Suppose that eye gene is sex linked, and wing is autosomal. A red eyed female, long wing is crossed to a male with yellow eyes, vestigial wings. Diagram the cross if the female is heterozygous for both traits.

Mutations

Compiled by Siti Sarah Jumali

Room 14, Level 3

06-4832123

-Gene Mutation- Chromosome Mutation

5 Ways of Creating Genetic Diversity in Bacteria

A. Mutations

B. Transformation

C. Conjugation

D. Transposition

E. Transduction

MUTATIONSMutation – any changes in the DNA sequence that affects

genetic information and the appearance of offspring.

• Occur naturally at low level (also known as spontaneous mutations), during DNA replication ; or

• Caused by UV Light, X-Rays, mutagens error during DNA replication by the effects of chemical agents called mutagens; or by physical agents like radiation.

Types of Mutations

• Gene mutation – a mutation that occurs in a single gene and affects one trait.

Eg: Eye color, Sickle cell Anemia, Hemophilia

• Chromosome mutation – a mutation that occurs in many genes and affects many traits at once.

Eg: Down Syndrome (an extra 21st chromosome)

• Genome mutation – mutation on ploidy

1. GENE MUTATIONS

Gene Mutation

• Involve insertion or removal of 1 or more base pairs

• Gene mutation is a change in single base pair within DNA sequences

Effects of Gene Mutations

Most mutations are neutral - they have no effect on the polypeptide.

Some mutations result in a less active product;

Less often an inactive product;

Very few mutations are beneficial.

Effects of Gene Mutations cont’d

• Affects molecular changes in the DNA sequence of a gene

• Alter the coding sequence within a gene• Causes permanent change in DNA sequence

Body (Somatic) and Gamete (Germ)mutation

Body cell mutations can cause cancer.

- only the individual is affected.

Gamete cell mutations affect the egg and the sperm.

- all offspring of the individual can be affected.

In multicellular organisms (plants or animals) mutations may occur in the somatic cells of the organism. Somatic cells are the cells involved in growth and repair and maintenance of the organism. A mutation in these cells may lead to cancer and certain of chromosomal mutations may be involved in aging. Other mutations happen in the germ cells and these mutations  may appear in the gametes and then in the offspring produced by sexual reproduction.  These sorts of mutations are called germ cell mutations.

Types of Mutations

1. Point mutations - a one base change in DNA.

2. Frame Shift Mutations - the addition or deletion of 1 or more bases. These are due to powerful mutagens; chemical or physical.

Normally..

DNA (antisense strand)

mRNA

Polypeptide

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids

The antisense strand is the DNA strand which acts as the template for mRNA transcription

© 2010 Paul Billiet ODWS

The amino acid chart

The amino acid chart with diseases

1. Point Mutation

3 types:

a. silent mutation - single base substitution in the 3rd base nucleotide position of a codon. This results in NO change in amino acid. Note that the first 2 letters of the genetic code are the most critical.

b. missense mutation - single base substitution in 1st or 2nd base nucleotide position. This results in changed amino acid.

c. nonsense mutation - single base substitutions that yield a stop codon. Note: there are 3 nonsense codons in the genetic code = NO PROTEIN

Silent or neutral mutation

• Silent mutation can result in enhancing new protein, but all other mutations reduce the function

Silent mutation

Missense mutation

Nonsense mutation

2. Frameshift Mutations

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids

Addition mutation

GGTGCTCCTCACGCCA

↓

CCACGAGGAGUGCGGU

↓

Pro-Arg-Gly-Val-Arg

Additions

© 2010 Paul Billiet ODWS

2. Frameshift Mutations cont’s

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids

Deletion mutation

GGTC/CCTCACGCCA

↓

CCAGGGAGUGCGGU

↓

Pro-Gly-Ser-Ala-Val

Deletion

© 2010 Paul Billiet ODWS

Frameshift mutation

Frameshift mutation

Mutations Can Be Neutral

• They may have little or no effect on the survival of an organism or on its ability to reproduce.

• They may result in the same kind of organism - meaning that the change still tells the cell to do what it should, so there is no difference.

• It is estimated that the average human has 50-100 mutations within their DNA - most (if not all) are neutral or beneficial

Mutations Can Be Beneficial

• Bacterial resistance to antibiotics

• Insecticide resistance in bugs

• Rapid mutation rates in virus’s proteins allowing them to adapt to new “hosts”

Mutations Can Be Beneficial

• In humans, it can be a different set of circumstances… Here’s an example:

• Sickle-Cell Anemia is a genetic disorder in which there is a defect in the structure of red blood cells. This leads to fatigue and anemia when not treated.

• However, it has been found that people who are carriers for Sickle-Cell Anemia also has some genetic protection against another disease, malaria.

Mutations Can Be Beneficial

• In evolutionary studies, scientists have connected the presence of a brain chemical microcephalin (a proposed mutation) with the human’s development of art, music, and complex tool-making practices

• This same research indicates that the human brain is still evolving and becoming more and more capable of more complex tasks

• Some humans have been found to have mutations that protect them from other diseases, such as AIDS

Compare the following types of base-substitution mutation.

Silent mutationMis-sense mutation

Nonsense mutation

Number of bases substituted

1

Effect on polypeptide

Stop codon produced early –

polypeptide shortened

Example illness Sickle cell disease

mRNA

amino acid

Self-Quiz

• Describe the effects of sickle cell disease on sufferers in terms of:

• Hemoglobin production• Symptoms and mortality

 • Identify parts of the world where a single

sickle cell (Hbs) allele could be beneficial

2. CHROMOSOME MUTATION

Chromosome Mutation

Chromosome structure become influenced by

1. Change in amount of genetic information in chromosome because of – Deletion– Duplication

2. Similar amount of genetic information but the materials are rearranged– Inversion– Translocation

Chromosome Mutation cont’d

• Deletion– Loss of chromosomal segment

• Duplication– Repetition of chromosomal segment

• Inversion– A change in the direction of the genetic material along a single chromosome

• Translocation– A segment of one chromosome becomes attached to a different

chromosome– Simple translocation

• One way transfer

– Reciprocal translocation• Two way transfer

Duplications

• Insertion of an extra copy of a region of  a chromosome into a neighboring position.

• Zygotes produced from gametes involving duplications are often viable and may or may not have any serious problems.

• Various sorts of duplications are  related to color vision conditions many of which are quite subtle in their effects e.g certain anemias involving abnormal hemoglobins  called the thalassemias.

Deletions

• Deletions result when a gene is mistakenly removed from a chromosome, as a result of  unequal crossing over.

• Often zygotes produced by gametes  involving deletions are not viable since they do not have the full compliment of genes.

Inversions

• Inversions happen when a whole region of genes on a chromosome gets flipped around .

• 2 types of inversions. – paracentric inversions the centromere is not included in the

inversion. – pericentric inversions, the centromere is involved in the

inversion.

Both these types of inversions lead to abnormalities in crossing over and meiosis resulting in some chromosomes which are not viable, while others are viable but have new combinations of genes. These sorts of  inversions are thus important in reshuffling genes on a chromosome.

Translocations

• Movement of part of a chromosome to another part of the genome.

• May happen with the same chromosome. – translocation is an intrachromosome translocation.

Other translocations involve transfer of a region of a chromosome to a non homologous chromosome. For example certain types of Down syndrome involve translocations between chromosome 14 and chromosome 21. This type of  translocation between non homologous chromosomes is called an inter-chromosomal translocation.

• Base substitution changes is in pair• 2 types of changes– Transition (within same group AT and GC)– Transversion (between 2 groups)

Transition vs Transversion

Inversion mutation

Normal gene

GGTCTCCTCACGCCA

↓

CCAGAGGAGUGCGGU

Codons

↓

Pro-Glu-Glu-Cys-Gly

Amino acids

Inversion mutation

GGTCCTCTCACGCCA

↓

CCAGGAGAGUGCGGU

↓

Pro-Gly-Glu-Cys-Gly

Inversion mutations, also, only affect a small part of the gene

© 2010 Paul Billiet ODWS

GENOME MUTATION

Changes in chromosome number

• Aneuploidy• Polyploidy• Autopolyploidy• Allopolyploidy

Aneuploidy

• Normally 2N ends up either with extra copies of homologous chromosomes or fewer than the normal diploid number.

• Happens when homologous chromosomes fail to segregate properly during meiosis (non disjunction).

• Monosomy (2n-1) in which the diploid  individual has only one member of a  certain homologous chromosome.

• The other common type of aneuploidy is called trisomy (2n+1) because the individual has three copies of the chromosome.

Aneuploidy leads to a number of syndromes in humans. For example trisomy 21 leads to Down syndrome, characterized by mental retardation and other abnormalities. Aneuploidy involving the sex chromosomes is common. XYY males are normal but XXY males and XXXY males have a syndrome called Klinefelter syndrome. These males are often actually intersexed or hermaphroditic with partially developed sexual organs of both genders. These individuals are sterile and are often subjected to hormones and surgery to bring them into conformance with social gender roles.

Polyploidy• 3N or sets of chromosomes in a nucleus.  • Can happen because of a failure of the spindle fibers in mitossis or meiosis to segregate chromosomes

into separate groups. • Many organisms have specialized polyploid tissues even organisms we typically consider as diploid.  

– For example in plants a so called double fertilization leads to the genesis of a diploid zygote from the union of two gametes produced by the haploid gametophytes, but also a specialized triploid tissue (3N) called endosperm. This tissue is produced when a male gamete fertilizes special diplid tissue from the flower. In mammals, cells of the liver are typically polyploid.

• Believed to be an important mechanism in the development of new species and a common pattern in plants is to find populations of two species both of which might be diploid. Where the species overlap a series of localized polyploid populations are often found. These polyploid populations are often effectively reproductively isolated from the parent species and thus can be considered species in their own right.

• E,g plant species and some fish and amphibians; – domestic wheat is hexaploid(6N). ‘– Seedless' plants are usually triploid (3N).

Consider a  tetraploid plant (4N). The gametes of this plant are going to be effectively diploid (2N) and if they are fertilized by a normal haploid gamete (N), the result is a triploid plant. Since triploid plants have an odd number of chromosomes, typically the gametes have variable number of chromosomes are usually not viable. This is why triploid plants are used to produce seedless plants.  Since most plants can self fertilize, the tetraploid plant can breed with itself and produce viable tetraploid populations.

Autopolyploidy

• Autopolyploidy is polyploidy in which all the chromsomes originate from the same diploid parent species. Domestic banana and various seedless plants are often triploid autoployploids.

Allopolypoidy

• Allopolypoidy is a polyploidy in which the sets of chromosomes are from differrent species. Usually hybrid plants (N1 + N2) from such crosses are not fertile since proper pairing of chromsomes does not occur in meiosis. But sometimes the the chromosome number spontaneously doubles leading to tissues with 2N1 + 2N2. If this tissue is germ tissue, tissue that can give rize to haploid tissue via meisosis the result can be gametes with the N1 + N2 chromosome complement. When two of these gametes fuse, the result is an allopolyploid plant with a viable chromosome complement (2N1 + 2N2).

Factors that causes mutation

A. Chemical mutagens - used in research to study mutagenesis. There are 3 kinds of chemical mutagens.

1. Alkylating agents. Adds alkyl group, CnH(2n+1)

Eg. formalin, nitrogen, mustard, and ethylene oxide (reacts with G changing it to bind with T).

2. Base analogs. Mimics a nitrogen base. Ex. AZT is a modified sugar that substitutes for T. Eg. 5 - bromouracil binds with A or G.

3. Intercalating agents. Inserts into DNA and pushes bases apart. Eg. AFLATOXIN - a chemical produced by peanut and grain molds. The mold is Aspergillus flavus (fungus).

B. Physical mutagens:

1. nonionizing radiation - Causes the formation of T= T dimers. UV light @ 260 nm.

2. Ionizing radiation - damages DNA by causing the formation of “free radicals” leading to mutations. 3 Ex. X-rays. Gamma rays from radioactive fallout penetrates the body. Alpha rays from inhaled dust containing radioactive fallout.

TRANSFORMATION

B. TRANSFORMATION

The passage of homologous DNA from a dead donor cell to a living recipient cell. Occurs in Streptococcus pneumoniae. When S. pneumo dies the DNA can be absorbed by a living S. pneumo and recombined into the chromosome. The gene for capsule formation is obtained in this way, as is a gene for penicillin resistance. Discovered in 1929 by Fredrick Griffith.

GA sp07

• Transform

ation Graphic

Griffith’s Transformation Experiment

C. CONJUGATION

1. A “mating” process between a donor F+ (bacteria with fertility factor =plasmid) and an F- recipient cell. 2. Occurs in Gram - enteric bacteria like

E.coli3. Discovered in 1946 by Joshua Lederberg

and Edward Tatum.4. Plasmids carry genes that are nonessential

for the life of bacteria. Ex. gene for pili (sex pilus). Ex. plasmid replication enzymes. Ex. Medical Problem: R-Factor = antibiotic resistance!

Conjugation continued

“Normal - Sex” plasmid transfer (usually ~20 of 100 genes).a. Requires a sex pilusb. F + bacteria transmits a copy of the plasmid

to F- bacteria. This converts the F- cell into an F + cell. Medical Problem: The R factor (antibiotic resistance) on the F factor is transmitted! http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/conjugation/f.html

6. Hfr (High Frequency Recombination)a. Hfr- bacterial plasmid integrates into the chromosome.

b. Medical Problem: Hfr antibiotic resistance genes are passed during binary fission (every time the cell divides). Therefore, antibiotic resistance spreads very rapidly!

c. When Hfr mate with F – bacteria, only the bacterial genes cross NOT plasmid genes. Genetic diversity results in this case due to recombination. http://www.cat.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombination/conjugation/hfr.html

•

D. TRANSPOSITION p 285

1. Transposons (jumping genes) are big chunks of DNA that randomly excise and relocate on the chromosome.

2. Transposons were discovered in 1950 by Barbara McLintock in corn.

3. Causes antibiotic resistance in Staph. aureus, the famous methicillin

resistant Staphlococcus aureus (MRSA) strain!

E. TRANSDUCTION

the transfer of genetic material from donor bacteria to recipient bacteria via a transducing agent (virus!). Bacterial viruses are called bacteriophage.

1. Discovered in 1952 by Zinder & Lederberg.

2. Two kinds of transduction: generalized and specialized.

•

2. Generalized transduction: Starts with the LYTIC CYCLE where a T- even phage (Fig. 8.5 pg 210) infects E.coli killing the host cell, and synthesizing 2,000 copies of itself. The T-even phage randomly packages bacterial DNA in a few defective phages. Once a T –even phage infects another E. coli, this genetic information can be recombined into the host cell without causing the lytic cycle. New genetic information is thereby transduced from one bacteria to another.

• Generalized Transduction

• Generalized Transduction

Specialized Transduction3. Specialized transduction

Lambda phage infects E.coli. The phage does not lyse the cell immediately. Instead it integrates into chromosome of the bacteria as a prophage and remains dormant. This is called the LYSOGENIC CYCLE. Phage genes are replicated and passed to all daughter cells until the bacteria is under environmental stress, from lack of nutrients, etc. Then phage gene will excise from the nucleoid and enter the LYTIC CYLE taking one adjacent gene for galactose metabolism.

Specialized Transduction Cont.

The gal transducing phage (lambda) makes ~ 2,000 copies of itself with the gal gene, and infects other E.coli. When gal integrates into the nucleoid of other E. coli, it may provide these bacteria with a new capacity to metabolize galactose.

S p ecialized T ran sd u ctio n G rap h ic

Comparison of Bacteriophage

3. Comparison of bacteriophage transduction in E.coli.

Generalized Specialized

T even phage lambda phage

lytic cycle lysogenic

random packaging specific gal gene

End of Slides