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Unit 1: Understanding Biological
Inheritance
Bio 40S Words – What do you think
they mean?
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Genetics
DNA
Mitosis
Meiosis
Evolution
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Bacteria
Species
Ecosystem
Biodiversity
Global Warming
Mutation
WHMIS
Workplace Hazardous Materials
Information System
Mitosis Vocabulary
• Chromosomes – thread-like structures in nucleus
that contain genetic information.
• Chromatin – material in chromosomes composed of
DNA and protein.
• Chromatid – one of two distinct strands that make up
each chromosome.
• Cytoplasm – liquid area between the nucleus and the
cell membrane of a cell.
• DNA – (Deoxyribonucleic acid) - stores and transmits
genetic information - codes for proteins.
More vocabulary
• Gametes: reproductive cells – sex cells (eggs and
sperm); haploid cells ( ½ the number of
chromosomes: in humans – 23 chromosomes).
• Somatic Cells: regular body cells with full
chromosome content (diploid cells); in humans:
46 chromosomes.
• Centromere: the structure that holds the
chromatids together.
• Centriole: spindle fibre involved in cell division.
What is Mitosis?
1. Cell division in eukaryotic cells
2. Separates chromosomes into two identical
sets
3. Followed by cytokinesis - divides the nuclei,
cytoplasm, organelles & cell membrane into
two equal shares
4. result 2 daughter cells (identical to each
other and to parent cell).
5. http://www.youtube.com/watch?v=ZEwddr9ho-4
Part of the Cell Cycle
2. Different phases of mitosis.
Interphase: the time between cell division.
at least 4 things happen:
1. Cell grows (small cell  big cell)
2. ATP is made (NRG)
3. DNA replication
4. protein synthesis (enzymes)
Steps of cell division
1) Prophase
Chromatin condenses into chromosomes (46 in
humans). Nuclear envelop disintegrates.
2) Metaphase (M for middle)
Chromosomes align at the equatorial plate.
3) Anaphase
Chromosomes split apart. Sister chromatids separate.
Centromere divides.
4) Telophase
Chromatin expands. Cytoplasm divides (cytokinesis).
Two identical daughter cells are formed.
Significance of Mitosis
• 1. Development and growth: multicellular
organisms
• 2. Cell replacement e.g. cells of skin & digestive
tract, RBCs have short life span (~ 4 months)
• 3. Regeneration: e.g. starfish regenerate lost
arms
• 4. Asexual reproduction: e.g. hydra (fresh water
animal) reproduces by budding
• - vegetative propagation in plants
• Review…
•
http://www.stolaf.edu/people/giannini/flashanimat/celldivision/crome3.swf
Binary Fission
• Cell division of Prokaryotic cells
• e.g. Bacteria cells
• http://www.youtube.com/watch?v=hOyUcjqc
GpQ&feature=related
Meiosis…What is it used for?
• cell division of sex-cells
• No meiosis … too many chromosomes!! (92)
• halves # of chromosomes ~ new generations
receive correct # of chromosomes
• the egg (23) + the sperm (23) = baby (46)
=
Meiosis…What is it used for?
• It allows for genetic variation which is
important for survival of the species – we are
all not identical to each other (and so a
disease will not wipe all of us out at once).
• Leads to Evolution.
Meiosis
1. What is meiosis and what is it used for?
• Meiosis is the process of cell division that results in the
formation of gametes (sperm and egg cells).
• Remember that gametes have only ½ the number of
chromosomes than other cells in the body (somatic
cells).
• Somatic cells (human) – 46 chromosomes (diploid)
• Sex cells (human) – 23 chromosomes (haploids)
• Meiosis takes care to ensure that all gametes are
different (and that you’re not the same as your
siblings!).
2. Name and explain the different phases of
meiosis.
Meiosis is composed of 2 stages (Cell divisions)
Meiosis I
• Interphase I: chromosomes duplicate into
sister chromatids (DNA replication)
• Prophase I: chromosomes contract, nuclear
membrane disintegrates, chromosomes
partner up
Crossing Over
Sometimes during prophase, the chromotids of
each pair of homologus chromosomes may wind
around each other and pieces of chromosomes
or pairs of sister chromatids are exchanged. This
is called CROSSING OVER.
• Metaphase I: the homologus chromosomes
line up a the centre of the cell in pairs, the
centromeres attach to the spindle fibers that
run the length of the cell.
• Anaphase I: after all chromosomes are
aligned, one of each pair begins to move to
opposite poles of the cell (sister chromatids
remain connected to one another).
*This is the stage where the chromosome # is
reduced by half.*
• Telephase I – cytoplasm divides  2 haploid
cells result.
Meiosis II (may begin with a short resting phase,
called interphase II)
• Prophase II – chromosomes begin to move to
the cell’s equator (happens at the same time
for all cells). Each chromosome still has 2
sister chromatids joined at a centromere.
• Metaphase II – centromeres for each
chromosome are attached to spindle fibers
and are lined up at the cells equator.
• Anaphase II – sister chromatids are pulled
apart toward opposite poles of the cell. Each
sister chromatid takes part of the centromere
with it.
• Telephase II – cytoplasm splits for each cell
resulting in 4 haploid gametes.
Sperm = spermatogenesis; Egg = Oogenesis
•
http://www.youtube.com/watch?v=D1_-mQS_FZ0&feature=related
Meiosis ~ Gametogenesis - “creation
of gametes.”
• Spermatogenesis (the formation of sperm)
• Male testes have tiny tubules diploid cells spermatogonium (diploid cells)
• these mature to become sperm (haploid cells)
• each one spermatogonium becomes 4 sperm
• Starting at puberty, a male will produce
literally millions of sperm every single day for
the rest of his life.
Spermatogenesis
• http://www.youtube.com/watch?v=POpbN6R
HOO0
Oogenesis
• formation of haploid cells from an original diploid (primary
oocyte.
• The female ovaries contain the primary oocytes.
• Two major differences between the male and female
production of gametes.
• 1. Oogenesis only leads to the production of one final
ovum (large egg cell)
– three come out much smaller than the final ovum. These are
called polar bodies
– they eventually disintegrate, leaving only the larger ovum.
• 2. The production of one egg cell via oogenesis normally
occurs only once a month, from puberty to menopause.
Oogenesis
Part One http://www.youtube.com/watch?v=VPezOuOnq1g
Part Two http://www.youtube.com/watch?v=pK7qjcgIox0&feature=relmfu
• Meiosis ensures that:
• The chromosome # remains constant from one
generation to the next.
• That each sexually reproduced offspring will
receive 2 complete sets of genetic instructions.
• Allows for genetic diversity.
Remember
- chromosomes are found in the cell nucleus.
-
chromosomes contain genes (segments of DNA that
control heredity traits).
- chromosomes occur in pairs (homologus pairs)
More Information!
Extra Information
• n = # of chromosomes in a gamete cell
• 2n = # of chromosomes in a diploid cell
• Synapsis – is when Homologus chromosomes
pair up
Meiosis Videos
• http://www.youtube.com/watch?v=35ncSrJO
wME&feature=related
• http://www.youtube.com/watch?v=JKXAdwCi
bsA&feature=related
• http://www.youtube.com/watch?v=_IzfJSxauA&feature=related
Unit 1: Genetics
Understanding Biological Inheritance
Genetics is…
• The study of heredity.
• Heredity is the transmission of traits from parents
to offspring.
• Genes are particular segments of DNA molecules
that determine the inheritance and expression of
a particular character, e.g. eye colour.
• Alleles are two or more alternative forms of a
gene, e.g. Tall (T) vs. short (t); alleles occupy the
same locus on homologus chromosomes.
More vocabulary
• Genotype: the genetic composition of an
organism – the combination of alleles, e.g. Bb.
• Phenotype: The physical appearance of the
individual based on their genotype, e.g. brown
eyes.
• Punnett square: A chart that shows possible
genotype/phenotype of offspring.
• Homozygous: Two copies of the same
allele/gene, e.g. BB or bb
• Heterozygous: Two different alleles for the same
trait, e.g. Bb.
More vocabulary
• Purebred: The same as homozygous; used in
breeding circles.
• Hybrid: Same as heterozygous.
• Dominant traits: Expressed in both homozygous
and heterozygous forms (alleles denoted by
capital letters, e.g. B)
• Recessive traits: Expressed in only the
homozygous form (alleles denoted by lowercase
letters, e.g. b)
• Carrier: Someone who carries the recessive allele
but doesn’t show it.
Recessive vs. Dominant
• When the dominant allele is present in the
genotype, it is always expressed in the
phenotype.
• When the recessive allele is present in the
genotype, it is only expressed in the phenotype if
it is paired with another recessive allele for the
same trait.
• Example: Brown eyes (B) are dominant to blue
eyes (b).
– BB = homozygous dominant (brown eyes)
– Bb = heterozygous (brown eyes)
– bb = homozygous recessive (blue eyes)
Mendel
• Gregor Mendel (1822 – 1884) is considered the
“Father of Genetics”
– He was the first to study how traits were passed from
one generation to the next.
– Studied garden pea plants in an Austrian monestary.
– Pea plants were ideal to study heredity because they
self-pollinate  the sperm fertilizes the ovule in the
same plant.
– In a pea plant, the gene for producing seed shape may
occur in two alternative forms: R = round; r = wrinkled
Questions on Gregor Mendel
1. What were the 7 traits that Mendel studied in pea
plants?
2. Which were the dominant of these traits? (Name all
7)
3. Which were the recessive of these traits? (Name all 7)
4. What is self-pollination?
5. What is cross-pollination?
6. What is purebred?
7. What is hybrid?
8. What is segregation?
Generations
• Parent Generation (P): The parents used for the
first cross represent the parent generation.
• F1 generation: The progeny (product) produced
from a cross between two parents.
• F2 generation: The progeny resulting from selfhybridization or inbreeding of F1 individuals.
• Inbreeding: When individuals of a progeny are
allowed to cross with each other (e.g. 2
individuals from F1)
Mendel’s Pea-Plant Traits
Trait
Phenotype
Genotype
(dominant, recessive)
Seed shape
Round, wrinkled
Seed colour
Yellow, green
Seed coat colour
White, grey
Pod shape
Smooth, wrinkled
Pod colour
Green, yellow
Flower position
Axial, terminal
Plant height
Tall, short
RR, Rr, rr
YY, Yy, yy
WW, Ww, ww
NN, Nn, nn
GG, Gg, gg
AA, Aa, aa
TT, Tt, tt
Punnett Squares
The segregation and combination of the male and
female cells (gametes) produced as a result of
meiosis can be expressed using a simple matrix.
This checkerboard diagram is used to illustrate the
possible results of a cross between the gametes of
two individuals.
• Test Cross: involves crossing a F1 offspring with a
homozygous recessive individual. Used to
determine whether or not the F1 offspring is
purebred or not.
Punnett Squares
• Shows what type of offspring could be, given the
genotypes of the parents. Probability
(predictions) of offspring genotypes/phenotypes.
• Mendel’s plants  Tall = TT or Tt; short = tt
• If a heterozygous tall pea plant (Tt) was crossed
with a homozygous recessive short pea plant (tt),
what will the offspring’s genotypes be? What
would the phenotypes be?
t
t
Genotypes 
Phenotypes 
T
Tt
Tt
t
tt
tt
2 Tt : 2 tt ratio
2 tall : 2 short ratio
50% probability that the offspring will be
tall or short.
Males vs. Females
What is the difference between boys and girls?
• Both males and females have 44 autosomes (non-sexlinked chromosomes), and 2 sex-linked chromosomes.
Sex-linked chromosomes (2 each)
• The males have an X chromosome and a Y
chromosome.
• The females have two X chromosomes.
How much of our DNA is the same as another human of
the same sex?
• 99%. One percent of our DNA is different.
A Karyotype of a Human’s
Chromosomes - Male or female?
Mendel’s Laws
Law #1: Law of Gene Character
Genetic characters are controlled by unit factors
(genes) that exist in pairs in individual organisms
and are passed from parents to their offspring.
When two organisms produce offspring, each
parent gives the offspring one of the factors
from each pair.
Law #2: Law of Dominance
When two unlike factors responsible for a single
character are present in a single individual, one
factor can mask the expression of another
factor. That is, one factor is said to be dominant
to the other, which is said to be recessive.
Law #3: Law of Segregation (also known as The
Principle of Segregation)
During the formation of gametes, the paired
factors separate (segregate) randomly so that
each gamete receives one factor or the other.
Law #4: Law of Independent Assortment (also
known as The Principle of Independent Assortment)
• During gamete formation, segregating pairs of
factors assort independently of each other.
(In humans, that’s a mixture of 30,000 genes!)
• The inheritance of a pair of alleles affecting one
characteristic occurs independently of alleles
affecting any other characteristic.
• i.e. The gene that controls one trait has no
influence on the inheritance of a gene with a
different trait.
e.g. The gene that controls if a seed is round or wrinkled is
NOT linked to the gene that determines if the seed if yellow
or green (the genes are not on the same chromosome).
Laws of Segregation and Independent Assortment on Wikipedia
BIG Punnett Square
(Di-hybrid Cross)
• P-Generation
– Cross a homozygous Tall, Green plant (dominant
traits) with a short, yellow (recessive) plant. What
will the offspring look like?
T = Tall
tt = short
G = Green
gg = yellow
Cross TTGG (homozygous dominant)
with ttgg (homozygous recessive)
What are the genotypes of the gametes for each plant in the
cross? (Remember, offspring inherit one allele from each
parent.)
“Male” plant gametes = TG, TG, TG and TG
“Female” plant gametes = tg, tg, tg and tg
tg
tg
tg
tg
TG
TtGg
TtGg
TtGg
TtGg
TG
TtGg
TtGg
TtGg
TtGg
TG
TtGg
TtGg
TtGg
TtGg
TG
TtGg
TtGg
TtGg
TtGg
• F1 generation
– All genotypes are TtGg
– All phenotypes are 100% Tall and Green
– Each offspring produced will have the same
genotype and phenotype.
• Now cross two members of the F1 generation
to interbreed and work out the geno and
phenotype combinations. How many will be
Tall and Green?
– What are the genotypes of each parent plant?
– What are the genotypes of each parent plant’s
gametes (list all combinations).
– Test cross.
– Find the genotype and phenotype ratios.
TtGg x TtGg
“Male” gametes = TG, Tg, tG and tg
“Female” gametes = TG, Tg, tG and tg
TG
TG
Tg
tG
tg
Tg
tG
tg
TTGG TTGg TtGG
TtGg
TTGg
TTgg
TtGg
Ttgg
TtGG
TtGg
ttGG
ttGg
TtGg
Ttgg
ttGg
ttgg
Genotypic ratio
1 TTGG : 2 TTGg :
2 TtGG : 4 TtGg :
1 TTgg : 2 Ttgg :
1 ttGG : 2 ttGg :
1 ttgg
Phenotypic ratio
9 Tall, Green plants
3 Tall, yellow plants
3 Short, Green plants
Short, Yellow plants
Genotypic ratio
1 TTGG : 2 TTGg : 2 TtGG : 4 TtGg : 1 TTgg : 2
Ttgg : 1 ttGG : 2 ttGg : 1 ttgg
Phenotypic ratio
9 Tall, Green plants
3 Tall, yellow plants
3 Short, Green plants
1 Short, Yellow plant
All Heterozygous
Dihybrid Crosses will
give this 9:3:3:1
ratio.
Exceptions to Mendel’s Laws
• We know today that there are many
exceptions to Mendel's laws (i.e. not
every gene has alleles that are strictly
dominant or recessive). Does this mean
that Mendel was "wrong"? NO, it means
that we know more today about
disesase, genes, and heredity than we
did 150 years ago!
Exceptions to Mendel’s Laws
Exceptions to Mendel’s Laws
1) Co-dominance – Both alleles are dominant
and expressed.
e.g. A red flower crossed with a white flower =
red and white striped flowered plants.
RR = red flowers
WW = white flowers
RW = red and while striped flowers
What would the phenotopic ratio be if we
crossed 2 RWs?
R
W
R
RR
RW
W
RW
WW
Genotypic ratio -- 1 RR : 2RW : 1 WW
Phenotypic ratio – 1 red : 2 striped : 1 white
2) Incomplete dominance – Both alleles are
blended and expressed.
e.g. Cross a red flower and a white flower = pink
flowers.
RR = red flowers
WW = white flowers
RW = pink flowers
What would the phenotopic ratio be if we
crossed 2 RWs?
R
W
R
RR
RW
W
RW
WW
Genotypic ratio -- 1 RR : 2RW : 1 WW
Phenotypic ratio – 1 red : 2 pink : 1 white
3rd Exception – Lethal Alleles
• Sometimes the phenotype that results from
an allele is death.
• These usually occur as mutations with
essential genes (genes you need to survive).
• Both dominant and recessive lethal alleles
exist.
Lethal Genes
e.g. Huntington’s Disease
– caused by a dominant and lethal gene
– HH and Hh – homozygous and heterozygous
– person lives long enough (usually in their 30s) so they
can pass along the lethal gene onto their offspring.
e.g. Cystic Fibrosis
– caused by a recessive and lethal gene
– life expectancy is 5 years without medical treatment
– this genetic disorder exists only in the homozygous
state (cc), This occurs when both parents are carriers
(Cc).
e.g. Dwarfism - dominant (A)
– lethal only in the homozygous state (AA)
– Spontaneous abortion
– in the heterozygous state, dwarf only.
•
•
•
AA (die early)
Aa (dwarf)
aa (normal)
• What is the probability that two dwarfs have a
normal child?
More Exceptions
4) Polygenic Traits – traits controlled by a
number of different genes.
– These genes may be on the same or on different
chromosomes.
– Each gene contributes a small but equal increment
to the trait being expressed – a blending result.
– Examples include skin colour, height, eye colour,
hair colour and intelligence.
Is this an Exception to Mendel?
5) Multiple Alleles – three or more alleles of the
same gene but only 2 alleles required to express
the trait. e.g. blood groups
• 3 alleles
• 4 different blood types
• Determined by the presence or absence of
antigens in the blood.
Genotype
Phenotype
IAIA
Type A Blood
Iai
Type A Blood
IBIB
Type B Blood
IBi
Type B Blood
IAIB
Type AB Blood
ii
Type O Blood
What are the genotypes/phenotypes from the
cross between 2 AB parents?
A
B
A
AA
AB
B
AB
BB
Genotypes: 1 AA, 2 AB, 1 BB
Phenotypes: 25% Type A, 50% Type AB, 25% Type AB
Show the cross between IAi and Ibi.
Mendel’s 6th Exception
Sex-linked Traits (X-linked)
• Many genes are located on the X chromosome
(some on the Y). X is a BIG chromosome, Y is a smaller
chromosome.
• In humans there are 46 chromosomes, and only 2
of these are sex chromosomes (X and Y). Females
– XX and males – XY. The other 44 are autosomes.
• In meiosis, each egg (female) gives an X
chromosome.
• In meiosis, each sperm (male) give either an X or
a Y chromosome (50 : 50).
At fertilization (XX cross XY)
X
X
X
XX
XX
Y
XY
XY
Geno: 2 XX and 2 XY Pheno: 50% girl, 50% boy
• Because the Y chromosome carries less DNA than the
X, the Mendelian ratio does not occur if the genes
are on the X chromosome and are recessive.
Fruit Flies
• Thomas Morgan (scientist) experimented with
Drosophilias (fruit flies). He found that there
were more white-eyed males than white-eyed
females. Red-eyed fruit flies were dominant.
R = Red, r = white
Genotypes
Phenotypes
XRXR
female, red eyes
XRXr
female, red eyes
X rX r
female, white eyes
XRY
male, red eyes
X rY
male, white eyes
Cross a homozygote red-eyed female with a
white-eyed male.
XRXR cross with XrY
XR
XR
Xr
XR Xr
XR Xr
Y
XRY
XRY
Geno
½ X RX r
½ XRY
Pheno
½ female carrier
½ red-eyed male
All the offspring will have red eyes; no whiteeyed children.
• Morgan showed that in his experiments with
fruit flies that some off-spring had
combinations different from either parents 
these new individuals are called
RECOMBINANTS
– e.g. In fruit flies body colour and wing size are
linked most of the time, but not always. This can
be explained by crossing over that takes place
during the first meiotic division when the
homologus chromosomes are paired.
Colourblindness
• A recessive sex-linked disorder. Most common
is red-green colourblindness.
B = normal, b = colourblind
•
XBXB
cross
XB
XB
Xb
XBXb
XBXb
How many of the children
b
XY
will be colourblind?
Y
XBY
XBY
Geno
2 XBXb, 2 XBY
Pheno
50% Normal males
50% Female carriers
Other diseases on X-chromosome –
hemophilia, muscular dystrophy.
Can a female
carrier have
a
colourblind
girl?
Chromosomal Mutations
• These occur when segments of chromosomes, entire
chromosomes or even complete sets of
chromosomes are involved in genetic change. Effects
are due to chromosome arrangement.
A. Changes in chromosome # -- Non-disjunction.
•
•
This is a failure of chromosomes to separate
during meiosis, resulting in an abnormal number
of chromosomes.
A gamete with +/- 1 chromosome may still fuse
with an egg or sperm. Some survive, but most
are spontaneously aborted.
Common Non-Disjunction Disorders
1. Down Syndrome, “Trisonomy 21”
The individual is born with 47 chromosomes.
The frequency of this disorder increases with increasing
maternal age. 50% of individuals die by 4 yars old, most
live to approximately 30 years.
Mental retardation, epicanthic folds of the eye, short
stature, cardiac deformities.
1. Turner Syndrome (XO)
45 chromosomes, short stature, webbed neck, may have
slight retardation, immature genitals, sterile, occurs 1 in
2500 conceptions.
2. Kleinfelters Syndrome (XXY)
47 chromosomes, tall, female-like breasts, some mental
retardation, (50%), normal male, small testes, produce
little to no sperm.
It doesn’t matter how many X-chromosomes a person has,
it is the presence of the Y chromosome that makes an
individual a male. The Y chromosome has a “testis
determining factor” that stimulates growth of male
reproductive organs.
Chromosomal Mutations (cont’d)
B. Changes in chromosomal structure (3 types)
i.
Deletions: due to loss of a chromosome segment after
breakage. e.g. Cri-du-chat Syndrome – deletion of
portion of the arm of chromosome 5, severe retardation,
cry resembles cat.
ii. Duplication: due to an increase in the amount of genetic
material carried by a chromosome, usually not
problematic and may actually provide genetic variation.
iii. Inversions, Shifts and Translocations: when a portion of
the chromosome breaks and it may rotate 180° and
reattach on the same/original chromosome (inversion), if
it becomes inserted in a different region on the same
chromosome (shift), or may be inserted on a
different/non-homologous chromosome (translocation).
These all may be fatal to the zygote.
“Boy With an Extra X”
• Read story. Answer these questions in your notebook
(complete sentences).
1. Did Tom have all the Kleinfelter’s Syndrome
symptoms? Which symptoms did he have?
2. What is a good idea to have genetic testing
done? Why?
3. How would you feel if you found out you had a
genetic disorder? What would you do about it?
4. Likewise if you were to have a child with a
genetic difference. How would you feel? What
would you do?
Pedigrees
• A geneticist’s way of charting the passage of a
trait from one generation to the next.
• In a pedigree chart, the darkening of
squares/circles indicates the presence of the
Pedigree Legend
trait under study.
How to Draw a Pedigree
Draw a pedigree for a family with a husband and
wife and 4 children – 2 girls and 2 boys (in that
order). The father is colour-blind (a recessive,
sex-linked disorder) and the two girls are
carriers.
I
II
Xd
Y
XD XDXd XDY
XD XDXd XDY
Draw a pedigree of the following family showing
the genotypes of all the individuals (place these
under the individuals in the pedigree). Make a
legend!
The inability to roll one’s tongue is recessive to
the ability to roll one’s tongue. It is not sexlinked.
A man who can roll his tongue marries a woman
who cannot roll her tongue. They have three
children: a daughter followed by two sons. The
oldest and youngest children are able to roll
their tongues, but their middle child cannot.
The daughter marries a man who is able to roll
his tongue, but their son cannot. The middle
son marries a woman who is able to roll her
tongue. The youngest child marries a woman
who is unable to roll her tongue, but they have
no children.
Pedigree Activities
•
•
•
•
Pedigree Studies
Applied Genetics
Baby Pierre
Queen Victoria
Heredity vs. Environment
• “Nature vs. Nurture”
• Environment can affect the expression of a gene.
– e.g. 1) height genes determine approximate height of
a person, but environment (i.e. nutrition may or may
not allow the individual’s potential to be reached
(poor diet  shorter ; poor posture  shorter)
– e.g. 2) intelligence affected by prenatal environment
(alcohol – FAS – or nutrition), as well as early years
environment (stimulating environment helps mental
development).
– e.g. 3) high blood pressure: predisposition
inherited, but influenced by diet, exercise, stress,
smoking.
– e.g. 4) coat colour in siamese cats: dark legs, face
and tail result because the black fur gene can only
be expressed at cool temperatures; fur at
extremities darkens, fur close to warm body stays
light.
Karyotypes
• The “picture” of the arrangement of all
homologus pairs of chromosomes in an
individual.
• Karyotypes can be studied to identify the
presence of a genetic disorder, and pinpoint
the chromosome responsible for the disorder.
Normal Karyotype (Male)
Down Syndrome (Trisonomy 21) in a Female
Klinefelter Syndrome (XXY)