1 Diversity, Classification And Variation

Question 1

Explain gene mutations.

Answer 1

• involve a change in the base sequence of chromosomes.
• substitution, one base is substitute with another.
• deletion, one base is deleted
• order of DNA bases in a gene determines order of amino acids in particular protein, so if mutation occurs in gene, sequence of amino acids it codes for could be altered.
• mutagenic agents increase rate of gene mutations

Question 2

Why do not all mutations affect the order of amino acids.

Answer 2

• degenerate nature of genetic code means some amino acids are coded for by more than one DNA triplet, so not all substitution mutations will result in change to amino acid sequence of protein-some substitutions will code for same amino acid.
• deletion will change amino acid sequence as it changes number of bases present, which will cause a shift in all base triplets after it.

Question 3

What does meiosis produce?

Answer 3

4 haploid cells that are genetically different from each other.

Question 4

Describe chromosome mutations.

Answer 4

Can arise spontaneously by chromosome non-disjunction, failure of chromosomes to separate properly, during meiosis.

Question 5

Describe what happens in prophase 1.

Answer 5

• chromosomes condense

- nuclear membrane breaks down

Question 6

Describe what happens in metaphase 1.

Answer 6

• homologous pairs line up next to each other
• spindle forms
• attaches to centromeres

Question 7

Describe what happens in anaphase 1.

Answer 7

• homologous pairs are separated

- pulled apart to opposite poles

Question 8

Describe what happens in telophase 1.

Answer 8

• nuclei reform

- cell divides

Question 9

Describe what happens in prophase 2.

Answer 9

-nuclei break down

Question 10

Describe what happens in metaphase 2.

Answer 10

• chromosomes line up on equator
• spindle forms
• attaches to centromeres

Question 11

Describe what happens in anaphase 2.

Answer 11

• chromatids are separated

- pulled apart to opposite poles

Question 12

Describe what happens in telophase 2.

Answer 12

• nuclei reform

- cell divides

Question 13

How does crossing over of chromatids create genetic variation.

Answer 13

• crossing over of chromatids occurs in meiosis 1 where a homologous pair of chromosomes pair up, the chromatids twist around each other and bits of chromatids swap over. Chromatids still contain same genes but now have different combination of alleles.
• means that each of 4 daughter cells formed contains different alleles.

Question 14

How does independent segregation of chromosomes create genetic variation.

Answer 14

• each homologous pair in cell has 1 maternal chromosome and 1 paternal chromosome.
• when homologous pairs separated in meiosis 1, it’s random which chromosomes from each pair ends up in which daughter cell.
• so 4 daughter cells have completely different combinations of those maternal and paternal chromosomes. This leads to genetic variation.

Question 15

Define genetic diversity.

Answer 15

The number of different alleles of genes in a population. It’s a factor enabling natural selection to occur.

Question 16

Explain the principles of natural selection.

Answer 16

• random mutation resulting in new alleles of gene.
• many mutations harmful but, in certain environments, the new allele of gene might benefit its possessor, leading to increased reproductive success.
• advantageous allele inherited by members of next generation.
• as a result, over many generations, the new allele increases in frequency in the population.

Question 17

Describe how antibiotic resistance shows directional selection.

Answer 17

• some individuals in population have alleles that give them resistance to an antibiotic.
• population exposed to the antibiotic, killing bacteria without resistant allele.
• resistant bacteria survive and reproduce without competition, passing on allele that gives antibiotic resistance to offspring.
• after some time, most organisms in population will carry antibiotic resistance allele.

Question 18

Define directional selection.

Answer 18

Where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce.

Question 19

Define stabilising selection.

Answer 19

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.

Question 20

Describe how human birth weight shows stabilising selection.

Answer 20

• humans have range of birth weights.
• very small Babies less likely to survive.
• giving birth to large babies can be difficult, so large babies less likely to survive too.
• conditions most favourable for medium-sized babies, so weight of human babies tends to shift towards the middle of the range.

Question 21

Describe 3 ways in which natural selection adapts species.

Answer 21

Behavioural adaptations- ways and organism acts that increase its chance of survival and reproduction.
Physiological adaptations- processes inside organisms body that increase chances of survival.
Anatomical adaptations- structural features of organism’s body that increases its chance of survival.

Question 22

What is the calculation of an index of diversity?

Answer 22

d= N(N-1)
———
Sum of n(n-1)
N is total number of organisms of all species.
n. Is total number of organisms of each species.

Question 23

What is a phylogenetic classification system?

Answer 23

A system that attempts to arrange species into groups based on their evolutionary origins and relationships. It uses a hierarchy in which smaller groups are placed within larger groups, with no overlap between groups. Each group called a taxon. One hierarchy comprises the taxa: domain, kingdom, phylum, class, order, family, genus and species.

Question 24

Describe courtship behaviour.

Answer 24

• Carries out by organisms to attract a mate of the right species.
• it’s species specific, only members of same species will do and respond to that courtship behaviour. This allows members of same species to recognise each other, prevent interbreeding and make reproduction more successful.
• can be used to classify organisms.

Question 25

Define phylogeny.

Answer 25

The study of evolutionary history of groups of organisms.

Question 26

What is the binomial naming system?

Answer 26

• How each species is universally identified.
• first part of name is the genus name and has a capital letter.
• second part of name is the species name and begins with a lower case letter.
• names always written in italics

Question 27

Define species richness.

Answer 27

A measure of the number of different species in a community.

Question 28

What is an index of diversity?

Answer 28

Describes the relationship between the number of species in a community and the number of individuals in each species.

Question 29

How can biodiversity be considered at different levels.

Answer 29

Local biodiversity- consider variety of different species living in a small local habitat.
Global biodiversity- consider variety of different species on earth.

Question 30

what are some farming techniques that reduce biodiversity?

Answer 30

• woodland clearance
• hedgerow removal
• pesticides
• herbicides
• monoculture

Question 31

What are some conservation schemes?

Answer 31

• legal protection to endangered species.
• creating protected areas, restrict further development.
• the environmental stewardship scheme which encourages farmers to conserve biodiversity.

Question 32

How can genome sequencing clarify evolutionary relationships?

Answer 32

Advances in genome sequences meant that entire base sequence of an organisms DNA can be determined. DNA base sequence of 1 organism compared to another organisms. Closely related species will have higher % of similarity in their DNA base order.

Question 33

How can comparing amino acid sequence clarify evolutionary relationships?

Answer 33

Sequence of amino acids in protein corded for by base sequence in DNA. Related organisms have similar DNA sequences + so similar amino acid sequences in their proteins.

Question 34

How can immunological comparisons clarify evolutionary relationships?

Answer 34

Similar proteins will also bind to same antibodies. Eg. If antibodies to human version of protein added to isolated samples from some other species, any protein lime the human version will be recognised.

Question 35

How can the genetic diversity within or between species be determined?

Answer 35

By comparing the: frequency of measurable or observable characteristics, the base sequence of DNA, the base sequence of mRNA and the amino acid sequence of proteins encoded by DNA and mRNA

Question 36

What are the limitations of comparing observable characteristics like the shape of size?

Answer 36

• characteristics could be coded for by more than one gene
• same characteristics could have arisen separately
• characteristics could be influenced by the environment and not the genes.