To assemble a genetic map of corn plants based on four recessive mutant loci: br
ID: 53452 • Letter: T
Question
To assemble a genetic map of corn plants based on four recessive mutant loci: brown mid-rib (bm), virescent (v), purple aleurone (pr), and petite (pt), here is the experiment design: Cross two true breeding corn plants that are either completely wild-type or are mutant for all four loci and get F1 plants. Then the F1 tree was self-crossed to obtain F2 seeds. You plant the F2 seeds from F1 self-crossing for a corn of resultant F2 plants. Additionally, it has been known these four loci located at two different chromosomes. Based on the following frequencies of mutant classes: (1) Determine which loci are likely to be on the same chromosome and which locus (loci) appear to segregate independently (2) For the linked loci, calculate the mapping distance and draw the genetic linkage map. You need to show the detailed analysis to make the conclusion. (attention: you do not need to consider the situation in which the parental phenotype in F2 population were derived from the formation of two recombinant gametes since the chance of such parental F2 plants is very low),
Data (phenotype and # of plants): Normal 402 brown mid-rib and purple aleurone 37 petite 127 brown mid-rib 18 purple aleurone 115 virescent, purple aleurone, and petite 12 brown mid-rib and virescent 108 virescent 11 virescent and purple aleurone 54 brown mid-rib and petite 10 brown mid-rib, virescent, and petite 42 brown mid-rib, virescent, purple aleurone, and petite 8 brown mid-rib, virescent, and purple aleurone 41 virescent and petite 3 purple aleurone and petite 38 brown mid-rib, purple aleurone, and petite.
How do I calculate the expected number of offspring? I already know how to do the Chi-square, etc., any other relevant help is highly appreciated.
Phenotype
# of plants
Phenotype
# of plants
Normal
402
brown mid-rib and purple aleurone
37
petite
127
brown mid-rib
18
purple aleurone
115
virescent, purple aleurone, and petite
12
brown mid-rib and virescent
108
virescent
11
virescent and purple aleurone
54
brown mid-rib and petite
10
brown mid-rib, virescent, and petite
42
brown mid-rib, virescent, purple aleurone, and petite
8
brown mid-rib, virescent, and purple aleurone
41
virescent and petite
3
purple aleurone and petite
38
brown mid-rib, purple aleurone, and petite
2
Phenotype
# of plants
Phenotype
# of plants
Normal
402
brown mid-rib and purple aleurone
37
petite
127
brown mid-rib
18
purple aleurone
115
virescent, purple aleurone, and petite
12
brown mid-rib and virescent
108
virescent
11
virescent and purple aleurone
54
brown mid-rib and petite
10
brown mid-rib, virescent, and petite
42
brown mid-rib, virescent, purple aleurone, and petite
8
brown mid-rib, virescent, and purple aleurone
41
virescent and petite
3
purple aleurone and petite
38
brown mid-rib, purple aleurone, and petite
2
Explanation / Answer
Firt calculate observed frequency of each phenotype
Observed frequency = number of each phenotype / total number of plants
For example frequency of normal plants = 402/1028 (sum of number of all phenotypes) = 0.391
Since, there are 16 phenotypic classes of F2 offspring produced, each 4 phenotypic classes segregate according to 9:3:3:1. This means first 4 phenotypes (9): next 4 phenotypes (3): next 4 phenotypes (3): last 4 phenotypes (1)
Now for example,
Expected frequency of normal plants = 402 x 9/ 1028 = 3.51
In this way you can calculate expected frequency for first 4 phenotypes = observed frequency x 9
next 4 phenotypes = observed frequency x 3
next 4 phenotypes = observed frequency x 3
last 4 phenotypes = observed frequency x 1.
Then Chi - square analysis gives that the genes are linked or not and the alleles segregate independently or together.
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