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GCSE AQA Biology > TOPIC 6 - Inheritance, variation and evolution > Flashcards

TOPIC 6 - Inheritance, variation and evolution Flashcards

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1
Q

DNA

A

Chemical that all genetic material is made up from. It is a polymer and contains 2 strands coiled together to form a double helix.

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2
Q

Gene

A

A small section of DNA. Each gene codes for a sequence of amino acids which are put together to form a specific protein.

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3
Q

Genome

A

An entire set of genetic material of an organism.

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4
Q

Why has understanding human genome been important?

A
  • Search for genes linked to diseases.
  • Understanding, treating inherited disorders.
  • Used in tracing human migration patterns in the past.
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5
Q

DNA strands are polymers made up of repeating units called _____.

A

Nucleotides

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6
Q

Each nucleotide consists of…

A

Phosphate, sugar and a base

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7
Q

Name the different types of bases and their complimentary base pair.

A

A, T, C, G
A->T
C->G

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8
Q

mRNA

A

Molecule which copies code of DNA and carries it between DNA and ribosomes to make correct proteins

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9
Q

Examples of proteins.

A

Enzymes, hormones, structural proteins

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10
Q

Mutation

A

A random change in an organism’s DNA. Changes sequence of DNA bases in a gene, which produces a genetic variant.

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11
Q

Most mutations have very little effect but some can be serious for example:

A
  1. Shape of enzyme active site may change. So, substrate may no longer be able to bind.
  2. Structural proteins may lose strength if shape is changes
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12
Q

Name 3 types of mutation.

A

Insertion, deletion and substitution.

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13
Q

Sexual reproduction

A

Involves the fusion of male and female gametes (produced by my meiosis). The mixing of genetic information leads to variety in offspring.

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14
Q

Asexual reproduction

A

Involves only on parent and no fusion of gametes. This leads to genetically identical offspring, they are clones. Mitosis involved.

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15
Q

Process of meiosis

A
  1. Genetic material is duplicated, forming two armed chromosomes. Each arm is genetically identical.
  2. Chromosomes are arranged into pairs.
  3. In the 1st division, chromosome pairs line up in the centre of cell and are pulled apart, so each new cell has one copy of each chromosome.
  4. In the 2nd division, chromosome pairs line at centre and arms of chromosomes are pulled apart.
  5. 4 gametes produced with a single set of chromosomes in each.
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16
Q

Why are gametes genetically different?

A

There are tiny changes and chromosomes are shuffled.

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17
Q

After two gametes have been fused, the resulting new cell divided by _____.

A

Mitosis.

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18
Q

Advantages of sexual reproduction.

A
  • Produces variation in offspring.
  • If the environment changes, variation gives survival advantage by natural selection.
  • Natural selection can be sped up by humans in selective breeding to increase food production.
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19
Q

Advantages of asexual reproduction.

A
  • Needs only one parent
  • More time and energy efficient as no need to find a mate
  • Many identical offspring can be produced in favourable conditions
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20
Q

Name some organisms that can reproduce sexually and asexually…

A
  • Malaria parasites reproduce asexually inside human host and sexually inside the mosquito.
  • Many fungi reproduce asexually by spores and also sexually to give variation.
  • Many plants produce seeds sexually and reproduce asexually by runner e.g. strawberry plant.
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21
Q

Ordinary human body cells contain ____ ____ of chromosomes.

A

23 pairs

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22
Q

___ ___ control characteristics only, but only the ___ ___ carries genes that control sex.

A

22 pairs, 23rd pair

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23
Q

Female sex chromosomes are ___.

A

XX

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24
Q

Male sex chromosomes are _____.

A

XY

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25
Q

Allele

A

Different versions of the same gene.

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26
Q

Homozygous

A

If organism has 2 alleles for a particular gene which are the same. e.g AA or aa

27
Q

Hetrozygous

A

If an organism has 2 alleles for a particular gene which are different. e.g. Aa

28
Q

Dominant allele

A

The allele for which the characteristic is shown. Represented by a capital letter.

29
Q

Recessive allele

A

The allele which is not shown in the characteristic. Represented by a lowercase letter.

30
Q

Genotype

A

Combination of alleles you have. They operate at a molecular level to develop characteristics that can be expressed as a phenotype.

31
Q

Phenotype

A

Physical characteristics of an organism. e.g. normal or super powered.

32
Q

Name 2 inherited diseases…

A

Cystic fibrosis, polydactyly.

33
Q

Cystic firbrosis

A

Genetic disorder of cell membranes. Caused by a recessive allele.

34
Q

Polydactyly

A

Genetic disorder of having extra fingers or toes. Caused by a dominant allele.

35
Q

Embryonic screening

A

Embryos are fertilised in a laboratory and DNA is removed from cell for gene analysis. Genetic disorders can be detected and embryos with ‘bad’ alleles’ would be destroyed.

36
Q

Against embryonic screening

A
  • Implies people with genetic disorders are undesirable, creates prejudice.
  • May come a time when everyone want to screen embryos to pick out most desirable offspring
  • Screening is expensive
37
Q

For embryonic screening

A
  • It will help people stop suffering.
  • Treating disorders costs a lot of money for government.
  • There are laws to stop it from being excessive and unnecessary.
38
Q

What did Gregor Mendel?

A

Mendel had shown 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 the unit for the tall plants, T, was dominant over the unit for the dwarf plants, t.

39
Q

Mendel reached 3 important conclusions…

A
  1. Characteristics in plants are determined by “hereditary units”.
  2. Hereditary units are passed on to offspring unchanged from both parents, one unit from each parent.
  3. Hereditary units can be dominant or recessive.
40
Q

Using Mendel’s work and other scientists’, it contributed to the current understanding of genes. For example…

A
  1. In the early 20th century, it was observed that chromosomes and Mendel’s ‘units’ behaved in similar ways. This led to the idea that the ‘units’ now called genes were located on chromosomes.
  2. In the mid 20th century, the structure of DNA was determined. This helped find out genes functioned.
  3. In the late 19th century, the behaviour of chromosomes during cell division was observed.
41
Q

Variation

A

Differences within a species.

42
Q

2 types of variation

A

Genetic variation, environmental variation

43
Q

Genetic variation

A

Variation caused by the genes inherited from parents. e.g. eye colour, hair colour.

44
Q

Environmental variation

A

Variation caused by the environment. e.g. amount of sunlight, losing body part in battle.

45
Q

Mutations occur continuously. Very rarely a mutation will lead to a new ___.

A

Phenotype. If the phenotype is is suited to an environmental change, it can lead ti a relatively rapid change in the species.

46
Q

Theory of evolution by natural selection

A

All species of living things have evolved from simple life forms that first developed more than 3 billion years ago.

47
Q

How does does evolution occur through natural selection of variants that give rise of well-suited phenotype to their environment?

A

New phenotypic variations arise because of genetic variants produced by mutations. Beneficial variations are passed onto future generations in the genes.

48
Q

Speciation

A

Over a long period of time, the phenotype of an organism can change so much due to natural selection that a completely new species are formed. So populations of the same species cannot interbreed to produce fertile offspring.

49
Q

Species can become extinct because of…

A
  1. The environment changes too quickly e.g destruction of a habitat.
  2. A new predator kills them all e.g. humans
  3. A catastrophic event happens e.g collision with an asteroid.
50
Q

Not everyone agreed with Darwin’s theory of Evolution because…

A
  1. It went against many religious beliefs.
  2. Darwin could not explain why these new useful characteristics appeared or how they were passed on.
  3. There was not a lot of evidence to convince other scientists.
51
Q

What was Lamark’s idea about evolution?

A

Lamark argued that changes in an organism acquired during its lifetime will be passed on to its offspring. If an organism used a specific characteristic a lot, it would become more developed and be passed on.

52
Q

Why was Lamark’s theory rejected?

A

Experiments did not support it.

53
Q

Selective breeding

A

Process by which humans breed plants and animals to have a particular genetic characteristics

54
Q

Process of selective breeding

A

Parents with desired characteristic are chosen from a mixed population. They are bred together. This continued over many generations until all offspring show desired feature.

55
Q

Name some example of a desired feature of an animal or plant by selective breeding…

A
  • Disease resistance
  • Animals produce more meat or milk
  • Decorative large flowers
56
Q

Inbreeding

A

Selective breeding can lead to inbreeding where some breeds are particularly prone to disease or inherited dieases.

57
Q

Genetic engineering

A

The transfer of a gene responsible for a desired characteristic from one organism’s genome into another organism’s genome, so it also has the desired characteristic.

58
Q

Process of genetic engineering

A
  1. Enzymes are used to isolate the required gene which is inserted into a vector (usually a bacteria or plasmid).
  2. The vector is used to insert the gene into the required cells.
  3. Genes are transferred to cells at an early stage in their development so that they develop with desired characteristic.
59
Q

Give some examples of how genetically engineering is used…

A
  • Bacteria have been genetically modified ti produce human insulin that can treated diabetes.
  • Genetically modified crops have had theirs gene modified to make them disease resistant
60
Q

Pros of GM crops

A
  • Characteristics of GM crops can increase yield.
  • GM crops can provide additional nutrients in crops.
  • GM crops are already being grown without any problems.
61
Q

Cons of GM crops

A
  • GM crops could affect number of wild flowers living in and around crops, reducing farmland biodiversity.
  • GM crops may not be safe as long-term effects of eating them are not understood yet.
  • Transplanted genes may get into natural environment.
62
Q

Plants can be cloned by tissue culture. What is tissue culture?

A

Using small groups of cells from part of a plant to grow identical new plants. This is important for preserving rare plant species or commercially in nurseries.

63
Q

Plants can also be cloned by cuttings. What are cuttings?

A

An older, but simple, method used by gardens to produce many identical new plants from a parent plant.

64
Q

Embryos transplants

A

Splitting apart cells from a developing animal embryo before becoming specialised, then transplanting the 2 identical embryos into host mothers.

GCSE AQA Biology (1 decks)

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