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Mark Schmuckler

Psyb64-ch 2 Heredity and the environment Genotype: the particular set of genes that a person inherits from her parents. No one has the same genotype besides identical twins The genotype interacts with the environment in complex ways to produce the phenotype Phenotype: the observable and measurable expression of an individual’s physical and behavioral characteristics The process of genetic transmission Zygote: results from the union of the male and female gamete and carries the genetic info Ovum: the egg, woman gamete is the largest human cell Sperm: the male gamete, the smallest of all human cells Chromosomes and genes -chromosomes and genes are located inside the nucleus -23 chromosomes from each of these cells join to make 23 pairs 46 total -chromosomes: they carry the genetic information that helps direct development -each chromosome is homologous -each reproductive cell contains only 23 single chromosomes instead of the usual 46, because when they join they create one cell composed of 46 during development -the gametes undergo a special form of cell division meiosis where the 23 pairs are halved -the halving process mixes the chromosomes that originate from the individual’s father with the chromosomes that originated from the individuals mother -further genetic variability is added during meiosis by a process called crossing over where equivalent sections of homologous chromosomes randomly switch places -mitosis: occurs in all autosomes (chromosomes that contain matching pairs) and sex chromosomes, where a cell duplicates its chromosomes and then divides into daughter cells that have the exact same number of chromosomes as their parent cell Meiosis: chromosome split an mix mitosis: autosomes (matching pair chromos) and sex chromosomes duplicate then divide (daughter cells) for the same # of chromos as parents Genes, DNA , and proteins -DNA: deoxyribonucleic acid, a molecule that stores genetic info and transmits it during the reproduction, made up of nucleotides -nucleotide: compounds of nitrogen base, a simple sugar and a phosphate group -only those with bases compatible with each other will bind together to form the “staircase” - adenosine (A) and thymine (T) bind and cytosine (C) and guanine (G) -portions of the chromosomes DNA, genes, are located on particular sites on the chromosome where they code for the production of certain kinds of proteins -the gene or DNA segment splits down the midd;e so that its pairs of bases are no longer joined -the free nucleotides are up to form new pairs -the resulting copy of the gene then acts as a template for building protein molecules -the proteins have different functions such as giving physical properties, some may do others jobs as triggering chemical reactions, carrying chemical messages… -proteins work together to function the body Genetic influences on development Genes never work in isolation but always in combination with environmental influences. Its coded message cannot be read unless it Is embedded in an environment The transmission of traits: a basic model -principle of segregation: each inherited trait comes from one’s parent as a separate unit -principle of independent assortment: inheritance of various traits occurs independently of one another -at any given gene’s position on two homologous chromosomes (chromosomes that are the same), there can be more than one form of that gene -alleles: alternative form of a gene, a gene has 2 alleles, 1 from the mother 1 from the father -if the alleles from the two parents are the same, the organism Is homozygous (AA) -if the alleles are different, the organism is heterozygous (Aa) -if A represents one allele and a another, then there are clearly 3 possible combinations: AA, aa, Aa (aA) -the combination of two dissimilar alleles will produce an outcome intermediate between the traits, for which each single allele codes -both alleles will express their traits simultaneously, that is the two traits will combine but not blend. This is co-dominance as seen in blood types Codominance is where 2 traits get together but they don’t blend they just combine ex: blood -a heterozygous combination the characteristics associated with only one of the alleles is expressed -the more powerful is dominant, the least is recessive -many inherited characteristics follow this dominant-recessive type of relation -many harmful alleles are recessive, which greatly reduces the incidence of genetic abnormalities Genes on the sex chromosomes: exceptions to the rule -one of 23 pairs, or two of the 46 chromosomes are called sex chromosomes -they have important function of determining the individual’s gender, they differ in males and females -a female has 2 large homologous XX chromosomes -the male has XY, X from the mother and the Y from the father -X is 5 times longer than Y and so it carries more genes -x linked genes: genes that are carried on the X chromosome and that may have no analogous genes on the Y chromosome in males -hemophilia: example of x linked recessive characteristic. A female may have lesser chance because she has an extra X chromosome. For men, if it is on the X chromosome he has a greater danger of developing hemophilia -disorders are more common inn men than in women, such as certain types of blindness. And certain childhood diseases A lot of disorders are on the recessive genes on the X chromosome that’s why men are more prone to abnormalities than woman. Ex: hemophilia color blindness is also x linked Interactions among genes -most of the characteristics that are of the greatest interest to psychologists, such as intelligence, creativity, sociability and style of emotional expression, are probably influenced by the interaction of multiple genes -development of traits depends on a certain configuration of many genes, and that particular configuration is not likely to be passed on from parent to child - a single pair of alleles may influence more than one trait -modifier genes: genes that exert their influence indirectly, by affecting the expression of still other genes -ex: nature of cataract formation is influenced by modifier genes Modifier genes: influence outcomes indirectly by aiding another gene Genetic disorders -genes can have both positive and negative effects on development Why harmful alleles survive -alleles survive, they are not harmful in the heterozygous state -PKU: phenylketonuria. Caused by recessive allele that fails to produce an ezyme necessary to metabolize the protein phenylalanine in milk -1 out of every 20 people of European ancestry carries the recessive PKU allele and does not even know it -problems arise only in infants who are homozygous for the recessive gene -most people who carry the PKU allele also have a normal allele. So they do not succumb to the disorder -some potentially harmful alleles may survive because they are beneficial in combination with a normal allele ex: sickle cell anemia Chromosomal abnormalities -caused by defects in entire chromosomes -almost 1 percent of all newborns have diagnosable chromosome abnormalities -it has been estimated that 60 percent of early spontaneous abortion and 5 percent of later miscarriages are attributable to aberrations in chromosomes -they generally arise during the process of meiosis when the eggs or the sperms are formed -zygote produced by the union of the sperm and the egg spontaneously aborts -a zygote is able to survive the abnormal condition and a baby with a chromosomal defect is born ***Chromosome abnormalities are usually cause during meiosis when egg and sperm are formed Down syndrome -is a physical and mental retardation with a distinctive physical appearance -susceptibility to such illness as leukemia, heart disorders, and respiratory infections and their moderate to severe mental retardation -70 percent of individuals with Down syndrome live into their sixties with today’s research but they are at greater risk of developing Alzheimer’s disease -it is caused by a deviation in the set of chromosomes labeled number 21 -instead of a pair they have 3 chromosomes st -the exsta 21 chromosome most often comes from the mother’s egg -the 21 pair fails to separate during meiosis -this error occurs more often when older woman become pregnant -down syndrome births are higher for men over 40, and woman over 35 -the children are generally slow to learn to speak, with a difficulty articulating words and producing complex sentences in adolescence Sex chromosomal anomalies -some females are born with only one X chromosomes, rather than the normal XX pattern -this occurs because the father sperm contained neither an X nor Y chromosome -girls with this XO pattern,called Turner Syndrome remain short, with stubby fingers, webbed necks and unusually shaped mouths and ears -as teenager, they do not develop secondary sex characteristics, such as breasts and pubic hair, unless given female hormones -they remain sterile throughout their whole lives -woman with Turner have difficulty discriminating and interpreting emotional cues and facial expressions in other -XXX pattern girl inherits three X chromosomes instead of the normal two -normal development but their cognitive abilities are affected -short term memory and verbal skills -when a male inherits an extra X chromosome, producing an XXY pattern known as Klinefelter’s syndrome -he is sterile and has many female characteristics, such as breast development and a rounded, broad hipped figure, verbal language decifits and reading problems memory and reasoning problems, along with inhibitory skills and is sometimes retarded -XYY is to be accompanied by excessive aggressiveness -XYY men are generally taller than normal men -some people carry an X chromosome that appears to be pinched or narrowed in some areas, causing it to be quite fragile -fragile X syndrome: more frequent in males than in females -people with fragile X syndrome often have physical abnormalities and psychological and social problems -males may have deficits in social interaction, and females may be more likely to suffer from depression and also to show and linguistic deficits Prenatal diagnostic techniques Commonly used tests -amniocentesis: where inserts a needle into the amniotic sac, or the fluid filled membranous cover that surrounds and protects the fetus -this fluid contains cells sloughed off from the fetus (such as skin cells), and pathologists can then analyze for their chromosomal genetic makeup. -this technique does carry a small risk of miscarriage -chorionic villi sampling: physicians draw cells from the chorion villi, the finger like protections from the chorion, which is the outermost membrane that surrounds the amniotic sac -the villi help the zygot embed itself in the uterine lining and then multiply to form placenta -with sample cells, it is possible to examine the fetus’ chromosomes and genes for any signs of chromosomal disorder -genetic markers serve as indicators of many disorders caused by one or more defective genes Ex: cystic fibrosis located on the midsection of chromosome 7 -huntingtons disease: fatal deterioration of the nervous system that begins in mid adulthood, has a marker that was located near one end of chromosome 4 -alphafetorpotein assay: is a maternal blood test that can reveal fetal problems, such as Down syndrome or defects of the central nervous system, as well as the presence of multiple embryos -ultrasound: method of visualizing deep body structures, commonly used to detect gross physical abnormalities in a fetus Ethical and policy issues -even the ultrasound could result in ethical problems -in some cultures, the male is preferred over female, so determining the sex thorugh ultrasound could result in higher rate of abortions Gene therapy -gene therapy involves inserting normal alleles into patients cells to compensate for defective alleles -uses modified viruses to carry new genes into patients cells -target cells are first removed from the person’s body infused with the new gene by way of the virus, and then returned to the body -few effective treatments hav
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