7.0 mutation

7.0 MUTATION

Lecture 1 Learning Outcomes At the end of this topic, students should be able to: Explain mutation Classify mutation State types of mutation Define mutagen State types of mutagen Explain gene mutation/point mutation Classify gene mutation

Describe base substitution as point mutation

Explain frameshift mutation

Describe base insertion as a frameshift mutation

Describe base deletion as a frameshift mutation

Blue lobster a kind of mutant arising from a mutation

E.g: blue lobster is an example of mutant

(An organism carrying a gene that has undergone a mutation)

What is mutation?

7.1 CLASSIFICATION & TYPES

MUTATION Definition : Mutations are changes in the DNA

sequence of an organism caused by changes in genes or chromosomes

Down syndrome

Mutation produces new trait that can be inherited

Mutation occurring in gamete cell are inherited to offspring

Mutation occurring in the somatic cell can only be inherited by daughter cells produced by mitosis

It changes the phenotypes or physiological process in the organism

Mutation can occur in during DNA replication

Many mutations result in the change of a protein therefore the protein cannot function as it should be

Classify of mutation

1. Gene mutation / Point mutation

2.Chromosomal mutation

Types of mutation

Spontaneous mutation

Induced mutation

Types of mutation

1. Spontaneous mutation:

Mutation that occurs in natural conditions, errors happens spontaneously during DNA replication. (e.g. non-disjunction during metaphase I or II)

2. Induced mutation

organism exposure to mutagens.

Mutations can be induced by several methods. The general approaches used to generate mutations are radiation and chemical.

Mutagen

A mutagen is an environmental agent that increases the chances of a mutation, induces changes in DNA.

Types of mutagen

Chemical mutagen :E.g: colchicine and ethidium bromide

Physical mutagen : E.g: Ultraviolet rays and gamma rays

7.2 Gene mutation / Point mutation

Mutation that change the sequence of bases in the DNA of a gene

the mutation can take the form of :

1. base substitution

2. base insertion

3. base deletion

4. base inversion

Base substitution – the replacement of one nucleotide & its partner with another pair of nucleotides Base insertion – addition of 1 or a few base pairs in the nucleotide sequences in genes Base deletion – loss of 1 or a few base pairs in nucleotide sequences Base inversion – 2 base pairs or more are inverted in nucleotide sequence

AGCTTA

TCGAAT

AGCGTTA

TCGCAAT

AGCGTA

TCGCAT

AGCTA

TCGAT

AGTCTA

TCAGAT

Normal

Base Deletion Base Substitution

Base Insertion Base Inversion

Point / Gene Mutation

Gene Mutation / Point Mutation

Base substitution – the replacement of one nucleotide & its partner with another pair of nucleotides

3 bases / nucleic acid = 1 codon ( code for 1

amino acid)

Changes in codon may cause: a) NONSENSE MUTATION b) MISSENSE MUTATION c) SILENT MUTATION

Base Substitution

Change in a nucleotide pair may transform 1 codon into another that is translated into the same amino acid = SILENT MUTATION

Change 1 amino acid to another one = MISSENSE MUTATION

Missense mutations is a mutation that results in one wrong codon and one wrong amino acid in a polypeptide or protein

NONSENSE MUTATION = happened if a point mutation changes a codon for an amino acid into a stop codon, translation will be terminated prematurely.

Example of disease cause by point mutation (base substitution) SICKLE CELL ANAEMIA (DISEASE) Sickle cell anaemia happens because of point

mutation

Happens because base substitution of a single nucleotides in the DNA’s template

strand There is a change that leads to the production of

an abnormal protein

Amino acid valine replaces glutamic acid at a single position in the protein (-strand)

In the DNA T is substituted by A

Mutant mRNA has U instead of A

There is a slight change in the primary structure of hemoglobin

Normal red blood are disk-shaped, but in sickle-

cell anaemia, the abnormal hemoglobin molecules tend to crystallize, deforming some of the cells into a sickle shape

Defective red blood cell

Patient suffer from anaemia Hb is not efficient of transporting oxygen

Frameshift Mutation

Involve insertion/deletion of a base pair or more into the nucleotides sequence of DNA

Many of these deletions/insertion start in

the middle of a codon Shifting the reading frame by one or two

bases

Frame shift mutations cause the gene to be read in the wrong three base groups (codon)

From the mutation point,

It abrupt the coding sequence of amino acid.

Changes in codons results changes in amino acids

Different polypeptide is produced

Effect ~ usually harmful to human

E.g.: Major Thalasemia

(mutant homozygote alleles)

Base Insertion

Addition of one or a few bases to triplet sequence in DNA

Normal code: GAG-GUU-CCU-AAA-CCU

glu val pro lys pro

Insertion : GAG-GUU-CCU-GAA-ACC

glu val pro glu thr

Base Deletion loss of 1 or a few base pairs in nucleotide

sequences Normal code: GAG-GUU-CCU-AAA-CCU

glu val pro lys pro

Deletion : GAG-UUC-CUA-AAC-CUA

glu ser leu asn leu

Why deletion of one base pair in any part of the DNA strand can be lethal compared to the substitution of one base pair? It causes frame shift mutation

When the deletion starts in the middle of a codon, it shifts the reading frame by one base

Frame shift mutations cause gene to be read in the different three base groups

From the mutation point, it disrupts the coding sequence of amino acid

Changes in codons result in changes in amino acid sequence and different polypeptide is produced

As a result, different protein is produced

Lead to non-functional protein

The effect is usually harmful to human

Lecture 2 Learning Outcomes At the end of this topic, students should be able to: Explain chromosomal mutation Classify chromosomal mutation Explain chromosomal aberration State and describe types of chromosomal

aberration

7.3 Chromosomal mutation

As alterations in the number or structure of the chromosome.

It can be passed to the offspring (inherited) if mutation occurs in gamete cell

Increase variation

Occur during :

1. When chromosome are condensing and being pulled apart in mitosis or meiosis.

2. When DNA replicates in interphase.

3. During crossing over in prophase I.

Classify of chromosomal mutation: a) Chromosomal aberration (change in

structure of chromosome) b) Alteration of chromosome number

(change in chromosome number)

a. Chromosome Aberration

Rearrangement a certain segment or parts of chromosome (change of structure)

are most frequently formed during mitosis or meiosis

Types of chromosomal aberration

4 types :

Deletion

Inversion

Translocation

Duplication

ABCDEFGHI

Break off

Break off

ABC

GHI

ABCGHI

Losing middle section

Deletions – happen to chromosome 5

ABCDEFGHI

Break off

Break off

ABC

GHI

ABCGHI

Losing middle section

•When the chromosome breaks at two places and lead to the loss of the middle segment •The segment lost may contain one or more genes •The remaining end of chromosome will join again and become shorten

Loss of a small part of the short arm of chromosome 5 caused by a deletion

Cri du chat is a rare syndrome (1 in 50,000 live births)

The name of this syndrome is French for "cry of the cat," referring to the distinctive cry of children with this disorder.

The cry is caused by abnormal larynx

development, which becomes normal within a few weeks of birth.

Infants with cri du chat have low birth weight and may have respiratory problems.

Some people with this disorder have a shortened lifespan, but most have a normal life expectancy.

Where does the abnormal chromosome 5 come from? In 80 percent of the cases, the chromosome carrying the deletion comes from the father's sperm.

Inversion : a region of a chromosome breaks off and rotates through 180° before rejoining the chromosome

ABCDEFGHI

break

off

break

off

ABC

GHI

DEF

ABCFEDGHI

Two types of inversion that are pericentric inversion and paracentric inversion: Pericentric inversion include centromeres

during mutation

Paracentric inversion does not include centromere during mutation

There is no change in the genotype

But phenotype may changes

Also known as the position effects

Duplication : a region of a chromosome becomes duplicated; an additional set of genes exists

When a single locus or a large piece of a chromosome is present more than once in the genome

ABCDEFGHI

ABCDEFGHIFGHI

Additional set of genes

Translocation

Involves a region of a chromosome breaking off And rejoining at either end of the same chromosome Or another non-homologous chromosome

Translocation : involves a region of a chromosome breaking off and reattach to another part of the same or other chromosome.

ABCDEF

Break

off

WXYZ

ABC

DEF

WXYZ

DEF

WXYZ

ABC

1

2

Simple translocation/ non-reciprocal translocation

Chromosome segment translocate to another

region of the same chromosome or another chromosomes

Interchromosomal translocation occurs when segment of one chromosome translocate to another chromosome

Intrachromosomal translocation occurs when segment of one chromosome translocate to another region of the same chromosome

Reciprocal translocation

- Occurs when exchanges of segment between two nonhomologous chromosomes

- Changes in position of the genes involved - There is no gain or loss of genetic materials - No changes in genotype but phenotype may

changes - Reciprocal translocation can change the linkage

groups

Lecture 3 Learning Outcomes

At the end of this topic, students should be able to: Explain alteration of chromosome number State the types of the alteration of chromosome

number Explain aneuploidy - explain sex chromosomal abnormalities - explain autosomal abnormalities Explain autosomal abnormalities and their effects - Monosomy - Trisomy

b. Alterations of chromosome number

Alterations of chromosome number is the changes in the chromosome number

Caused by non-disjunction:

If non-disjunction occurs during meiosis I homologous chromosome fail to separate

If non-disjunction occurs during meiosis II sister chromatid fail to separate

Types alteration of chromosome number

a. aneuploidy (2n+1,2n+2, - -)

b. polyploidy (3n, 4n,….)

Alterations of chromosome number consist of : 1.Aneuploidy Condition where the diploid cell (2n) gain or

loss 1 or more chromosomes. Can cause by non- disjunction

Aneuploidy

Aneuploidy

a)Abnormalities in the sex chromosome number

Non disjunction during spermatogenesis

Non disjunction during oogenesis

b)Abnormalities in the autosomal chromosome number

a)Abnormalities in the sex chromosome number: Non disjunction during

spermatogenesis

If non disjunction during meiosis I & II

sperm will have the abnormal sex chromosome : XY, XX @ YY

Abnormal sperm x ovum (X)

Klinefelter syndrome (XXY)

Super male syndrome (XYY)

3X female (metafemale, XXX)

Turner

XY

X X

XXY XXY

Non disjunction during meiosis

I XY

XY XY

XY XY

Klinefelter syndrome Klinefelter syndrome

XY

X X

XXX XYY

Non disjunction during meiosis

II XX

Y X

YY

XX YY

Super male syndrome 3X female (metafemale

Non disjunction during Oogenesis

If non disjunction happened

Some ovum might not carry any chromosome X & some others might carry 2 chromosome X

Abnormal ovum (O) x sperm

Turner syndrome (XO)

YO : dead

Abnormal ovum (XX) x sperm

Klinefelter syndrome (XXY)

3X female

XX

X X

XXX XO

Non disjunction during meiosis

I

XX 0

X X

XX

XXY

Y Y

YO

XX

0

0

XX

0 0

Symptoms

Klinefelter Syndrome (XXY) : 2n+1 (Trisomy) – Sterile male (small testis), failed to produce

sperm – Feminised male (soft voice) & big breast, long

hand and leg – Non disjunction during oogenesis and

spermatogenesis Turner Syndrome (XO) : 2n-1 (Monosomy) – Sterile female (failed to ovulate) – Small breast & undeveloped ovary – dwarf, deaf, abnormal heart & low IQ

Klinefelter Syndrome Turner Syndrome

b) Autosomal abnormalities caused Monosomy and Trisomy

Monosomy (2n - 1) occurs when an individual has only one of a particular type of chromosome.

Trisomy (2n + 1) occurs when an individual has three of a particular type of chromosome (Down Syndrome / Trisomy 21)

Abnormalities in autosomal

chromosome number

Non disjunction could also happen to autosome

E.g. : Down Syndrome – non disjunction of chromosomes 21 during gametogenesis

Individual with 47 chromosomes (instead of 46) appearance of 3 chromosome at chromosome 21

No 21chromosome move to the same pole

MEIOSIS I

MEIOSIS II

Sperm with 2 chromosome at chromosome 21

Zygote with 3 chromosome at chromosome 21

Second polar body

Polar body 1 lack of chromosome 21

Down Syndrome Down syndrome (Trisomy 21) is caused by

three copies of chromosome 21.

result from non-disjunction of

chromosome 21

Fusion gametes between chromosome (n+1) and normal gamete (n), produced embryo with chromosome (2n+1) : Trisomy; eg. Down’s syndrome

Non disjunction Normal

Non disjunction Normal Normal Normal

MEIOSIS I

MEIOSIS II

Trisomy 21: Symptoms of Down Syndrome Suffer mild to severe mental retardation Short stocky body type Large tongue leading to speech difficulties Those who survive to middle-age, a propensity to develop Alzheimer’s Disease

Symptoms of Monosomy 21

Short distance between eyes

Large ears

Contracted muscle

Euploidy

• Changes of the chromosome number which involved the whole chromosome set (3n, 4n, 5n, ..)

• Occurred when a set of chromosome did not separate during gametogenesis

• Common in plants than in animals

• Gametes fusion will produce cell or organism which have more than 2 set of chromosome

• The condition of having more than two sets of chromosomes ( 3n, 4n, 5n, ………) known as polyploidy

• 2 types of polyploidy - Autopolyploidy

- Allopolyploidy

Genome Polyploidy 3n Triploid 4n Tetraploid 5n Pentaploid 6n Hexaploid 8n Octaploid 10n Decaploid

Triploid (3n) occurs when

i) a gamete (2n) fused with a normal gamete (n)

ii) chromosomes disable to segregate during meiosis to produce diploid gamete

iii) gamete from tetraploid organism (4n) fused with diploid organism gamete (2n).

Tetraploid plants can be produced by :

1) Somatic duplication of chromosome number

i) Involving homologous chromosome set

P : AA (2n)

(Duplicate)

F1: AAAA (4n)

7.3 Alteration of chromosomes number Karyotype

LECTURE 3 Learning Outcomes

At the end of this topic, students should be able to: e) Explain alteration of chromosome number f) State the types of the alteration of chromosome

number i) aneuploidy ii) euploidy / polyploidy

g) Explain aneuploidy i) explain sex chromosomal abnormalities ii) explain autosomal abnormalities

h) Explain autosomal abnormalities and their effects

i) Monosomy (monosomy 21) ii) Trisomy (Down syndrome / trisomy 21)

i) Explain sex chromosomal abnormalities

i) Klinefelter syndrome (47 , XXY)

ii) Turner syndrome (45 , XO)

j) Explain euploidy ( polyploidy )

i)Autopolyploidy

ii) Allopolyploidy

Alterations of chromosome number

• Alterations of chromosome number is the

changes in the chromosome number in a chromosome set.

• The change is caused by non-disjunction in anaphase I or anaphase II of meiosis process.

Disjunction: chromosomes separated to the opposite poles during meiosis

What is the Non-disjunction process?: failure of pair of chromosome to separate and to move to the opposite poles both sets of chromosomes pass to the same pole of the cell

When non-disjunction could occurs?

If non-disjunction occurs during meiosis I homologous chromosome fail to separate

If non-disjunction occurs during meiosis II sister chromatids fail to separate

Non-disjunction will lead to aneuploidy Nondisjunction in Anaphase I & II during

meiosis process

Aneuploidy is a condition in which the number of chromosomes is abnormal due to extra or missing chromosomes, in other words, it is a chromosomal state where the number of chromosomes is not a multiple of the haploid set.

Normal diploid species have 2n chromosomes, where n is the number in the haploid set.

Aneuploid individuals would have 2n-1 chromosomes (monosomy), 2n+1 chromosomes (trisomy), or some other such arrangement.

A change in the number of chromosomes can lead to a chromosomal disorder. Aneuploidy is common in cancerous cells.

What is meant by aneuploidy?

Anaphase I

44 XY

44 XX

22 X

22 Y

22 X

22 X

22 X

22 X

22 Y

22 Y

22 X

22 X

22 X

22 X

22 X

22 Y

22 Y

22 X

22 X

Anaphase II

Normal disjunction

Non disjunction Normal

Non disjunction Normal Normal Normal

Anaphase I

Anaphase II

Nondisjunction

Half the daughter cells produced have an extra chromosomes (n+1) whilst the other half have a chromosome missing (n-1)

Fusion gametes between chromosome (n+1) and normal gamete (n), produced embryo with chromosome (2n+1) : Trisomy; eg. Down’s syndrome

Fusion gametes between chromosome (n-1) and normal gamete (n), produced embryo with chromosome (2n-1) : Monosomy; eg. Turner Syndrome

Nondisjunction in anaphase of meiosis

Autosomal abnormalities

i.Monosomy 21

ii.Trisomy 21 (down syndrome)

Monosomy 21 Trisomy 21

Normal Human Karyotype

Normal chromosomes Normal human somatic cells have 46 chromosomes: 22 pairs, or homologs, of autosomes (chromosomes 1-22) and two sex chromosomes. This is called the diploid number. Females carry two X chromosomes (46,XX) while males have an X and a Y (46,XY). Germ cells (egg and sperm) have 23 chromosomes: one copy of each autosome plus a single sex chromosome. This is referred to as the haploid number. One chromosome from each autosomal pair plus one sex chromosome is inherited from each parent. Mothers can contribute only an X chromosome to their children while fathers can contribute either an X or a Y.

Monosomy

Monosomy is the presence of only one chromosome from a pair in a cell's nucleus.

Monosomy 21

The syndrome is generally lethal and only several cases of living newborn infants have been reported, most of whom die between 3 weeks and 20 months of life but some survive into childhood.

Monosomy 21 Symptoms: - Short distance between

eyes - Large ears -Contracted muscle -Large nose with a broad base -cleft lip and/or palate -Short neck -Short thorax -Small hands and feet, overlapping and/or flexed fingers and toes, -hyperactive reflexes (nervous system)

Trisomy

A trisomy is the presence of three, instead of the normal two, chromosomes of a particular numbered type in an organism.

Thus the presence of an extra chromosome 21 in human autosome with many individuals surviving for more than a year is called trisomy 21, or Down’s

Syndrome

Trisomy 21

Down syndrome/trisomy 21

Symptoms Short stature. A child often grows

slowly and, as an adult, is shorter than average.

Weak muscles (hypotonia) throughout the body. A child may seem to have less strength than other children of the same age.

A short, wide neck with excess fat and skin. Usually, this trait is less obvious as the child gets older.

Short, stocky arms and legs. Some children also have a wide space between the big toe and second toe.

Where does the extra chromosome come from?

In 90% of Trisomy 21 cases, the additional chromosome comes from the mother's egg.

This karyotype is an example of Down Syndrome (trisomy 21), the most common numerical abnormality found in newborns. It is characterized by an extra chromosome 21 and the karyotype is written as: 47,XY,+21. The key to the karyotype description is as follows: 47: the total number of chromosomes (46 is normal). XY: the sex chromosomes (male). +21: designates the extra chromosome as a 21.

Human trisomy A trisomy can occur with any chromosome. Most

trisomies, like most other abnormalities in chromosome number, result in distinctive and serious birth defects. Most trisomies result in spontaneous abortion; the most common types that survive to birth in humans are:

Trisomy 21 (Down syndrome) Trisomy 18 (Edwards syndrome) Trisomy 13 (Patau syndrome) Trisomy 9 Trisomy 8 (Warkany syndrome 2) Trisomy 16 is the most common trisomy in

humans, occurring in more than 1% of pregnancies. This condition, however, usually results in spontaneous miscarriage in the first trimester.

7.3 Sex chromosomal abnormalities

• Aneuploidy can invlove sex chromosomes causing various syndromes mentioned below:

i. Klinefelter syndrome (47,XXY)

ii. Turner syndrome (45,XO)

i) Explain sex chromosomal abnormalities

i. Klinefelter syndrome (47, XXY)

ii. Turner syndrome (45, XO)

LEARNING OUTCOMES

Sex Chromosome Aneuploidy

Abnormalities in the sex chromosome number

Non disjunction during spermatogenesis

Non disjunction during oogenesis

Abnormalities in sex chromosomes

Spermatogenesis Klinefelter syndrome (XXY)

Super male syndrome (XYY) 3X female (metafemale, XXX)

Oogenesis Turner syndrome (XO) Klinefelter syndrome (XXY)

3X female (XXX)

Non disjunction during

spermatogenesis

If non disjunction in Anaphase I & II during meiosis

sperm will have the abnormal sex chromosome : XY, XX @ YY

Abnormal sperm x ovum (X)

Klinefelter syndrome (XXY)

3X female (metafemale, XXX)

Super male syndrome (XYY)

XY

X X

XXY XXY

Non disjunction

during anaphase I

XY XY

XY

X X

XXX XYY

Non disjunction

during anaphase II

XX YY

Non disjunction during Oogenesis

If non disjunction happened

Some ovum might not carry any chromosome X & some others might carry 2 chromosome X

Abnormal ovum (O) x sperm (X or Y)

Turner syndrome (XO)

YO : dead

Abnormal ovum (XX) x sperm (X or Y) 3X female

Klinefelter syndrome (XXY)

XXX XXY XO YO

Ovum with 2

X chromosome

Ovum without

X chromosome

Non disjunction

Normal sperm

XX

X Y X Y

O

Klinefelter syndrome (47,XXY)

Klinefelter's syndrome, 47, XXY or XXY syndrome is a condition caused by a chromosome nondisjunction in males; affected individuals have a pair of X sex chromosomes instead of just one

It is named after Dr. Harry Klinefelter, a medical researcher at Massachusetts General Hospital, Boston, Massachusetts, who first described this condition in 1942. The condition exists in roughly 1 out of every 500 males.

Symptoms delayed speech sensory integration difficulties, including sensitivity to noise hypotonia or low muscle tone auditory processing problems language-based learning disabilities, including reading difficulties anxiety depression gynecomastia or swelling of breast tissue during puberty Feminised male (soft voice) Sterile male (small testis), failed to produce sperm long hand and leg

Turner syndrome (45,XO) Turner syndrome results from a chromosomal abnormality in which a female infant is born

Only one X chromosome (instead of the usual two) or is missing part of one X chromosome.

Turner syndrome

Symptoms short stature "webbing" of the skin of the neck (extra folds of skin extending from the tops of the shoulders to the sides of the neck) a low hairline at the back of the head low-set ears abnormal eye features, including drooping of the eyelids abnormal bone development, especially the bones of the hands and elbows a lack of breast development at the expected age (usually by age 13) an absence of menstruation (amenorrhea) a larger than usual number of moles on the skin

T U R N E R SYNDROME PATIENTS

Abnormal Phenotype

Klinefelter Syndrome (XXY) : 2n+1 (Trisomy)

Sterile male (small testis), failed to produce sperm

Feminised male (soft voice) & big breast, long hand and leg

Non disjunction during oogenesis

Turner Syndrome (XO) : 2n-1 (Monosomy)

Sterile female (failed to ovulate)

Small breast & undeveloped ovary

dwarf, deaf, abnormal heart & low IQ

Klinefelter’s syndrome Turner’s syndrome

7.3 Euploidy (Polyploidy)

Learning Outcomes: j) Explain euploidy / polyploidy i. Autopolyploidy ii. Allopolyploidy

• Describing a nucleus, cell or organism that has an exact multiple of the haploid number (n) of chromosomes.

* For example: diploid (2n), triploid(3n), and tetraploid

(4n) nuclei or cell are euploid

* Compare aneuploidy

Euploidy (Polyploidy)

EUPLOIDY

Changes of the chromosome number which involved the whole chromosome set

Occurred when a set of chromosome did not separate during gametogenesis

Common in plants than in animals

Gametes fusion will produce cell @ organism which have more than 2 set of chromosome

Cell with only ONE set of chromosome: monoploid, this occurrence is usually rare and cannot survive.

Cell with 3 or more chromosome set : polyploid

2 types of polyploidy

i) Autopolyploidy

ii) Allopolyploidy

Polyploidy

The condition of having more than two sets of chromosomes ( 3n, 4n, 5n, ………)

Genome Polyploidy 3n Triploid 4n Tetraploid 5n Pentaploid 6n Hexaploid 8n Octaploid 10n Decaploid

Polyploidy

• Polyploidy usually causes death in animals, but many plants survived polyploidy.

• This is because plants are less sensitive to sex determination and most plants are capable of self-fertilization.

• Polyploidy occurs frequently in plant population and is very, very rare in animals.

• Polyploidy plants are usually more resistant to pests and diseases and are stronger than most diploid organisms.

• These beneficial characteristics have influenced the evolutionary patterns of many plants, such as wheat, maize and a few types of weeds.

TRIPLOID

Triploid (3n) occurs when

i) a gamete (2n) fused with a normal gamete (n)

ii) chromosomes disable to segregate during meiosis to produce diploid gamete

iii) gamete from tetraploid organism (4n) fused with diploid organism gamete (2n).

TETRAPLOID

Tetraploid plants can be produced by :

A) Somatic duplication of chromosome number

i) Involving homologous chromosome set

P : AA (2n)

(Duplicate)

F1: AAAA (4n)

ii. Involving non-homologous sets P : AA (2n) BB (2n) G : A B F1: AB (sterile)

doubling of chromosome number

AABB (fertile)

B) Fusion of two diploid gametes P : AA (2n) AA (2n) G : AA AA FI: AAAA

Polyploidy

Autopolyploidy : Is an individual that has more than two chromosome sets, all derived from a single species

The chromosomes set are homologous with the parent cell

Involve homologous chromosome

Autopolyploidy is caused by non-disjunction in meiosis that cause the formation of diploid gametes

The fertilization of a normal gamete (haploid) with diploid gamete will produce triploid organism.

Importance in economic value which autopolyploid plants produce flowers and fruits bigger than normal diploid plants

Allopolyploidy A polyploid resulting from 2 different species (hybridization) interbreeding and combining their chromosomes

The chromosome sets are different to parental cell

Homologous chromosome sets not involve

A good example is the wheat plant, Triticum aestivum, which is a 6n organism with 42 chromosomes.

T. aestivum has chromosomes complements from 3 species of plants

F1 hybrids produced from different species are usually sterile (haploid set of chromosome from one species cannot pair during meiosis with the haploid set from the other species) Chromosome number in a sterile hybrid becomes doubled and produces fertile hybrids (synapsis and segregation can occur and viable gametes can be produced) Importance in producing new species

Triticum monococcum (Einkorn wheat)

AA (2n = 14 )

Triticum searsii (Wild grass)

BB (2n = 14 )

Triticum aestivum

AA BB CC

(2n = 42) Hexaploid of original einkorn wheat

Triticum turgidum (Emmer wheat)

AA BB (2n = 28 )

X

Triticum tauschii (Wild grass)

CC (2n = 14 )

X

Sterile hybrid AB

Sterile hybrid ABC

Example 1

Spartina alternifora BB (2n=70)

Spartina maritina AA (2n=56)

x

n=28 n=35

AB

Spartina anglica (fertile) AABB

4n=126

duplication

2n =63

Hybrid Spartina x townsendii

Example 2

Primula floribunda AA

(2n = 18 ) n=9

Primula verticillata BB

(2n = 18 ) n=9

X

Primula kewensis Sterile hybrid

AB (2n = 18)

Doubling of chromosome number

Primula kewensis fertile AABB (4n = 36)

tetraploid

Example 3