Question 19M.2.HL.TZ1.2d.i
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.HL.TZ1.2d.i |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Draw | Question number | d.i | Adapted from | N/A |
Thomas Hunt Morgan established that genes for body colour and wing size in Drosophila are autosomally linked. The allele for grey body (b+) is dominant over that for black body (b) and the allele for normal wing size (vg+) is dominant over that for vestigial wing (vg).
A fly that is homozygous dominant for both body colour and wing size mates with a fly that is recessive for both characteristics. In the table, draw the arrangement of alleles for the offspring of this mating and for the homozygous recessive parent.
[2]
This was generally well answered, with more than two thirds of candidates getting at least one of the genotypes correct. The best answers gave the alleles on lines that symbolised linked genes on a chromosome, but there was a potential pitfall here. If the alleles were arranged in a way that was impossible, given the nature of the cross, one mark was deducted. For example, each chromosome must have one of each gene, not two copies of one gene.
