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Chapter 3

developmental chap 3

8 Pages

Course Code
PSYC 2450
Jennifer Mc Taggart

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Chapter 3: Forming a New Life ~ Conception, Heredity, and Environment Becoming Parents: How Conception Occurs: Bronfenbrenner’s bioecological approach includes factors in the  Microsystem: birth planned/accident, wanted/unwanted, parents married/unmarried, etc.  Macrosystem: if culture encourages large/small families, values one sex over the other, etc. How does conception normally occur, and how have beliefs about conception changed?  Early beliefs about conception reflected incorrect beliefs about nature and male and female anatomy o Aristotle thought birth of male was natural order, female was when development was disturbed (woman only receptacle, child formed of sperm). o Hippocrates thought fetus results from joining male/female seeds. o 18 century, finally, Kaspar Friedrich Wolff said embryos are forms with equal contributions from each parent.  Fertilization: o Union of sperm and ovum (gametes) fuse to produce a zygote; also called conception  Zygote: o One-celled organism resulting from fertilization  Duplicates itself by cell division to form an infant. Infertility:  Infertility: o Inability to conceive after 12 months of trying 7% of Canadians Common causes of infertility in men and woman chart (p. 57) What causes infertility, and what are alternative ways of becoming parents?  Most common cause in men: low sperm count o As low as 60/200 million makes conception unlikely o Some just can’t swim well or ejaculatory duct is blocked o Some genetic basis in this  Most common cause in women: blockage of Fallopian tubes (many cases is from scar tissue from STI’s. o Mucus in cervix may prevent sperm from penetrating it o Disease of uterine lining may prevent implantation of fertilized ovum  Women fertility begins to decline late 20’s, especially 30’s, and men; age does not affect it as much, but declines in late 30’s. Sometimes hormone treatment, drug therapy, or surgery may correct it; but fertility dugs may increase likelihood of high-risk births. Men in fertility treatment have increased risk of producing sperm with chromosomal abnormalities. A daily supplement of coenzyme Q10 (antioxidant) increases sperm motility. Unless this is a known cause for failure to conceive, chances of success after 18 months – 2 years are high, but after a year or so of trying, pregnancies must be monitored closely.  Assisted reproduction involve ethical and practical issues o About 76% are successful, much fewer end in live births (24% in Canada). o Artificial insemination: injection of sperm into a woman’s vagina, cervix or uterus (man has low sperm count). Stimulating her ovaries to produce excess ova can increase success. o In vitro fertilization (most common)  Multiple births can occur by fertilization of more than one ovum (or one ovum that has split) or by the splitting of one fertilized ovum  Intracytoplasmic sperm injection (ICSI): sperm injected into ovum o In Vitro maturation (IVM) is earlier in monthly cycle, when 30-50 egg follicles are developing. You harvest many follicles before ovulation is complete, and allow them to mature in the lab can diminish likelihood of multiple births. o Blastocyst transfer: fertilized ovum is kept in the culture until it grows into blastocyst stage (linked to increase in identical twins). o Surrogate Motherhood: fertile woman impregnated by prospective father (usually artificial insemination), carries the baby and gives the baby to the father and his mate. o 2004, Canadian gov’t passed Canadian Assisted Human Reproductive Act: strict conditions on the practice, including ban on payment to surrogate mothers. Mechanisms of Heredity What genetic mechanisms determine sex, physical appearance, and other characteristics?  Monozygotic (one-egg) twins: o Twins resulting from the division of a single zygote after fertilization; also called identical twins  Same genetic make up but may differ in some ways  About 4 per 1,000 births  Dizygotic (two-egg) twins: o Twins conceived by the union of two different ova (or a single ovum that has split) with two difference sperm cells; also called fraternal twins.  Different genetic make up  Rate varies  Deoxyribonucleic acid (DNA): o Chemical that carries inherited instructions for the formation and function of body cells.  Carries biochemical instructions, or genetic code, that governs bodily functions and determines inherited characteristics.  Double helix made of pairs of chemical units called bases.  Genetic Code: o Sequence of base pairs within DNA, which determine inherited characteristics.  Adenine (A), Thymine (T), Cytosine (C), Guanine (G).  Chromosomes: o Coils of DNA that carry the genes  Genes: o Small segments of DNA located in specific positions on particular chromosomes o Basic functional units of heredity. o Each seems to be located by function in a definite position on a particular chromosome. o Sequence of bases in a gene tells the cell how to make proteins that enable it to do specific functions. o Human Genome:  Complete sequence or mapping of genes in the human body and their locations Meiosis: cell division which the sex cells undergo when they are developing. At conception, each human being receives 23 chromosomes from mother, and 23 from father. They form 23 pairs of chromosomes (22 pairs of autosomes, 1 pair of sex chromosomes). 3/4 of genes every child receives are identical to other children: monomorphic genes 1/4 are polymorphic genes, which define each person as an individual. Mitosis: process in which the cells divide in half over and over again. When a cell divides, DNA spirals replicate themselves, so each structure has t he same DNA as othe others. Genetic action that triggers growth of body and brain is often regulated by hormonal levels—both in the mother and the baby, which are effected by environmental conditions like nutrition and stress.  Autosomes: o The 22 pairs of chromosomes not related to sexual expression  Sex Chromosomes: o Pair of chromosomes that determines sex: XX in the normal female, XY in the normal male o The Y chromosome contains the gene for maleness, called the SRY gene. Initially, the reproduction system is identical in males in females until 6-8 weeks after conception, male embryos begin producing testosterone. Hormones must first signal the SRY gene, which triggers cell differentiation. o The development of female reproductive system depends on a signally molecule called Wnt-4. The extra X chromosome may explain why women are generally healthier and more long-lived. 1860’s—Gregor Mendel laid foundation for understanding patterns of inheritance. He crossbread pea plants with green seeds with plants with yellow seeds—found a dominant and recessive. He found hat colour and shape were independent of each other. He showed that hereditary traits are transmitted separately.  Alleles: o Two or more alternative forms of a gene that can occupy the same position on paired chromosomes and affect the same trait  Genes can produce alternative expressions of a characteristic (roll tongue).  Homozygous: o Possessing two identical alleles for a trait  Heterozygous: o Possessing differing alleles for a trait  Dominant Inheritance: o Pattern of inheritance in which, when a child received contradictory alleles, only the dominant one is expressed  Heterozygous for a particular trait: When offspring receives contradictory alleles for a trait, only one of them, the dominant one, will be expressed.  Recessive Inheritance: o Pattern of inheritance in which a child receives identical recessive alleles, resulting in expression of a nondominant trait  Need a recessive allele from each parent.  Polygenic Inheritance: o Pattern of inheritance in which multiple genes at different sites on chromosomes affect a complex trait o Interaction of several genes. Most normal humans are this or multifactorial transmission. Except monozygotic twins (each child has unique genotype—but phenotype may not express underlying genotype).  Mutations: o Permanent alterations in genes or chromosomes that may produce harmful characteristics  Multifactorial transmission: o Combination of genetic and environmental factors to produce certain complex traits  Ex. children with ADHD more likely to show early anti-social behaviour if they were of low birth weight.  Phenotype: o Observable characteristics of a person  Is the product of a genotype. The difference between genotype and phenotype helps explain why a clone can never be an exact duplicate.  Ex. curling your tongue.  Genotype: o Genetic makeup of a person, containing both expressed and unexpressed characteristics  Experience modifies the expression of the genotype.  Clone: o To make a genetic copy of an individual Genetic and Chromosomal Abnormalities: How are birth defects and disorders transmitted? Birth disorders are fairly rare (3%), and most are usually cleft lip or palate, followed by Down syndrome. Serious malformations involve the eye or circulatory, orofacial, gastronomical, or musculoskeltal systems. Birth disorders are 27% of infant deaths in Canada. Serious ones involves circulatory or central nervous system. Birth defects chart on p. 64 In genetic defect we see the dominant and recessive transmission in humans and the sex-linked inheritance. Some are mutations. Birth defects and diseases may result from simple dominant, recessive, or sex-linked inheritance, from mutations; genome imprint
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