Biochemical Genetics of Algae

8/7/2019 Biochemical Genetics of Algae

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BIOCHEMICAL GENETICS OF

ALGAEBy

Vinay. B.PII SEM

Molecular biology


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STUDY OF CHLAMYDOMONASSTUDY OF CHLAMYDOMONAS

It is a is single celled organism,It is a is single celled organism,

very useful to study chloroplastvery useful to study chloroplast

geneticsgenetics

There is the presence of nucleus,There is the presence of nucleus,

nucleolus, single large chloroplast,nucleolus, single large chloroplast,

mitochondria, golgi apparatus andmitochondria, golgi apparatus andcell wallcell wall

There are two mating types + andThere are two mating types + and

-- strains strains

Mating occurs between these twoMating occurs between these twostrains leading to the formation ofstrains leading to the formation of

diploid zygote.diploid zygote.

This undergoes meiotic divisionThis undergoes meiotic division

leading to the formation of haploidleading to the formation of haploid

individualsindividuals


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LIFE CYCLE OF CHLAMYDOMONASLIFE CYCLE OF CHLAMYDOMONAS


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CHLOROPLAST MUTATION IN CHLAMYDOMONASCHLOROPLAST MUTATION IN CHLAMYDOMONAS

The haploid eukaryotic organism has a single largeThe haploid eukaryotic organism has a single large

chloroplast containing 50 copies of double strandedchloroplast containing 50 copies of double stranded

DNA.DNA.

The first cytoplasm mutant, streptomycin resistanceThe first cytoplasm mutant, streptomycin resistancewas reported in 1954 by Ruth sagerwas reported in 1954 by Ruth sager

The drug resistance gene is obtained from mtThe drug resistance gene is obtained from mt++

strainstrain

The + DNA is methylated, whereas the The + DNA is methylated, whereas the DNA isDNA isnot methylated.not methylated.

After the fusion there is a machinery within theAfter the fusion there is a machinery within the

zygote which recognizes the unmetylated DNA andzygote which recognizes the unmetylated DNA and

this is selectivly cleaved.this is selectivly cleaved.


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LINKAGE AND MAPPINGLINKAGE AND MAPPING

Linkage and mapping studies is important toLinkage and mapping studies is important to

determine the distance between the gene and thedetermine the distance between the gene and the

centromerecentromere A cross between two strains aaA cross between two strains aa xx ++ is considered++ is considered

According to the Mendelian principle ofAccording to the Mendelian principle of

independent assortment the unlinked genes move toindependent assortment the unlinked genes move to

the F1 generation in equal proportionthe F1 generation in equal proportion This should have led to the formation of only fourThis should have led to the formation of only four

types of tetrads, two + types and two a typestypes of tetrads, two + types and two a types

Non parental varieties were also observed leadingNon parental varieties were also observed leading

to the prediction of crossing over between twoto the prediction of crossing over between two


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The origin of the third type involves cross overThe origin of the third type involves cross over

between one of the genes and the centromerebetween one of the genes and the centromere It can be of two types:It can be of two types:

1. Between gene a and the centromere1. Between gene a and the centromere

2. Between gene b and the2. Between gene b and the

centromerecentromere Genes a and b are linked and the results obtainedGenes a and b are linked and the results obtained

by crossing aaby crossing aa xx ++++

Since the parent and non parental categories areSince the parent and non parental categories arenot produced in equal proportion it can benot produced in equal proportion it can be

concluded that the genes a and b are linkedconcluded that the genes a and b are linked

PP NP NP TT

6464 66 3030


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The analysis of the data reveals the thpoe of tetradThe analysis of the data reveals the thpoe of tetrad

in which the exchange in genetic material hasin which the exchange in genetic material has

occurredoccurred1. The parental ditype tetrads (p) arise when1. The parental ditype tetrads (p) arise when

there is no crossing over between genesthere is no crossing over between genes

2. The non parental ditype (NP) occurs when2. The non parental ditype (NP) occurs when

there is a double exchange involving all fourthere is a double exchange involving all fourchromatids occurs between two geneschromatids occurs between two genes

3. The tetratype tetrad (T) occurs when either a3. The tetratype tetrad (T) occurs when either a

single cross over or alternative type of doublesingle cross over or alternative type of double

exchange occurs between two genesexchange occurs between two genes

When the proportion of the three tetrad has beenWhen the proportion of the three tetrad has been

determined the distance between two linked genesdetermined the distance between two linked genes

can be calculatedcan be calculated

Exchange frequency (EF)=Exchange frequency (EF)= NP+1/2(T)NP+1/2(T)XX100100


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EXTRA CHROMOSOMAL INHERITANCE

A non- Mendelian pattern of inheritance is universally applicableto distinguish extra nuclear from nuclear inheritance

This is established in chlamydomonas resistance to drugs

There are two verities of chlamydomonas based on the

resistance to the drug Streptomycin, mt+ and mt

The studies were carried out by crossing a antibiotic resistantstrain and a wild type antibiotic sensitive strain


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INHERITANCE OF MITOCHONDRIA

The inheritance of mitochondria is also uniparental, occurring

through the mt parent

This is observed for the gene MUD 2 mutations occurring in

cytochrome b gene present in the mitochondrial DNA

This gene product is responsible for conferring the organism

resistance to the antibiotic myxothiozol

The cross is carried between mutant anitibiotic resistance

and a wild type antibiotic sensitive varieties


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STUDY OF ACETABULARIASTUDY OF ACETABULARIA

TheseThese plantsplants areare aboutabout 55cmcminin heightheight withwith aa cupcup ofof aboutabout11cmcm inin diameterdiameter

PlantsPlants areare usuallyusually calcifiedcalcified

StemStem andand cupcup areare singlesingle

celledcelled andand thethe plantsplants arearegenerallygenerally foundfound growinggrowing ininshallowshallow waterswaters attachedattached totorocksrocks

TheseThese areare unicellular unicellularorganismsorganisms withwith aacharectersticcharecterstic umbrellaumbrella likelikeshapeshape

TheyThey areare famousfamous fromfrom

JoachimJoachim HammerlingHammerling


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HAMMERLINGS EXPERIMENTHAMMERLINGS EXPERIMENT

In the late 1930's J. Hammerling wasIn the late 1930's J. Hammerling was

wondering where the genetic traits were storedwondering where the genetic traits were stored

inside the eukaryotic cell.inside the eukaryotic cell.

These were single celled organisms, and theyThese were single celled organisms, and theywere asymmeticalwere asymmetical

The heads of the algae withered whenThe heads of the algae withered when

detached, and only the feet regenerated. Hedetached, and only the feet regenerated. He

was pretty sure that the "traits" werewas pretty sure that the "traits" were


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His experiment involved switching of the top halvesHis experiment involved switching of the top halves

of the different strains of the algae.of the different strains of the algae. He needed a control and for this a single plant wasHe needed a control and for this a single plant was

usedused

He cut off the top portion and then grafted it back toHe cut off the top portion and then grafted it back to

the ame organism and this organism survived andthe ame organism and this organism survived and

hence the control was positivehence the control was positive


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He now switched the top halves of two verities ofthe same species

Non of the portion of the plant withered but the

entire organism survived

The top halves were changed into the form that wasdictated by the "traits'" instructions in the respective

bases.

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Biochemical Genetics of Algae