Question

Two Drosophila with genotypes AABBCC and aabbcc are crossed to produce a heterozygous offspring, AaBbCc (the gene order is unknown). This AaBbCc Drosophila is crossed with an aabbcc Drosophila, resulting in the offspring below: Number: Phenotype: 600 ABC and abc 200 AbC and aBc 150 ABc and abC 50 Abc and aBC a. Which phenotype represents the double crossovers

Answer 1

In the cross between AaBbCc and aabbcc Drosophila, the double crossover phenotypes are the least frequent, which are Abc and aBC.

Step-by-step explanation:

The phenotype representing the double crossovers in this Drosophila genetics question is identified by comparing the phenotypic frequencies from the cross between heterozygous AaBbCc and homozygous recessive aabbcc parents. In genetics, double crossovers refer to the least frequent phenotypes that arise when two separate recombination events occur during meiosis, which causes alleles at two loci to swap places. Based on the given offspring numbers, the double crossover offspring are the least frequent, which in this set are the phenotypes Abc and aBC. Double crossovers are important in determining gene order and distances in genetic mapping.

Answer 2

The double recombinant individuals are less frequent ---> Abc and aBC

Step-by-step explanation:

We can know if genes are linked, by looking at the progeny distribution. In a tri-hybrid cross, If individuals, whose genes assort independently, are test crossed, they produce a progeny with equal phenotypic frequencies 1:1:1:1:1:1:1:1. If we observe a different distribution, meaning that phenotypes appear in different proportions, we can assume that genes are linked in the heterozygote parent.

We can recognize the parental gametes because their phenotypes are the most frequent in the descendants, while the double recombinants are the less frequent. Finally, the simple recombinant gametes are the ones with intermediate phenotypes frequencies.

In the present example, the phenotypic ratio shows different proportions than the expected ones if they were not linked.

We can recognize the parental gametes in the descendants because their phenotypes are the most frequent,

• ABC and abc 600

while the double recombinants are less frequent.

• Abc and aBC 50

And simple recombinant gametes produced by the cross, which frequencies are intermediate.

• AbC and aBc 200
• ABc and abC 150

a. Which phenotype represents the double crossovers

The double recombinants are less frequent ---> Abc and aBC