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*Biology Paper 5 tips*

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Irfan1995

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Guys, I really don't know why you guys are over-complicating the problem. In part (a) to the question, you can clearly see that the 'without tail' allele is dominant, and that the gene is autosomal (not sex-linked).

In cross 1, you have two parents 'without a tail'. As you have some offspring that do have tails, you can be sure that both parents are heterozygous. If one of them were homozygous, then ALL the offspring would be 'without a tail'.

Now, we know that when two heterozygous parents cross, the ratio of the phenotypes of the offspring would be 3:1 (dominant allele:recessive allele).
In this case, we have two heterozygous parents, out of every 4 offspring, we expect 3 of them to be 'without a tail' and 1 to have a tail. So 3/4 of the offspring are expected to be 'without a tail' and 1/4 with a tail. This is just a simple monohybrid cross.
Now, to get the expected number of offspring:
Total number of offspring = 40 + 72 = 112 (taken from the observed results)
Expected number of offspring without a tail = (3/4) * 112 = 84
Expected number of offspring with a tail = (1/4) * 112 = 28
 
knowitall10

knowitall10

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Irfan1995 said:
Guys, I really don't know why you guys are over-complicating the problem. In part (a) to the question, you can clearly see that the 'without tail' allele is dominant, and that the gene is autosomal (not sex-linked).

In cross 1, you have two parents 'without a tail'. As you have some offspring that do have tails, you can be sure that both parents are heterozygous. If one of them were homozygous, then ALL the offspring would be 'without a tail'.

Now, we know that when two heterozygous parents cross, the ratio of the phenotypes of the offspring would be 3:1 (dominant allele:recessive allele).
In this case, we have two heterozygous parents, out of every 4 offspring, we expect 3 of them to be 'without a tail' and 1 to have a tail. So 3/4 of the offspring are expected to be 'without a tail' and 1/4 with a tail. This is just a simple monohybrid cross.
Now, to get the expected number of offspring:
Total number of offspring = 40 + 72 = 112 (taken from the observed results)
Expected number of offspring with a tail = (3/4) * 112 = 84
Expected number of offspring without a tail = (1/4) * 112 = 28
Click to expand...

*clapping hands* (y)
 
knowitall10

knowitall10

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biba said:
i know that :p but seriously i thought bio was the easiest subject in the universe! but a2 changed my views!
Click to expand...

it is the best...it's just the stats part i really hate.. bio is my favorite..i describe my world in terms of bio :p
LOL..please don't run away now..i know i'm a weirdo ;)
 
biba

biba

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knowitall10 said:
it is the best...it's just the stats part i really hate.. bio is my favorite..i describe my world in terms of bio :p
LOL..please don't run away now..i know i'm a weirdo ;)
Click to expand...

no u arnt.. even p5 could not stop me loving bio either! and u are not a weirdo u r an awsumazing person!
 
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god's gift

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plz give me some tips on the stats portion of biology.. i don't take maths and i m having very difficulty in doing those..
 
kelly sheers

kelly sheers

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knowitall10 said:
C'mon..you're making me feel so shy now..hehehe..
You're an epic person too:)
Click to expand...
nah...(y)
more info if u need em

a dihybrid cross results in a 9:3:3:1 ratio whereas a monohybrid cross gives a 3:1 ratio
a monohybrid cross is performed only once, whereas a dihybrid cross is performed twice.
Monohybrid- tall and short: TT tt
Dihybri-tall and fat..short and thin: TTFF and ttff
 
I

Irfan1995

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biba said:
i know that :p but seriously i thought bio was the easiest subject in the universe! but a2 changed my views!
Click to expand...

Believe me, you've seen nothing. A2 Biology is as easy as 7th grade math.
It gets much much harder. We spend the entire year last year learning about a much broader range of topics. We also spend 2 whole months just learning about evolution! It also gets a lot weirder. We actually had to learn last year on how mushrooms go about 'sexual reproduction' in bed.
 
kelly sheers

kelly sheers

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god's gift said:
plz give me some tips on the stats portion of biology.. i don't take maths and i m having very difficulty in doing those..
Click to expand...
standard deviation
  1. Calculate the mean or average of each data set. To do this, add up all the numbers in a data set and divide by the total number of pieces of data. For example, if you have found numbers in a data set, divide the sum by 4. This is the meanof the data set.
  2. Subtract the devianceof each piece of data by subtracting the mean from each number. Note that the variance for each piece of data may be a positive or negative number.
  3. Square each of the deviations.
  4. Add up all of the squared deviations.
  5. Divide this number by one less than the number of items in the data set. For example, if you had 4 numbers, divide by 3.
  6. Calculate the square root of the resulting value. This is the sample standard deviation.
 
Ramsha007

Ramsha007

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kelly sheers said:
nah...(y)
more info if u need em

a monohybrid cross results in a 9:3:3:1 ratio whereas a dihybrid cross gives a 3:1 ratio
a monohybrid cross is performed only once, whereas a dihybrid cross is performed twice.
Monohybrid- tall and short: TT tt
Dihybri-tall and fat..short and thin: TTFF and ttff
Click to expand...


As far as i know monohybrid is 3:1 and dihybrid is 9:3:3:1o_O Right?
 
kelly sheers

kelly sheers

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god's gift said:
plz give me some tips on the stats portion of biology.. i don't take maths and i m having very difficulty in doing those..
Click to expand...
where E(dat weird symbol) = sum of
x=individual values in the sample
n= total no of individuals in the sample
 

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I

Irfan1995

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kelly sheers said:
standard deviation
  1. Calculate the mean or average of each data set. To do this, add up all the numbers in a data set and divide by the total number of pieces of data. For example, if you have found numbers in a data set, divide the sum by 4. This is the meanof the data set.
  2. Subtract the devianceof each piece of data by subtracting the mean from each number. Note that the variance for each piece of data may be a positive or negative number.
  3. Square each of the deviations.
  4. Add up all of the squared deviations.
  5. Divide this number by one less than the number of items in the data set. For example, if you had 4 numbers, divide by 3.
  6. Calculate the square root of the resulting value. This is the sample standard deviation.
Click to expand...
Actually, most scientific calculators have a cute little "standard deviation" button. It has the small Greek "sigma" sign.
 
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