4.3 Genetic diversity can arise as a result of mutation or during meiosis

Question 1

Gametes

Answer 1

The sperm and egg cells. They join together at fertilisation to form a zygote, divides and develops into a new organism. Have a haploid number of chromosomes

Question 2

Diploid number of chromosomes

Answer 2

Each cell contains two of each chromosome, one from the mum, one from the dad

Question 3

Haploid number of chromosomes

Answer 3

Gametes contain a single copy of each chromosome, either the dad’s or mum’s

Question 4

Meiosis

Answer 4

1. Before meiosis, DNA unravels and replicates so there are two copies of each chromosome (chromatids)
2. Sister chromatids joined together in the middle by centromere
3. Chromosomes arranged into homologous pairs, these are separated
4. Meiosis 2, pairs of sister chromatids separated
5. Four haploid cells that are genetically different are produced

Question 5

Crossing over

Answer 5

During meiosis 1, homologous pairs of chromosomes come together and pair up. Bits of chromatids swap over. Chromatids contain same genes but now have different combinations of alleles

Question 6

Independent segregation of chromosomes

Answer 6

When homologous chromosomes are separated during meiosis 1, it is random so the daughter cells have different combinations of maternal and paternal chromosomes. Leads to genetic variation in any potential offspring

Question 7

Outcomes of meiosis

Answer 7

Produces cells with half the number of chromosomes as parent cell, daughter cells are genetically different from one another and the parent cell, produces four daughter cells

Question 8

Chromosome mutations

Answer 8

Caused by errors during meiosis, can result in variations in number of chromosomes or parts of chromosomes

Question 8

Non-disjunction

Answer 8

Failure of chromosomes to separate properly. Non-disjunction in chromosome 21 results in Down’s syndrome

Question 9

Substitution mutation

Answer 9

One base is substituted with another

Question 10

Deletion mutation

Answer 10

One base is deleted, will always result in changes in amino acid sequences because number of bases is changed so a shift in base triplets

Question 11

Degenerate nature of genetic code

Answer 11

Some amino acids are coded for by more than one DNA triplet

Question 12

Mutagenic agents

Answer 12

Can increase the rate of mutations. Ultraviolet radiation, ionisation radiation, some chemicals and some viruses