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Biology A-level > 4B Diversity, Classification and Variation > Flashcards

4B Diversity, Classification and Variation Flashcards

1
Q

How is DNA passed on from one generation to the next?

A

By gametes

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2
Q

What are gametes?

A

The sperm cells in males and egg cells in females

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3
Q

What is a zygote?

A

When a sperm cell fertilises an egg cell, the zygote divides and develops into a new organism

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4
Q

How many chromosomes do normal body cells have?

A

They have the diploid number (2n)

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5
Q

What does the ‘diploid number’ mean?

A

It means each cell contains two of each chromosome, one from the mum and one from the dad

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6
Q

How many chromosomes do gametes have?

A

The haploid number (n)

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7
Q

What does the ‘haploid number’ mean?

A

There’s only one copy of each chromosome

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8
Q

How is the diploid number of chromosomes achieved?

A

At fertilisation, a haploid sperm fuses with a haploid egg, making a cell with the normal diploid number of chromosomes

Half the chromosomes are from the father (the sperm) and half are from the mother (egg)

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9
Q

How is fertilisation random?

A

During sexual reproduction, any sperm can fertilise any egg

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10
Q

How does random fertilisation affect the zygotes?

A

It produces zygotes with different combinations of chromosomes to both parents

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11
Q

How does random fertilisation affect diversity?

A

The mixing of genetic material in sexual reproduction increases genetic diversity within a species

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12
Q

How are gametes formed?

A

Via meiosis

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13
Q

What is meiosis and where does it take place?

A

It is a type of cell division and it takes place in the reproductive organs

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14
Q

Why is meiosis necessary for gametes?

A

Cells that divide by meiosis are diploid to star with, but the cells formed from meiosis are haploid (halved)

Without meiosis you’d have double the no. chromosomes when the gametes are fused which would not be good

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15
Q

What happens in the first 2 stages of meiosis?

A

1) Before meiosis starts, the DNA unravels & replicates so there are two copies of each chromosome, called chromatids.
2) The DNA condenses to form double-armed chromosomes, each made from two sister chromatids. Sister chromatids are joined in the middle by a centromere.

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16
Q

What happens in Meiosis I (stages 3 & 4 of meiosis)?

A

3) (First division) - the chromosomes arrange themselves in homologous pairs
4) These homologous pairs are then separated, halving the chromosome number

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17
Q

What happens in Meiosis II (stages 5 & 6 of meiosis)?

A

5) (second division) - the pairs of sister chromatids that make up each chromosome are separated (the centromere is divided)
6) Four haploid cells (gametes) that are genetically different from each other are produced

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18
Q

How many cells are produced from meiosis?

A

4

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19
Q

When in Meiosis do the chromatids cross over?

A

In Meiosis I

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20
Q

How do the chromatids cross over in Meiosis I?

A

Homologous pairs of chromosomes come together & pair up

The chromatids twist around each other & bits of chromatids swap over

The chromatids still contain the same genes but now have a different combination of alleles

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21
Q

What are the cells like that meiosis produces?

A

They are genetically different

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22
Q

What are the two main events in meiosis that lead to genetic variation?

A

1 - Crossing over of chromatids

2 - Independent segregation of chromosomes

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23
Q

How does the crossing over of chromatids in meiosis create genetic variation?

A

The crossing over of chromatids in meiosis I means that each of the four daughter cells formed from meiosis contains chromatids with different alleles

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24
Q

How does independent segregation of chromosomes in meiosis create genetic variation?

A

1) Each homologous pair of chromosomes in your cells is made up of one chromosome from your mum (maternal) and one from your dad (paternal)
2) When the homologous pairs are separated in meiosis I, it’s completely random which chromosome from each pair ends up in which daughter cell
3) So the four daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes
4) This is called independent segregation (seperation) of the chromosomes
5) This ‘shuffling’ of chromosomes leads to genetic variation in any potential offspring

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25
What are the stages of crossing over in meiosis?
1 - The chromosomes of homologous pairs come together 2 - Chromatids cross over 3 - One chromosome from each homologous pair ends up in each cell 4 - Each cell has a different chromatid and therefore a different set of alleles, which increases genetic variation
26
How are the number of chromosomes produced different in meiosis vs mitosis?
Mitosis --> Produces cells with the same no. chromosomes as the parent cell Meiosis --> Produces cells with half the no. chromosomes as the parent cell
27
How is the genetic material produced different in meiosis vs mitosis?
Mitosis --> Daughter cells are genetically identical to each other and to the parent cell Meiosis --> Daughter cells are genetically different from one another and the parent cell
28
How are the number of cells produced different in meiosis vs mitosis?
Mitosis --> Produces two daughter cells Meiosis --> Produces four daughter cells
29
How many divisions do mitosis and meiosis involve?
Mitosis - one Meiosis - two
30
Why can't crossing over or independent segregation take place during mitosis?
There's no pairing or separation of homologous chromosomes so they can't cross over etc This produces genetically identical daughter cells - unlike meiosis
31
What are chromosome mutations caused by?
Errors in cell division (during meiosis)
32
When an error in cell division occurs, how can this affect the chromosomes?
When meiosis goes wrong the cells produced can contain variations in the numbers of whole chromosomes or parts of chromosomes
33
What do chromosome mutations lead to?
Inherited conditions - because the errors are present in the gametes (the hereditary cells)
34
What is non-disjunction?
It's a failure of the chromosomes to separate properly
35
What causes Down's Syndrome in humans?
The non-disjunction of chromosome 21 during meiosis Someone having an extra copy of chromosome 21
36
How does the non-disjunction of chromosome 21 cause someone to have Down's Syndrome
It means that chromosome 21 fails to separate properly during meiosis - one cell will have an extra copy of 21 and another gets none When the gamete with the extra copy fuses to another gamete at fertilisation, the resulting zygote will have 3 copies of chromosome 21
37
What are mutations?
Changes to the base sequence of DNA
38
What are the two types of mutations that can occur?
Substitution and deletion
39
What is a substitution mutation?
One base is substituted with another e.g. AAGCT becomes ATGCT (A is swapped for T)
40
What is a deletion substitution?
One base is deleted e.g. AAGCT becomes AGCT (A is deleted)
41
What does the order of DNA bases in a gene determine and how does a mutation affect this?
The particular protein that is going to be made If a mutation occurs, the sequence may be changed and the protein formed could be altered
42
Do all mutations affect the order of the amino acid chain?
No - some substitutions and have no effect on the order
43
How does the degenerate nature of the genetic code affect mutations?
It means that some amino acids are coded for by more than one DNA triplet - therefore not all substitutions will change the amino acid sequence e.g. TAT, TAC both code for tyrosine
44
Will substitutions always lead to a change in the amino acid sequence?
No - due to the degenerative nature of the genetic code, some amino acid sequences code for the same proteins so there can be no change
45
Will deletions always lead to a change in the amino acid sequence?
Yes - the deletion of a base will change the number of bases present, which will cause a shift in all the base triplets after it
46
What are mutagenic agents?
They increase the rate of mutation Mutations occur randomly, however some things can cause an increase in the rate of mutations
47
What are some examples of mutagenic agents?
- Ultraviolet radiation - Ionising radiation - Some chemicals - Some viruses
48
What do lots of different alleles mean for a species?
There is high genetic diversity
49
What is genetic diversity?
The number of different alleles of genes in a species or population
50
What can increase genetic diversity in a population?
- Mutations in the DNA | - Different alleles being introduced into a pop.
51
How do mutations in DNA cause genetic diversity?
They form new alleles
52
What is gene flow?
Different alleles being introduced into a pop. when individuals from another pop. migrate into them & reproduce
53
Genetic diversity allows what to occur?
Natural selection
54
What can reduce genetic diversity?
A genetic bottleneck
55
What is a genetic bottleneck?
An event that causes a big reduction in a population e.g. when a large no. organisms within a population die before reproducing
56
How does a genetic bottleneck reduce genetic diversity?
It reduces the no. different alleles in the gene pool - so reduces genetic diversity Survivors reproduce & a larger pop. is created from a few individuals
57
Give an example of a genetic bottleneck
Northern Elephant Seals They were hunted by humans in the late 1800s - their original pop. was reduced to around 50 seals who then produced a pop. of around 170 000 New pop. has little genetic diversity compared to Southern elephant seals who didn't suffer this reduction in numbers
58
What is the founder effect?
A type of genetic bottleneck
59
Define the founder effect
It describes what happens when just a few organisms from a pop. start a new colony & there are only a small no. different alleles in the initial gene pool
60
What does Phylogeny tell us about?
Evolutionary history of organisms
61
Where have all organisms evolved from?
From shared common ancestors
62
What are the domains?
``` Kingdom Phylum Class Order Family Genus Species ```
63
What is taxonomy?
Science of classification, organising organisms into groups
64
What are the 3 domains?
Eukarya, Bacteria and Archaea
65
What is the order for naming an animal?
Genus - Species
66
What is courtship behaviour?
Behaviour carried out by animals to attract mate of right species
67
What can courtship behaviour help to identify?
Used to classify organisms through there specific behaviour
68
Give 3 examples of animals courtship behaviour
- Fireflies give off pulses of light - Crickets make sounds similar to morse code - Male peacocks show off colourful tails
69
What has technological advances been useful for?
Clarifying evolutionary relationships
70
What 3 things has technology been useful in?
- Genome sequencing - Comparing amino acid sequence - Immunological comparison
71
What has advancements in genome sequencing allowed us to do?
- Determine entire base sequence of organisms DNA | - Help compare how closely related species are
72
How does genome sequencing tell you species are closely related?
Shows closely related species will have higher % of similarity in DNA base order
73
How does comparing amino acids tell you species are closely related?
Related organisms have similar amino acid structure
74
How does immunological comparisons tell you species are closely related?
Similar proteins bind to same antibodies, if add antibodies to isolated sample any similar antibodies will be recognised
75
When can the founder effect occur?
It can occur as a result of migration leading to geographical seperation or if a new colony is seperated from the original population for another reason, such as religion
76
Give an example of the founder effect
The Amish - they descended from a small number of Swiss who migrated there They have remained isolated due to their religious beliefs - showing little genetic diversity The population has an unusually high incidence of certail genetic disorders
77
How is natural selection beneficial to populations?
It increases advanageous alleles in a population Also leads to populations becoming better adapted
78
What are the 3 types of adaptions that organisms can gain through natural selection?
- Behavioural adaptions - Physiological adaptions - Anatomical adaptions
79
What are behavioural adaptions?
Ways an organism acts that increase its chance of survival & reproduction e.g. possums sometimes 'play dead' if they're being threatened by a predator to escape attack
80
What are physiological adaptions?
Processes inside an organism's body that increase its chance of survival e.g. brown bears hibernate over winter - they lower their rate of metabolism. This conserves energy, so they don't need to look for food in the months when its scarce
81
What are anatomical adaptions?
Structural features of an organism's body that increase its chance of survival e.g. whales have a thick layer of blubber (fat) which helps them to keep warm in the cold sea
82
What are the two key factors in evolution?
Adaption and selection
83
What is evolution?
The gradual change in species over time Evolution has led to huge diversity of living organisms on earth
84
How were early estimates of genetic diversity found?
Observing characteristics
85
How can befenficial mutations allow for natural selection?
The beneficial mutations allow the organism to survive better than other members of the species, therefore allowing for natural selection e.g. giraffes having longer necks
86
How can advantageous alleles increase in a population through natural selection?
1) Not all individuals are as likely to reproduce as each other. Differential reproductive sucess in a pop. - individuals that have allele that increases their chance of survival & are more likely to survive, reproduce and pass on their genes 2) This means that a greater proportion of the next generation inherits the beneficial allele 3) They are more likely to survive, reproduce & pass on their genes 4) So the freq. of the beneficial allele increasesfrom generation to generation 5) Over generations leads to evolution as the advantageous alleles become more common in the pop.
87
Why can some mutations be better than others?
Harmful mutations normally lead to the the allele quickly dying out Beneficial mutations may help the organism to survive in their environment - this allows for natural selection
88
How can befenficial mutations allow for natural selection?
The beneficial mutations allow the organism to survive better than other members of the species, therefore allowing for natural selection e.g. girrafes having longer necks
89
What can cause genetic variation between/within species?
Different species have different genes - causes variation between species Individuals of same species have same genes but different alleles - causes variation within a species
90
What can variation be caused by?
Genes, the environment or both
91
How can genetic & environmental factors cause variation within a species?
Genes determine how tall an organism can grow, but nutrient availability affects how tall the organism actually grows
92
yo
man
93
How can variation within a species be caused by the environment?
Climate, food, & lifestlye
94
How can genetic & environmental factors cause variation within a species?
Genes determine how tall an organism can grow, but nutrient availability affects how tall the organism actually grows
95
What is biodiversity?
Variety of living organisms in an area
96
What is a habitat?
Place where organism lives
97
What is a community?
All the populations of different species in a habitat
98
What are the 2 types of biodiversity?
- Local biodiversity | - Global biodiversity
99
What is local biodiversity?
Variety of different species living in a small habitat thats local
100
What is global biodiversity?
Variety of species on earth
101
How can biodiversity be measured?
Using index of diversity | species richness, population size
102
What is species richness?
Number of species in a community
103
What does a high index of diversity show?
A more diverse area
104
What agricultural methods reduce biodiversity?
- Woodland clearance - Hedgerow removal - Pesticides - Herbicides - Monoculture
105
How do conservations protect biodiversity?
- Legal protection to endangered species - Protected areas like the SSSI - Environmental Stewardship scheme
106
What is monoculture?
Farmers have fields containing one type of plant
107
What is variation?
Differences that exists between individuals
108
How is there variation between different species?
Different species have different genes
109
How is there variation within a species?
Same genes but different alleles
110
What is most variation within a species caused by?
Combination of genetic and environmental factors
111
How can you study a whole population?
Use a sample of the population
112
What does the sample need to be?
Random so its more accurately representative
113
How can you test if there is variation between samples?
Mean
114
How can you test variation within a sample?
Standard deviation
115
What does a large standard deviation mean?
Means values in sample vary a lot (values are not close to mean)
116
What can standard deviation be used to draw?
Error bars (longer the bar the larger the SD)

Biology A-level (20 decks)

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