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Edexcel GCSE Biology > Genetics > Flashcards

Genetics Flashcards

1
Q

What type of cells do sexual reproduction produce?

A

Genetically different cells due to the parents both giving gametes (w half the number of chromosomes) to produce a diploid cell. The zygote produces from the fusion of the gametes then undergoes cell division (by mitosis) and develops into an embryo which inherits a mixture of jeans from the parents.

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2
Q

How are gametes produced? How is it different to mitosis?

A

Gametes are produced via meiosis (type of cell division). It doesn’t produce identical cells and only occurs in the reproductive organs to produce four genetically unique haploid daughter cells.

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3
Q

What happens during division 1 of meiosis?

A

The cells’ DNA duplicates and forms ‘X shaped chromosomes’. The chromosomes then line up in pairs of mother/father chromosomes. These pairs are then split apart so that each cell has each parent. This then forms 2 cells with GENETIC VARIATION.

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4
Q

What happens during division 2?

A

The chromosomes then line up again in the cell and the arms are split apart by mitosis. This produces 4 genetically different haploid daughter cells.

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5
Q

Asexual reproduction

A

When cells produce 2, diploid, genetically identical daughter cells via mitosis.

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6
Q

Sexual reproduction

A

Production of genetically different haploid gametes that fuse to form a diploid cell at fertilisation.

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7
Q

Advantages of asexual reproduction

A

Can produce much offspring very quickly as the reproductive cycle is so fast. (Eg E Coli can divide every half hour)
This allows organisms to colonise an area rapidly

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8
Q

Advantages of sexual reproduction

A

Cause genetic variation within a population (causing different characteristics). This means that they are more likely to survive / adapt during a change in environment, ultimately leading to natural selection and evolution.

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9
Q

Disadvantages of asexual reproduction

A

No genetic variation within a population, meaning whole population can be affected by environmental change. Eg: black Sigatoka outbreaks can wipe out whole populations of banana plants.

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10
Q

Disadvantages of sexual reproduction

A

Requires attraction to find a mate which takes time and energy. In general takes more time and energy to reproduce sexuallly so produce fewer offspring in lifetime.
2 parents need to be involved for fertilisation which is difficult if an individual is isolated.

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11
Q

Monomer of DNA and what the monomer is composed of?

A

Nucleotide is a monomer of DNA, composed of one penthouse sugar molecule, one phosphate molecule and a base

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12
Q

What forms the backbone of DNA strands?

A

Alternating molecules of sugar and phosphate.

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13
Q

What are the four different bases and which ones are complimentary?

A

CYTOSINE pairs with GUANINE.

ADENINE pairs with THYMINE.

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14
Q

What shape is DNA?

A

It has 2 strands coiled together to form a DOUBLE HELIX.

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15
Q

What are complimentary base pairs joined by?

A

Weak hydrogen bonds

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16
Q

Chromosome

A

Long, coiled up piece of DNA found in the nucleus of eukaryotic cells.

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17
Q

Gene

A

A section of DNA on a chromosome that codes for a particular protein.

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18
Q

Genome

A

The whole of an organism’s DNA

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19
Q

How do you extract DNA from fruit and veg?

A

Mash up the substance and mix it in a solution of detergent and salt. Mix well.
Filter the mixture to get the froth without big insoluble parts of cell.
Leave the mixture at 60 degrees Celsius for 15 mins.
Add some ice cold ethanol into the filtered mixture.

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20
Q

What’s the purpose of detergent in the production of DNA from fruit and veg?

A

The detergent breaks down the cell membrane and so will release the DNA.

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21
Q

What’s the purpose of salt in the production of DNA from fruit and veg?

A

Salt makes the protein stick together.

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22
Q

What will occur after ice cold ethanol is poured into the solution of salt, detergent and fruit in the production of DNA? Why?

A

The DNA will precipitate as it is not soluble in cold alcohol, the precipitate can be fished out with a glass rod.

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23
Q

What controls protein synthesis in a cell? Whee does it occur?

A

DNA controls protein synthesis in the cell cytoplasm through subcellular structures called RIBOSOMES.

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24
Q

What are proteins made up of?

A

Chains of amino acids in particular numbers and orders; these fold up to give each protein a specific shape for its FUNCTION.

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25
Q

What decides the order of amino acids in a protein?

A

The order of bases in a gene.

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26
Q

Base triplet

A

A sequence of three bases that codes for a particular amino acid.

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27
Q

A triplet code

A

A code based on base triplets

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28
Q

What’s a non-coding region of DNA?

A

A region that doesn’t code for any amino acids. Can still be used in protein synthesis.

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29
Q

Mutation

A

A rare, random change to an organism’s DNA base sequence that can be inherited.

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30
Q

A genetic variant

A

A different version of the same gene.

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31
Q

What effect can a genetic variation have on an organism?

A

It can change the sequence of amino acids making up a protein and so change the protein’s shape which affects its function/activity. This therefore can change an organisms phenotype.

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32
Q

What are the two stages of protein synthesis?

A

1 TRANSCRIPTION

2 TRANSLATION

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33
Q

Why does protein synthesis occur?

A

Because DNA found in the nucleus of a cell are too big to move through the nuclear membrane and need to pass information from the DNA to the ribosome in the cytoplasm.

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34
Q

What’s messenger RNA?

A

A chemical (made in the nucleus) that carries a copy of base sequence out of a nucleus to the cytoplasm to attach to ribosomes.

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35
Q

Difference between DNA and mRNA?

A

RNA is a single strand in comparison to DNA’s double helix.
Has a deoxyribose sugar backbone in the nucleotide rather than a ribose sugar backbone.
Has URACIL as a complementary base pair to adenine rather than thymine.

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36
Q

Transcription

A

Process by which information on a strand of DNA is copied.

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37
Q

RNA polymerase

A

Enzyme involved in joining RNA nucleotides to made mRNA.

38
Q

How does transcription work?

A

1 RNA polymerase binds to a region of ‘non-coding DNA’ in front of a gene.
2 the two strands are unzipped by an enzyme called helicase and so the RNA polymerase moves along one of the strands of DNA.
3 it uses the coding DNA in the gene as a template to make the mRNA. Free RNA nucleotides form complimentary base pairs with the coding strand of DNA. (AU TA CG GC). RNA polymerase bonds the RNA nucleotides together to form a complementary strand of mRNA.
4 The RNA peels off the gene and leaves through a pore in the membrane to join w a ribosome.

39
Q

What is needed for transcription

A

Gene (DNA)
Supply of free RNA nucleotides.
ATP
Enzymes (helicase, polymerase)

40
Q

ATP

A

Adenosine triphosphate

41
Q

Codon

A

A triplet of bases on the mRNA

42
Q

Anti-codon

A

A triplet of bases on tRNA

43
Q

What is helicase’s function?

A

To ‘unzip’ the DNA and so break the hydrogen bonds between the bases.

44
Q

Function of RNA polymerase

A

Makes sugar phosphate bond the RNA nucleotides

45
Q

Stages of translation

A

1 specific amino acids aretransported to the ribosome by tRNA.
2 the codons pair (are complimentary)with the anticodon , meaning that the amino acids are brought to the ribosome in the correct order.
3 peptide bonds form between adjacent amino acids to form a polypeptide (protein)
4 once the polypeptide is formed, tRNA molecules leave the ribosome and pick up new specific amino acids.

46
Q

How many bases long are ribosomes?

A

6-9 bases long

47
Q

How many amino acids are there?

A

20

48
Q

Which amino acid starts every protein?

A

Methionine

49
Q

T RNA

A

Molecules that transport amino acids to the ribosome

50
Q

Peptide bonds

A

Bond amino acids to form polypeptides (protein)

51
Q

How do genetic variants influence the bindings of RNA polymerase and therefore the phenotype of the organism?

A

A genetic variant may cause a mistake in the bases that make up the RNA polymerase enzyme and so affect its activity/ ability to bind to the non coding region. This therefore affects the overall translated mRNA and the amount of protein produced, overall affecting the phenotype.

52
Q

Who was the Austrian monk who did genetic experiments with pea plants?

A

Gregor Mendel (1822-1884) whose work was published in 1866 and eventually became the foundation of genetics.

53
Q

What were traits affecting phenotype called before genes were discovered?

A

Factors

54
Q

Why did Mendel choose to work with pea plants?

A

Because they are easy/ quick to grow

They have distinguishable traits

55
Q

How do you manually cross fertilise flowers?

A

He took pollen from the stamen, cut it off and put pollen in the pistil of another flower.

56
Q

What were the seven traits that peas had?

A 
Stem length
Flower position
Pod shape
Pod colour
Seed shape
Seed colour
Pea colour
57
Q

How do you obtain a pure bred flower?

A

You self cross it until it only has one colour.

58
Q

What 3 conclusions did Mendel come to?

A

Characteristics in plants were determined by hereditary ‘units’/factors.
These hereditary units were passed on to offspring unchanged from both parents, one unit from each parent.
These units can also be dominant/recessive, if an individual has both dominant and recessive, the dominant will be expressed.

59
Q

Why was his work only famous after his death?

A

Because it was new to scientists of his day as scientists didn’t have the background knowledge to understand his findings, genes hadn’t been discovered.

60
Q

Alleles

A

Different versions of the same gene

61
Q

What are characteristics controlled by?

A

Multiple genes but sometimes a single gene.

62
Q

How many alleles of each gene do you have in your body?

A

2, one on each chromosome in a pair.

63
Q

Homozygous

A

If an organism has 2 alleles for a particular gene that are the same.

64
Q

Heterozygous

A

Having 2 alleles for a particular gene that are different.

65
Q

Dominant alleles

A

Alleles that overrule recessive alleles and so determine the characteristic present.

66
Q

Recessive alleles

A

Alleles that are overruled by dominant alleles and therefore need 2 of the same to show up in an organism’s characteristics

67
Q

Genotype

A

The combination of alleles you have. They determine your phenotype.

68
Q

Phenotype

A

The characteristics that organisms have and show up in an organism’s features.

69
Q

Monohybrid inheritance

A

Inheritance of a single characteristic. A monohybrid cross/ punnet squares can be used to show how recessive and dominant traits for a single characteristic are inherited.

70
Q

How many matched pairs of chromosomes are there in each human body cell?

A

23, the 23rd pair decides the sex.

71
Q

Male chromosomes

A

X and Y (Y causes male characteristics)

72
Q

Female chromosomes

A

2 X’s

73
Q

Family pedigree

A

Family tree of genetic disorders

74
Q

Carriers

A

People with one version of a recessive allele that causes a genetic disorder, meaning they don’t have the disorder themselves.

75
Q

Sex-linked characteristic

A

Alleles that codes for it is located on a sex chromosome

76
Q

What’s the difference between X and Y chromosomes?

A

Y chromosomes are smaller and so contain fewer genes. This means that men often only have one allele for sexlinked genes.

77
Q

Why are men more vulnerable to genetic disorders?

A

Because they often only have one allele for sexlinked genes so can receive only one recessive allele for it to show up.

78
Q

Example of sex linked genetic disorders

A

Colourblindness

Haemophilia

79
Q

Which alleles determine blood type

A

Multiple alleles, Io (recessive), Ia and Ib (codominant)

80
Q

Codominant

A

Will both show up if they are present in a genotype, one allele isn’t dominant over the other.

81
Q

Four potential blood types

A

O (Io Io)
A (IaIo/IaIa)
B (IbIo/IbIb)
AB(IaIb)

82
Q

Variation

A

Differences within a species due to environmental/ genetic factors.

83
Q

What’s genetic variation caused by?

A

Organisms having different alleles which lead to differences in a phenotype.
Sexual reproduction leads to variation in these alleles.
New alleles can arise due to mutations in the cell which change the base sequence. Can be neutral, however can completely change shape of protein and so its function. This is what happens in cystic fibrosis.

84
Q

How does cystic fibrosis work?

A

A mutation causes the protein that controls movement of salt and water in and out of cells to stop working. This leads to the production of thick, sticky mucus in lungs and digestive system, making it difficult to breathe/ digest food.

85
Q

Environmental variations

A

Acquired characteristics (eg intake of sun or CO2)

86
Q

What has the genome helped to do?

A

Predict/prevent disease.
Test/treat inherited disorders.
Produce new/ more effective medicines

87
Q

How has the genome helped predict/ prevent disease?

A

Doctors could look at genes to check an individual’s susceptibility to a particular disease and therefore tailor advice on lifestyle choices and so keep regular checkups to start early treatment for those who have the disease.

88
Q

How has the genome affected testing and treatment for inherited disorders?

A

Scientists can now identify the alleles that cause an inherited disorder to test people for them. This means that they can create/ tailor treatments of it to find a cure.

89
Q

How has the genome affected the production of new and better medicines?

A

Genetic variation affects how bodies react to particular dosages/ treatments/ diseases. This means that scientists can now develop new drugs that fit to your genotype and so make more effective treatments with fewer side effects.

90
Q

What are some of the drawbacks of the genome project?

A

Increased stress: patients who know that they are susceptible to different diseases may panic at smaller symptoms.
Gene-ism: people w genetic problems may be encouraged not to have kids.
Discrimination from employers/insurers: life insurance may be vv expensive for those more susceptible to disease and employers may discriminate.

Edexcel GCSE Biology (12 decks)

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