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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