CHROMOSOME MUTATION

These are the processes that result in rearranged chromosome parts, abnormal numbers of individual chromosomes, or abnormal numbers of chromosome sets.

Chromosome mutations

Abnormalities from chromosomal mutations are frequently due to

1. Change in total number of chromosomes

2. Deletion or duplication of genes or segments of a chromosome

3. Rearrangements of the genetic material either within or among chromosomes

Chromosome mutatuons can occur in ______________, _______________ and ___________

somatic cells

germinal cells

gametes

How can you detect a chromosomal mutation?

1. Cytological examination of the actual chromosomes

2. Genetic analysis of inheritance

Variation in chromosome number ranges from the addition or loss of one or more chromosome to the addition of one or more _____ sets of chromosomes

haploid

In ____________, an organism gains or loses one or more chromosomes but not a complete set

aneuploidy

• The loss of a single chromosome from a diploid genome is called _________. • The gain of one chromosome results in ______.

monosomy

trisomy

In ______, the complete haploid sets of chromosomes are present.

euploidy

If more than two sets are present, the term ________ applies

polyploidy

Organisms with three sets are specifically _______.

• Organisms with four sets are __________

triploid

tetraploid

ROot cause of Anueploidy

• Nondisjucntion

• Results of chromosome structure mutations

Root cause of Euploidy

• nondisjunction

• Autoreduplication

_______________ - Multiples of the same genome

______________________ - Multiples of closely related genomes

Autopolyploidy

Allopolyploidy (amphidiploidy)

-• It is the addition of one or more extra sets of chromosomes, identical to the normal haploid complement of the same species.

• Often involving individuals within the same species.

• Infertile (propagation is by cloning).

Autopolyploidy

• It is the combination of chromosome sets from different species occurring as a consequence of hybridization

• Often involving individuals from different species

• Fertile

Allopolyploidy

It is the loss of one chromosome that produces a 2n – 1 complement.

Monoso,y (Monosomy for any of the autosomes is not usually tolerated in humans or other animals)

In general, the effects of this parallel those of monosomy.

• However, the addition of an extra chromosome produces somewhat more viable individuals in both animal and plant species that does the loss of a chromosome.

Trisomy

• 47,_________ – occurs in 1:1200 female births

• 47,____– occurs in 1:1000 male births

• 47,_________________ – occurs in 1:660 male births

• In plants, it occurs in Jimson Weed (Datura) and Rice Plant (Oryza sativa)

• XXX (Triplo-X)

• XYY

• XXY (Klinefelter Syndrome)

The only human autosomal trisomy that enables significant number of individuals survive longer than a year past birth.

Down syndrome: trisomy 21

DOwn syndrome was discovered in 1866

Langdon Down

The condition is now known to result from trisomy of chromosome 21, one of the

__ group, and is called Down syndrome or simply trisomy 21 (designated 47,21+)

G group

It is found in approximately 1 infant in every 800 live births.

Trisomy 21 down sydnrome

Striking resemblance of Down syndrom eindividuals

• epicanthic fold in each eye

• typical flat face

• round head

Those with Down syndrome are also characteristically short and may have a protruding, ________tongue (which causes the mouth to remain partially open) and short, ____hands with characteristic palm and fingerprint patterns.

furrowing

broad

What are retarededs in Down syndrom e

physical

psychomotor

mental development

Poor muscle tone is characteristic in what Syndrome

down syndrome

death in older Down syndrome adults is frequently due to ________ disease, the onset of which occurs at a much earlier age than in the normal population.

Alzheimer

Children afflicted with Down syndrome are also prone to respiratory disease and heart malformations, and they show an incidence of _________ approximately

20 times higher than that of the normal population

leukemia

Deletion of Gene or Segment in Chromosome

• Types:

1. _______________ – not at the end of the chromosome

2. _________– near the end of the chromosome

Interstitial (Intercalary)’

Terminal

It requires two breaks in the chromosome followed by loss of the chromosomal segment and rejoining of the ends.

Deletion of gene or segment in chromosome

The deleted fragment is acentric (without a _________) and will be lost upon multiple rounds of cell division

centromere

Homozygous for multigenic deletion = usually ________

lethal

Heterozygous for multigenic deletion = frequently lethal because:

a. Unmasking of ____allele on homologus chromosome without the deletion

b. Upset balance of _____ ____

a, lethal

gene number

Detection of Deletion of gene or segment

1. Genetic

• Failure of __________to survive

• Inability of the mutation to revert back to _________

• _______ ______ between the genes flanking the deletion is lower than in the wild type.

• Unmasking of a __________ allele present on the homologous chromosome without the deletion (pseudodominance of the recessive allele)

• homozygotes

• wilf type

• recombinant frequency

• recessive allele

Detection of Deletion of gene or segment

2. Cytological

• a. _____________ in meiosis

• b. Change in ___________

deletion loop

banding patterns

In humans, this syndrome results from the deletion of a small terminal portion of chromosome 5.

Cri du chat syndrome (46, 5p-)

CDC syndrome was first reported by ________ _______ in 1963, when he described the clinical symptoms, including an eerie cry similar to the meowing of a cat, after which the syndrome is named

Jérôme LeJeune

CDC syndrome is associated with the loss of a small, variable part of the short arm of ______________

chromosome 5.

nfants with this syndrome may exhibit anatomic malformations, including gastrointestinal and cardiac complications, and they are often mentally retarded.

Cri di chat syndrome

Abnormal development of the _____ and ______ (leading to the characteristic cry) is typical of this syndrome

glottis and larynx

An incidence of 1 in 25,000–_________live births has been estimated in CDC syndrome

50,000

Most often, tCDC is not inherited but instead results from the sporadic loss of __________ ______ in gametes.

chromosomal material

CDC syndrome

The length of the short arm that is deleted varies somewhat; ______ deletions appear to have a greater impact on the physical, psychomotor, and mental skill levels of those children who survive

longer

Although the effects of the CDC syndrome are severe, most individuals achieve ____and ___________skills and may be home-cared

motor and language skils

3 types od duplication

Tandem

Reverse Tandem

Nontandem

adjacent to each other in same order

Tandem

adjacent to each other in reverse order

Reverse Tandem

at a different chromosomal location

Nontandem

Tandem duplications can occur due to ___________________ where homologous chromosomes pair inaccurately during meiosis I

unequal crossing over

• Nontandem duplications may result from crossing over during meiosis within segments of the chromosome that contain __________ or ___________

inversions

translocations

Duplications are ____

rare

Heterozygous for duplication = can be ____because of imbalance generated by extra copies of the duplicated region

lethal

Homozygous for duplications is ________in medical genetics

unknown

Detection is difficult. ‘

• _______is the main tool (change in bands and duplication loop in meiosis I)

Cytology

Duplications have been proposed to be important for evolution because they provide an extra copy of genes that can then undergo ________while still leaving the original gene unaffected.

mutation

The process of gene duplication is hypothesized to be the major source of new genes, as proposed in 1970 by ________ ______ in his provocative monograph, Evolution by Gene Duplication

Susumu Ohno

Ohno’s thesis is based on the supposition that the products of many genes, present as only a single copy in the genome, are _________ to the survival of members of any species during evolution.

indispensable

Duplications can cause _________variation that might at first appear to be caused by a simple gene mutation.

• The Bar-eye phenotype in Drosophila is a classic example

phenotypic variatopn

In the early 1920s, ______________ and _______________ discovered and investigated this “mutation.”

A;lfred H. Sturtevant

Thomas H. Morgan

About 10 years later, Calvin Bridges and Herman J. Muller compared the ________ _ chromosome banding pattern of the Bar fly with that of the wild-type fly. • These chromosomes contain specific banding patterns that have been well categorized into regions.

polytene X

These observations provided evidence that the Bar phenotype is not the result of a simple chemical change in the gene but is instead a ________

duplication

The flipping of chromosomal segment relative to the rest of the chromosome

inversions

Types:

1. ___________– centromere outside the inversion

2. __________– centromere inside the inversion

1. Paracentric

2. Pericentric

Inversions require two breaks in the chromosome followed by a __° rotation of the chromosomal segment and rejoining of the ends.

180

In meiosis I cells heterozygous for the inversion, ____________ is formed to get proper alignment of the homologous chromosomes.

inversion loop

In meiosis I cells homozygous for the inversion, crossover is normal but linkage map shows inverted____ ___

gene order

Effects of inversions are _________ because there is no change in the genetic material.

However, those heterozygous for inversions produce abnormal _______ crossover products and possibly abnormal progeny (if they survive at all).

negligible

meiotic

Detection of Inversion

1. ________ - recombinant progeny are usually not recovered from heterozygotes

genetic

Detection of Inversion

2. CYtological

• If the duplication is pericentric, the__________ change

• CHange in ______ ____

• _______ _____ in meiosis for paracentric inversion

• arm lengths

• banding pattern

• Dicentric bridge

The movement of a chromosomal segment from one location to another

Translocation

Types of Translocations:

1. _________– exchange of segments

2. ___________– 1 segment moves to a new location without an exchange

1. Reciprocal

2. Nonreciprocal

__________ translocations require two breaks in two different chromosomes followed by rejoining of the ends.

reciprocal

Effects of translocations:

1. __________due to adjacent segregation in meiosis

2. _________ ____: altered expression of a gene when it is moved to a new location

1. Semisterility

2. position effetds

Transloctions

Detection:

1. Genetic

• ____________, apparent linkage of genes on separate chromosomes, and position effects

2. Cytological

• Can change the _______of the centromere,

change in the ___ of the chromosome, and ___ _________in meiosis I.

• semistreility

location

size

cross formation