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AQA GCSE - Biology - paper 2 > Inheritance, Variation and Evolution > Flashcards

Inheritance, Variation and Evolution Flashcards

1
Q

What is variation?

A

All the differences in the characteristics of individuals in a population

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2
Q

What are the causes of variation?

A
  • Genetic causes
  • Environmental causes
  • Combination of genes and environment
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3
Q

What are the genetic causes of variation?

A

Alleles inherited from parents

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4
Q

Give an example of genetic variation:

A
  • hair colour
  • eye colour
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5
Q

Give an example of environmental variation:

A
  • Colour of flowers depending on pH of soil
  • Language in humans
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6
Q

Give an example of combination of genes and environment:

A

Height in humans

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7
Q

What is genetic variation caused by?

A

Genetic variation in a population is due to mutations

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8
Q

What are genetic mutations?

A

Changes to DNA

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9
Q

What is DNA?

A

deoxyribonucleic acid - it is the chemical that all genetic material in a cell is made from. It contains coded information for the cell.

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10
Q

What is a chromosome?

A

The structure made of DNA that codes for all the characteristics of an organism.

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11
Q

What is the structure of DNA?

A

DNA is a polymer made up of two strands forming a double helix. The DNA is contained in structures called chromosomes.

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12
Q

What is a gene?

A

A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein.

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13
Q

What is a genome?

A

Genome refers to the entire set of genetic material in an organism. The whole human genome has now been studied and this will have great importance for medicine in the future.

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14
Q

Describe the nucleotide structure:

A

Every nucleotide is made of one sugar molecule, one phosphate molecule and one base.

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15
Q

What is the sugar-phosphate backbone?

A

The sugar and phosphate molecules in the nucleotide form a backbone to the DNA strands. The sugar and phosphate molecules alternate. One of four different bases (A,T,C,G)

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16
Q

How do the bases pair together?

A

A always pairs up with T, and C always pairs to G. The order of bases in a gene determines the order of amino acids in a protein. In the complementary strands a C is always linked to a G on the opposite strand and a T to an A.

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17
Q

How are amino acids formed?

A

Each amino acid is coded for by a sequence of three bases in a gene. The amino acids are joined together to make various proteins, depending on the order of the gene’s bases.

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18
Q

Does all DNA code for proteins?

A

No - there are parts of DNA that do not code for proteins. Some of these non-coding parts switch genes on and off, so they control whether or not a gene is expressed (if it is used to make a protein)

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19
Q

What is protein-synthesis?

A

1) Proteins are made in the cell cytoplasm on tiny structures called ribosomes
2) To make proteins, ribosomes use the code in the DNA. DNA is found in the cell nucleus and can’t move out of it as it is too big. So the cell needs to get the code from the DNA to the ribosome.
3) This is done using a molecule called mRNA - made by copying the code from DNA. The mRNA acts as a messenger between the DNA and the ribosome (carries it between the two)
4) The correct amino acids are brought to the ribosomes in the correct order by carrier molecules

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20
Q

Describe how a protein might be used?

A

When a chain of amino acids has been assembled, it folds into a unique shape which allows the protein to perform a task:
- Enzymes
- Hormones
- Structural proteins

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21
Q

Explain a mutation:

A

Mutations occur continuously. Mutations change the sequence of the DNA bases, producing a genetic variant (different form of gene). As the sequence of DNA bases codes for amino acids to make a protein, a mutation can change the protein produced.

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22
Q

What is mRNA?

A

mRNA - Messenger RNA is a linear molecule which carries a copy of the gene to be expressed from the nucleus. Every group of three bases (a ‘triplet’) is described as a codon because each one codes for an amino acid.

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23
Q

What is tRNA?

A

tRNA - Transfer RNA has a cloverleaf shape. It is made from a single strand of RNA which folds due to base pairing to form this unusual shape. It has a triplet anti-codon site and an attachment site for a specific amino acid.

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24
Q

what is rRNA?

A

rRNA - Ribosomal RNA and proteins form the ribosome. The ribosome is the structure where protein synthesis takes place.

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25
Q

What are the three types of mutation? explain them.

A

Insertion - when a new base is inserted into the DNA sequence where it shouldn’t be. It can have a knock-on effect on the bases to the right of the insertion
Deletion - when a random base is deleted from the DNA sequence. They can have a knock-on effect on the bases further down the sequence
Substitution - when a random base in the DNA sequence is changed to a different base. This is less likely to have a knock-on effect on other bases.

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26
Q

What happens during sexual reproduction?

A

1) Sexual reproduction is where genetic information from two organisms (mother + father) is combined to produce offspring which are genetically different to either parent.
2) In sexual reproduction, the mother and father produce gametes by meiosis
3) In humans, each gamete is 23 chromosomes - half the number in a normal cell - it does not have 2 of each chromosome, only 1
4) The egg and sperm then fuse together to form a cell with the full number of chromosomes (half from each parent)

IMPORTANT: sexual reproduction involves the fusion of male and female gametes. Because there are 2 parents, the offspring contain a mixture of their parents’ genes - causing genetic variation.

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27
Q

what happens during asexual reproduction?

A

1) In asexual reproduction, there is only one parent so the offspring will be genetically identical to the parent
2) Asexual reproduction happens by mitosis - an ordinary cell makes a new cell by dividing by two
3) The new cell has exactly the same genetic information (like genes) as the parent - it is a clone
4) Bacteria, some plants, and some animals reproduce asexually

IMPORTANT: asexual reproduction only needs one parent. There is no fusion of gametes, no mixing of chromosomes and no genetic variation between parent and offspring.

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28
Q

What is the process of meiosis?

A

1) before the cell starts to divide, it duplicates its genetic information, forming two armed chromosomes - one arm of each chromosome is an exact copy of the other arm. After replication, the chromosomes arrange themselves into pairs.
2) In the first division in meiosis the chromosome pairs line up in the middle of the cell
3) the pairs are then pulled apart so each new cell only has one copy of each chromosome. A mix of both the mother and father chromosomes go into each new cell
4) In the second division, the chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart

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29
Q

What is the result of meiosis?

A

You get four gametes, each with only a single set of chromosomes in it. Each of the gametes is genetically different from the others because all the chromosomes are mixed together and each gamete only gets half of them, at random.

30
Q

How do the gametes produce an organism?

A

1) After the two gametes have fused during fertilisation, the resulting new cell divides by mitosis to make a copy of itself.
2) Mitosis repeats many times to produce lots of new cells in an embryo
3) As the embryo develops, these cells then differentiate into the different types of cells of specialised cell to form a whole organism

31
Q

What are the advantages of sexual reproduction over asexual reproduction?

A
  • offspring has a mixture of two sets of chromosome, so there is variation
  • variation means that there is a higher chance of some of the offspring surviving a change in environment
  • Because some offspring are better adapted to the environment, they are more likely to survive and breed successfully, passing the genes on. This is Natural Selection
  • We can use selective breeding to speed up natural selection. This allows us to produce animals with desirable characteristics. We can also use it to increase crop yield and therefore increase food supply
32
Q

what are the advantages of asexual reproduction over sexual reproduction?

A
  • only requires one parent
  • uses less energy
  • faster than sexual reproduction
  • many identical offspring can be produced in favourable conditions
33
Q

Describe the 3 examples of organisms that can reproduce by both methods:

A

1) malaria - malaria is caused by a parasite that is spread by mosquitos. When a mosquito carrying the parasite bites a human, the parasite is transferred. The parasite reproduces sexually when in the mosquito but asexually in the human
2) Many species of fungus - These species release spores which can become new fungi when they land. Spores can be both sexually and asexually produced.
3) Lots of plants - asexual reproduction might be used to produce “runners” (strawberry plants) or sexual reproduction can be used.

34
Q

How many chromosomes does a human body cell have? What are the 2 chromosome that determine your sex?

A
  • every body cell has 23 pairs of chromosomes (so 46 individual chromosomes)
  • Male chromosome pair: XY
  • Female chromosome pair: XX
35
Q

What is a genetic diagram?

A

Also known as a Punnett square. It is a method of showing the possible gamete combinations. You draw it like this:
1) Identify gametes for each parent.
2) Draw the grid based on the number of traits.
3) Fill in the alleles to find possible genotypes.
4) Calculate probabilities to interpret results

36
Q

what is a dominant allele?

A

It means that this allele is always expressed (visible) if this allele is present

37
Q

what is a recessive allele?

A

It means that this allele is only expressed if both of the alleles are this recessive one.

38
Q

what does it mean to be homozygous?

A

The two alleles for a gene are the same

39
Q

what does it mean to be heterozygous?

A

The two alleles for a gene are different

40
Q

What is cystic fibrosis caused by?

A

Cystic fibrosis is a genetic disorder, affecting the cell membranes. It results in the body producing a lot of thick sticky mucus in the air passages and in the pancreas. The allele is recessive, so both parents must carry the allele for the child to have the disorder. If somebody carries the allele but has a more dominant allele too, they are a carrier.

41
Q

What is polydactyly caused by?

A

Polydactyly is caused by a dominant allele. It is a genetic disorder which causes a child to have extra fingers or toes. It means that the child could have the disorder if one parent carries the defective allele.

42
Q

Why are people against Embryonic screening?

A
  • It implies that people with genetic problems are “undesirable”, could increase prejudice
  • There may be a point where everyone wants to screen their embryos so they can pick the most “desirable” one
  • Screening is expensive
43
Q

Why are people for Embryonic screening?

A
  • It will help to stop people suffering
  • Treating disorders costs the government (and taxpayers) a lot of money
  • There are laws to stop it going to far (at the moment parents cannot choose the sex of the baby unless for medical reasons)
44
Q

What did Gregor Medel do?

A

Medel carried out an experiment with pea plants to show that the height characteristic in pea plants was determined by separately inherited “hereditary units” passed on from each parent. The ratios of tall and dwarf plants in the offspring showed that the unit for tall plants was dominant over the unit for dwarf plants

45
Q

What 3 conclusions did Mendel reach?

A
  • Characteristics in plants are determined by “hereditary units”
  • Hereditary units are passed on to offspring unchanged from both parents, one unit from each parent
  • Hereditary units can be dominant or recessive
46
Q

what is the theory of evolution?

A

All of today’s species have evolved from simple life forms that first started to develop over three billion years ago

47
Q

What did Charles Darwin suggest?

A

Theory of evolution by natural selection - which basically means that the best animals will survive and pass on the successful genes so that over time organisms become more adapted

48
Q

why was Darwin’s theory controversial?

A
  • his ideas went against religious beliefs
  • there was a lack of evidence
  • Darwin could not explain why or how the useful characteristics appeared and were past onto offspring
49
Q

What is extinction?

A

when all of a species of plant or animal has died - no longer exists on earth

50
Q

What can lead to a species becoming extinct?

A
  • the environment changes too quickly
  • a new predator kills them all
  • a new disease kills them all
  • they can’t compete with new species for food
  • a catastrophic event happens that kills them all
51
Q

what is selective breeding?

A

It is when humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population.

52
Q

Give an example of an organism that has been selectively bred:

A
  • animals that produce more meat or milk
  • crops with a resistance to disease
  • dogs with a good temperament
  • decorative plants with unusual flowers
53
Q

What is the process of selective breeding?

A

1) from your existing stock, select the ones with the desired characteristics
2) breed them with each other
3) select the best of the offspring and breed them together
4) continue this process over several generations. The desirable trait gets stronger each time so (eventually) all offspring will have it

54
Q

What is a gene pool?

A

it is the number of different alleles (forms of a gene) in a population

55
Q

What is the main issue with selective breeding?

A

It reduces the gene pool. This is because it is inbreeding, and there are risks of health problems linked with this due to the reduced gene pool

56
Q

What is genetic engineering?

A

to transfer a gene responsible for a desirable characteristic from one organisms’ genome into another organism so that it also has the desired characteristic.

57
Q

How can plants be cloned through tissue culture?

A

This is when a few plant cells are put in a growth medium with hormones, and they grow into new plants - clones of the parent plant. These can be made very quickly, in very little space, and be grown all year round.

58
Q

How can plants be cloned through cuttings?

A
  • Gardeners can take cuttings from parent plants, and then plant them to produce clones of the parent plant
  • these plants can be produced quickly and cheaply. This is an older, simpler method than tissue culture.
59
Q

How can animal clones be made?

A

the sperm from the best male animal can be used to artificially fertilise the egg from the best female animal. The embryo that develops is then split many times (to form clones) before any cells are specialised.

60
Q

How does adult cell cloning work?

A

Adult cell cloning involves taking an unfertilised egg cell and removing the nucleus. The nucleus is then removed from an adult body cell and is inserted into the “empty” egg cell. The egg is then stimulated to make it divide. When the embryo is a ball of cells it is implanted into an adult female. It grows into a clone of the original adult body cell. (this was done to create dolly - a cloned sheep)

61
Q

What are some of the issues around cloning?

A
  • reduced gene pool
  • if we clone humans, there will be unsuccessful attempts - unfair on the child
  • cloned animals may not be as healthy as normal ones
62
Q

What are fossils?

A

The remains of organisms from thousands of years ago, which are found in rocks.

63
Q

Explain how fossils are formed from gradual replacement by minerals:

A
  • things like teeth, shells and bones do not decay easily so they last a long time when buried.
  • they are replaced by minerals as they decay, forming a rock like substance
  • the surrounding sediments turn to rock, but the fossil stays distinct until it is found
64
Q

Explain how fossils are formed from casts and impressions:

A
  • if an organism is buried in a soft substance (like clay), a fossil is formed
  • the substance hardens around it, and the organism decays, leaving a cast of itself
  • Things like footprints or root traces are formed this way
65
Q

Explain how fossils are formed from preservation where no decay happens:

A
  • in amber and tar pits there is no oxygen or moisture so decay microbes can’t survive
  • in glaciers, it is too cold for the decay microbes to work
  • in peat bogs it is too acidic for decay microbes
  • this means the organism is perfectly preserved
66
Q

What is speciation?

A

It is the development of a new species

67
Q

What is isolation?

A

it is where populations of a species are separated. This (and natural selection) means that different populations may have different traits to help it survive. Over time they become different species, and can no longer breed together.

68
Q

Who was Alfred Russel Wallace?

A

He was a scientist working at the same time as Charles Darwin. He realised that warning colours are used by species to deter predators, and he developed the idea of speciation.

69
Q

Why does reproducing rapidly benefit bacteria?

A

It means they can become resistant to antibiotics quickly, and can spread at high rates.

70
Q

What is classification?

A

The process of organising living organisms into groups, but this system has changed over time

71
Q

What are the three domains (broad categories) in the three-domain system?

A

1) ARCHAEA - a type of prokaryotic cell
2) BACTERIA - true bacteria
3) EUKARYOTA - broad range of organisms

72
Q

in the three-domain system, what is each domain split into?

A

phylum, class, order, family, genus, species

AQA GCSE - Biology - paper 2 (3 decks)

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