Unit 3 Review This version is for posting to the class web site.

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.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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?


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?


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?


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?


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?


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?


Sporophytes produce __ploid ______s by ___osis.

Gametophyes produce __ploid _______s by ___osis.


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


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


How are these virusus the same?

How are they different?


Same in all eukaryotes, from yeast to you. KNOW IT!


What are restriction enzymes?

What are they used for?


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


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?


Figure 17.26

KNOW IT!


• 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:


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?


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


• The ribosomal subunits

– Are constructed of proteins and RNA molecules named ribosomal RNA or rRNA

Figure 17.16a


• 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


• 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


Know how to use this table to determine which amino acids the mRNA is coding for!


Substitutions

• A base-pair substitution can cause

– missense or

– nonsense


• DNA replication is semiconservative…

– Each new daughter molecule has one old strand and one newly made strand

Unit 3 Review This version is for posting to the class web site.

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