Biology P1 doubts.

[LimeReem]

Place for anyone to clear their P1 doubts!
http://www.xtremepapers.me/CIE/Cambridg ... _qp_11.pdf
q30 AND 32. why is the answer C?

 

[shan5674]

Place for anyone to clear their P1 doubts!
http://www.xtremepapers.me/CIE/Cambridg ... _qp_11.pdf
q30 AND 32. why is the answer C?

in q30 since they have off springs of both types of animals it immediately crosses out option A and D and if u look at the number of animals with and without spots u would see that they are almost equal, almost (1:1 ratio) and if they were of genotypes shown in B there would be way more normal skin animals than spotted as both parents have the dominant gene it would be a ratio of 4:1 and so they would not be able to have almost equal number of both off springs hence its C

and in q32 the taster gene is dominant and they both have partners who are non tasters meaning they do not have the taster gene so if they were also homozygous they would not be able to have kids who are non tasters(both of them are in the same situation) thats why they are both heterozygous as they have a kid who is a non taster as well


Hope i helped

 

[LimeReem]

http://www.xtremepapers.me/CIE/Cambridg ... 6_qp_1.pdf
q30 and 31? explain pls D=

 

[shan5674]

http://www.xtremepapers.me/CIE/Cambridge%20IGCSE/0610%20-%20Biology/0610_w06_qp_1.pdf
q30 and 31? explain pls D=

30 will be D: coz the allele for white hair is recessive and will need 2 recessive alleles to have the white hair phenotype so 1 parent has homozygous allele for white hair and the other has grey hair which is the dominant allele but for it to produce an offspring with recessive alleles it has to have 1 recessive allele and 1 dominant as the off springs get 1 allele from the mother and 1 from the father and the pair has produced white haired off springs which means 2 recessive alleles

31 will be D aswell: if u do the genetic cross ull see why, ill show it below

Tt x Tt - cross them all up with eachother, you'll get:
TT Tt

TT tt

Hope i helped

 

[LimeReem]

thank you soo much D= i suck at genetics.
im just confused for 30, there should always be 1 heterozygous and 1 homozygous recessive? when should it be 1 heterozygous and 1 homozygous dominate and in what conditions should there be only heterozygous or homozygous? D=

 

[shan5674]

thank you soo much D= i suck at genetics.
im just confused for 30, there should always be 1 heterozygous and 1 homozygous recessive? when should it be 1 heterozygous and 1 homozygous dominate and in what conditions should there be only heterozygous or homozygous? D=

Um..i dont really get your question but ill explain what i think your asking anyways

Basically for a recessive gene to be shown in the phenotype of a person they should have 2 recessive genes coz if they have 1 recessive and 1 dominant the dominant 1 will stand out so for a person to show the recessive gene they should be homozygous recessive but if they show the dominant gene they can be either homozygous dominant(2 dominant alleles) or heterozygous dominant(1 dominant and 1 recessive allele)

Now if the person who has a homozygous recessive allele mates with a homozygous dominant person there is no chance at all for them to produce off springs showing the recessive gene phenotype as each of their off springs will have 1 recessive gene and 1 dominant gene they will be heterozygous dominant but if a person with a homozygous recessive gene mates with a heterozygous dominant person there is a chance where the recessive allele from the heterozygous person joins with a recessive allele from the homozygous person to produce a homozygouse recessive off spring


I hope i helped i tried to make it as simple as possible

 

[LimeReem]

tysm i think i get it now! =DD