unit 3 review this version is for posting to the class web site
TRANSCRIPT
Unit 3 Review
This version is for posting to the class web site.
Genes are located on chromosomes and are the basic unit of heredity that is passed on from parent to child, through generations.
A. Explain how a chromosome mutation could occur and why mutations are detrimental to the organism in which they take place.
B. Explain why human males may suffer from having just one copy of the X chromosome, while females have two.
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O
–O O
OH
O
–O O
O
H2C
O
–OO
O
H2C
O
–O O
O
OH
O
O
OT A
C
GC
A T
O
O
O
CH2
O O–
OO
CH2
CH2
CH2
5 end
Hydrogen bond 3 end
3 end
G
P
P
P
P
O
OH
O–
OO
OP
P
O–
OO
OP
O–
OO
OP
(b) Partial chemical structure
H2C
5 endFigure 16.7b
O
H2CRemember:
phive-phosphate
What do 3 and 5 stand for???
What does antiparallel mean?
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Punnett Squares
• Punnett squares help us visualize segregation of allelles:
All F1’s show dominant trait
3:1 F2 ratio on eye color trait indicates heterozygous cross.
Operons are ___karyotic
mRNA 5'
DNA
mRNA
Protein
Allolactose(inducer)
Inactiverepressor
lacl lacz lacY lacA
RNApolymerase
Permease Transacetylase-Galactosidase
5
3
(b) Lactose present, repressor inactive, operon on. Allolactose, an isomer of lactose, derepresses the operon by inactivating the repressor. In this way, the enzymes for lactose utilization are induced.
mRNA 5
lac operon
Why can’t this dad give hemophilia to his sons?
How could a girl end up with hemophilia?
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Crossing Over
• Crossing over:
– when does this happen?
– the closer two alleles are on a chromosome, the ____ chance of being separated by crossing over.
Figure 13.11
Prophase Iof meiosis
Nonsisterchromatids
Tetrad
Chiasma,site ofcrossingover
Metaphase I
Metaphase II
Daughtercells
Recombinantchromosomes
How can you show that this pedigree is of an autosomal recessive trait?
What’s the diff between autosomal & sex-linked?
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Multiple Alleles
• Most genes exist in more than two allelic forms
– Ex: ABO blood groups
– Which type of blood cell(s)would be rejectedby a person withtype B blood?
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A B
? A B
? A B
momda
d
What is Dad if 50% of offspring come out type A, and 50% come out type B?
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12. Y yY YY Yyy Yy yy
If Y is a lethal allele, and it’s dominant, who will survive here?
Can you think of an example of a lethal dominant that does persist in the populationbecause it doesn’t kill tillmiddle age?
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Sporophytes produce __ploid ______s by ___osis.
Gametophyes produce __ploid _______s by ___osis.
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Key
Maternal set ofchromosomesPaternal set ofchromosomes
Possibility 1 Possibility 2
Metaphase II
Daughtercells
Combination 1 Combination 2 Combination 3 Combination 4
• What is Independent assortment?
– pairs of maternal and paternal homologues sort into gametes independently of the other pairs
Figure 13.10
Two equally probable arrangements ofchromosomes at
metaphase I
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W=waxy, w=dull; G=green, g=yellow
•You can do a dihybrid Punnett for this problem, (WwGg x WwGg) or…
– find probability of each character
separately (dull and green)
– then, multiply probabilities of dull
and green together.
– dull Green = wwGG or wwGg
F1 W w
W WW Ww
w Ww ww
F1 G g
G GG Gg
g Gg gg
x = ¼ x ¾ = 3/16 3/16 x 144 = 27
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How are these virusus the same?
How are they different?
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Same in all eukaryotes, from yeast to you. KNOW IT!
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What are restriction enzymes?
What are they used for?
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TransposonNew copy oftransposon
Transposonis copied
DNA of genome
Insertion
Mobile transposon
(a) Transposon movement (“copy-and-paste” mechanism)
RetrotransposonNew copy of
retrotransposon
DNA of genome
RNA
Reversetranscriptase
(b) Retrotransposon movement
Insertion
Movement of Transposons and Retrotransposons• Eukaryotic
transposable elements are of two types
– Transposons, which move within a genome by means of a DNA intermediate
– Retrotransposons, which move by means of an RNA intermediate
Figure 19.16a, b
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DNA Methylation
• methylation of cytosines on the DNA strand lead to tight packing & reduces transcription
• methylation patterns are copied during mitosis
• what do we call it if methylation is passed to the next generation?
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Figure 17.26
KNOW IT!
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• Histone acetylation …
– loosens chromatin structure and enhance transcription
Figure 19.4 b(b) Acetylation of histone tails promotes loose chromatin structure that permits transcription
Unacetylated histones Acetylated histones
Lytic & Lysogenic phage infections:
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The Telemere problem in DNA Replication
• The ends of eukaryotic chromosomes get shorter with each round of replication
Primer removed butcannot be replacedwith DNA becauseno 3 end available
for DNA polymerase
Figure 16.18
End of parentalDNA strands
Leading strandLagging strand
Last fragment Previous fragment
RNA primerLagging strand
Removal of primers andreplacement with DNAwhere a 3 end is available
Second roundof replication
New leading strand
New lagging strand 5
Further roundsof replication
Shorter and shorterdaughter molecules
5
3
5
3
5
3
5
3
3
Telemerase can restore these ends
DNA Amplification:
• PCR procedure:– use specific primers
to bind to each end of the segment you want.
– use a heat resistant DNA polymerase
– after about 20 cycles, target DNA (white boxes) greatly outnumber longer strands.
Targetsequence
53
5
Genomic DNA
Cycle 1yields
2 molecules
Cycle 2yields
4 molecules
Cycle 3yields 8
molecules;2 molecules
(in white boxes)match target
sequence
5
3
3
5
Primers
Newnucleo-tides
3
Denaturation:Heat brieflyto separate DNA strands
1
Annealing: Cool to allow
primers to hydrogen-bond.
2
Extension:DNA polymeraseadds nucleotidesto the 3 end of each primer
3
• Restriction fragment analysis– Is useful for
comparing two different DNA molecules, such as two alleles for a gene
Figure 20.9a, b
Normal -globin allele
Sickle-cell mutant -globin allele
175 bp 201 bp Large fragment
DdeI DdeI DdeI DdeI
DdeI DdeI DdeI
376 bp Large fragment
DdeI restriction sites in normal and sickle-cell alleles of -globin gene.
Electrophoresis of restriction fragments from normal and sickle-cell alleles.
Normalallele
Sickle-cellallele
Largefragment
201 bp175 bp
376 bp
(a)
(b)
How many cuts to get 9 pieces?
Why would we want to “steal” a gene and put it in a bacterial plasmid?
How could you do it?
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RNA Polymerase Binding and Initiation of Transcription
• Promoters signal the initiation of RNA synthesis
• Transcription factors
– Help eukaryotic RNA polymerase bind to promoter sequences
Figure 17.8
TRANSCRIPTION
RNA PROCESSING
TRANSLATION
DNA
Pre-mRNA
mRNA
Ribosome
Polypeptide
T A T A AA AA T A T T T T
TATA box Start point TemplateDNA strand
53
35
Transcriptionfactors
53
35
Promoter
53
355
RNA polymerase IITranscription factors
RNA transcript
Transcription initiation complex
Eukaryotic promoters1
Additional transcriptionfactors
3
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• The ribosomal subunits
– Are constructed of proteins and RNA molecules named ribosomal RNA or rRNA
Figure 17.16a
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• The DNA template (gene) determines the order of bases in the mRNA transcribed alongside.
• mRNA determines the order of Amino Acids during translation
Figure 17.4
DNAmolecule
Gene 1
Gene 2
Gene 3
DNA strand(template)
TRANSCRIPTION
mRNA
Protein
TRANSLATION
Amino acid
A C C A A A C C G A G T
U G G U U U G G C U C A
Trp Phe Gly Ser
Codon
3 5
35
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• Spliceosomes remove the __ons from pre mRNA
Figure 17.11
RNA transcript (pre-mRNA)
Exon 1 Intron Exon 2
Other proteins
Protein
snRNA
snRNPs
Spliceosome
Spliceosomecomponents
Cut-outintron
mRNA
Exon 1 Exon 2
5
5
5
1
2
3
sn = small nuclear
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Know how to use this table to determine which amino acids the mRNA is coding for!
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Substitutions
• A base-pair substitution can cause
– missense or
– nonsense
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• DNA replication is semiconservative…
– Each new daughter molecule has one old strand and one newly made strand