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Edexcel Biology > Topic 3: Genetics > Flashcards

Topic 3: Genetics Flashcards

1
Q

Explain some of the advantages of asexual reproduction.

A

Advantages:

  1. Produces variation, variation provides a survival advantage by natural selection, selective breeding can be used to increase food production
  2. Can produce lots of offspring very quickly because the reproductive cycle is fast. This can allow organisms to colonise a new area very rapidly.
  3. Only one parent is needed which means organisms can reproduce when conditions are favourable without having to wait for a mate.
  4. requires less energy
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2
Q

Explain some disadvantages of Asexual reproduction.

A

Disadvantages:

  1. No genetic variation between offspring. So if the environment changes and conditions become unfavourable the whole population could be affected.

e.g. if no plants are resilient to a disease they’ will all get it and die

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3
Q

What is sexual reproduction? (Meiosis)

A
  1. Sexual reproduction is a process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote (fertilised egg cell)
  2. Genetic information from each gamete is mixed so the resulting zygote is unique
  3. The gametes of animals are the sperm cells and egg cells
  4. The gametes of flowering plants are the pollen cells and egg cells
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4
Q

What are gametes?

A

Sex cells (sperm cells, egg cells)

Haploid (half the number of chromosomes)

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5
Q

Explain some of the advantages of sexual reproduction.

A

It creates genetic variation, increasing the probability of a species adapting to and surviving environmental changes

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6
Q

Explain some disadvantages of sexual reproduction

A
  1. Two parents are required. This makes reproduction difficult in endangered populations or in species which exhibit solitary lifestyles
  2. More time and energy is required so fewer offspring are produced
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7
Q

explain the role of meiotic cell division

A
  1. Form of cell division
  2. involved in the formation of gametes
  3. Chromosome number is halved
  4. Involves two divisions
  5. 4 genetically different cells are made
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8
Q

Stages of meiosis

A

Meiosis has two stages of division, where one cell divides into two and then the two cells divide to form a total of four cells

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9
Q

mieosis steps

A
  1. The cell makes copies of its chromosome, so it has double the amount of genetic information
  2. The cell divides into 2 cells, each with half the amount of chromosomes (46)
  3. The cell divides again producing 4 cells, each with quarter amount of chromosomes (23)
  4. These cells are called gametes and they are all genetically different from each other because the chromosomes are shuffled during the process, resulting in random chromosomes ending in each of the four cells.
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10
Q

First divisive stage of meiosis

A

A human cell that has undergone genetic replication divides to form two daughter cells, each with 46 chromosomes

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11
Q

Second divisive stage of meiosis

A

The two daughter cells each containing 46 chromosomes divide to form a total of four daughter cells, each with 23 chromosomes

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12
Q

Products of meiosis

A

Four non-identical daughter cells called gametes are produced, each with half the number of chromosomes of the parent cell

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13
Q

Explain the role of meiotic cell division. The stages of meiosis are not required.

A
  1. Meiosis is a type of cell division that doesn’t produce identical cells.
  2. It produces gametes
  3. The gamete-making cell has two sets of chromosomes. It is diploid.
  4. The chromosomes replicate (and the copies stick to one another).
  5. The cell divides into two and then two again.
  6. Each of the final four daughter cells has half the number of chromosomes (4 diploid cells made)
  7. this results in genetically different haploid gametes
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14
Q

Why is meiosis important for sexual reproduction?

A

It increases genetic variation

It ensures that the resultant zygote is diploid

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15
Q

Define zygote

A

Cell formed when two gametes combine

A fertilised egg

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16
Q

Define fertilization

A

joining of sperm and egg (gametes)

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17
Q

Describe a haploid cell

A

having half the normal number of chromosomes

(23 chromosomes)

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18
Q

Describe a Diploid cell

A

Having the normal number of chromosome (46 chromosomes)

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19
Q

Describe a diploid cell

A

having the normal number of chromosomes

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20
Q

Genetic variation

A

Differences in the DNA between individuals due to genetic reshuffling in meiosis, which can result in different displayed characteristics

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21
Q

Define gene and genotype.

A

The genome is the entire DNA of an organism and most cells contain a complete copy of an organism’s genome.

A gene is a section of a DNA molecule that codes for amino acids

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22
Q

What is DNA?

A

A double-stranded polymer of nucleotides, wound to form a double helix

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23
Q

Describe DNA

A

1) Two strands coiled to form a double helix

2) Strands linked by a series of complimentary base pairs joined together by weak hydrogen bonds

3) Nucleotides that consist of a sugar and phosphate group with one of the four different bases attacher to the sugar

  1. Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds
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24
Q

What are the monomers of DNA?

A

nucleotides

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25
Q

What are DNA nucleotides made of?

A
  1. Common sugar
  2. Phosphate group
  3. One of four bases: A, T, C or G
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26
Q

State the full names of the four bases found in nucleotides

A
  1. Adenine
  2. Thymine
  3. Cytosine
  4. Guanine
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27
Q

Describe the method used to extract DNA from fruit

A
  1. Place a piece of fruit in a beaker and crush it
  2. Add detergent and salt to the beaker and mix.
  3. The detergent breaks down the cell membranes, the salt makes the DNA stick together.
  4. Filter the mixture to get froth and big insoluble bits out.
  5. collect the liquid in a test tube
  6. Pour chilled ethanol (alcohol) into the test tube that contains the filtered mixture.
  7. DNA will start to come out of solution as it is not soluble in cold alcohol. It will appear as a white stringy precipitate.
  8. Use a glass rod to collect the DNA sample
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28
Q

Why is detergent added to the crushed fruit?§

A

It disrupts the cell membranes, releasing DNA into solution

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29
Q

Why is salt added to the crushed fruit?

A

Salt encourages the precipitation of DNA

30
Q

Why is chilled ethanol added rather water?

A

DNA is insoluble in ethanol, encouraging its precipitation

31
Q

What is a chromosome?

A

A long, coiled molecule of DNA that carries genetic information in the form of genes

32
Q

Define gene

A

A section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein

33
Q

Explain how a gene codes for a protein

A
  1. A sequence of three bases in a gene forms a triplet
  2. Each triplet codes for an amino acid
  3. The order of amino acids determines the structure (i.e. how it will fold) and function of protein formed
34
Q

Explain how the order of bases in a section of DNA decides the order of amino acids in the protein and that these fold to produce specifically shaped proteins such as enzymes.

A
  1. To enable genes to code for proteins, the bases A, T, G and C get together not in pairs but in triplets.
  2. Each protein is made up of large numbers of amino acid molecules.
  3. Each triplet of bases codes for one particular amino acid.
  4. Amino acids are made in the number and order dictated by the number and order of base triplets.
  5. Finally, the amino acid molecules join together in a long chain to make a protein molecule.
  6. The number and sequence of amino acids determines which protein results.
35
Q

Why is the ‘folding’ of amino acids important in proteins such as enzymes?

A

The folding of amino acids determines the shape of the active site which must be highly specific to the shape of its substrate

36
Q

What is protein synthesis?

A

The formation of a protein from a gene.

37
Q

What are the two stages of protein synthesis?

A
  1. Transcription
  2. Translation
38
Q

What does transcription involve?

A

The formation of mRNA from a DNA template

39
Q

Describe the steps of transcription

A
  1. DNA double helix unwinds
  2. RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand
  3. RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand
  4. mRNA formation complete.
  5. mRNA detaches and leaves the nucleus.
40
Q

Describe the differences between mRNA and DNA

A

mRNA is single stranded whereas DNA is double stranded

mRNA uses U whereas DNA uses T

41
Q

Why is mRNA used in translation rather than DNA?

A

DNA is too large to leave the nucleus so cannot reach the ribosome.

42
Q

What does translation involve?

A

A ribosome joins amino acids in a specific order dictated by mRNA to form a protein.

43
Q

Describe translation steps

A
  1. Once the mRNA is bound to the ribosome, the protein can be assembled.
  2. tRNA (transfer RNA) transfers amino acids to the ribosomes. Every 3 bases on mRNA is called a codon - tRNA has the anticodon which connects the amino acid.
  3. The ribosome moves along the mRNA and tRNA brings specific amino acid to match the codon in the correct order.
  4. The amino acids are joined together by the ribosome. This makes a polypeptide (protein)
  5. A polypeptide chain is formed from the sequence of amino acids which join together
44
Q

How is a tRNA molecule adapted to its function

A

Each tRNA molecule has an anticodon which is specific to the codon of the amino acid that it carries

45
Q

What is a mutation?

A

A random change in the base sequence
of DNA which results in genetic variants

46
Q

Describe the effect of a gene mutation in coding DNA

A
  1. If a mutation changes the amino acid sequence, protein structure and function may change
  2. If a mutation does not change amino acid sequence, there is no effect on protein structure or function
47
Q

What is non-coding DNA?

A

DNA which does not code for a protein but instead controls gene expression

48
Q

Describe the effect of a gene mutation in non-coding DNA

A

A mutation may affect the ability of RNA polymerase to bind to non-coding DNA

This may affect protein production and the resulting phenotype of the organism

49
Q

Describe how genetic variants in the non-coding DNA of a gene can affect phenotype by influencing the binding of RNA polymerase and altering the quantity of protein produced.

A
  1. A mutation may affect the ability of RNA polymerase to bind to non-coding DNA
  2. If the RNA polymerase does not bind properly, it can affect how much mRNA is transcribed and therefore how much protein is produced.

Depending on the proteins function, the phenotype of the organism may be affected by how much is made.

50
Q

Describe how genetic variants in the coding DNA of a gene can affect phenotype by altering the sequence of amino acids and therefore the activity of the protein produced

A

If a mutation changes the amino acid sequence, protein structure and function may change

if a mutation does not change amino acid sequence, there is no effect on protein structure or function

51
Q

Describe the work of Mendel in discovering the basis of genetics and recognise the difficulties of understanding inheritance before the mechanism was discovered.

A

Mendel crossed tall pea plants and dwarf pea plants - offspring produced were all tall pea plants. Then bred two tall off spring together. He found that when offspring from the first cross where crossed together, three tall offspring and one dwarf. Produced a 3:1 ratio of tall:dwarf plants.

52
Q

B3.11 What had Mendel showed?

A

Height characteristics in pea plants were determined by separately inherited “hereditary units” passed on from each parent. The ratios of tall and dwarf in the offspring shoes that the unit for tall plants, T, was dominant over the unit for dwarf plants, t.

53
Q

B3.11 Mendel’s three important conclusions

A

1) characteristics in plants are determined by “hereditary units”
2) Hereditary units are passed onto offspring unchanged from both parents, one unit from each parent
3) Hereditary units can be dominant or recessive - if an individual has both the dominant and the recessive unit for a characteristic, the dominant character is expressed.

54
Q

B3.11 Recognise the difficulties of understanding inheritance before the mechanism was discovered.

A

At the time Mendel’s work was cutting edge and new. Now we know that hereditary units are genes but at the time scientists didn’t have the background knowledge to properly understand Mendel’s findings - no idea about DNA, genes, chromosomes.
It wasn’t until after his death that people realised how significant his work was and that mechanism of inheritance could be fully explained.

55
Q

B3.12 Explain why these are differences in the inherited characteristics as a result of alleles

A

Genes for the same characteristic can contain slightly different instructions that create variations. Different forms of the same gene are called alleles. There are two copied if every chromosome in a body cell nucleus, a body contains two copies of every gene. Each copy of a gene may be a different allele. There are many alleles and the different combinations of alleles in each person gives each of us slightly different characteristics.

56
Q

B3.13 Explain the terms: dominant, recessive,

A

Dominant - dominant alleles overrule recessive alleles (represented as a capital letter e.g. D). If alleles are DD or Dd then dominant characteristics will show
Recessive - represented with lower case letter e.g. d. Recessive traits will only shown if both alleles are recessive “dd”.

57
Q

B3.13 Explain the terms: homozygous, heterozygous,

A

If both alleles are the same, an organism is homozygous for that gene. e.g DD or dd.
If alleles are different, an organism is hetrozygous for that gene e.g Dd .

58
Q

B3.13 Explain the terms: genotype, phenotype and zygote.

A

The alleles in an organism are its phenotype. What the organism looks like are its genotype.
A zygote is a fertilised egg cell

59
Q

B3.14 Explain monohybrid inheritance using genetic diagrams.

A

The inheritance of a single characteristic is called monohybrid inheritance. A monohybrid cross can be used to show how recessive and dominant traits for a single characteristic are inherited

60
Q

B3.14 Explain monohybrid inheritance using Punnett squares and family pedigrees.

A

Punnet squares are used to work out the theoretical probability of offspring inheriting certain genotypes.
Punnet squares are used to work out the probabilities of different phenotypes caused by alleles.
A family pedigree chart shows how genotypes and their resulting phenotypes are inherited in families

61
Q

B3.15 Describe how the sex of offspring is determined at fertilisation, using genetic diagrams.

A

GENETIC DIAGRAM: Means of determining all possible genetic characteristics of Offspring based on genetic characteristics of prospective parents

GENDER DETERMINATION OF OFFSPRING:
s
Females possess two copies of the X Chromosome (XX)
Males possess one X and a shorter Y Chromosome (XY)

62
Q

B3.17 Describe the inheritance of the ABO blood groups with reference to codominance and multiple alleles.

A

There are four blood types - O, A, B and AB. The gene for blood type in humans has three different alleles - I^O, I^A and I^B.
A person with the genotype I^AI^B shows the effect of both alleles and has the blood type AB. They are both dominant alleles so I^A and I^B are codominant with each other.
I^O is recessive so bloody type O only happens when there are two recessive alleles (I^OI^O)

63
Q

H B3.18 Explain how sex-linked genetic disorders are inherited - male

A

Chromosomes in diploid cells come in pairs. Most pairs, the chromosomes have the same genes. However Y chromosomes miss some genes found in the x chromosome. This means a man (XY) will have only one allele for some genes on the X chromosome (because those genes are missing on the Y chromosome). If the allele for on of these X chromosome genes causes a genetic disorder, the man will develop this.
If a woman inherits the disorder allele, she may have a healthy allele on her other X chromosome. If the disorder allele is recessive she will not get the disorder. If she inherits two recessive disorder alleles she will develop the disorder. Probability of a woman developing it is lower a man.

64
Q

B3.19 State that most phenotypic features are the result of multiple genes rather than single gene inheritance.

A

Most phenotypic features are the result of multiple genes rather than single gene inheritance.

65
Q

B3.20 Describe the causes of variation that influence phenotype including: (a) genetic variation - different characteristics as a result of mutation and sexual reproduction.

A

Genetic variation:
Genetic variation is caused by the different alleles inherited during sexual reproduction.
Mutations are changes to the base sequence of DNA. When they occur within a gene they result in an allele, or a different version of a gene.

66
Q

Human Genome project

A

Researchers managed to map over 20, 000 human genes. The big idea was to find every single human gene.

67
Q

B3.21 Discuss the outcomes of the Human Genome Project and its potential applications within medicine.

A

Mapping a person’s genome can indicate their risk of developing diseases that are caused by different alleles of genes. It can also help identify which medicines might be best to treat a person’s illness, because the alleles we have can affect how medicines work in the body.
-Predict and prevent diseases.
-testing and treatment of diseases
-new and better medicines.
However: increase stress, gene-ism and discrimination

68
Q

B3.22 State that there is usually extensive genetic variation within a population of a species and that these arise through mutations

A

There is usually extensive genetic variation within a population of a species and that these arise through mutations

69
Q

B3.23 State that most genetic mutations have no effect on the phenotype, some mutations have a small effect on the phenotype and, rarely, a single mutation will significantly affect the phenotype.

A

Most genetic mutations have no effect on the phenotype.
Some mutations have a small effect on the phenotype.
Rarely, a single mutation will significantly affect the phenotype.

70
Q

B3.20 Describe the causes of variation that influence phenotype including:
(b) environmental variation - different characteristics caused by an organism’s environment (acquired characteristics)

A

Variation caused by the surroundings is called environmental variation.
Characteristics that are changed by their environment during the life of the individual are called acquired characteristics.

71
Q

B3.20 Describe the causes of variation that influence phenotype including: (a) genetic variation - different characteristics as a result of mutation and sexual reproduction (b) environmental variation - different characteristics caused by an organism’s environment (acquired characteristics)

A

Most variation in a phenotype is determined by a mixture of genetic and environmental factors.

Edexcel Biology (9 decks)

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