Multiple Choice
When completing fruit fly crosses to study Mendel's laws, which of the following best explains why the F2 generation often displays a phenotypic ratio of approximately 3:1?
3
views
2. Mendel's Laws of Inheritance
Mendel's Experiments and Laws
Struggling with Genetics?
Join thousands of students who trust us to help them ace their exams!Watch the first videoMultiple Choice
In a cross involving a gene located near the centromere, a geneticist observes 20 asci, of which 16 show a 4:4 arrangement of ascospores and 4 show a 2:2:2:2 arrangement. How many of these asci contain an ascospore arrangement that resulted from crossing over?
A
20
B
16
C
4
D
0
Verified step by step guidance1
Understand the types of ascospore arrangements: a 4:4 arrangement indicates no crossing over (parental type), while a 2:2:2:2 arrangement indicates that crossing over has occurred between the gene and the centromere.
Identify the total number of asci observed, which is 20 in this problem.
Count how many asci show the 4:4 arrangement (non-recombinant) and how many show the 2:2:2:2 arrangement (recombinant). Here, 16 asci show 4:4 and 4 asci show 2:2:2:2.
Recognize that only the asci with the 2:2:2:2 arrangement result from crossing over events.
Conclude that the number of asci containing an ascospore arrangement resulting from crossing over is equal to the number of asci showing the 2:2:2:2 pattern, which is 4.
Related Videos
Related Practice
Mendel's Experiments and Laws practice set
Problem sets built by lead tutorsExpert video explanations