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IB Biology
Chapter 3-Genetics
• _____________________________=science
of how inherited info is passed fron one
generation to the next by using genes and
DNA
Genetics
I.Genes
• What is a gene?
• Heritable factor that consists consists of DNA and influences
a specific characteristic
• Heritable__________________________________________________
______________________________
• The estimated 21,000 genes we have are organized into
chromosomes
Passed on from
parent to
offspring,and
characteristic refers
to genetic traits,such
as eye color
A. A gene is a particular locus on a chromosome
• Gene for a specific trait occupies a specific location-LOCUS
• Geneticists map out the locus of each sequence
• Of particular significance for research if they find a specific
sequence controls a heritable factor
• eg. They have found that a locus of a gene controls
protein______________________that allows for color vision
on chromosome #1.A mutation of this gene stops a person
from making this protein properly,thus a person will not see
color-achromatopsia
• being able to see color actually means 2 things• 1-that person has DNA code for making color vision possible
or
• 2-they not have the genetic code for that
transducin
The locus is the specific position of a gene on a c’some
• 2 copies of each gene in body-same gene @
same locus on other chromosome-one from
mom and 1 from dad-not necessarily
identical
• -genes come in different forms
B. Alleles:versions of genes
• Alleles-variations/versions of genes-specific
form of gene,differing from other alleles by 1
or a few bases
• w/transducin, a single base pair sequence
between most common allele(C at position
235) and the rare mutated allele(T @ the
same position)-all the difference that decides
whether you can see color
• allows for variants in traits
• Cystic fibrosis
• difference between 2 alleles for a single trait is
the difference that causes cystic fibrosis
• a gene called CFTR-on chromosome 7-plays key
role in production of mucus
• standard version allows mucus-producing cells
to function properly
• mutation of CFTR gene causes Cystic Fibrosisabnormally excessive qty of mucus in various
organs-esp. respiratory and digestive systems
C.One base can make a difference• Importance of every letter of genetic code be in
proper place,one sm difference can be critical
• Gene-ABBCC11-determines whether-cerumen-ear
wax-wet(amber) or dry-also flaky or grey-decided by
gene on chromosome 16-G=dry ear wax (European
and African)-A variant(wet) among Asians
• This can reveal a lot about how populations have
migrated and reveal items relevant to health
• Same gene also involved with underarm sweat and
breast milk-possible link to breast cancer
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How new alleles are formed
Look @ example p.117
RNA sequences from p.117:
1-GUG GAC CUG ACU CCU GAG GAG
2-GUG GAC CUG ACU CCU GUG GAG
sequence 1-valine-histidine
a)_________b)________c)_______d)_________-glutamic acid
• sequence 2-valine-histidine
e)_________f)_________g)_______h)________glutamic acid
• use genetic code to solve the above
• this will change the structure of resulting protein-mutation
• Mutations
• Random,rare change in genetic material
• 1 type involves change in DNA sequence,which should not
happen if replication works,but such mistakes occur in
nature—eg.T may replace A-affects transcription-can be a
positive or negative effect
Are mutations good or bad for us?
• LRP5-gene that helps immune system make certain protein
that acts as a receptor on their surface/research indicates it
is used by HIV to infect cells
• Those that have mutation of this gene cannot make this
receptor protein and HIV CANNOT infect them-naturally
immune---a rare mutation
• A mutation that increases chance for survival has a better
chance for being passed on to next generation,whereas
detrimental ones are less likely to be inherited-since they
decrease chances for survival
• When mutation successfully passed on it becomes a new
_______________-new version of original gene
• We all have mutations-whether harmful,beneficial,or
neutral depends on the gene and the environment in which
you are required to survive
allele
A gene to help digestion• We have mostly been hunter-gatherers and genes are
adapted for this life
• We mostly had only drank milk-as mammals-at infancy,so
adults have become lactose intolerant and still prevalent
today(>50% of population)
• However,past 10,000 yrs we have developed an agricultural
–based lifestyle-consuming milk as adults,and many such
societies have shown an increase of those that tolerate
lactose-increasing our evolved ability to survive harsh
climatic change
• Read about gene therapy on p.120
Base substitution mutation• Results in a single letter being changed
• Could change amino acid which may or may
not be major effect
Sickle-cell disease(sickle-cell anemia)• Mutation for gene that codes for hemoglobin on RBCs in
humans(base substitution mutation)
• Gives different shape to molecule-curved sickle shape rather than
biconcave disk
• 6th codon in sequence of hemoglobin is _____,rather than GAGinstead of glutamic acid,valine instead
• hemoglobin will have different properties(valine has a different
shape and properties)
• symptoms--________________________-O2 cannot be carried as
well by sickle-shaped RBC’s
• the different hemoglobin also tends to crystallize w/in blood cellsso less flexible-get stuck in capillaries-slowing or stopping blood
flow-great pain
GTG
Weakness,fatigue,shortness
of breath
The advantages of sickle cell disease
• resistant to malaria infection
• caused by ________________mosquito
carrying______________________.
• attacks RBCs-high fever ,chills,possible death
• we carry 2 genes for RBC shape-standard shaped RBC higher
chance of getting malaria
• people w/ 1 gene for sickle shape and 1 normal
have____________________both shapes in their
bloodstream and usually do not have sickle-cell disease
Anopheles
Plasmodium
Sickle-cell trait
• have better resistance to malaria
because_____________________________.
• insufficient amounts of ____________ in sickle cells cause
Plasmodium to die
• people w/ sickle cell disease have highest resistance to
malaria
K
Of chemical
imbalances
that make the
survival of
Plasmodium
in blood more
difficult
D. A genome
• although we have mapped many genes,b there remains
much mapping yet to do and many sequences for which we
do not know function
• Sequencing DNA
• scientists have highly specialized sequencers to locate and ID
bases
• complete set of any organism’s base sequence is its
____________________.
• billions of bases –yet found in any typical cell in your body
• the complete genomes of some organism have been foundeg-Drosophila melanogaster and Esherichia coli,because
used so much in bio labs
genome
Summary of __________________technique to completing a
genome:
Sanger
• 1-Once DNA is obtained,copied and copies of fragments made_________________
• 2-To determine sequence-_________________________ attaches to one copy
of 1st fragment(we’ll call it fragment 1).It will start to add free nucleotides by
____________________________ 2 kinds of nucleotides added
• 3-Some nucleotides standard,but some special dideoxynucleotide
triphosphates(ddNTP labeled ddA,ddT,ddC,ddG-figure 3.7-p.123)-added as DNA
chain terminators-means that ______________________________________previously marked w/florescent markers to ID.Chain termination may happen
all way to end of fragment 1-but usually it stops before the end-happens on
each of many copies of fragment 1
A DNA
polymerase
A primer sequence enzyme
is added to help
The principle of
start the process
When 1 is reached,the
elongation of the strand
is stopped
complementary base pairing
Sanger Technique cont’d
• 4-result is a series of new strands(maybe dozens of bases
long,some a few less,some w/ all the bases of fragment 1)
• 5-ready for sequencing:multiple chains of varying lengths(ea
w/florescent marked end) put in order from longest to
shortest-done by using
__________________________________.
• 6__________________________________________________
______________________________________________
Gel
electrophoresis
To recognize ea letter,laser activates
florescent markers on nucleotides as they
go through the process.A sensor hooked up
to a computer analyzes the wavelength of
light and determines whether A,T,C,G
Sanger cont’d
• 7-process repeated many times-for A.T,G,and C—to
ensure no errors(there will be many copies fragment 1
so that can be checked)
• 8-when fragment 1 is done,the lab technicians must
process fragment 2,3,etc…until all fragments of original
sequence processed
• 9-Now need to put all sequenced fragments of code
together-When original sequence was chopped upmixed up and out of order….now knowing
sequence,we will know their order---basically lining up
any overlapping segments until all match
since this technique developed many ways have been
developed to analyze ea fragment only 1x-so don’t
have to make multiple copies-reduces time and cost
Be sure to see p.123!
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Human Genome Project
1990 this cooperative task was began to catalogue all the
bases in human DNA
2003-declared goal reached
now the work is to determine which sequences are genes
and which are not
human genome shows locus of any gene on any 1 of 23 prs
of chromosomes
before the project,< 100 loci for genetic diseases
known,after-> 1400 known---now 1000’s and increase
by comparing genetic makeup around the world,it tells a lot
about ancestries ,migrations,and mixing of genes in
populations over time
Using DNA to make medicines
• steps:
• 1-find beneficial molecules that are produced naturally in
healthy people
• 2-find out which gene controls synthesis of desired molecule
• 3-copy that gene and use instructions to synthesize molecule
in a lab
• 4-________________________________________
• eg.-genes controlling aging-think about ethical and financial
implications
Distribute the beneficial
therapeutic protein as a
new medical treatment
Can human genes be patented?
• 2013-US supreme court decided on case – AMP(Association
for Molecular Pathology v. biotech company(Myraid
Genetics) –Myriad had patent on BRCA genes(breast or
ovarian cancer)-AMP felt BRCA gene sequences should be
available freely for diagnostic purposes-Myriad said since
the genes occur naturally-since found in nature all genes
connected to each other but scientifically accessed so can be
patented---plaintiff said this made it impossible to get 2nd
opinion….Supreme court said unconstitutional to patent
DNA sequence found in nature
II. Chromosomes• A. The chromosome in prokaryotes
• single,long continuous,circular thread in nucleoid region
• only 1 c’some because only 1 parent
Some prokaryotes also have plasmids but eukaryotes do not
• Escherichia coli and others have small loops of DNA that
are extra copies of some of the genetic
material=plamsids
• not connected to main c’some
• replicate independently of c’somal DNA
• not req’d by cell under normal conditions,but can help
cell adapt in unusual circumstances
• also found in Archae
• used in genetic engineering
• not in eukaryotes
C. Eukaryote chromosomes
• usually DNA in form of c‘somes
• info for cell’s existence
• not visible when cell is not dividing—chromatin @ this
point.Chromatin made of________________________.
• unfolded DNA in electron microscope looks like string of
beads-Ea of the beads being a
____________________________
• Nucleosome consists of
__________________________________
Strands of DNA
and proteins
called histones
nucleosome
2 molecules of each of
4 different histones
• DNA wraps 2x around 8 protein molecules
• DNA attracted to histones
because______________________________________
• between the nucleosomes is single strand of DNA
• There is often a 5th type of histone attached to the linking
string of DNA near ea nuclesome.5th histone leads to more
wrapping-_____________- of DNA and finally to a highly
condensed or supecoiled chromosomes
• when DNA is wrapped around histones and even further
wrapped it is
_______________________________________________.So,
wrapping or packaging regulates transcription-allowing only
certain areas of DNA to be involved in making proteins
DNA is
negatively
charged and
histones (+)
packaging
In elaborate
structures,it is
inaccessible to
transcription
enzymes
D.Multiple chromosomes
E.Homologous chromosomes: the same genes but not always
the same alleles
• humans have 23 pairs of homologous c’somes-homologous
means _____________________________________
Similar in shape
and size & means
that the 2
chromosomes
carry the same
genes
• There are 2 c’somes because 1 from each parent,but not
identical because alleles for genes can differ
• locus contains different bands in picture(see color on
ppt) showing 1 allele from mom and 1 from dad
• the c’somes pictured are doubled because of
replication-They only look like this when ready to
divide-2 sister chromatids connected @
________________________ and after division will be 2
separate identical c’somes
centromere
F. Diploid and haploid cells
• _____________________-describes a nucleus w/c’somes
organized into prs homologous c’somes
• most in human body diploid w/23 sets from ea parent,ie. 46
total
• gametes are ________________ and contain 1 c’some from
each pair
• adult animal cells rarely haploid-exception male
bee,wasp,and ant haploid
• usually only gametes are haploid
diploid
Sex cells
• n -_____________________________________
• for a human egg,n=23
• __________________ are fertilized eggs and are 2n,2n=46 in
humans
Represents haploid #
and refers to # sets of
c’somes that a nucleus
can have
G. Chromosome number: a defining feature
• usually # of c’somes is a characteristic feature of the cells of
a species(exception-RBCs) and some anomalies, such as
Down’s Syndrome
• Caenorhabditis elegans-worm well studied-genome
sequenced in 1998(6 c’somes---n=3)
H. Karyograms and karyotypes
• __________________-representation of c’somes in a cell arranged in
standard format-in order by size and shape-shape depending mostly on
position of centromere
• a karyogram shows a person’s __________________-specific number
and appearance of c’somes in his or her cells
• cells obtained from amniocentesis or chorionic villus sampling are grown
in culture and karyogram made by the following steps:
• 1-cells stained and prepared on slide for examination under light
microscope
• 2-photomicrograph images are obtained of c’somes during mitotic
metaphase
• 3-images are cut out and separated-w/scissors or by computer
• 4-images of ea pair placed in order by size and position of
centromeres.Generally,by decreasing length(except sex c’somes in maleXY)
karyogram
I. Sex determination
• 23rd pr sex c’somes
• x longer than y w/many more genes/only pr of c’somes
w/different sizes and shapes
• female=XX- each gamete will have 1 x
• male=Xy and ½ gametes get x and ½ get y
• therefore 50% chance of boy or girl offspring
• non sex c’somes are called
_________________________________________-.Humans have
22 pr of autosomes
• if a trait or gene is described as autosomal,its on prs 1-22
• when a gene is more common in 1 gender,good chance it is sexlinked-either on y or x
autosomes
Autoradiography
• technique in which radiation from a substance is captured on
photographic film or by camera sensor
• autoradiograms are exposed to radiation coming off of substance itself
• DNA describe as “taking its own pictures”-used to get images of DNA
strands so length can be measured
• ____________________________-produced by injecting radioactive
materials into DNA samples that will expose the film faster-such
materials called ______________________________
• in measuring lengths of DNA strands,the DNA forming during replication
is given a radioactive form of thymidine,which is
______________________________________________________.
radioactive form added in the experiment is called 3H-thymidine(3 is
radioactive isotope of H)-used as radio marker to keep track of where
thymidine molecules are-which leaves traces on photographic film
• _________________(1862) used this technique to demo that a
bacterium’s c’some is made of a single circle of DNA replicated by being
unzipped-He called the images theta structures
Cairns’ Technique
Radio markers
A component of a DNA
nucleotide made up of a
pentose sugar bonded
to thymine
John Cairns
IV. Inheritance
• A.Mendel’s experiments with pea plants
• Who was Gregor Mendel ?
• (1865)-monk –published results on pea plants and how
they passed on characteristics-@ that time genes were not
yet known-He used term-factor-DNA not discovered
• Questions he had:
• How can I be sure I will get smooth peas and not rough
ones?
• How can I be sure the resulting plants will be short or tall?
• How can I be sure to obtain only flowers of a certain color?
Key Terminology
• Genotype-_____________-eg-Bb,GG
• Phenotype-characteristics or traits of an organismeg-hair color
• Dominant allele-an allele w/same effect on
phenotype whether homozygous or heterozygouseg- Aa with trait from A expressed-a is masked-not
transcribed or translated
• Recessive allele-an allele w/ effect on phenotype
only if homozygous,eg-aa showing recessive trait
because no dominant allele to mask it
The symbolic representation of the pr of
alleles an organisms has,usually shown
by 2 letters
• Co-dominant alleles_____________________________________
• eg-curly x straight producing degrees between 2 traits-both
alleles influence
• ________________-particular position on homologous
c’somes of a gene-ea gene has a specific place on a specific
pr. of c’somes
Prs of alleles that both
affect the phenotype
when in a heterozygous
Locus
Homozygous-having 2 identical
alleles of a gene-eg-AA,aa
Heterozygous-having 2 different
alleles of a gene-due o paternal allele
is different from maternal one…eg-Aa
• Carrier-____________________________________________
• eg-Aa-carrier for albinism- but has pigmented skin,thus
ancestor must have been albino and offspring might be
• _________________-testing suspected heterozygote plant or
animal by combining w/known homozygous recessive-Since
recessive allele can be masked-it is often impossible to tell if
homozygous or heterozygous dominant unless offspring
shows recessive trait
Test
cross
An individual who
has a recessive
allele of a gene that
does not have an
effect on
phenotype
B.Gametes only have 1 allele of each gene
• Constructing a Punnett grid• -used to show how the alleles of parents are split between
gametes and how new combinations of alleles can show
up/shows all possible combinations in a mono hybrid crossparents have different alleles and only shows 1 trait
C. The two alleles of each gene separate
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tracing inheritance using albinism as example/to set up Punnett grid:
1-Choose letter to show alleles/capital-domiant and lower caserecessive(A and a)/do not mix letters(like a P and an A)
2-Determine parents genotypes(homozygous dominant
heterozygous,or homozygous recessive)
3-Determine gametes parent could produce
4-Draw a Punnett grid
5-Work out the chances of each genotype and phenotype occurring
-ea grid shows 1 of 2 possible statistics-ea square 25%
- the probable proportions only work for large #’s of offspring
Big letter goes before small in
heterozygous
D. Fusion of gametes
• The results should be referred to as 50%
chance in humans –whereas 50% offspring in
plants,which produce much more offspring
• -each offspring result of gamete fusing-make
zygote
• deduce phenotype from genotypes----eg Aanormal pigmentation/aa-albino
E. Dominant alleles and co-dominant alleles
• Short or tall pea plants
• Mendel crossed purebred tall w/ purebred short(purebred-known to be
all tall or all short)-question was would he get all tall,some tall ,both,or
all short
• took months to confirm-but we can predict in seconds w/grid-Because
tall dominant over short
• F1(1st filial) shows results to cross
• F2-
• %chance of tall/25% chance of short….the talls have
differing genotypes
• In a real experiment,unlikely exact results---due to chance…if
there are hundreds of results---will be close to predicted