Chapters 12,13,14

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Midterm 2

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polygenic diseases
ex: heart disease & cancer; based on many genes working in concert with a given set of genes only predisposing a person toward sickness or health, rather than insuring it
x-linked disorders
the genes that cause them lie on the x-chromosome; claim more male victims than femaleex: hemophilia, duchenne muscular dystrophy, red-green color blindness
recessive disorder
a genetic disorder that will not exist in the presence of a functional allele
autosomal recessive disorder
a recessive dysfunction related to an autosome  (chromosomes other than X & Y)ex: albinism, sickle-cell anemia, cystic fibrosis (impaired lung function, lung infections), phenylketonuria (mental retardation), Tay-Sachs disease (nervous system degeneration in infants), Werner syndrome (premature aging)
a person who does not suffer from a recessive genetic debilitation, but who carries an allele for it that can be passed along to offspring
dominant disorders
genetic conditions in which a single faulty allele can cause damage, even when a second, functional allele exists
autosomal dominant disorder
dominant genetic disorder caused by a faulty allele that lies on an autosomal chromosomeex: Huntington disease (brain tissue degeneration), Marfan syndrome (ruptured blood vessels), Polydactyly (extra fingers or toes)
a familial history intended to track genetic conditions; can be used to ascertain whether a condition is dominant or recessive, and x-linked or autosomal; can help establish probabilities for future inheritance of a condition; can sometimes tell which persons are heterozygous carriers of a recessive conditiona circle is used for a female & a square for a male
a condition in which one or more entire sets of chromosomes has been added to the genome of a diploid organism; occurs if 2 sperm fuse with one egg, or when meiosis malfunctions & gives a single egg or sperm 2 sets of chromosomes; tolerated well in some organisms, but disastrous in humans
a condition in which an organism has either more or fewer chromosomes than normally exist in its species' full set; in humans occurs commonly & goes largely unrecognized; most common outcome is a pregnancy that ends in miscarriage (except in the case of an additional chromosome 13, 18,21)
a failure of homologous chromosomes or sister chromatids to separate during meiosis; when it occurs in meiosis I, 100% of the resulting gametes are abnormal, when in meiosis II, only 50% are abnormal
Down syndrome
the most well-known outcome of aneuploidy in humans; caused by the gain of an additional chromosome 21; results in smallish, oval heads, IQs well below normal, infertility in males, short stature & reduced life span in both sexes; when women pass the age of about 35, their risk of giving birth to a Downs child increases dramatically
Turner syndrome
produces people who phenotypically female, but who have only one X chromosome and 45 chromosomes; sometimes referred to as XO ("O" signifying the missing X); have ovaries that don't develop properly (causing sterility), are generally short, & often have brown spots (nevi) over their bodies
Klinefelter syndrome
XXY men, phenotypically male in most respects, tend to have a number of feminine features: some breast development, a more feminine figure, tall stature, dysfunctional testicles, & lack of facial hair
It is also possible for aneuploidy to occur in mitosis
as one cell divides, a given chromatid can fail to migrate to its proper "pole" and 1 resulting daughter cell ends up with 1 chromosome too many, while the other ends up with 1 chromosome too few; most die, but a few can survive; often seen in cancer cells (almost all cancerous cells have the wrong number of chromosomes in them)
occurs when a chromosome fragment breaks off & then does not rejoin any chromosomeex: cri-du-chat syndrome (mental retardation, improperly constructed larynx)
PGD (preimplantation genetic diagnosis)
can be used by couples who have no known genetic risk factors but are having a hard time conceiving or those who are likely to produce a child with genetic defects; a large proportion of human embryos have genetic defects; screens embryos for genetic problems before implantation in the uterus, increasing chances of bringing a child to term; 
genetic screening that can provide information about conditions; cells are obtained from an embryo that has been developing in a mother's uterus for a minimum of 14 weeks
when a chromosome fragment rejoins the chromosome it came from, with its orientation "flipped" so the fragment's chemical sequence is out of order
a chromosomal abnormality that occurs when two chromosomes that are not homologous exchange pieces, leaving both with improper gene sequences, which can have phenotypic effects
adding a gene to a chromosome can "free up" an existing gene, such that it can be altered through mutation and go on to produce a new protein for an organism
Thomas Hunt Morgan of Columbia
linked a particular trait to a particular chromosome, and found that genes on the same chromosome do not always travel together; used fruit flies
molecular biology
the investigation of life at the level of its individual molecules
James Watson & Francis Crick
presented the structure of DNA in 1953
X-ray diffraction
a purified form of a molecule is bombarded with X rays, the way the rays scatter on impact then reveals something about the structure of the molecule; Rosalind Franklin; aided the discovery of DNA's helical structure
DNA structure
1. phosphate group2. deoxyribose (sugar)3. 4 possible DNA bases: adenine, guanine, thymine, cytosine
the linkage of a phosphate group, a deoxyribose molecule, & one of the four bases; the basic building block of DNA
A always pairs with _G always pairs with _
any two bases that can pair together across the helix are said to be ___________
each single strand of DNA serves as a ________ for the synthesis of a new single strand
because new nucleotides can be added to only one end of a DNA strand, the nucleotides are added in _________ directions
enzymes that unind the double helix, separating its two strands to make the bases on them available for base pairing
DNA polymerases
move along each strand of the double helix, joining together nucleotides as they are added, one by one, to form the new, complementary strands of DNA; perform a kind of DNA editing- they remove a mismatched nucleotide and replace it with a proper one
a permanent alteration of a DNA base sequence
point mutation
a permanent mistake; a mutation of a single base pair in the genome; a slight change in the chemical form of a base might cause a G to link up with a T- the cell might "repair" this error in a way that a permanent mistake is made
somatic cells
cells that do not become eggs or sperm; most mutations come about in these cells
germ-line cells
cells that become egg or sperm
germ-line cell mutations
heritable, can be passed on from one generation to the next
substances that can mutate DNAex: cigarette smoke, UV light
UV light
a form of radiation that can link adjacent T's together in a single strand of DNA; sometimes it even causes both strands of the DNA helix to break. enzymes can successfully repair the damage, or the cell will recognize that the damage can't be repaired, in which case it may either stop dividing (senescence) or commit suicide (apoptosis), or simply keep on dividing (in which case a mutation occurs)
when a cell recognizes that damage cannot be repaired and stops dividing
cell suicide
it is the order of _____ _____ that determines which protein is synthesized
amino acids
an organelle, located in the cell's cytoplasm, that is the site of protein synthesis; mRNA sequences and amino acids come together to make proteins
the process by which the genetic information encoded in DNA is copied onto messenger RNA; a section of DNA unwinds & nucleotides on it form base pairs with nucleotides of messenger RNA, creating an mRNA chain, which then leaves the cell nucleus, headed for a ribosome in the cell's cytoplasm, where translation takes place
the process by which information encoded in messenger RNA is used to assemble a protein at a ribosome; Amino acids join the mRNA chain at the ribosome, brought there by transfer RNA molecules. the length of messenger RNA is then "read" within the ribosome, resulting in a chain of amino acids linked together in the order specified by the mRNA sequence; when the chain is finished and folded up, a protein has come into existence
structurally very similar to DNA; usually single-stranded; uses adenine, guanine, cytosine, and uracil (instead of thymine); 
RNA polymerase
enzyme that unwinds the DNA sequence and then strings together the chain of RNA nucleotides that is complementary to it, thus producing the initial RNA chain
messenger RNA
a type of RNA that encodes and carries to ribosomes information for the synthesis of proteins
how many DNA basis does it take to code for an amino acid?
an mRNA triplet that codes for a single amino acid or a start or stop command in the translation stage of protein synthesis
genetic code
the inventory of linkages between nucleotide triplets and the amino acids they code for
transfer RNA
a form of RNA that, in protein synthesis, binds with amino acids, transfers them to ribosomes, and then binds with messenger RNA
the end of the transfer RNA molecule that can bind with a particular codon on the mRNA transcript
ribosomal RNA
a type of ribosomal RNA that, along with proteins, forms ribosomes
the mRNA codon ___ is the usual "start" codon for a polypeptide chain
termination codons
3 separate codons that don't code for any amino acid but act as stop signals for polypeptide synthesis
the genetic code is redundant
almost all the amino acids are coded for by more than one mRNA codon
with only a few exceptions, the genetic code is universal in all living things
evidence that all life on Earth is derived from a single ancestor
"junk DNA" 
DNA that came mostly from outside our genome (from invading viruses) and has never had any function within it
promoter sequence
the site on a segment of DNA to which RNA polymerase attaches prior to beginning transcription
enhancer proteins
does not code for anything; serves as a binding site for proteins that help get RNA polymerase position at the promoter
sequences that are cut out in editing out noncoding sequences; "intervening" sequences; account for more than 90% of the length of the average human gene
sequences that are retained in editing out noncoding sequences; most are "expressed" as proteins
alternative splicing
another form of genetic regulation; a process in which a single primary transcript can be edited in different ways to yield multiple messenger RNAs; thanks to alternative splicing, our genes can produce many more proteins
when some classes of introns insert themselves into genomes such as ours, a mutation can occur within the intron, creating a new exon (the mutation turns a noncoding DNA sequence into a coding sequence)
enabled organisms such as ourselves to produce more proteins and hence to become more complex; humans have more introns per gene than any other organism
not all RNA codes for proteins
transcription an also produce noncoding RNA segments that are regulatory
only about 22 bases long; reduce production of specific proteins, most commonly by interfering with messenger RNAs, actually targeting them for destruction
there is ______ relationship between the number of genes an organism has and the complexity of that organism
complexity is necessary because it enables life