4.3 - 4.4 Genetic diversity and meiosis

Question 1

define mutation

Answer 1

a mutation is a random change in DNA that alters the sequence of bases. during replication or at the other points in the cell cycle the order and sequence of bases can change. these changes are permanent and heritable

Question 2

which type of mutation causes a frame shift

Answer 2

deletions/insertions

Question 3

what does the genetic code being degenerate mean

Answer 3

that some triplets code for the same amino acids

Question 4

explain non-disjunction

Answer 4

sometimes during meiosis individual homologous pairs of chromosomes fail to separate. this is known as non-disjunction and usually results in a gamete having one more or one less chromosome. an example of this is Down’s syndrome

Question 5

what does meiosis produce

Answer 5

gametes for sexual reproduction

Question 6

define diploid and haploid

Answer 6

diploid - the presence of two complete set of chromosomes
haploid - the presence of a single set of chromosomes

diploid = 23 pairs
haploid = 23 unfused strands

Question 7

what happens in meiosis 1

Answer 7

the first division, homologous chromosomes pair up and their chromatids wrap around each other. equivalent portions of these chromatids may be exchanged in a process called crossing over, one chromosome from each pair

Question 8

what happens in meiosis 2

Answer 8

the second meiotic division, the chromatids move apart and 4 cells are formed

Question 9

what happens at independent assortment

Answer 9

when the homologous pairs pair up, whole they must be next to their partner it doesn’t matter which side they are on.
so the resulting two cells will have a new mix of maternal/paternal DNA in, ready to split again

• the chromatids of each pair become twisted around one another
• during this twisting process tensions are created and portions of the chromatids break off
• these broken portions might then rejoin with the chromatids of its homologous partner
• usually it is the equivalent portions of homologues chromosomes that are exchanged
• in this way new genetic combinations of maternal and patronal alleles are produced.