| Date | November 2017 | Marks available | 2 | Reference code | 17N.2.HL.TZ0.05 |
| Level | Higher level | Paper | Paper 2 | Time zone | TZ0 / no time zone |
| Command term | Explain | Question number | 05 | Adapted from | N/A |
Question
Describe the process of crossing over.
[2]
a.
Explain the reason for linked genes not following the pattern of inheritance discovered by Mendel.
[2]
b.
Markscheme
a. occurs during prophase I/during meiosis
b. homologous chromosomes form bivalents/pair up
c. breakage and rejoining of chromatids
d. exchange «of DNA/alleles» between non-sister chromatids/homologous chromosomes
[Max 2 Marks]
a.
a. «linked genes are» on the same chromosome
b. Mendel's genes were on different chromosomes
c. linked genes are inherited together
OR
no independent assortment
d. «linked genes» only separated by crossing over
OR
fewer recombinants than with unlinked genes
Reject sex-linkage
b.
Examiners report
[N/A]
a.
[N/A]
b.
