Topic 6: Inheritance, Variation and Evolution Flashcards
1
Q
What does ‘DNA’ stand for?
A
Deoxyribonucleic acid
2
Q
Describe the structure of DNA
A
A polymer made up of two strands forming a double helix
3
Q
What is a polymer?
A
A long chain of repeating units
4
Q
What is a chromosome?
A
A thin strand of DNA
5
Q
What is a gene?
A
A small section of DNA on a chromosome
6
Q
What do genes do?
A
They code for a particular sequence of amino acids, to make a specific protein
7
Q
What is a genome?
A
The entire set of genetic material in an organism
8
Q
How many chromosomes are there in a human cell?
A
46
9
Q
How many pairs of chromosomes are there in a human cell?
A
23
10
Q
What can the human genome be used to investigate? [3]
A
- Search for genes linked to diseases
- Understanding and treatment of inherited disorders
- To trace human migration patterns in the past
11
Q
What is an allele?
A
Different versions of the same gene
12
Q
How many alleles of each gene do you have?
A
2 (one from each parent)
13
Q
Define ‘homozygous’
A
When the two alleles present are the same
14
Q
Define ‘heterozygous’
A
When the two alleles present are different
15
Q
Is a domiant allele always expressed?
A
Yes, even if there is only 1
16
Q
How can a recessive allele be expressed?
A
If 2 copies are present (no dominant allele)
17
Q
Define ‘genotype’
A
The collection of alleles that we have
18
Q
Define ‘phenotype’
A
Characteristics that you get as a result of your genotype
19
Q
What does each nucleotide consist of in DNA?
A
Sugar, phosphate and a base
20
Q
How is a particluar protein made from DNA? [3]
A
- The cells reads the sequence as a series of triplet codes
- Each triplet would then code for a particular amino acid
- The amino acids would then combine and fold up in that order to create a protein
21
Q
Explain how mRNA carries a code to the ribosomes [4]
A
- The code in DNA to make proteins is found in the nucleus however proteins are actaully made in the ribosomes
- However, DNA is too big to move out of the nucleus
- Therefore, a molecule called mRNA (made by copying the code from DNA) acts as a messenger
- It carries the code between the nucleus and the ribosomes
22
Q
What are the functions of proteins [3]
A
- Enzymes
- Hormones
- Structural proteins (eg. collagen)
23
Q
Define ‘mutation’
A
A random change in an organism’s DNA
24
Q
What can increase the risk of mutations?
A
Exposure to radiation
25
# Enzymes, structural proteins
What 2 things could a mutation lead to?
1. Change the shape of an enzyme's active site - no longer able to bind to its substrate
2. Structural proteins can lose their strength
26
Explain how insertion mutations occur
A new base is inserted into the DNA base sequence where it shouldn't be
27
What are the consequence of insertion mutations? [2]
1. It changes the way the triplets of bases are 'read', which can change the amino acid they code for
2. More than one amino acid can be changed as they have a knock-on effect on the bases further on in the sequence
28
Explain how a deletion mutation occurs
A random base is deleted from the DNA base sequence
29
What are the consequences of deletion mutations? [2]
1. It changes the way the triplets of bases are 'read', which can change the amino acid they code for
2. More than one amino acid can be changed as they have a knock-on effect on the bases further on in the sequence
30
Explain how a substitution mutation occurs
A random base in the DNA base sequence is changed to a different base
31
Characteristics of sexual reproduction [3]
1. Fusion of male and female gametes
2. Mixing of genetic information
3. Variety in offspring
32
Characteristics of asexual reproduction [4]
1. One parent and no fusion of gametes
2. No mixing of genetic information
3. Genetically identical offspring
4. Only mitosis involved
33
Advantages of sexual reproduction [2]
1. Variation
- population is less likely to be wiped out by a single event
- population can adapt to changing conditions
34
Advantages of asexual reproduction [3]
1. Only one parent - more time and energy efficient
2. Faster
3. Many identical offspring can be produced when conditions are favourable
35
Which organisms reproduce both sexually and asexually? [3]
1. Malarial parasites (sexually in mosquito, asexually in host)
2. Fungi (asexually by spores and sexually to give variation)
3. Plants (produce seeds sexually and asexually by buld division)
36
Cells which divide via meiosis form what?
Gametes
37
Describe the stages of meosis [7]
1. Genetic information is duplicated, forming two armed chromosomes
2. Chromosomes arrange themselves in pairs
3. Chromosome pairs line up along the centre of the cell
4. Pairs are pulled apart so each new cells only has one copy of each chromosome
5. Chromosomes line up again along the centre of the cell
6. The arms of each chromosome are pulled apart
7. You get 4 gametes with 23 chromosomes in each
38
What does GG show?
Homozygous dominant
39
What does Gg show?
Heterozygous
40
What does gg show?
Homozygous recessive
41
What is polydactyly?
Having extra fingers or toes
42
What is polydactyly caused by?
A dominant allele
43
What is cystic fibrosis?
Disorder of cell membranes, leading to thick sticky mucus in air passages
44
What is cystic fibrosis caused by?
A recessive allele
45
Arguments against embryonic screening [3]
1. Implies that people with genetic disorders are undesirable
2. Could lead to screening for other traits - eye colour etc
3. Screening is expensive
46
Arguments for embryonic screening
1. Reduce overall suffering
2. Saves money (reduction in disorder treatment)
47
What did Gregor Mendel do in the mid 19th Century?
Carried out breeding experiments on plants
48
What did Mendel conclude? [3]
1. Characteristics in plants are determined by 'heredity units'
2. These units are passed on, unchanged, to offspring
3. These units can be dominant or recessive
49
What happened in the late 1800s?
Discovered chromosomes and could observe how they behaved during cell division
50
What happened in the early 1900s?
Noticed similarities between chromosomes and Mendel's 'units'. These units are now known as genes on chromosomes
51
What happened in the 1950s?
Double helix structure of DNA discovered
52
What happened in 2003?
Sequenced the entire human genome
53
What 2 things is variation influenced by?
1. Genes
2. Environment
54
State the 'theory of evolution'
All of today's species have evolved from simple life forms that first started to develop over 3 billion years ago
55
Describe the stages of natural selection (survival of the fittest) [4]
1. Organisms with the most suitable characteristics for the environment would be more likely to survive
2. These organims that survived would be more likely to reproduce and pass on their genes
3. Organisms that are less well adapted would be less likely to survive and reproduce and pass on their genes
4. Over time, beneficial characteristics would become more common
56
What is speciation?
When the phenotype of organisms change so much due to natural selection that a completely new species is formed
57
When does speciation occur?
When populations of the same species change so much that they can't interbreed to produce fertile offspring
58
Describe Lamarck's theory of evolution (giraffes) [3]
1. Giraffes started with short necks adapted to lower vegetation
2. They stretched their necks to reach higher branches for food, resulting in longer necks during an individual's lifetime
3. This longer neck trait was passed onto offspring
59
Why was Lamarck's theory of evolution incorrect?
Characteristics aquired by an organism during their lifetime does not affect their DNA sequence, and cannot be passed down from one generation to the next
60
What were Darwin's 3 important observations?
1. Individuals within a species show a wide range of variation for a specific trait
2. Variations between species adapted to different environments
3. Older layers of rock contained fossils of less complex organisms, while more recent layers showed more complex organisms
61
Why was Darwin's theory of evolution not widely accepted? [3]
1. Religious reasons
2. Lack of evidence
3. DNA had not been discovered
62
Define 'selective breeding'
Process by which humans breed plants and animals for particular genetic characteristics
63
What are some examples of selective breeding? [4]
1. Animals that produce more meat or milk
2. Crops with disease resistance
3. Dogs with a good, gentle temperament
4. Plants with large or unusual flowers
64
Describe the basic process of selective breeding [6]
1. From an existing stock, select the ones which have the characteristics you're after
2. Breed them with each other
3. Select the best offspring and breed them together
4. Continue this process over several generations
5. The desirable trait will get stronger and stronger
6. Eventually all of the offspring will have the characteristic
65
What are the drawbacks of selective breeding? [3]
1. Reducing the gene pool, leading to inbreeding
2. Inbreeding can lead to health problems
3. Lack of variation makes new diseases more fatal
66
Describe the process of genetic engineering [3]
1. A useful gene is isolated (cut) from one organism's genome using enzymes
2. It is inserted into a vector (virus or bacterial plasmid)
3. When the vector is introduced to the target organism, the useful gene is inserted into its cells
67
Examples of genetic engineering [3]
1. GM crops have had their genes modified to improve the size and quality of their fruit
2. Bacteria have been modified to produce human insulin that can be used to treat diabetes
3. Sheep have been modified to produce substances like drugs in their milk
68
Pros of GM crops [3]
1. Crops can be grown with desirable charctersitics - e.g. more fruit
2. More food can be made for less money
3. Helps people in developing countries
69
Cons of GM crops [2]
1. Unsure of how GM plants may affect our health
2. May change the ecosystem and reduce biodiversity
70
Describe how animals can be cloned by **adult** cell cloning [4]
1. Nucleus is removed from an unfertilised egg cell
2. Nucleus from an adult body cell (such as a skin cell) is inserted into the egg cell
3. An electric shock stimulates the egg to divide to form an embryo
4. Embryo is inserted into the womb of an adult female to continue development
71
Describe how cows can be cloned using **embryo transplants** [6]
1. Pick a male and a female cow that have the most desirable traits
2. Take sperm from the male and use it to fertilise an egg from the female, forming a zygote
3. Let the zygote develop into an embryo
4. Separate the embryo into lots of smaller embryos
5. Implant each embryo into the uterus of a surrogate cow
6. The offspring will all be identical clones
72
Describe how a plant can be cloned using **cuttings** [4]
1. Find a desirable plant that you want to clone
2. Cut off a small part (ideally a shoot)
3. Place the cutting in some soil, with some nutrients
4. The cutting will grow into a clone of the original plant
73
Describe how a plant can be cloned using **tissue culture** [6]
1. Find a desirable plant that you want to clone
2. Take very small pieces of plant tissue from the tips of shoots
3. Sterilise them to remove any microorganisms
4. Place them in growth medium with plant hormones to allow them to grow into calluses
5. Transfer the calluses to soil where they can grow into plantlets
6. The plantlets can be transferred to their own pots to develop into genetically identical adult plants
74
What is cloning using **tissue culture** used for?
Preserving rare plant species
75
Describe how fossils are formed from **gradual replacement** by minerals [3]
1. Things like teeth, shells and bones, which don't decay easily, can last a long time when buried
2. They are eventually replaced by minerals as they decay, forming a rock-like substance shaped like the original hard part
3. The surrounding sediment also turns to rock, but the fossil stay distinct inside the rock
76
Describe how fossils are formed by **casts** [3]
1. An organism is buried in a soft material like clay
2. Clay hardens around it and the organism decays
3. This leaves a cast of the organism
77
Describe how fossils are formed by **impressions** [2]
1. Footprints are pressed into a soft material
2. Material hardens and an impression is left
78
Describe how fossils are formed by **preservation** [3]
1. An organism dies in something like amber or tar pits
2. There is no oxygen or moisture so no decay occurs
3. The fully preserved organism remains
79
Why are there no fossil records dated to when life began? [2]
1. Many early life forms were soft-bodied, so decayed completely and were not fossilised
2. Early fossils may have been destroyed by geological activity
80
What can cause a species to go extinct? [3]
1. New predator kills them
2. New disease kills them
3. Environment changes too quickly
81
What are fossils?
Remains of organisms from millions of years ago, which are found in rocks
82
What is a species?
A group of similar organisms that can reproduce to produce fertile offspring
83
Describe how a new species can arise [6]
1. Two populations become separated (by a river/mountain)
2. Each population will be exposed to different environmental conditions
3. Populations have different gene pools so natural selection will occur
4. It will favour the alleles which are best suited to each environment
5. The populations will become genetically different
6. Eventually they cannot interbreed to produce fertile offspring and a new species has arised
84
Describe how bacteria can become resistant to antibiotics and be spread [4]
1. Mutations of bacterial pathogens produce new strains
2. Some strains might be resistant to antibiotics, and so are not killed
3. They survive and reproduce so the population of the resistant strain increases
4. The resistant strain will spread because people are not immune to it and there is no treatment
85
What is MRSA?
A 'superbug' which is resistant to many antibiotics
86
How can the development of antibiotic strains be reduced? [3]
1. Doctors should not prescribe antibiotics inappropriately
2. Patients should complete their course of antibiotics
3. Agricultural use of antibiotics should be restricted
87
Why can new antibiotics not keep up with resistant strains of bacteria?
Development of antibiotics is costly and slow
88
Who originally proposed a way to classify organisms?
Carl Linnaeus
89
The Linnaeus system was based off what? [2]
1. Characteristics
2. Structure
90
What is the order of the Linneaus system? [7]
1. Kingdom (king)
2. Phylum (prawn)
3. Class (curry)
4. Order (or)
5. Family (fat)
6. Genus (greasy)
7. Species (sausages)
91
Who proposed the improved 'three-domain system'?
Carl Woese
92
What are the components of the 'three-domain system'?
1. Archaea (primitive bacteria)
2. Bacteria (true bacteria)
3. Eukaryota (plants, animals, fungi, protists)
93
# THINK: homo sapiens
How are species referred to? [2]
1. Genus
2. Species
