[quote=Dr.G.AsgharMemon]Dear jtalpur, its reason is the fact that parents are ''heterozygous'' meaning each of them[parents] have one allele for the disease. so when u do the cross bw such parents the ratio comes out is 25 % or 1/4. u can understand this concept if u know how to make a cross bw traits.
Suppose a person has 't' allele for diabetes, 'T' [capital] for normal. one parent has 'Tt' and the other likewise has 'Tt' , now then cros [Tt into Tt] and make its possible subsets like this : TT, Tt, tT, tt. in this configuration u can see the letters ''tt'' stands for the disease and its ratio is 25% , therefore it is 1/4 .
hope this concept is clear enough for you.[/quote]

Dear Dr.G.AsgharMemon

Thank you very much for the explanation, It is very understandable but the definition of "heterozygous" that I am using according to a dictionary is creating confusion for me

Can you explain that how ''heterozygous'' means that each of them[parents] have one allele for the disease ?

[B]heterozygous[/B]
containing a dissimilar pair of genes for any hereditary characteristic

[B]heterozygote[/B]
an individual having two different alleles of a particular gene or genes, and so giving rise to varying offspring

I have never been a medical student so kindly pardon my ignorance at this :))

MOHSIN the definition which u have read from dictionary is right but while solving such problems related to GENETICS we have to do the TEST CROSS which gives us probability or ratio of certain trait in next generation.

[quote=sunlight]MOHSIN the definition which u have read from dictionary is right but while solving such problems related to GENETICS we have to do the TEST CROSS which gives us probability or ratio of certain trait in next generation.[/quote]

I am fine with the test cross i.e that "T" and "t" thing
but my problem is that how does ''heterozygous'' mean that each of them[parents] have [B]one [/B]allele for the disease ?

26) The position of earth in its orbit, when it is at its greatest distance from the sun causing northern summer is called:

a. Aphelion
b. Perihelion
c. Perigee
[B]d. Apogee[/B]
e. None of these

[url]http://en.wikipedia.org/wiki/Apsis[/url]

[quote=jtalpur]26) The position of earth in its orbit, when it is at its greatest distance from the sun causing northern summer is called:

a. Aphelion
b. Perihelion
c. Perigee
[B]d. Apogee[/B]
e. None of these

[URL="http://en.wikipedia.org/wiki/Apsis"]http://en.wikipedia.org/wiki/Apsis[/URL][/quote]

Brother Apogee and Perigee are terms referring to orbits around the [B]earth[/B] not around the sun. So moon or any other body orbiting the earth can be in apogee or in perigee

Aphelion and Perihelion are the terms referring to the orbits around the sun

This is also clear in the wikipedia article you have linked as reference (Para 3, Sentence 2) !!

[QUOTE=MohsinShah]I am fine with the test cross i.e that "T" and "t" thing
but my problem is that how does ''heterozygous'' mean that each of them[parents] have [B]one [/B]allele for the disease ?[/QUOTE]
the question statement reads like this '' heterozygous normal''
the word normal indicates that clinically the patient is not having the disease but on the other hand its genotype is not completely ''normal'' so it becomes Tt

its opposite situation will be '' homozygous normal'' meaning that the patient like in the above condition is clinically disease free and in addition both the alleles are normal or ''T'' so the genotype will be TT
so it follows that
heterozygous normal '' Tt "" no diseaes clinically,,although one disease allele is present "" t "'
homozygous normal '' TT '' no disease clinically,, and both alleles are ''normal''

words normal and diseased have been used in place of dominant and recessive for easy understanding

[QUOTE]Can you explain that how ''heterozygous'' means that each of them[parents] have one allele for the disease ?

heterozygous
containing a dissimilar pair of genes for any hereditary characteristic

heterozygote
an individual having two different alleles of a particular gene or genes, and so giving rise to varying offspring

I have never been a medical student so kindly pardon my ignorance at this [/QUOTE]
Dear MohsinShah Sahib:- heterozygous in a sense that for example one trait is color of eyes. all people have eyes, but color of eyes differ depending upon ''difference'' of allele for it. such differences are of three kinds depending upon whether or not the character shows up in progeny. 1. dominant character 2. recessive character 3. co dominant character.
expression of a gene is called showing up of its character in progeny. codominant means neither of two genes get expressed rather a different color than orginal shows up.
as far as cofusing part of your proposition is concerned ie "containing a dissimilar pair of genes for any hereditary characteristic " it is confusing because the gene is differnt and not different at the same time. not different in a sense that both genes stand for 'same character' and diffrnt in a sense that each has differnt 'say' on the same character. for color of eyes, one gene can be black coloring, the other may be blue. so they are dissimilar for the same trait.
about second part 'homozygote' part this difference is present in sex chromosomes. female contributes her 'x' chromosome ,while a male contributes either 'x' or 'y' . here xx are similar for the character, anc xy are dissimlar for the character. well, the character here is 'determination of sex' ie is it gonna be female or male respectively.
i hope its pretty much clear.
i m student of mbbs. i have read these concepts when i did my intermediates.
Thanks for posing this question.
pray for my success bro.
regards

[QUOTE]5) Laughing gas has chemical composition of following two elements.

a. Nitrogen + Hydrogen
b. Nitrogen + Carbon
c. Nitrogen + Oxygen
d. Oxygen + Carbon
e. None of these [/QUOTE]




laughing gas = nitrous oxide

chemical formula N2O.

[quote=snake]laughing gas = nitrous oxide

chemical formula N2O.[/quote]

N2O will decompose exothermically into nitrogen and oxygen, at a temperature of approximately 1300 °C

So Nitrogen and Oxygen is the right answer

(29) Which of the following explains the reason why there is no total eclipse of the sun?

a. Size of the earth in relation to that of moon
b. Orbit of moon around earth
c. Direction of rotation of earth around sun
[B]d. Area of the sun covered by the moon[/B]e. None of these

could anyone confirm me the answere of that question and what about option A because the size of the earth is bigger than moon soooo. wht will be the bst option