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biology > inheritance and variation > Flashcards

inheritance and variation Flashcards

1
Q

what is the purpose of mitosis?

A

growth and repair.

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2
Q

what are the three stages of mitosis?

A
  1. copies of DNA and organelles are made
  2. contents of the cell are re-arranged (pulled to the poles)
  3. cell splits into identical daughter cells
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3
Q

how is mitosis asexual?

A

doesn’t involve sex cells. only requires one to reproduce.

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4
Q

define ‘variation’:

A

the differences between individual organisms. to evolve, ‘survival of the fittest’ helps a population to survive, meaning they need to variate and adapt to their environment.

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5
Q

what is the purpose of meiosis?

A

production of gametes (sex cells) for sexual reproduction.

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6
Q

what are the two types of base pairs, and what do they make up?

A

Adenine - Thymine (apple in the tree)
Cytosine - Guanine (car in the garage)

each gene is either the pair Adenine and Thymine, or Cytosine and Guanine.

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7
Q

what is the process of meiosis?

A
  1. begins with an ordinary diploid cell in the ovaries/testes
  2. DNA duplicates, and each chromosome has a copy of itself
  3. the cell undergoes the first division, mitosis. the arms of the chromosomes are pulled to opposite poles by spindle fibres. a nuclear envelope forms around each set of chromosomes, creating two nuclei, and the cell then divides. the mother’s and father’s chromosomes go into new cells, mixing up the genes and creating genetic variation in the offspring.
  4. chromosomes line up in the centre again in both cells. these two cells both divide by mitosis again.
  5. the result is 4 genetically different daughter cells - haploid cells.
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8
Q

compare the details of asexual and sexual reproduction:

A

asexual:
- one parent
- fast
- mitosis only
- very limited variation
- identical (clones) to parents

sexual:
- two parents
- slow
- meiosis (divides by mitosis once the zygote is formed)
- significant variation
- different to parents

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9
Q

what are the advantages and disadvantages of asexual reproduction?

A

a:
- only requires 1 organism
- quicker, no need to find a mate
- creates exact replica (good for cloning endangered species)
- no energy required
- no need to make gametes
- good in favourable conditions

d:
- no variation (less evolution)
- bad in a changed environment. if one organism dies, as they’re all clones, the rest die

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10
Q

what are the advantages and disadvantages of sexual reproduction?

A

a:
- variation (they can adapt to different environments) - however, opposes natural selection

d:
- must find a mate (requires 2 organisms)
- requires gametes to fuse together
- takes longer
- lots of energy used

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11
Q

how do fungi reproduce?

A
  • reproduce sexually in poor conditions to generate variation
  • also release spores, carried by the wind/water, by asexual reproduction
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12
Q

how do certain plants reproduce?

A
  • plants use sexual reproduction to produce seeds. pollen from one flower must reach the female parts of another flower through pollination, to form seeds - either animal pollinators or the pollen is carried in the wind.
  • some plants reproduce asexually. e.g. when strawberry plants send out runners (long shoots from the base of the main plant, which new plants will grow on the end of), or when daffodil bulbs divide
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13
Q

how do malarial parasites reproduce?

A
  • reproduce sexually in the host mosquito
  • reproduce asexually in the human host
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14
Q

describe DNA:

A

DNA = Deoxyribonucleic Acid
- base pairs are bases held together by hydrogen bonds
- make up long sections, but can be broken up into 3s, and 3 pairs gives the code for one amino acid
- two polymer chains that come together to form a double helix structure. the monomers in the polymers are called nucleotides/bases (the monomer is a polynucleotide).

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15
Q

what are genes?

A

small sections of DNA. each gene codes for a specific sequence of amino acids to make a specific protein, which include the formation of the enzymes that control cell chemistry.

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16
Q

what is a genome?

A

the complete genetic makeup/profile of a person. their entire genetic material.
- includes DNA found in the chromosomes (DNA from both the mother and the father), and DNA found in the mitochondria (DNA from just the mother, as it comes from the mitochondria of the egg)

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17
Q

describe the Human Genome Project:

A
  • in 2003, scientists from across the globe working together announced they’d worked out the entire human genetic code.
  • the first sequence of the human genome took over 10 years to produce, now it only takes 2 weeks.
  • they have now sequenced over 1000 people’s genomes, and the aim is to find out as much as possible about human DNA.
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18
Q

describe how we can use the Human Genome Project to understand medicine and inherited disorders:

A
  • the information in the genome could tell you whether you’re at an increased risk of a particular disease e.g. cancer (there are genes linked to an increased risk of developing disease) and helps us to understand inherited disorders. we can then overcome them by medicine or by repairing faulty genes.
  • we can predict the risk of an inherited disorder for an individual, so they can make lifestyle choices to reduce this risk.
  • by analysing the genomes of cancer cells, and its changes, scientists can choose the best treatment for each individual.
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19
Q

how does the Human Genome Project help us understand human evolution and history?

A

people across the world can be linked by their DNA patterns, allowing scientists to trace human migration patterns since ancient history, and link us to our ancestors.

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20
Q

what did the scientists find out about the human genome in the Human Genome Project?

A
  • there are over 3 billion base pairs
  • there are 21,000 genes that code for proteins
  • you can make many different proteins from the same gene, by switching different parts of it on and off
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21
Q

what are the three parts that nucleotides are made up of?

A
  • phosphate group (little molecule attached to large ribose)
  • ribose (large molecule in the middle)
  • nitrogenous base (medium sized molecule attached to the ribose on the other side). this nitrogenous base is either the letter A, T, C, or G, which is what makes each base different.
22
Q

what are proteins?

A

polymers of amino acids. contain hundreds of amino acids joined together. there are 20 different amino acids in humans. the specific order and type of amino acids determines the shape of the protein. this determines its function (e.g. enzyme, structural protein, hormone).
- the order of amino acids in a protein is determined by the sequence of bases in the gene for that protein.

23
Q

how are proteins formed from a sequence of bases?

use ATG GGA CGC ATA TAC TTT

A

the cell reads the DNA sequence as triplets of bases. each triplet encodes for a specific amino acid in the protein.

24
Q

describe the process of protein synthesis:

A
  1. TRANSCRIPTION
    - the DNA double helix is separated
    - the base sequence of the gene on one of the strands of DNA c is copied into a complementary template molecule. this template is called the messenger RNA or the mRNA. it’s a single stranded molecule.
    - the mRNA now passes out of the nucleus and into the cytoplasm.
  2. TRANSLATION
    - the mRNA molecule attaches to a ribosome.
    - amino acids are now brought to the ribosome on carrier molecules. these are called transfer RNA or tRNA.
    - the ribosome now reads the triplets of bases on the mRNA and uses this to join together the correct amino acids in the correct order.

once the protein chain is complete, it folds into its unique shape. the shape enables the protein to do its specific job.

25
Q

what are alleles?

A

we have two copies of each chromosome (1 from each parent). therefore, we have 2 copies of each gene, too, and they’re usually different versions. they’re alleles.
- one chromosome in the pair comes from the father, and the other comes from the mother.

ALLELES ARE BASICALLY THE DIFFERENT VERSIONS OF A GENE.

26
Q

what is the difference between genes, chromosomes, and DNA?

A
  1. chromosomes are the biggest. they are molecules made up of many coiled up sections of DNA.
  2. DNA is responsible for building and maintaining your human structure.
  3. genes are segments/sequences of your DNA, that code for certain characteristics.
27
Q

what are the two alleles for the eye colour gene?

A
  • one causes blue eyes. the recessive gene (b), meaning there’s less of a chance as you need two, not just one.
  • one causes brown eyes. the dominant gene (B), meaning there’s a greater chance as you only need one.
28
Q

what does homozygous mean?

A

where the two alleles are the same. (e.g. a bb person is homozygous for the blue eye allele).

29
Q

what does heterozygous mean?

A

where the two alleles are different. (e.g. Bb is heterozygous, as there’s one blue eye and one brown eye allele).

30
Q

what does genotype mean?

A

it tells us which alleles a person has for a particular gene (tells us the alleles that are present). (e.g. a person with 2 copies of the blue eye allele has the ‘bb’ genotype).

31
Q

what does phenotype mean?

A

a characteristic caused by a particular genotype. (e.g. a ‘bb’ genotype causes blue eyes).

32
Q

what is the difference between a dominant and a recessive allele?

A
  • a dominant allele always produces its characteristic, even if there’s only one in the genotype. represented with an upper-case letter.
  • recessive alleles (represented with lower-case letter) only produces its characteristic if both of the alleles in the genotype are recessive.
33
Q

which gender matches with which chromosome?

  • XY
  • XX
A

XY = male
XX = female

34
Q

who are James Watson and Francis Crick?

A

discovered structure of DNA. realised it’s made up of two chains of nucleotide pairs that encode genetic information.
- used Rosalind Franklin’s image of DNA to make their discovery.

35
Q

who is Rosalind Franklin?

A
  • the discovery of the structure of the DNA was made possible by her X-ray diffraction work with Wilkins, although he took the credit for it and she didn’t.
  • she created Photo 51, where in her x-ray diffraction work, the lighter diamond shapes above and below the darkened x suggested a double helix pattern. provided a lot of structural information about DNA.
  • she was unaware that Wilkins, Watson, and Crick had used her x-ray photograph, so they didn’t have permission to use her data. they excluded her from winning the Nobel prize.
36
Q

who is Erwin Chargraff?

A
  • found that in DNA, the ratios of A to T and G to C are equal. provided clues into the chemical pairings that made up DNA. found that the amounts of A, T, C, and G varied from species to species.
  • observed the amounts of the 4 nitrogenous bases found in different samples of DNA. paper chromatography was used to separate the substances in the DNA and UV spectrophotometry was used to count the amount of each base in each sample.
  • discovered part of the structure of DNA, allowed Watson and Crick to make their final discovery.
37
Q

what are some examples of inherited diseases?

A
  • cystic fibrosis
  • sickle cell anaemia (however, anaemia is not inherited)
  • colour blindness
38
Q

how does an inherited disorder come about?

A

the result of a gene mutation. not always negative, but can affect your vision/quality of life.

39
Q

what is a mutation?

A

a change to a base. they’re very frequent.

40
Q

describe a harmless mutation in a section of bases of a gene:

A

e.g. ATG GGA … , and this creates a certain protein shape.
this could change to: ATG GGG, and it could still encode the same protein shape, by not changing the amino acid sequence. this is because different base triplets can sometimes encode for the same amino acid.

this mutation has no effect on the protein’s shape/function. this is the case for most mutations.

41
Q

what happens when a mutation actually has an effect on the amino acid produced from the base triplet?

A
  • the protein has a different amino acid, and this has altered its shape.
  • this can have a dramatic effect on its function.
  • e.g. the active site on an enzyme may have changed shape, so it can no longer attach to the substrate.
  • e.g. if it changes the shape of a structural protein (e.g. collagen), it may lose its strength
42
Q

describe the non-coding DNA in some chromosomes:

A
  • these regions switch genes on and off.
  • tell genes when to produce proteins.
  • mutations in these non-coding regions can affect how genes are switched on or off. e.g. a gene may be turned on that is supposed to be turned off.
  • as a result, the cell would produce a protein that it is not meant to have at that time. this could have a significant effect on a cell (e.g. uncontrolled mitosis, leading to cancer).
43
Q

what is cystic fibrosis?

A
  • disorder of the cell membranes
  • controlled by a single gene.
  • the allele for normal cell membranes is dominant (C), and the allele for defective cell membranes is recessive (c). therefore, in order to have cystic fibrosis, the person must have 2 copies of the defective allele.
  • a person with the Cc genotype does not have cystic fibrosis, but instead a carrier of the disorder.
44
Q

what is polydactyly?

A
  • people who have extra fingers or toes
  • caused by a dominant allele (only need one copy of the polydactyly allele to have the disorder)
  • not possible to be a carrier of this disorder, or of any dominant allele
45
Q

what is the use of embryo screening?

A
  • embryos tested to see if they have the alleles for inherited disorders
  • alleles without the defective alleles are implanted into the woman, and develop into healthy offspring
46
Q

what are the issues around embryo screening?

A
  • expensive. people believe the money should be spent elsewhere in the health service
  • often a large number of embryos are created, but only a small number are implanted. that means some healthy embryos are destroyed, and some think that’s unethical
  • in the future we may be able to screen embryos to produce offspring with desirable features (e.g. taller/more intelligent offspring). some find this unethical
47
Q

what is gene therapy?

A

where scientists correct faulty alleles and use this to treat inherited disorders.
- at the moment, however, this is still experimental

48
Q

go into more depth on cystic fibrosis: what are its symptoms, why?

A
  • most common life-threatening disease in the UK, affects 1 in 2500 people, affects around 100,000 people globally
  • usually develops in early childhood
  • build-up of sticky mucus, affects the lungs and digestion
  • can cause recurring chest infections (due to bacteria being stuck in the chest mucus); wheezing, coughing, shortness of breath; difficulty putting on weight. can develop other conditions such as diabetes, weakened bones (osteoporosis), male infertility (affects sperm ducts/testes), diarrhoea.
  • this is because it clogs the pancreatic duct and limits digestive enzyme secretion, limiting the absorption of fats, proteins, and vitamins.
49
Q

how would you test for cystic fibrosis during the person’s life?

A

the sweat test. checks for high levels of chloride in the sweat - people with CF have higher amounts of sodium and chloride in their sweat.

50
Q

what are the treatments for cystic fibrosis?

A
  • antibiotics to prevent/treat chest infections
  • medicines to thin the mucus and make it easier to cough it up
  • medicines to widen the airways and reduce inflammation
  • medicines to help digestion
  • physiotherapy loosens the mucus
  • enzyme and vitamin tablets help keep the levels up
  • oxygen gas improves breathing
51
Q

what are the two types of embryonic screening?

A

CHORIONIC VILLUS SAMPLING (CVS): sampling of embryonic cells between 10-12 weeks old. takes a sample of tissue from the developing placenta, from the chorionic villi, and test these cells. it’s a diagnostic test (gives a yes/no answer), but only tests for chromosome disorders such as down syndrome.

AMNIOCENTIS: (sampling of embryonic cells between 15-16 weeks). take fluid from around the foetus, this fluid contains the cells used for screening. this causes a small chance of miscarriage, but lab errors are rare.

biology (9 decks)

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