Genetics
IB Biology II
Van Roekel
1/15/14
What can you tell me about this
individual based on its Karyotype.
When finished, read the article.
Topic 4.1 Notes
• 4.1.1 State that eukaryote chromosomes
are made of DNA and proteins.
• 4.1.2 Define gene, allele and genome.
• 4.1.3 Define gene mutation .
• 4.1.4 Explain the consequence of a base
substitution mutation in relation to
theprocesses of transcription and
translation, using the example of sicklecell anemia.
Background Info
• Somatic Cells – typical body cell (non-sex cell)
• Gamete – Egg and sperm cells
• Haploid – a cell containing a single set of
chromosomes (N)
• Diploid – in an organism that reproduces
sexually, a cell that contains 2 homologous sets
of chromosomes.
Meiosis
• Meiosis is for the reproduction of sex cells.
(sperm and egg)
• It makes 4 daughter cells
• They are Haploid (half the number of
chromosomes as the parent cell)
• They are not identical
Chromosome Refresher
• Chromosomes are
made of DNA and
Protein.
• Unwinding DNA is
similar to unwinding a
ball of string…the
proteins help keep it
organized (histones).
Chromosome Refresher
• In eukaryotes, chromosomes always come
in homologous pairs in somatic cells (one
from mother, one from father)
• Humans have 23 pairs of chromosomes,
or 46 total
What is a gene?
• A gene is a heritable
factor that controls a
specific characteristic
(hair color, eyes, etc.)
• Humans have roughly
30,000 genes.
• Many genes have
variations of forms
called ALLELES.
Alleles cont.
• One specific form of a gene.
• Different alleles typically only differ by a
few base pairs (nucleotides).
• Alleles of the same gene occupy the same
LOCUS on each chromosome pair. Locus
is a corresponding region on chromosome.
Genome
• The complete set of an organism’s base
sequences is called it’s genome
Mutation
• A mutation, by definition, is a change in
the genetic material. (typically rare)
• Types of mutations:
– Insertion/DeletionFrameshift mutations
– Base substitutionMissense mutations
Insertion/Deletion
• Additions or losses of nucleotide pairs in a
gene
• Has disastrous effect on resulting protein
• Results in Frameshift mutation because
reading frame (codon grouping) is altered,
usually results in nonfunctional proteins
Base Substitution
• A single base substitution may or may not
have an effect on the overall gene (and
ultimately protein). Why?
• A base substitution would be like guanine
changing to adenine in the parent
sequence.
• Missense mutation: altered codon still
codes for an amino acid, although it may
not be planned amino acid
Base Substitutions-Sickle Cell
Anemia
• DNA is mutated from CTC
to CAC, so codon GAG
converted to GUG
• Valine is added instead of
Glutamic Acid to growing
polypeptide.
• Ultimate mutation is a
“sickle” shaped cell.
• Oxygen is ultimately not
carried as efficiently
throughout the body.
Define the following terms
• Chromosome:
– Bundled packages of DNA and protein
• Gene:
– Heritable factor that controls a specific
characteristic
• Allele:
– Specific forms of a gene
• Mutation:
– Random, rare change in the genetic material
Topic 4.3 Theoretical Genetics
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4.3.1 Define genotype , phenotype , dominant allele , recessive allele, codominant
alleles , locus, homozygous, heterozygous, carrier and test cross.
4.3.2 Determine the genotypes and phenotypes of the offspring of a monohybrid
cross using a Punnett grid.
4.3.3 State that some genes have more than two alleles (multiple alleles).
4.3.4 Describe ABO blood groups as an example of codominance and multiple
alleles.
4.3.5 Explain how the sex chromosomes control gender by referring to the
inheritance of X and Y chromosomes in humans.
4.3.6 State that some genes are present on the X chromosome and absent from the
shorter Y chromosome in humans.
4.3.7 Define sex linkage.
4.3.8 Describe the inheritance of colour blindness and hemophilia as examples of
sex linkage.
4.3.9 State that a human female can be homozygous or heterozygous with respect
to sex-linked genes.
4.3.10 Explain that female carriers are heterozygous for X-linked recessive alleles.
4.3.11 Predict the genotypic and phenotypic ratios of offspring of monohybrid
crosses involving any of the above patterns of inheritance.
4.3.12 Deduce the genotypes and phenotypes of individuals in pedigree charts.
Gregor Mendel
• Father of Genetics.
• Used pea plants to
construct crosses
between different
types of pea plants.
• Crossed tall with tall;
tall with short; etc. for
generations of pea
plants
Genotype
• The symbolic pair of
alleles possessed by an
organism…represented
by two letters.
• Bb, GG, tt
Phenotype
• The physical
characteristic or trait
of an organism.
• Hair color, shell color,
eye color, etc.
• “PHysical
characteristic”
Dominant vs. Recessive
• Dominant alleles are always expressed in
phenotype when present in genotype.
– BB, Bb
• Recessive are only expressed when they
are homozygous.
– bb
Codominance
• Pair of alleles that both affect the
phenotype when present in a
heterozygote.
Homozygous vs. Heterozygous
• Homozygous- having two identical alleles
of a particular gene (ex. AA rather than
Aa)
• Heterozygous – having two different
alleles of a particular gene (ex. Aa rather
than AA)
Carrier
• An individual with a
recessive allele that
does not effect
phenotype of the
individual.
• Ex. – Aa individual is
a carrier for the
albinism gene.
Test Cross
• Testing a suspected heterozygote plant
with a known homozygous recessive (aa).
• It is very difficult to tell just by phenotype
whether or not an individual is AA or Aa
until a test cross is done.
Setting up a Punnett Grid for
monohybrid crosses
Steps of setting up Punnett
Square
• Choose and indicate a letter to show
alleles.
• Determine the parents’ genotypes
• Determine possible gametes
• Draw and complete Punnett grid
• Determine percentages of genotypes and
phenotypes
• In dogs, the gene for fur color has two alleles. The dominant allele
(F) codes for grey fur and the recessive allele (f) codes for black fur.
• The female dog is heterozygous. The male dog is homozygous
recessive. Figure out the phenotypes and genotypes of their
possible puppies by using a Punnett Square.
• The female dog has black fur. The male dog has black fur. Figure
out the phenotypes and genotypes of their possible puppies by
using a Punnett Square.
• In fruit flies, red eyes are dominant (E). White eyes are
recessive (e).
• If both flies are heterozygous, then what are the possible
phenotypes and genotypes of their offspring?
• If the female fly has white eyes and the male fly has
homozygous dominant red eyes, what are the possible
phenotypes and genotypes of their offspring?
• Using CR and CW as alleles for incomplete
dominance in snapdragon flower color,
show how two plants could have some
white-flowered offspring, pink-flowered
offspring, and red-flowered offspring within
one generation?
• Having a widow’s peak is dominant to not having a
widow’s peak. Look at the pictures of Jay Z and
Beyonce. If these two have more children, could they
have widow’s peak? Why or Why not? Use a Punnett
Square to explain your answer.
Multiple Alleles
• Occurs when there are three of more
alleles for one gene, which results in more
than two possible phenotypes.
• Example: Blood Type in humans
• Type A, B, AB, or O
Blood Type
• Three alleles for gene
– IA – Allele for type A
– IB – Allele for type B
– i – Allele for type O
• Crossing these together can create 6
possible genotypes and 4 phenotypes
Blood Type
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IAIA or IAi = Type A
IBIB or IBi = Type B
IAIB = Type AB
ii = Type O
• Determine the possible blood types of a
child whose mother has type A blood, and
whose father has type O blood. The child’s
maternal grandparents had type A blood
and type O blood.
Sex chromosomes
• 23rd chromosomes are the sex
chromosomes
• XX = Female
• XY = Male
• X chromosome is longer and contains
more genes than Y chromosome
Sex Chromosomes
• Females - all gametes
carry the X
chromosome
• Males – 50 % of
gametes carry X
chromosomes, 50%
carry Y chromosome
• Always a 50/50 chance
of male or female
Sex-Linked Traits
• Any genetic trait whose allele has its locus
(location) on the X or Y chromosome.
• Examples:
– Color Blindness
– Hemophilia
Sex-Linked Alleles
• Color Blindness
– Xb = recessive allele for color blindness
– XB = allele for ability to distinguish colors
• Hemophilia
– Xh = allele for hemophilia
– XH = allele for ability for blood to clot
Sex Linked Traits
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XBXB = phenotype for non-affected female
XBXb = phenotype for non-affected female
XbXb = phenotype for affected female
XBY = phenotype for non-affected male
XbY = phenotype for affected male
• Rare in females because require two
recessive alleles, whereas males only
require one
Sex-Linked Carriers
• Only females can be carriers of sex-linked
traits
Autosomes vs Sex
Chromosomes
• Autosomes: any chromosome that is not a
sex chromosome. 22 pairs in humans
• Genes can be autosomal or sex-linked
– Autosomal means they are found on any of
the 22 autosomes
– Sex-linked means the genes loci are on the X
or Y chromosome.
Pedigree Charts
• Pedigree – refers to the record of an
organism’s ancestry
• Constructed to show biological
relationships, specifically how traits pass
from generation to generation
Pedigree Charts – Is this trait
dominant or recessive? Is it sex
linked? Explain your answer.
Topic 10 (Genetics Continued)
• 10.1.1 Describe the behavior of the chromosomes in the
phases of meiosis.
• 10.1.2 Outline the formation of chiasmata in the process
of crossing over.
• 10.1.3 Explain how meiosis results in an effectively
infinite genetic variety in gametes through crossing over
in prophase I and random orientation in metaphase I.
• 10.1.4 State Mendel’s law of independent assortment.
• 10.1.5 Explain the relationship between Mendel’s law of
independent assortment and meiosis.
• 10.2 Dihybrid crosses and gene linkage Assessment
statements
• 10.2.1 Calculate and predict the genotypic and phenotypic ratio of
offspring of 3 dihybrid crosses involving unlinked autosomal genes.
• 10.2.2 Distinguish between autosomes and sex chromosomes.
• 10.2.3 Explain how crossing over between non-sister chromatids of
a homologous
• pair in prophase I can result in an exchange of alleles.
• 10.2.4 Define linkage group .
• 10.2.5 Explain an example of a cross between two linked genes.
• 10.2.6 Identify which of the offspring are recombinants in a dihybrid
cross involving linked genes.
Mendel’s Law of Independent
Assortment
• What does it state?
• The separation of one pair of alleles is
independent of the separation of another
pair of alleles, provided that they are on
separate chromosomes (unlinked)
Dihybrid crosses
• Consider two traits on separate
chromosomes (unlinked genes)
• Example: Seed color (yellow-Y; green- y)
Seed shape (round-R; wrinkled-r)
Two parents each of which are heterozygous for
each trait mate, what are the possible offspring’s
genotypes?
R
Y
R
y
r
Y
r
y
R
Y
RR YY
RR Yy
Rr YY
Rr Yy
R
y
RR Yy
RR yy
Rr Yy
Rr yy
r
Y
Rr YY
Rr Yy
rr YY
rr Yy
r
y
Rr Yy
Rr yy
rr Yy
rr yy
Dihybrid Crosses
• When two heterozygous parents mate, the
following phenotypic ratio is expected:
– 9:3:3:1
– 9 represents both dominant traits expressed
– 3 represents one dominant one recessive trait
– 1 represents both recessive traits
Dihybrid Practice
• A pea plant with round yellow seeds is
crossed with a pea plant that has wrinkled
green seeds, what are the possible
genotypes of their offspring?
Dihybrid Cross
• In man, assume that spotted skin (S) is
dominant over non-spotted skin (s) and
that wooly hair (W) is dominant over nonwooly hair (w). Cross a marriage between
a heterozygous spotted, non-wooly man
with a heterozygous wooly-haired, nonspotted woman. Give genotypic and
phenotypic ratios of offspring.
Dihybrid Cross
• In horses, black is dependent upon a
dominant gene, B, and chestnut upon its
recessive allele, b. The trotting gait is due
to a dominant gene, T, the pacing gait to
its recessive allele, t. If a homozygous
black pacer is mated to a homozygous
chestnut trotter, what will be the
appearance of the F1 generation?
Autosomes vs Sex
Chromosomes
• Autosomes: any chromosome that is not a
sex chromosome. 22 pairs in humans
• Genes can be autosomal or sex-linked
– Autosomal means they are found on any of
the 22 autosomes
– Sex-linked means the genes loci are on the X
or Y chromosome.
Linked Genes
• Any two genes found on the same
chromosome are said to be linked to each
other.
• Linked genes usually pass from
generation to generation together.
• Any set of genes inherited together
because they are on the same
chromosome are referred to as a linkage
group.
Linked Genes
G
L
• Linked Genes are represented as G L
• Horizontal bars represent homologous
chromosomes, with G & L being on the
same chromosome
• Genotype is read by pairing vertical
alleles, i.e. GGLL
Linked Genes
• Crossing over still produces genetic
variations of linked genes.
• Offspring can have different combinations
of alleles of linked genes by crossing over,
new forms of chromosomes are referred to
as recombinants
• 10.3 Polygenic inheritance
Assessment statement
• 10.3.1 Define polygenic inheritance
• 10.3.2 Explain that polygenic inheritance
can contribute to continuous variation
using two examples, one of which must be
human skin color.
Polygenetic inheritance
• Characteristics are influenced by two or
more genes.
• Large number of possible genotypes and
phenotypes
• Most human traits are considered
polygenetic
– eye color, skin color, height, susceptibility to
certain illnesses, etc…
Continuous Variation
• Occurs in traits with large number of
possible genotypes, which leads to an
array of possible phenotypes that
transition from one to the next.
• Continuous variation results because of
the interaction between multiple genes
• Affected by genetics, as well as the
environment
• Results in a bell shaped distribution curve
Beak Depth in Finches
Skin Color
Discontinuous Variation
• Occurs when there are no transitions
between phenotypes for specific traits.
• Distinct phenotypes that can be easily
separated
BILL
• What is the difference between continuous
and discontinuous variation?
• Continuous variation occurs in polygenetic
genes and shows a transition between
phenotype. Discontinuous variations occur
in single gene traits, and the phenotype is
either present or it is not.
Genetic Engineering &
Biotechnology
• How can I use genetics in useful, real life
applications?
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DNA Profiling
The Human Genome Project
Gene Transfer
Genetically Modified Organisms
Cloning
DNA Profiling
• Use polymerase chain reaction (PCR) to
make millions of copies of DNA
• Often amounts of DNA collected are
limited
• Using PCR, forensics experts can obtains
millions of copies of DNA in order to have
enough to analyze it.
DNA Profiling
• Gel electrophoresis separates fragments of DNA
in order to identify its origin
• DNA is broken into pieces by enzymes and
placed in the gel
• Gel is Introduced to an electrical current
– Largest particles don’t move far
– Smaller particles pass through gel
• Results in unique banded patterns for each
individual based on DNA composition
What to do with DNA Profiling?
• Match unknown samples of DNA with
known sample to see if they correspond to
determine:
– Paternity cases
– Analyze crime scenes
– Study ecosystems to see which individuals
are related
The Human Genome Project
• Started in 1990, project set out to determine the
order of all the bases A, T, C, & G in human
DNA.
• Completed in 2003, now deciphering what
sequences represent which genes
• Used to:
– Determine which chromosomes carry specific genes
– Produce beneficial medications
– Compare ancestries
Gene Transfer
• Takes a gene out of one organisms and places it in
another organism
• Possible because DNA is universal, meaning that
A,T,C,& G are used in all organisms to code for protein
• Tomatoes resistant to cold
– Proteins used by fish to resist icy temps are now produced in
modified tomatoes
• Bt-corn
– Produces toxins that kill bugs which attack it, thanks to gene
from a soil bacterium that produces a protein fatal to certain
larvae
Gene Transfer – Cutting and
Pasting
• Cut specific sequences of DNA using
enzyme endonuclease
• Paste sequences using DNA ligase
• Sequences can be copied using host cells
such as E. coli
– Splice sections of DNA into plasmids (small
circles of extra copies of DNA), place host
cells in ideal conditions to grow and replicate
Genetically Modified Organisms
• Genetically modified organisms (GMO) is one
that has had an artificial change using
techniques of genetic engineering
• Transgenic plants: undesirable genes are
removed or replaced with desired sequences of
DNA
– Tomatoes that can grow in high salinity soil
– Rice plants that produce beta carotene
• Transgenic animals
– Use animals to produce substances for medical
treatment, i.e. transgenic sheep produce Factor IX
Cloning
• Clone: genetically identical organism
artificially derived from a single parent
• Usually done using an undifferentiated, but
fertilized egg cell
• Dolly, sheep whose genetic material did
not originate from egg cell
How Dolly was made
Therapeutic Cloning
• Interested in cloning only cells.
• Stem Cell research, aka culturing stem
cells in order clone healthy cells to be
used for medical treatment
Genetics Test
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Thursday, 1/30
Covers:
Chapter 4 & 10
Meiosis
Genetics
Genetic Engineering & Biotechnology