Chromosome theory. Genetics of sex
Answers are for parents and teachers.
1
What is crossing over and what is its biological importance?
Exchange of segments between homologous chromosomes in prophase of meiosis. It creates new allele combinations, increases variety and provides material for evolution.
2
A–B is 8, B–C is 5 and A–C is 13 morganides. Find the gene order.
A–B–C: 8 + 5 = 13, with B in the middle.
3
Write the number of chromosomes in a human sperm and an egg.
23 in both: egg 22 + X, sperm 22 + X or 22 + Y.
4
In a family of XY × XX parents with 4 children, will there certainly be 2 girls and 2 boys? Explain.
No. Each birth has probability 1/2 and is an independent event; the 1 : 1 ratio appears only approximately over very many births.
5
If the haploid chromosome number of Drosophila is 4, what is the diploid number? (Number only.)
8