Biology hereditary question

[dentistin2011]

Advertisement - Members don't see this ad

I got a question about test cross?

Normal wings are dominant to curly wings in ceratin fruit flies. To determine the genotype of a fly with normal wings, the following test cross should be conducted?


answer is 'cross with fly with curly wings'
any explanation?

Thank you.

 

[mayoree]

Think about it this way:
Make normal capital N and curly lower case N. You have two alleles on the gene so the fly can either be NN or Nn. In either case it will have normal wings because they are dominant. You would cross with a fly with curly wings (nn) because if the normal fly is NN you would expect none of the offspring to have curly wings because the only genotype would be Nn (NN x nn = Nn for all)
However, if half of the offspring have curly and half have normal, then you know that the normal parent had the genotype Nn (because Nn x nn = 50% Nn and 50% nn).
Review Punnett squares and Mendelian genetics. Good luck

I got a question about test cross?

Normal wings are dominant to curly wings in ceratin fruit flies. To determine the genotype of a fly with normal wings, the following test cross should be conducted?


answer is 'cross with fly with curly wings'
any explanation?

Thank you.

 

[dancedancekj]

Commonly known as the "back-cross".

 

[dentistin2011]

thank you guys~

 

[Resonance]

Commonly known as the "back-cross".

Actually a "backcross" usually refers to a cross between F1 hybrids to individuals that have genotypes of the parental generation. These are often used when studying polygenic traits, to produce F2 offspring that will differ with regard to their combinations of parental chromosomes. The cross being discussed here is a test-cross.

 

[asckwan]

Question along the lines of genetics and stuff. Can anyone help me with calculating the percent chance an offspring will end up with certain traits?

EX. parents are DDrr and DdRr calculate the ratio of all the different genotypes of the offspring.

I can write this out on the table and count, but there has to be a better way to calculate it. Anyone know?

 

[tinman831]

Question along the lines of genetics and stuff. Can anyone help me with calculating the percent chance an offspring will end up with certain traits?

EX. parents are DDrr and DdRr calculate the ratio of all the different genotypes of the offspring.

I can write this out on the table and count, but there has to be a better way to calculate it. Anyone know?

An easy way to do this would be to calculate using two separate punnett squares for each characterstic (DD x Dd) and then (rr x Rr).

So:

DD x Dd would give you 1/2 DD and 1/2 Dd.
rr x Rr gives you 1/2 Rr and 1/2 rr

Then you just multiply the each of the fractions to get your ratios.

1/2DD x 1/2 Rr = 1/4 chance of DDRr
1/2DD x 1/2 rr = 1/4 chance of DDrr
1/2Dd x 1/2 Rr = 1/4 chance of DdRr
1/2Dd x 1/2 rr = 1/4 chance of Ddrr

*answer edited* thanks checkamundo!

 

[checkamundo]

An easy way to do this would be to calculate using two separate punnett squares for each characterstic (DD x Dd) and then (rr x Rr).

So:

DD x Dd would give you 1/2 DD and 1/2 Dd.
rr x RR gives you 4/4 Rr

Then you just multiply the each of the fractions to get your ratios.

1/2DD x 4/4 Rr = 4/8 chance of DDRr
1/2Dd x 4/4 Rr = 4/8 chance of DdRr

Actually, the question asks for a cross with (rr x Rr) not (rr x RR). The answer is:

DD x Dd would give you 1/2 DD and 1/2 Dd.
rr x Rr would give you 1/2 Rr and 1/2 rr

Then you just multiply the each of the fractions to get your ratios.

1/2 DD x 1/2 Rr = 1/4 DDRr
1/2 DD x 1/2 rr = 1/4 DDrr
1/2 Dd x 1/2 Rr = 1/4 DdRr
1/2 Dd x 1/2 rr = 1/4 Ddrr

 

[dancedancekj]

Actually a "backcross" usually refers to a cross between F1 hybrids to individuals that have genotypes of the parental generation. These are often used when studying polygenic traits, to produce F2 offspring that will differ with regard to their combinations of parental chromosomes. The cross being discussed here is a test-cross.

Damnit, thank you Resonance.

 

[tinman831]

Actually, the question asks for a cross with (rr x Rr) not (rr x RR).

oopsie! i didn't read the question carefully. thanks for catching that! 🙂