Topic 4B - Diversity, classification and variation

Question 1

What are diploid and haploid numbers?

Answer 1

Normal body cells have the diploid number (2n) of chromosomes. Each cell contains 46 chromosomes and 23 chromosome pairs

Gametes have a haploid number (n) of chromosomes. Each cell has 23 single chromosomes

Question 2

What happens in meiosis I?

Answer 2

Prophase I - The chromosomes arrange themselves into homologous pairs. Crossing over results in recombinant chromosomes

Metaphase I - homologous pairs arrange themselves in the middle of the cell

Anaphase I - homologous pairs separate which halves the chromosome number

Telophase I (and cytokinesis) - 2 genetically different daughter cells are produced

Question 3

What happens in meiosis II?

Answer 3

Meiosis II the pairs of sister chromatids that make up each chromosome are separated
Prophase II - The spindle fibres form. No crossing over occurs
Metaphase II - The chromosomes line up in the middle of the cell
Anaphase II - chromatids are pulled to opposite poles of the cell by spindle fibres
Telophase II (and cytokinesis) - The 2 cells divide into 4 genetically different daughter/haploid cells (aka gametes)

Question 4

What is meiosis?

Answer 4

A type of cell division
Meiosis forms gametes in the reproductive organs of multicellular eukaryotes
The cells that divide by meiosis are diploid and the resulting cells are haploid

Question 5

How is genetic variation created in meiosis?

Answer 5

Crossing over of chromatids in meiosis I. The chromatids swap sections. They still contain the same genes but have a different combination of alleles

Fertilisation is random

Independent segregation of chromosomes

Question 6

What is non-disjunction?

Answer 6

A chromosome mutation
A failure of the chromosomes to separate properly resulting in an extra copy
In humans, non-disjunction of chromosome 21 during meiosis can lead to Down’s syndrome
An extra copy of chromosome 13 leads to Patau syndrome

Question 7

Different types of mutation

Answer 7

Substitution - one base is substituted with another
Deletion - one base is deleted
Addition - one or more bases are added to the DNA sequence

Question 8

What is a mutation?

Answer 8

Changes to the base sequence of DNA

Question 9

Why do some mutations not effect the order of amino acids?

Answer 9

Because the genetic code is degenerate (some amino acids are coded for by more than one DNA triplet)
Substitution mutations won’t always lead to changes in the amino acid sequence but deletion mutations will

Question 10

What is a mutagenic agent? + examples

Answer 10

Chemical, biological or physical agents that cause changes to the base sequence of DNA
They increase the rate of mutation
E.g. Ultraviolet radiation, ionising radiation, chemicals and viruses
They increase the rate at which mutations can occur

Question 11

What happens before meiosis starts?

Answer 11

The DNA unravels and replicates so there are two copies of each chromosome, called chromatids
The DNA then condenses to form chromosomes each made from two sister chromatids joined by a centromere

Question 12

What is genetic diversity?

Answer 12

Genetic diversity is the number of different alleles of genes in a species or population

Genetic diversity allows natural selection to occur

Question 13

How can genetic diversity within a population be increased?

Answer 13

Mutations in the DNA sequence can form new alleles
Different alleles can be introduced into a population due to the migration of another population. This is known as gene flow

Question 14

How do genetic bottlenecks decrease diversity?

Answer 14

A genetic bottleneck is an event that causes a reduction in population size. This reduces the number of different alleles in the gene pool and so reduces genetic diversity

Question 15

What is the gene pool?

Answer 15

The total number of alleles in a population

Question 16

What is the Founder effect?

Answer 16

Describes what happens when a very small population starts a new colony from only a small number of alleles in the initial gene pool

The frequency of alleles may be very different to that in the original population e.g. an allele that was rare may now be common

The Founder effect can occur as a result of migration leading to geographical separation

Question 17

What is natural selection?

Answer 17

There’s differential reproductive success in a population - individuals that have an allele that increases their chance of survival are more likely to survive, reproduce and pass on their useful alleles to their offspring
This means a greater proportion of the next generation inherits the beneficial allele
The frequency of the beneficial allele increases over time from generation to generation
This leads to evolution

Question 18

Name 3 types of adaptation

Answer 18

Behavioural e.g. acting dead to escape predators
Physiological e.g. hibernation
Anatomical e.g. whale’s blubber or elephant’s ears

Question 19

What is directional selection?

Answer 19

Where individuals with alleles for an extreme characteristic are more likely to survive and reproduce
This could be in response to an environmental change
E.g. Antibiotic resistance

Question 20

What is stabilising selection?

Answer 20

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce
Occurs when the environment isn’t changing and it reduces the range of alleles
E.g. human birth weight
It selects against extreme phenotypes and reduces the range of possible phenotypes

Question 21

What is phylogeny?

Answer 21

The study of evolutionary history of groups of organisms
The evolutions of common ancestors can be shown in a phylogenetic tree

Question 22

What is taxonomy?

Answer 22

The science of classification
The groups are called taxa
Each group is a taxon
3 large groups - domains consisting of Eukarya, Bacteria and Archaea
Then kingdoms, phylum then class, order, family, genus, species
King Prawn Curry or Fat Greasy Sausages

Question 23

What is a species?

Answer 23

A group of organisms that are able to interbreed and produce fertile offspring

Question 24

What is the binomial system?

Answer 24

The nomenclature used for classification
All organisms are give one internationally accepted scientific name in Latin
The first part is the genus and has a capital letter
The second is the species and is a lowercase letter
E.g. Homo sapiens
Written in italics or underlined if handwritten

Question 25

Using courtship behavior to help classify species

Answer 25

Releasing chemicals/a series of displays
Species specific which means it can be used for classification
Prevents interbreeding and makes reproduction more successful
The more closely related a species the more similar their courtship behavior

Question 26

What is phylogeny?

Answer 26

Classifying organism according to their evolutionary relationships

Question 27

What techniques have helped clarify evolutionary relationships?

Answer 27

Genome sequencing
Comparing amino acid sequences
Immunological comparisons

Question 28

How is variation caused?

Answer 28

There’s variation between and within species
Can be caused by genetic factors- within a species organisms will have different alleles, between species there will be different genes
Can also be due to environmental factors e.g. climate, food
Variation is mainly due to a combination of genetic and environmental factors e.g. genes determine how tall and organism can grow but nutrient availability affects how tall the organism will actually grow

Question 29

Studying variation

Answer 29

Samples of a population are used
Sample should be random
It’s important to analyse results statistically to prove the observations aren’t due to chance
The mean is used to average values
Most samples will include values either side of the mean so you end up with a bell-shaped graph. This is normal distribution which is symmetrical about the mean
The mean can be used to tell if there is variation between samples

Question 30

Using standard deviation to tell you about the mean

Answer 30

Standard deviation is a spread of values about the mean
A large standard deviation means the values in a sample vary significantly and vice versa
Standard deviations can be plotted on a graph using error bars
Error bars extend one standard deviation above and onw below the mean so the total length of the error bar is twice the standard deviation
The longer the bar the larger the standard deviation and the more spread out the sample data is from the mean

Question 31

What is biodiversity?

Answer 31

The variety of living organisms in an area
You can have local and global diversity

Question 32

What is a habitat?

Answer 32

The place where an organism lives

Question 33

What is a community?

Answer 33

All the populations of different species in a habitat

Question 34

What is species richness?

Answer 34

A measure of The number of different species in a community
It can be worked out by taking random samples of a community and counting the number of different species
A simple measure of biodiversity

Question 35

How do agricultural practices reduce diversity?

Answer 35

Woodland clearance
Hedgerow removal
Pesticides
Herbicides
Monoculture

Question 36

What conservation schemes are available to protect biodiversity?

Answer 36

Legal protection to endangered species
Creating protected area which restrict (agricultural) development
The Environmental Stewardship Scheme encourages farmers to conserve biodiversity e.g.. replanting hedgerows

Question 37

What is a zygote?

Answer 37

A diploid cell resulting from the fusion of two haploid gametes

Question 38

How can DNA replication cause a mutation?

Answer 38

When DNA replicates the base sequence is read and copied
There can be errors in the replication process which lead to mutations
Mutations involved with DNA replication are spontaneous

Question 39

What is a homologous pair?

Answer 39

Two chromosomes with identical genes but different alleles

Question 40

Quantitive investigation

Answer 40

Random sampling
Calculating the mean
Standard deviations