I am a high school student currently studying Mendelian genetics. 

I stumbled upon a question that said two plants with the genotypes PpQq each are selfed, resulting in the formation of 1000 seeds. The question then asks to find the frequencies of the following genotypes:

Ppqq, PpQq, ppQq and PpQQ

To solve this, I found the ratio (2:4:2:2), divided each by 16 and multiplied by 1000 to find the exact number of each progeny. This is probably a very basic and silly doubt, but I'm confused. 

I get that the probability of, say, 'Ppqq' is 2/16, but why do we have to multiply that by 1000? Can someone explain the right way to do this problem? 

Thanks. 

 

 

Edited June 20, 20241 yr by Mel122

To determine the frequencies of the genotypes, you first find their probabilities from the Punnett square (e.g., 2/16 for Ppqq). Multiplying by 1000, the total number of seeds, converts these probabilities into actual counts. For example, (2/16) * 1000 = 125 seeds with the Ppqq genotype. This approach ensures you have the correct number of seeds for each genotype, reflecting their expected proportions in a large sample.

2 sets of genes, recessive/dominant.

Original parent gene sets PpQq (both male and female plants have the same genotype)   

Possibilities:

1. PP, Pp, pP, pp, 4 genotypes

2. QQ, Qq, qQ, qq, 4 genotypes

Total combinations possible = 4 * 4 = 16 genotypes

For Ppqq there are 2 combinations: Ppqq and pPqq

For PpQq there are 4 combinations: PpQq, PpqQ, pPQq, pPqQ

For ppQq there are 2 combinations: ppQq, ppqQ

For PpQQ there are 2 combinations: PpQQ, pPQQ

Frequency of Ppqq  = 2/16

Frequency of PpQq = 4/16  

Frequency of ppQQ = 2/16 

Frequency of PpQQ = 2/16   

The answer to your question, why do we multiply by 1000, is hinted to by the word "frequency". The frequency of Ppqq for example is 2 in 16. What's the frequency of Ppqq in 1000? If it rains 3 times in every 15 days, how many times will it rain in 60 days?

Edited July 22, 20241 yr by Agent Smith

On 7/22/2024 at 3:16 PM, Agent Smith said:

 

The answer to your question, why do we multiply by 1000, is hinted to by the word "frequency". The frequency of Ppqq for example is 2 in 16. What's the frequency of Ppqq in 1000? If it rains 3 times in every 15 days, how many times will it rain in 60 days?

Thanks for the example, I get it now.