PSYB32H3 Chapter Notes -Chorionic Villus Sampling, Chromosome Abnormality, Turner Syndrome

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28 Feb 2013
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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
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-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
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-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
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Document Summary

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. 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 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 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.

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