G8 Science Q4- Week 3-Patterns-of-Inheritance.ppt

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1. Patterns of
Inheritance
PREPARED BY: TYPE YOUR NAME HERE

2. S8LT -IVf - 18
Predict phenotypic
expressions of traits
following simple patterns of
inheritance

3. Genetics
Branch of science that studies how the
characteristics of living organisms are inherited
Why do you have a particular blood type or hair
color?
Why do some people have the same skin color
as their parents while others don’t?
Why is it that generation after generation of
plants, animals, and microbes look so much like
members of their own kind?
GENETICS helps you address these and
related questions more effectively.

4. ABs Babies – chips off the old
block?

5. What is a gene?
A GENE is a portion of DNA that determines a
characteristic.
Through meiosis and reproduction, genes can
be transmitted from one generation to the
next.
The study of genes, how genes produce
characteristics, and how characteristics are
inherited is a field of biology called GENETICS.

6. Science and Society
Skin color, facial features, hair are commonly used as basis for
classifying individuals by race.

Today scientists are able to compare DNA of different
races.
Assuming that individuals of a race would be more similar to
each other than they would be to individuals of a different
race, scientists did a reality check.
About 90% of all genetic variety within the human species do
not involve characteristics that we typically view as
differences between races.

7. Background Check
DNA, Genes, Chromosomes
Meiosis
Movement of chromosomes
Segregation and independent
assortment

8. What Is Meant By
`Mendelian Genetics’?
The first person to systematically
study inheritence was an
Augustinian monk named Gregor
Mendel.
Because of his early work, the study
of the pattern of inheritance that
follows the laws formulated by
Gregor Mendel is often called
MENDELIAN GENETICS.

9. Genetics Jargon
1.Gene: Mendel thought of the gene as a
particle that could be passed from parents to
offspring (children, descendants, or progeny)
Today we know that genes are actually
composed of specific nucleotide sequences
2.Locus (Plural = loci): The specific site on the
chromosome where a particular gene is
located.
3.Ploidy: Diploid (2n) / Haploid (n)

10. Diploid cells have 2 sets of
Chromosomes
2(n) cell Meiosis (n) gametes

n+n gametesFertilization 2n
Diploid Organisms result from the
fertilization of Haploid Sperm and Haploid
Egg inheriting one gene of each type from
each parent.

11. More Definitions…
Homologous Chromosomes
A pair of chromosomes that have
genes coding for the same
characteristics at corresponding
locations (loci).
Alleles
The genes at corresponding loci of a
homologous pair of chromosomes
are called alleles.

12. Alleles

13. More Definitions…
A trait
may be any single feature or quantifiable
measurement of an organism.
A characteristic, especially one that distinguishes
an individual from others.
•Eye color
•Chin shape
•Eye color
•Hair color
•Nose shape
•Hair line
•Dimples
•Space between top teeth
•Ear lobe shape

14. Pixie ear deformity
Attached earlobe Free earlobe
Trait: earlobe shapeTrait: earlobe shape
Variants: attached, free, pixieVariants: attached, free, pixie

15. More Definitions…
Genotype
›The combination of alleles located on homologous
chromosomes that determines a specific
characteristic or trait.
›It is the genetic constitution of an organism or a
group of organisms.
Phenotype
›The observable physical or biochemical
characteristics of an organism, as determined by
both genetic makeup and environmental influences.
›The outward appearance of an organism; the
expression of a genotype in the form of traits that can
be seen and measured, such as hair or eye color.

16. Genotype vs Phenotype

17. Alleles and traits
As mentioned in a previous slide, diploid
organisms may have 2 different forms of a
gene.
In fact, there may be several alternative
forms of each gene within a population.
ALLELES are different forms of a gene present
at the same locus.
Example, In people there are 2 alleles for the
gene for earlobe shape – free and attached.
Alleles are located on a pair of homologous
chromosomes – one allele on each
chromosome.

18. Alleles
E E homozygous
E e heterozygous
E e homozygous

19. Dominant Alleles
The term DOMINANT allele refers to the allele that
causes a phenotype that is seen in a heterozygous
genotype. [Ex for the trait of earlobe shape, Ee will
imply free earlobe
If a genetic trait is dominant, one copy of the gene
is sufficient for the expression irrespective of the
other allele.
Dominant traits have a 50% chance to pass from
parent to child.
Dominant alleles are usually represented with a
CAPITAL LETTER. [Ex E for free earlobes]

20. Recessive Alleles
A RECESSIVE allele is one that is phenotypically
expressed in the homozygous state but has its
expression masked in the presence of a dominant
gene.
Recessive genes are usually represented by a
lowercase letter as opposed to the uppercase
letters of dominant genes. [Ex e for attached
earlobes]
If a genetic trait is recessive, a person needs to
inherit 2 copies of the gene for the trait to be
expressed [ee].
A CARRIER is a person who is heterozygous for a trait
[Ee].
If both parents are carriers, there is a 25% chance
with each child to show the recessive trait.

22. Dominant vs Recessive
Alleles
heterozygous
homozygous
homozygous

23. Recessive alleles are not
necessarily `bad’
The term `recessive’ has nothing to do
with the significance or value of the allele
It simply describes how an allele can be
expressed.
Recessive alleles are not less likely to be
inherited but must be present in the
homozygous condition to express
themselves.
Recessive alleles are not necessarily less
frequent in a population.

24. Mendel’s Laws of Heredity
Mendel started the idea of particulate inheritance
WHY Peas ????
Seven different traits each of which is in 2
different forms. [flowers are either purple or
white and seeds yellow or green and seed
shape round or wrinkled]
Male, female reproductive parts are contained
in the same flower. Control of crosses possible.
Plant small, grows easily, quickly producing
many offspring.

26. How did he carry out his experiments?
1.Mendel would cross-pollinate ( hybridize) two
contrasting, true-breeding (homozygous for
selected trait) pea varieties (Pureline Population).
2.He got true breeders by allowing self pollination for
several generations.
3.The true-breeding parents are the P generation.
4.and their hybrid offspring are the F
1
generation.
5.Mendel then allowed the F
1 hybrids to self-pollinate
to produce an F
2
generation.

29. Mendel cross-pollinated two strains (e.g. TT  x  tt )
Trait - plant height
              Alleles - T tall, t short
P
1
cross    TT  x  ttgenotype      --    Tt
 t t   phenotype    --    Tall
TTtTt   genotypic ratio --all alike
TTtTt   phenotypic ratio- all alike
The offspring of this cross were all hybrids showing only
the dominant trait & were called the First Filial or F
1
generation
Mendel reasoned that the heritable factor for white
flowers was present in the F1 plants, but it did not affect
flower color.

31. F1 Cross
Mendel then crossed two of his F
1
plants and tracked their
traits; known as an F
1 cross
When 2 hybrids were crossed, 75% (3/4) of the offspring
showed the dominant trait & 25% (1/4) showed the
recessive trait; always a 3:1 ratio
The offspring of this cross were called the F
2 generation
Trait - plant height
              Alleles - T tall, t short
F
1
cross    Tt  x  Ttgenotype      --    TT, Tt, tt
 T t   phenotype    --    Tall & short
TTTTt   genotypic ratio --1:2:1
tTttt   phenotypic ratio- 3:1

33. Mendels Laws
Law of dominance —an allele that is
expressed over the other allele is said to
be dominant.
Law of segregation —when gametes are
formed by a diploid organism, the alleles
that control a trait separate from one
another into different gametes, retaining
their individuality.
Law of independent assortment —
members of one gene pair separate
independent of other gene pairs.

34. What Mendel Learnt from his Experiments
The hereditary determinants are of a particulate
nature. These determinants are now called genes.  
The F
1 from a cross of two pure lines contains one allele
for the dominant phenotype and one for the recessive
phenotype. These two alleles comprise the gene pair.
 Law of Dominance was based on this observation.
One member of the gene pair segregates into a
gamete, thus each gamete only carries one member
of the gene pair.  Law of segregation was based on
this.
Gametes unite at random and irrespective of the other
gene pairs involved. Law of independent assortment
was based on this.

35. Trait: Pod Color
Genotypes: Phenotype:
GG
Green Pod
Gg
Green Pod
gg
Yellow Pod
Law of Dominance states that when different alleles
for a characteristic are inherited (heterozygous), the
trait of only one (the dominant one) will be expressed.
The recessive trait's phenotype only appears in true-
breeding (homozygous) individuals

36. What Mendel Learnt from his Experiments
Law of Segregation states that each genetic trait is
produced by a pair of alleles which separate
(segregate) during reproduction
Ex. R=round seed; r=wrinkled seed
Rr
R r

37. What Mendel Learnt from his Experiments
Law of Independent Assortment states that the alleles
of different genes separate independently of each
other during gamete formation
So one trait does not influence or control another.
Example: Not all dark haired people have dark eyes
Ex. Pea seeds: R=round, r=wrinkled; Y=yellow,
y=green
RrYy
RY Ry rY ry

38. Independent Assortment of
chromosomes during meiosis

39. Single Factor Crosses
The 1
st
type of problem we will consider is
the easiest type, a single-factor cross.
A single-factor cross or mono-hybrid cross
is a genetic cross or mating in which a
single characteristic is followed from one
generation to the next.

40. Single Factor CrossesSingle Factor Crosses
If you cross a true breeding tall pea plant with
another tall pea plant, all the offspring will be tall.

T T
 T
 T
To better understand the cross, we use the Punnett
square as shown above.
T T T T
T T T T

41. Single Factor CrossesSingle Factor Crosses
•If you cross a true breeding short pea plant with
another short pea plant, all the offspring will be
short.

t t
t
t
•Thus the probability of getting short offspring is
100% or 4:4
t t t t
t t t t

42. Single Factor CrossesSingle Factor Crosses
•If you cross a tall pea plant with a short pea plant, the
offspring will be as follows
t t
T
T
•Because tall is dominant, the phenotype is 100% tall
(4:4). The genotype is also 4:4 (all will be heterozygous
tall).
T t T t
T t T t

43. Single Factor CrossesSingle Factor Crosses
•If you cross a heterozygous tall pea plant with
another heterozygous tall pea plant,
T t
T

t
•One will be homozygous tall, two will be
heterozygous tall and one will be homozygous short.
•The genotypic ratio will be 1:2:1 and the phenotypic
ratio will be 3:1, that is, 3 will be tall and 1 will be
short.
T T T t
T t t t

45. Punette Punette
Square Square
Predictions for Predictions for
F1 and F2 F1 and F2
ProgenyProgeny
F1 = P x P
F2 = F1 x F1
+
+

46. Test Cross
Test Cross is
the cross
between any
F2 progeny
and recessive
parent.
Back Cross is
the cross
between any
F2 progeny
and any
parent.

47. Single Factor Crosses:
Example
Tourette Syndrome (TS) is a neurological disorder
characterized by tics
Tics are involuntary, rapid, sudden movements or
vocalizations that occur repeatedly in the same
way.
Motor tics can be described as rapid, repetitive
muscle movements, such as rapid eye blinking or
head jerking.
Vocal tics, sometimes called phonic tics, are
phrases or sounds such as grunting, sniffing, barking,
throat clearing, and rarely, swearing.
In humans, the allele for Tourette syndrome (TS) is
inherited as an autosomal dominant allele.

48. Inheritance of Tourette Syndrome (TS)
If both parents are heterozygous (Tt), what is the
probability that they will have a child without TS?
Steps in solving heredity problems –
1.Assign a symbol for each allele [T, t]
2.Determine the genotype of each parent [Tt, Tt]
3.Determine all the possible kinds of gametes each
parent can produce [T, t]]
4.Determine all possible combinations that can result
when these gametes unite [Punette Square]
5.Determine the phenotype of each possible gene
combination

49. Allele GenotypePhenotype
T=TouretteTTTourette syndrome
t=NormalTtTourette Syndrome
ttNormal
gametesT t
T
t
Female genotype = Tt
Possible female gametes T, t
Male
genotype =
Tt
Possible
Male
Gametes T, t
1. Assign a symbol
for each allele
2. Determine the genotype of each parent [Tt, Tt]
3. Determine all the possible
kinds of gametes each parent
can produce

50. gametes T t
T TT Tt
t Tt tt
4. Determine all possible combinations that
can result when these gametes unite
[Punette Square]
GENOTYPIC RATIO IN PROGENY
1:2:1

51. 5. Determine the phenotype of each
possible gene combination
gametes T t
T TT
Tourette
Tt
Tourette
t Tt
Tourette
tt
normal
PHENOTYPIC RATIO IN PROGENY
3:1

52. Autosomal Autosomal
Dominant Dominant
MutationMutation
•Red = Mutant allele
•Mother has 2 copies
of the unaltered
chromosomes.
•50% of the children
will inherit a
chromosome with
the dominant
mutation

53. Autosomal recessive gene
Recessive genetic disorders occur when
both parents are carriers and each
contributes an allele to the embryo.
As both parents are heterozygous for the
disorder, the chance of two disease
alleles landing in one of their offspring is
25%
50% of the children are carriers.
When one of the parents is homozygous,
the trait will only show in his/her offspring if
the other parent is also a carrier.
In that case, the chance of disease in the
offspring is 50%.

55. The Double Factor cross
A double factor cross or di-hybrid cross is a genetic
study in which two pairs of alleles are followed from
the parental generation to the offspring.
Here you are working with 2 different characteristics
from each parent.
It is necessary to use Mendel’s law of independent
assortment when considering di-hybrid crosses.

56. Example
In humans the allele for free earlobes is
dominant over that for attached
earlobes.
The allele for dark hair dominates over
that for light hair.
If both parents are heterozygous for
earlobe shape and hair color, what types
of offspring can they produce? What is
the probability for each type?

57. 1.Assign a symbol for each trait
E=free earlobes; e=attached earlobes
D=dark hair, d=light hair
2.Determine the genotype and phenotype of each
combination
genotypephenotype
EE Free earlobes
Ee Free earlobes
ee Attached earlobes
HH Dark Hair
Hh Dark Hair
hh Light hair

58. Gametes
From each
parent
Genotype of both parents = EeDd
EH Eh eH eh
EH EEHH EEhh EehH Eehh
Eh EEhH EEhh EehH Eehh
eH eEHH eEHh eeHH eeHh
eh eEhH eEhh eehH eehh
3. Determine all the possible kinds of gametes each parent
can produce [EH, Eh, eH, eh]
4. Determine all possible combinations that can result when
these gametes unite [Punette Square]

59. EeHh
EH Eh eH eh
EHEEHH
P1
EEHh
P1
EeHH
P1
EeHh
P1
EhEEhH
P1
EEhh
P2
EehH
P1
Eehh
P2
eHeEHH
P1
eEHh
P1
eeHH
P3
eeHh
P3
eheEhH
P1
eEhh
P2
eehH
P3
eehh
P4
Phenotypic
Ratio
9:3:3:1
P1 Free earlobes / Dark Hair
P2  Free earlobes / light hair
P3  Attached earlobes / dark hair
P4  Attached earlobes / light hair
Phenotype
of Progeny
The probability
of having a
given
phenotype
9/16 = P1
3/16 = P2
3/16 = P3
1/16 = P4

60. He knew that he could get the F1
hybrids only if the alleles
segregated from each other during
gamete formation.
He also deduced that one of the
traits must be dominant if it is
capable of being expressed in the
heterozygous condition.
Mathematically he could prove that
if the alleles were assorted
independently, he should get a ratio
of 9:3:3:1 in his F2 generation.
He found that this was true in all 7
traits that he chose.
FORTUNE FAVORS THE PREPARED
MIND???
How Did Mendel Deduce His 3 Laws?How Did Mendel Deduce His 3 Laws?

62. Very Simple????
The relationship of genotype to phenotype is rarely
simple like in our examples because there are
exceptions to all rules.
Mendel lucked out in picking peas plants because
each trait is controlled by 1 gene, genetically
simple. But this is rare….
Lets examine some deviations from Mendels Laws…

63. Co-Dominance
In some inheritance situations, alleles lack
dominant and recessive relationships.
In cases of co-dominance, both alleles
are fully expressed phenotypically in the
heterozygous condition.
This is not consistent with Mendel’s law of
dominance.
With co-dominance, the two traits both
appear in the offspring, often showing up
in different parts of the plant or animal.

64. Co-dominance in flowers

65. Co-dominance in cattle
If a roan female is crossed with a roam male, what
would (a) the genotypic ratio and (b) the
phenotypic ratio of the progeny be?
When cattle of red coat are
crossed with the cattle of white
coat, the F
1
hybrid is found to
possess red and white hairs
which occur in definite patches
but no hair has intermediate
color of red and white. The
resulting coat color is referred
to as roan.

66. Solving problems on Co-
dominance
1. Assign a symbol for each trait
C
R
= red hair; C
W
= white hair;
2.Determine the genotype and phenotype of each
combination
C
R
C
R
= red coat, C
R
C
W
= Roan Coat, C
W
C
W
= White Coat
3.Determine all the possible kinds of gametes each
parent can produce: C
R
, C
W
in both cases
4.Determine all possible combinations that can result
when these gametes unite [Punette Square]
gametes C
R
C
W
C
R
C
R
C
R C
R
C
W
C
W
C
WC
R C
W
C
W
Phenotypic Ratio
1:2:1
Red:Roan:White

67. Incomplete Dominance
Incomplete dominance occurs in the heterozygous or
hybrid genotype where the 2 alleles blend to give a
different phenotype
Flower color in snapdragons shows incomplete
dominance whenever a red flower is crossed with a
white flower to produce pink flowers.

68. Incomplete Dominance in snapdragon flowers
C
R
C
R
C
W
C
W
C
R
C
W
C
R
C
W
C
R
C
R
C
R
C
W
C
R
C
W
C
W
C
W

69. Incomplete Dominance in
humans
The most well-studied example of
incomplete dominance in humans occurs
in the genes for curly hair.
Inheriting a gene for curly hair from one
parent and a gene for straight hair from
the other parent will give a hair texture
that is a blend of the two, wavy hair.

70. Co-dominance vs Incomplete Dominance
In plants, snapdragons exhibit incomplete
dominance for color traits.
When a red snapdragon and a white snapdragon are
crossed (mated), the color of the offspring is neither white
nor red.
Instead, the resulting snapdragon will be pink.
With co-dominance in flowers, on the other hand,
the resulting offspring between red and white
parents would not be pink.
Instead, they would be red with white spots or white with
red spots, the result of both colors being co-dominant.

71. Note:
Both incomplete dominance and
co-dominance genetics problems
work the same way.
The only difference is in the way the
cell cellular machinery works out
the phenotypic expression.

72. Multiple Allelism
Many Genes Have Multiple Alleles
A population might have more than
two alleles for a given gene.
Ex. ABO blood type genes
Even if more than two alleles exist in a
population, any given individual can
have no more than two of them: one
from the mother and one from the
father.

73. Human Blood Types
Human blood types are encoded by a single locus
with 3 possible alleles: I
A
, I
B
, I
O
.
I
A
, I
B
code for two different proteins, cell surface
antigens A and B and I
O
codes for lack of blood
antigen protein.
Since humans are diploid, we have a blood type
that depends upon the proteins on the surface of
the blood cells.
Blood group A results from the genotype I
A
I
A
, B
results from I
B
I
B
and O results from I
O
I
O
.
When the genotype is I
A
I
B
, co-dominance is seen,
and the blood type is AB

74. II
AA
andand II
BB
are dominant alleles, are dominant alleles, II
OO
(i)(i) is recessive.is recessive.

75. Human ABO Blood Group System
A man of blood type A marries a woman of blood type B.
Both are heterozgyous for blood antigen. What are the
possible phenotypes of the offspring?

76. Solving problems on multiple allelism
1.Assign a symbol for each trait
I
A
= A antigen; I
B
= B antigen; I
O
or i = no antigen
2.Determine the genotype and phenotype of each
combination
I
A
I
A
or I
A
I
O
= type A, I
A
I
B
= type AB, I
B
I
B
or I
B
I
O
= type B, I
O
I
O
= type O
3.Determine all the possible kinds of gametes each
parent can produce: I
A
, I
O
and

I
B
, I
O
Determine all possible combinations that can result
when these gametes unite [Punette Square]
gametesI
A
I
O
I
B
I
B
I
A
I
B
I
O
I
O
I
O
I
A
I
O
I
O
Phenotypic Ratio
1:1:1:1
AB:A:B:O

77. In this example, a father with blood type A and a mother
with blood type B have four children, each with a different
blood type: A, AB, B, and O.

78. Pleiotropy
Pleio = changeable
Multiple effects of a single gene on a phenotype.
Most genes are Pleiotropic, affecting more than
one phenotypic trait
Examples of diseases involving pleiotropy include:
 PhenylKetonUria
SICKLE CELL ANEMIA
 MARFAN SYNDROME

79. Pleiotropy:
1. Phenylketoneuria [PKU]-
This is a genetic disorder in which some
chemicals in the body do not break
down as they should. These chemicals
can harm brain cells.
Children born with PKU are given special
diets.
In this case, a single gene affects many
chemical reactions that depend on how
a cell metabolizes the amino acid
phenylalanine.
This phenomenon is referred to as
PLEIOTROPY.

80. PhenylketoneureaPhenylketoneurea [PKU] [PKU]

81. Pleiotropy:
2. Sickle cell
anemia
one mutant gene,
many symptoms
Single amino acid
substitution in the
hemoglobin
protein

82. Pleiotropy:
3. Marfan Syndrome
Marfan syndrome is an autosomal dominant
disorder that affects the connective tissue
but can also affect other tissues.
Symptoms include:
 disproportionately long arms and legs
 abnormally long fingers
 skinniness
 scoliosis of the spine
 abnormally shaped chest

83. Polygenic Inheritance
Polygenic inheritance, the inheritance of a
characteristic which is controlled by more than one
gene. It can cause a great range in the phenotypic out
come of an individual.
Ex. Human skin color controlled by ~5 genes.
Dark skin is dominant over light skin.
For simplicity, only 3 genes are considered.
D
1
D
2
D
3
individual has dark skin color and d
1
d
2
d
3
has
light skin color.
Crosses between two [D
1
d
1
D
2
d
2
D
3
d
3
] heterozygote
individuals would yield offspring covering a vast
range of shades.

85. Polygenic inheritance: additive effects (essentially,
incomplete dominance) of multiple genes on a single trait
AA = dark
Aa = less dark
aa - light
And similarly for the
other two genes - in all
cases dominance is
incomplete for each
gene.
Think of each “capital”
allele (A, B, C) as
adding a dose of brown
paint to white paint.

86. A brief note on skin color
Evolution has selected for greater melanin
production in areas of greater light intensity to
protect against UV radiation/skin cancer, and also
selected for less melanin production in lower light
intensity regions to allow greater vitamin D
production.
The selective advantages of particular skin colors
can now be overcome by the use of sun-block
creams and vitamin D supplements.
Point to ponder for regular users of `Fair and Lovely’
or `Fair and Handsome’

87. Black or white – does it really
matter?
Sidney Poitier and Gregory Peck

88. Sex Determination
Sex chromosomes differ between males and females of
the same species.
Autosomes carry the same genes in both sexes of a
species.
In many organisms including humans, sex is determined
by the presence of a certain chromosome combination.
In mammals, the genes that determine maleness are
located the Y-chromosome, a very small chromosome.
The X and Y chromosomes behave like homologous
chromosomes during meiosis.
Males = X Y
Females = X X

89. The Birds and the Bees… and the Alligators
Organism Sex Determination
Mammals XY = male
Birds XY = female; WZ is used for sex chromosomes in
birds
Bees Males (drones) are haploid, females (workers and
queen) are diploid
Alligators, turtles and
lizards (some sps.)
Egg incubation ; higher temperature causes the
embryo to develop into a female.
Boat Shell snails Males can become females but remain males if
they mate and remain in one spot.
Shrimp, orchids, and
some tropical fish
Males convert to females; on occasion females
convert to males, probably to maximize breeding.
African reed frog Females convert to males, probably to maximize
breeding.

90. Sex Linkage
Occurs when
genes are
located on sex
chromosomes.

91. Phenotype and Environment
The phenotype of an organism depends on
environment and genes.
How Much of each?
Ex. nutrition influences height and weight, exercise
alters build, sun-tanning darkens the skin, and
experience improves performance on intelligence
tests
Ex. The Artic Fox turns brown in summer and white in
winter so does snow shoe hair and grouse.
Ex. Sex in many animals is determined by temperature
[Ex salamander]

92. Coat Color In Arctic fox
SUMMER COAT WINTER COAT

93. Flower color in Hydrangea
Flower color in Hydrangea is
dependent on aluminum
and soil pH.
Aluminum is necessary to
produce blue pigment.
Most garden soils have
adequate aluminum, but the
aluminum will not be
available to the plant if the
soil pH is high (alkaline).

94. Flower color in Hydrangea
Blue flowers will be produced in acidic soil (pH 5.5 and lower),
whereas neutral to alkaline soils (pH 6.5 and higher) will usually
produce pink flowers.
Between pH 5.5 and pH 6.5, the flowers will be purple or a
mixture of blue and pink flowers will be found on the same
plant.

95. Fur color in cats
Cats of the Himalayan series (colour points, minks, sepias)
have heat-sensitive tyrosinase enzymes.
Normal tyrosinase converts the amino acid tyrosine into
melanin (pigment).
This enzyme denatures at normal body temperatures, the
color is formed only on the colder extremities of the body
(legs, tail ears, face).

96. Fur color in Siamese cats
This is why Siamese cats
get darker in winter and
paler in summer.
If you put socks on your
Siamese kitten for
several weeks, it would
end up with white
markings on its feet!

97. What are Identical Twins?
Identical, or monozygotic, twins develop
from a single egg/sperm combination that
splits a few days after conception.
Their DNA originates from a single source,
thus their genetic makeup is the same and
the characteristics that are determined by
genetics will be similar.
Monozygotic twins are always of the same
gender, except in extremely rare cases of
chromosomal defect.

98. Fraternal or Dizygotic Twins
On the other hand, fraternal, dizogotic
twins occur when two separate eggs
are fertilized by separate sperm in a
single ovulation cycle.
They are no more alike than any sibling
set, sharing about 50% of their genetic
markers in a unique combination of
genes from both parents.

99. Why Are Identical Twins Different?
Despite their shared genetic component, identical
multiples are unique individuals.
Though they do share similarities, they also have
many differences.
While identical twins form with the same set of
genes, human development is not just genetic.
The environment also has an impact
So, beginning in the early environment of the
womb, external influences can change the
appearance of twins.

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belong to the rightful owner. No
copyright infringement intended.