OCR 2010 A2 Biology Unit 2 - Control, Genome and Environment

pinksham

hii! could anyone explain epistasis 2 me pleease! i dont get it at all.. i understand that it when it masks 1 gene or works in a complemetary way with another gene. but i dont undersatnd the examples. thanks!!!

I explained epistasis in some depth a couple of spreads back, so see if you can find the post.

Epistasis is the interaction between different gene loci, where one locus masks or suppresses the expression of another gene locus. Epistasis will not result in the normal ratios that you would expect from dihybrid/monohybrid crosses i.e 9:3:3:1 and 3:1

There are different ways that genes can interact. Firstly antagnositically to cause masking, or in a complementary way.

When genes are acting antagonistically this can be due to either dominant epistasis or recessive epistasis. Dominant epistasis is where the presence of a dominant allele at the first locus prevents the expression of the allele at the second locus, the first locus is termed epistatic to the second, of which is called hypostatic.

In recessive epistasis the prescence of a homozygous recessive allele prevents the epression of the genes at the second locus.

When they are working in a complementary fashion, then the homozygous presence of a recessive allele will work to prevent the expression of the allele at either locus. So if aa, was expressed on the first, it prevents anything being expressed on the second, and if aa is present on the second, then it prevents anything from being expressed on the first.

I used some examples in my other explanation.

Reply 981

blueberry123

finished the whole biology book yaaay :woo:

Reply 982

ViolinGirl

9

blueberry123

finished the whole biology book yaaay :woo:

Reply 983

redfanatic

11

Is nobody scared about how synoptic this paper is said to be? like 50% synoptic and they can ask you anything from the last 2 years! + the unit is so big, so i dont know what to do really!

How is everyone else feeling or doing for this?

Reply 984

win2kpro

10

redfanatic

Is nobody scared about how synoptic this paper is said to be? like 50% synoptic and they can ask you anything from the last 2 years! + the unit is so big, so i dont know what to do really!

How is everyone else feeling or doing for this?

Where did you hear that it is going to be 50% synoptic? :eek3:

... I hope not... pfff .. we surely deserve a decent paper after january's?

Reply 985

redfanatic

11

win2kpro

Where did you hear that it is going to be 50% synoptic? :eek3:

... I hope not... pfff .. we surely deserve a decent paper after january's?

My teacher. And that this is how it has always been, as it is the last paper we will do hence supposed to show all our knowledge. But i know what you mean. I was terrified to hear that.

Also, can someone give me the links to all the revision packs and questions that have been uploaded, as theres 55 pages and i didnt want to really have to look through each page!

thanks

Reply 986

ibysaiyan

16

redfanatic

Is nobody scared about how synoptic this paper is said to be? like 50% synoptic and they can ask you anything from the last 2 years! + the unit is so big, so i dont know what to do really!

How is everyone else feeling or doing for this?

I am feeling good.Really forward to it.Bring it on OCR!

Reply 987

clad in armour

16

win2kpro

Where did you hear that it is going to be 50% synoptic? :eek3:

... I hope not... pfff .. we surely deserve a decent paper after january's?

we definately do, I hope they've sorted themselves out now because this is the last chance
I didnt think that the Jan paper was all that synoptic even though people were banging on about revising all AS stuff. If it does I hope it just comes back
not an excellent strategy

:frown:

Reply 988

ibysaiyan

16

clad in armour

we definitely do, I hope they've sorted themselves out now because this is the last chance
I didnt think that the Jan paper was all that synoptic even though people were banging on about revising all AS stuff. If it does I hope it just comes back
not an excellent strategy

:frown:

Although no one told me about it being synoptic but its def. gonna be one.... as lots of AS along with f214 mod. parallels with f215. Go for nervous system for instance or perhaps the conversion of ATP / *hint* gibberlins.

Reply 989

clad in armour

16

ibysaiyan

Although no one told me about it being synoptic but its def. gonna be one.... as lots of AS along with f214 mod. parallels with f215. Go for nervous system for instance or perhaps the conversion of ATP / *hint* gibberlins.

actually your right, theres the muscles stuff isnt there
forgive my ignorance but what do plant hormones have to do with ATP?

Reply 990

ibysaiyan

16

Completed the f215 module today :shock:

Anyhows the last chapter was quite dull *yawns* on memory,learning. If anyone has got any question on f215 stick it down =}

Reply 991

win2kpro

10

ibysaiyan

Completed the f215 module today :shock:

Anyhows the last chapter was quite dull *yawns* on memory,learning. If anyone has got any question on f215 stick it down =}

Well done man :thumbsup:

- Im nearly done too! Am on the sliding filament model atm, hopefuly done with f215 by midnight, or maybe 2moro if I am lazy :p:

Reply 992

ibysaiyan

16

clad in armour

actually your right, theres the muscles stuff isnt there
forgive my ignorance but what do plant hormones have to do with ATP?

Yep. There was this past paper question on it. Basically GA is made in the embryo fo the seed. From there it diffuses outside to the aleurone layer (enzyme layer) where GA+enzymes +endosperm(food source) = Energy.
How this is acheived is by the work of amylase on starch which breaks it into glucose and so forth.
=}

Reply 993

ibysaiyan

16

win2kpro

Well done man :thumbsup:

- Im nearly done too! Am on the sliding filament model atm, hopefuly done with f215 by midnight, or maybe 2moro if I am lazy :p:

cools muslce work heh? yep is fun x D myosin/actin/myso troponin/myosin/power stroke/the bands/Ca ions/along with sarcomere and sacroplasmic reticulum. Now whats the name of that filament which covers the pores where myosin head attach? :mad:

Reply 994

win2kpro

10

ibysaiyan

cools muslce work heh? yep is fun x D myosin/actin/myso troponin/myosin/power stroke/the bands/Ca ions/along with sarcomere and sacroplasmic reticulum. Now whats the name of that filament which covers the pores where myosin head attach? :mad:

tropomyosin subunits? :biggrin:

Reply 995

ibysaiyan

16

win2kpro

tropomyosin subunits? :biggrin:

err sure? xD ok then xD
although i bet mary jones says anything but that let me look. :p:

edit: yes xD

Reply 996

blueberry123

ibysaiyan

Yep. There was this past paper question on it. Basically GA is made in the embryo fo the seed. From there it diffuses outside to the aleurone layer (enzyme layer) where GA+enzymes +endosperm(food source) = Energy.
How this is acheived is by the work of amylase on starch which breaks it into glucose and so forth.
=}

excuse my slow brain but I'm still confused and you've lost me after the GA was made in the embryo :confused:

Reply 997

ibysaiyan

16

blueberry123

excuse my slow brain but I'm still confused and you've lost me after the GA was made in the embryo :confused:

GA aka gibberlins is diffused out from the embryo to the enzyme layer.There GA stimulates amylase enzyme which hydrolyzes starch into glucose.The starch (food source) is called endosperm.Glucose then is used in Aerobic respiration.

Reply 998

blueberry123

ibysaiyan

GA aka gibberlins is diffused out from the embryo to the enzyme layer.There GA stimulates amylase enzyme which hydrolyzes starch into glucose.The starch (food source) is called endosperm.Glucose then is used in Aerobic respiration.

much better ,thanks

Reply 999

ibysaiyan

16

blueberry123

much better ,thanks

OCR 2010 A2 Biology Unit 2 - Control, Genome and Environment

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