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  • In Neurospora a cross between the genotypes 'A' and 'a' results in an ascus with ascospores of genotypes as shown below: <table border="1" cellpadding="0" cellspacing="0" sty

In Neurospora a cross between the genotypes 'A' and 'a' results in an ascus with ascospores of genotypes as shown below:

 A  A  a  a  a  a  A  A

Statements P to S are events that could have occurred during meiosis

P. Crossing over between the centromere and the gene.

Q. Segregation of alleles 'A' and 'a' in meiosis I.

R. Segregation of alleles 'A' and 'a' in meiosis II.

S. Assortment of alleles 'A' and ‘a'.

Which of the above events could correctly explain the observation shown in the figure?

 

Option: 1

P followed by R


Option: 2

P followed by O

 


Option: 3

R alone


Option: 4

S alone


Answers (1)

best_answer

P. Crossing over between the centromere and the gene:

From the genotypes of the ascospores, we can see that there are recombinant genotypes present (Aa and aA). This indicates that crossing over has occurred between the centromere and the gene, resulting in the exchange of genetic material between homologous chromosomes.

Q. Segregation of alleles 'A' and 'a' in meiosis I:

In the given genotypes (A A a a a a A A), we can observe both alleles 'A' and 'a' segregated in the ascospores. This indicates that during meiosis I, the homologous chromosomes containing alleles 'A' and 'a' have segregated independently and moved to separate daughter cells. Therefore, statement Q is also supported by the given data.

Based on the observed genotypes, it is likely that both events P (crossing over between the centromere and the gene) and Q (segregation of alleles 'A' and 'a' in meiosis I) have occurred during meiosis in Neurospora and P is followed by R.

Hence, the correct answer is option 1.

 

Posted by

jitender.kumar

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