Chapter 2 Human Development

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University of Guelph
Family Relations and Human Development
FRHD 1010
Susan Chuang

FRHD*1010 nd th September 22 – 29 2013 Chapter 2: From Conception to Birth The Beginning of life  Every person starts life as a single cell (zygote)  Zygote is like a snowflake unlike any other cell but contains genes that have been passed down for thousands of years Genes & Chromosomes  All living things are composed of cells that promote growth & sustain life according to instructions in their molecules of DNA  Each molecule of DNA is called a chromosome  Each chromosome has instructions called genes  In a process called methylation, the DNA & RNA surrounding each gene enhances, transcribes, connects, empowers, alters and silences genes  Process continues throughout life  Can alter gene’s expression even after a person is born  Every cell in a human has copies of that person’s 46 chromosomes, arranged in 23 pairs  The exception to this is the reproductive cell gamete  Each gamete (sperm or ovum) has only 23 chromosomes one from each person’s 23 pairs Variations Among People  Since each gamete only has 1 of each person’s pair of chromosomes, each man or woman can produce 2 23 different gametes (more than 8 million versions of their chromosomes)  When sperm & ovum combine they create new cell in which 8 million possibilities from dad meet with 8 million possibilities of mom Allele: Any of the possible forms in which a gene for a particular trait could occur  Most alleles only cause small differences  Every zygote inherits many alleles from its sperm or ovum meaning many gene pairs don't exactly match in every triplet  Mutations occur as gametes form Genotype: An organism’s entire genetic inheritance or genetic potential Phenotype: The observable characteristics of a person, including appearance, personality, intelligence and all other traits More on Shared & Divergent Genes Genome: The full set of genes that are the instructions to make an individual member of a certain species The 23 pair  The material around a gene can halt, or expand, the instructions from that gene  Hormones or proteins or other factors can shape the phenotype begin w/ a gene but don't end there  Sex differences originate from 1 gene (SRY) on 1 chromosomes  22 of the 23 chromosome are autosomes and could be inherited by either male or female  The 23 pair in females if XX and 23 in males has 1 X and 1 Y  The Y chromosome has the SRY gene that directs the developing fetus to make male organs  Therefor the sex of the developing organism depends on which sperm penetrates the ovum Twins  Although every zygote is genetically unique…not every newborn is 1  About 1/250 human conceptions, the zygote not only duplicates but splits apart create multiple separate st zygotes each genetically identical to the 1 single cell Monozygotic twins: Twins who originate from 1 zygote that splits apart very early in development (identical twins)  B/c monozygotic multiples originate from the same zygote, they have same genotypes w/ identical instructions for physical appearance, psychological traits, vulnerability for disease & everything else  Don't have same phenotypes Dizygotic Twins: Twins who are formed when 2 separate ova are fertilized by 2 separate sperm at roughly the same time (fraternal twins)  Occur about twice as often as mono  Half their genes in common Genetic Interactions  Almost every trait is polygenic, affected by many genes & multifactorial, influenced by many factors Additive Genes: A gene that adds something to same aspect of the phenotype. Its contribution depends on additions from the other genes, which may come from either the same or the other parent  Height, hair curliness, skin colour etc. influenced by additive genes Dominant-recessive pattern: The interaction of a pair of alleles in such a way that the phenotype reveals the influence of 1 allele (the dominant gene) more than that of the other (recessive gene) Carrier: A person whose genotype includes a gene that isn’t expressed in the phenotype.  Such an unexpressed gene occurs in half the carriers gametes & thus passed to half the children who will most likely be carriers too From Zygote to Newborn  The most dramatic transformation of entire life span occurs before birth  Prenatal development split into 3 main periods Germinal Period  The 1 2 weeks of prenatal development after conception  Rapid cell division and the beginning of cell differentiation  Zygote begins duplication & division just hours after conception Stem Cells: Cells from which any other specialized type of cell can form  First cells  After approx. eight-cell stage, duplication and division occur into a third process differentiation  Soon cells specialize taking diff forms and reproducing various rates, depending on where they are located  Differentiation means that though every cell carries the complete genetic code, some cells become part of eye, some a finger etc.  The outer cells form a shell that will become the placenta and the inner cells form a nucleus that will become the embryo Implantation: Beginning approx. 10 days after conception the developing organism burrows into the tissue that lines the uterus, where it can be nourished and protected as it continues to develop rd th Embryo: From the 3 Through the 8 Week Embryo: The name for the developing human organism from about the 3 week through the 8 week after conception  The formless mass of cells becomes a thing 2  For approx.. 14 days a thin line (primitive streak) appears down the middle of the embryo, becoming the neural tube 22 days after conception and eventually develops into the central nervous system, brain and spinal column  Head appears in the 4 week and eyes, ears, nose & mouth start to form  In 4 week a little blood vessel that will become the heart begins to pulsate st  Head develops 1 , in a cephalocaudal (head-to-toe) pattern, and the extremities form last in a proximodistal (near-to-far) pattern  At end of 8 week embryo has all the organs and body parts except sex organs th Fetus: From the 9 Week Until Birth th Fetus: The name for a developing human organism from the start of the 9 week after conception until birth  Grows their sex organs in 9 week soon visible via ultrasound  As prenatal growth continues, the cardiovascular, digestive, and excretory systems develop th th  Brain increases 6x its size in 4 -6 month Age of Viability: The age (approx. 22 weeks after conception) at which a fetus may survive outside the mother’s uterus if specialized medical care is available  A preterm infant born in the 7 month is a tiny creature requiring intensive care for each gram of nourishment and every shallow breath Finally, a Baby  About 38 weeks after conception the fetal brain signal the release of hormones which prepares the fetus for delivery and starts labor st  Avg. baby born after about 12 hours of active labor for 1 births and 7 hours for subsequent births The Newborn’s 1 Minutes  1 breaths of air brings oxygen to the lungs and blood, and infant colour changes from blue-ish to pinkish  Eyes open wife Apgar Scale: A q
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