Assume that a cross is made between AaBb and aabb plants, and the offspring occur in the following numbers: 106 AaBb, 48 Aabb, 52 aaBb, 94 aabb. These results are consitent with which arrangement of genes?
these results are consistent with linkage with approximately 33 map units between the two gene loci
Ab&Ba
find the % of each offspring category. Write out the cross in a square and see if the ratio is the same between the observed and calculated.
To determine the arrangement of genes, we need to analyze the observed numbers of offspring and compare them to the expected ratios according to Mendelian genetics.
Let's first understand the expected ratios of offspring from the cross between AaBb and aabb plants. When two individuals with heterozygous alleles (AaBb) and homozygous recessive alleles (aabb) are crossed, we can use a Punnett square to predict the possible genotypes in the offspring:
AaBb Aabb aaBb aabb
AaBb | AABb AAbb aaBb aabb
aabb | AaBb Aabb aaBb aabb
From the Punnett square, we can see that there are 9 possible combinations. Since each combination has an equal chance of occurring, we can expect the phenotypic ratio to be 1:1:1:1 for AaBb:Aabb:aaBb:aabb.
Let's calculate the expected numbers of offspring based on these ratios:
Total offspring = 106 (AaBb) + 48 (Aabb) + 52 (aaBb) + 94 (aabb) = 300
Expected AaBb offspring = Total offspring * (1/4) = 300 * 1/4 = 75
Expected Aabb offspring = Total offspring * (1/4) = 300 * 1/4 = 75
Expected aaBb offspring = Total offspring * (1/4) = 300 * 1/4 = 75
Expected aabb offspring = Total offspring * (1/4) = 300 * 1/4 = 75
Now let's compare the expected and observed numbers of offspring:
Observed AaBb offspring = 106
Observed Aabb offspring = 48
Observed aaBb offspring = 52
Observed aabb offspring = 94
By comparing these numbers to the expected ratios, we can determine if the observed results are consistent with the expected ratios.
The observed numbers are very close to the expected numbers, which suggests that the observed results are consistent with a 1:1:1:1 phenotypic ratio for AaBb:Aabb:aaBb:aabb. Therefore, the arrangement of genes for the parents is likely to be in a 1:1:1:1 arrangement.