is dominate)  incomplete dominance- the phenotype is influenced primarily but not exclusively by the dominant gene. Example- sickle-cell trait in African Americans  most characteristics in human development are not determined solely by a single pair of genes, however sometimes single pairs of genes play a crucial part such as the sickle-cell anemia  polygenic inheritance- interaction of multiple genes rather then just one/ expression of phenotypic characteristics due the inheritance of multiple genes 2. Sex Chromosomes  of the 23 pairs of chromosomes, one pair is different, these are sex chromosomes (determine whether a person is male/female) o female pair XX ,male pair XY o Y is smaller, contains one third of genetic material o Mothers eggs contain only X, but sperm may carry X or Y (fathers sperm determines sex of the baby)  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  X-linked inheritance- pattern of inheritance in which a recessive characteristic is expressed because it is carried on the male X chromosome o Males are more vulnerable to disorders carried on X chromosome Genes and Environment in Human Development 3. Principles of Behavior in Genetics  Nature-nurture debate – debate among scholars as to whether human development is influenced mainly by genes (nature) or environment (nurture)  Behaviour genetics – field in the study of human development that aims to identify the extent to which genes influence behavior, primarily by comparing persons who share different amounts of their genes (use twin studies, and adoption studies) o Monozygotic (MZ) twins – twins with the exact same genotype; identical twins o Dizygotic (DZ) twins – twins that result when two ova are released by the female instead of one, and both are fertilized by sperm; fraternal twins  Heritability – is the estimate of the extent to which genes are responsible for the differences among persons within a specific population with value ranging from 0 to 1.00  Concordance rate- degree of similarity in phenotype among pairs of the family members, expressed as a percentage o Rates range from 0%-100%, the higher the concordance rate, the more similar the more similar the two persons are 4. Gene-Environment Interactions: Epigenesis and reaction ranges  Epigenesis- in development, the continuous bidirectional interactions between genes and the environment o Development is influences by genes but not purely determined by them  Reaction range- range of possible developmental paths established by genes; environment determines where development takes place within that range o Example – genes for height is known to be influenced by genes, the genes for your height establish the reaction ranges upper and lower boundaries, where a persons actual height ends up –the phenotype- is determined by environmental influences such as nutrition and disease 5. The Theory of Genotype  Environmental Effects  Influential theory of behavior genetics o Theory of genotype  environment effects  Proposing that genes influence the kind of environment we experience (to a considerable extent)  Proposed by Sandra Scarr and Kathleen McCartney o Three forms of this theory: passive, evocative, active  Passive genotype  environment effects  Occur in biological families – parents provide both genes and environment for their children  Evocative genotype  environment effects  Occurs when a persons inherited characteristics evoke responses from others in the environment  Example – son who started reading early and loved it, you may buy him books  Active genotype environment effects  Results when people seek out environments that correspond to their genotypic characteristics o Process called niche-picking  Example- child who is faster then peers may be motivated to try out for a sports team o All forms operate throughout childhood, adolescence, and adulthood, but relative balance changes overtime 6. Sperm and Egg Formation  Gametes- cells distinctive to each sex, that are involved in reproduction (egg cells in the ovaries of the female, sperm in the testes of the male) o The only cells in the human body that do not contain 46 chromosomes are the reproductive cells called gametes o Ovum – in female, mature egg that develops in ovaries, about every 28 days (plural, ova) o Gametes – the sperm in the male and the egg or ovum in the female  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 o Variation of mitosis o In males meiosis is completed before sperm are released, in females meiosis only takes place when and if the ovum in fertilized o In males, outcome id four viable sperm, females only produce one viable ovum along with three
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