| Date | November 2016 | Marks available | 1 | Reference code | 16N.2.SL.TZ0.4 |
| Level | Standard level | Paper | Paper 2 | Time zone | TZ0 |
| Command term | State | Question number | 4 | Adapted from | N/A |
Question
The diploid number of chromosomes in horses (Equus ferus) is 64 and the diploid number in donkeys (Equus africanus) is 62. When a male donkey and a female horse are mated, the result is a mule which has 63 chromosomes.
State the haploid number for horses.
Explain reasons that mules cannot reproduce.
Discuss whether or not horses and donkeys should be placed in the same species.
A mule was born at the University of Idaho in the USA with 64 chromosomes. Suggest a mechanism by which this could happen.
Markscheme
32
a. because the chromosome number is not an even number/63
b. (so) cannot divide by two during meiosis/cannot perform meiosis/chromosomes cannot pair up during meiosis
c. one chromosome has no homologue/WTTE
d. because unlikely to/cannot produce viable gametes/sperm/egg cells
a. to be in same species two organisms must have the same genes arranged on the same chromosomes
OR
must have the same number of chromosomes
b. members of same species produce fertile offspring and a mule is not fertile
non-disjunction
Accept description of non-disjunction.
