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What did Morgan do/discover? Bred fruit flies;
found flies w white eyes were all male;
discovered sex linked traits
Chromosomal basis of sex determination:
humans X and Y (y determines boy in testis); XX
is girl; XY is boy; Chickens were ZW (girl, the
female determines the sex) ZZ is boy; X O
system in grasshoppers female has XX males
only have X
Sex linkage: certain trait is attached to the sex
chromosomes (USUALLY THE X); usually more
males than females get these disorders;
colorblindness, duchenne muscle dystrophy,
hemophilia
Sex linked dominant: disorder will express its
genotype if either homo dom or hetero for
females (males only have to have one dominant
allele to express)
Sex linked recessive: disorder will express its
genotype only in homo rec for females (males
only need one bad allele)
Female carriers wont show trait but carry the
recessive allele; boys either have disorder or
dont
Autosomal dominant: inherited on autosomes
phenotype expressed in either homo dom or
hetero genotype
NO CARRIERS- either have disorder or don’t
Autosomal recessive: inherited on autosomes
phenotype expressed in homo rec genotype
only
CARRIERS POSSIBLE-possible to have one
recessive allele and not express the phenotype
Autosomal dominant disorders and symptoms:
Achondroplasia dwarfism- short stature,
disproportionate arms;
Huntingtons: shows phenotype around 30 yrs
of age, nervous generation
Autosomal recessive disorders and symptoms:
cystic fibrosis: mucus buildup; chloride ions
build up on the extracellular side of membrane;
chronic bronchitis, asmtha, poor absorption of
nutrients; extra salty sweat
Albinism: no pigments
Nondisjunction – homologous chromosomes
(anaphase 1) or sister chromatids (anaphase 2)
do not separate correctly resulting in daughters
cells with either too many cs or not enough
(can be a complete set of cs or just individual
cs)
Nondisjunction during meiosis 1 pg 297 figure
15.13
Nondisjunction during meiosis 2 see above
Nondisjunction disorders and symptoms:
trisomy 21 (down’s syndrome) occurs when a
cell gets an extra copy of cs 21; mental
retardation; only autosomal nondisjunction
that can survive past a few months
Turner’s syndrome: only known viable
monosomy that can survive in humans; XO
genotype (nondisjunction of the sex cs); female,
sterile, shorter stockier appearance, web neck,
normal intelligence
Klinefelter’s: XXY (nondisjunction of the sex cs),
male phenotype, sterile, abnormally small
testis, taller, more soft rounded physical traits,
below normal intelligence
Linked genes: located close to each other on a
cs. and recombine with the same frequency
Law of segregation: alleles separate into
gametes independently of each other based on
their random alignment along the metaphase
plate
Law of independent assortment: alleles
segregate independently of each other (on non
homologous cs) during gamete formation
Barr body: the inactivated X cs (X-ist might
cover the X cs that is supposed to be
inactivated; or methylation could occur to
inactivate the X)
X inactivation: in females, one x cs is “turned
off”; tortoiseshell cats show this, all tortoise
shells are female, the fur color pattern is
determined by which X is activated. A different
X is inactivated in each cell.
Multiple alleles: more than 2 alleles exist that
can determine a trait. ABO blood typing.
Polygenetic: multiple genes influence a
character; skin color works this way
Pleiotropy: one gene influences multiple
characteristincs
Epistasis: when one gene controls the
expression of another gene at a different locus
Incomplete dominance: heterozygote
genotype has an intermediate phenotype
(between the two homo genotypes);
snapdragons red flower crossed with white
flower made pink babies
Codominance : sickle cell disorder,
heterozygous genotype shows both the
dominant and recessive phenotype, homo dom
is normal, homo rec has full blown trait
Multifactorial basis: how genotype and
environmental factors interact to influence the
phenotype; epigenetics, cancer
SRY: sex determining region on the y cs. makes
boys express their boyness
Gene Mapping: use of recombination
frequencies (or map units) to determine the
location of a gene on a cs
Monosomy: having only one copy of a cs
Trisomy: having 3 copies of a cs
Polyploidy: having an extra full set of cs.
Aneuploidy: occurs when gametes that were
products of nondisjunction mate and create a
zygote with abnormal cs number
Inversion: a segment of dna gets flipped in the
code
Translocation: a segment of dna moves to
another locus on a nonhomologous
chromosome
Deletion: removal of a dna segment
Duplication: copy of a segment of dna
Base pairings: A with T (have 2 hydrogen bonds
connecting them); C with G (have 3 hydrogen
bonds connecting them)
Purines: A and G (two rings)
Pyrimidines: T, C and U (one ring)
Chemical bonds between nucleotides:
hydrogen bonds
Chemical bonds along the phosphate backbone:
phosphodiester bonds
Antiparallel: 5’ to 3’ paired with a 3’ to 5’ strand
Difference between prokaryotic and eukaryotic
DNA replication: prokaryote has circular DNA;
one origin of replication; smaller genome;
faster replication; doesn’t have a telomere
because it is circular
Eukaryotic: linear dna, double helix, multiple
origins of replication, more complicated lots of
enzymes, have telomeres, histones
RNA primase: synthesizes RNA primer (using A,
U, C, G) about 5-10 bases; 5’ to 3’
Primer see above
DNA polymerase: enzymes that help in
replication, DNA pol 1 cleaves 2 P from the
nucleoside triphosphate base to allow the base
to join the DNA strand; DNA pol digests RNA
primer and replaces the RNA nucleotides; DNA
pol 3 attaches DNA nucleotides onto the RNA
primer sequence
Helicase: enzyme that unzips the dna strands
Topoisomerase: enzyme that untangles the dna
strand upstrand from the origin of replication
to keep the DNA helix from tangling
Single strand binding protein: protein that
holds the single strand of a DNA until it is able
to be replicated (adds stability)
DNA ligase: connects the okazaki fragments to
each other; also joins the replaced RNA primer
to the strand
Direction of replication of new strand: 5’ to 3’
Histones: keeps the DNA from tangling and
helps to organize the strand into cs.; helps in
condensing of cs.
Nucleosomes: “beads on a string” (the histone
with the DNA wrapped around it)
Nuclease: removes any “improper” DNA and
replaces it with the correct DNA
Leading strand: the template strand that gets to
replicate “smoothly” from the origin of
replication; 5’ to 3’
Lagging strand: the template strand that
replicates discontinuously from 5’ to 3’
Okazaki fragments: the fragments that “piece”
together to lagging strand, joined to each other
by DNA ligase
Telomere: a special nucleotide sequence that is
the cap on the end of eukaryotic cs that finishes
off the strand; compensates for the progressive
shortening of the cs after each replication;
allows for gametes to have the full sized cs
necessary; might be associated with cancer and
aging
Telomerase: catalyzes the lengthening of the
telomeres in eukaryotic germ cells
Heterochromatin: thickened chromatin
Euchromatin: true chromatin, less condensed
than the heterochromatin
Mendel: Austrian monk, did monohybrid
crosses and studied 7 diff traits of pea plants;
came up with dominant vs recessive; came up
with genotypic and phenotypic ratios
Sturtevant: created genetic maps based on
assumptions from crossovers
Griffith: tested the two diff types of strep
pneumonia in mice to determine outcomes;
termed “transformation” as a way that the
nonvirulent strain became virulent; injected in
mice
Avery- Mcloud- Mcarty: focused on RNA, DNA,
protein; used protease, dnase, rnase to
inactivate each individual type of potential
inheritance factor. Discovered DNA was the
transforming factor.
Hershey Chase
Messelsahn stahl