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Edexcel GCSE Biology (9-1) > SB3 - Genetics ✓ > Flashcards

SB3 - Genetics ✓ Flashcards

1
Q

SB3a - How may a plant such as a strawberry reproduce asexually?

A
  • By using specail stems called runners which grow out from the root of the plant.
  • These can also provide water and nutrients to the daughter plant until it is well develpoed.
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2
Q

SB3a - In what 3 scenarios would an aphid decide to reproduce asexually rather than sexually?

A
  • when they couldn’t find a mate
  • when they are very well adapted to a new environment
  • when they needed to reproduce qucikly
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3
Q

SB3a - What are the advantages and disadvantages for asexual reproduction?

A

Pros:

  • Very quick and takes up very little energy
  • No need to find a mate
  • many identical offspring can be produced for well adapted organisms in an unchanging environment

Cons:

  • No variation meaning that if they are vulnerable to a disease there is a high risk of extinciton
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4
Q

SB3a - What are the advantages and disadvantages of sexual reproduction?

A

Pros:

  • Creates variation meaning that a species is more likely to survive a disaster.
  • It also allows them to move to different environments

Cons:

  • Time consuming from fertilisation to birth
  • mate required
  • smaller number of offspring
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5
Q

SB3a - What is the difference asexual and sexual reproduciton?

A
  • Sexual reproduction involves fertilisation of a female gamete by a male gamete (two organisms)
  • Asexual reproduction only requires one parent anf the offspring is genetically identical to their parent
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6
Q

SB3a - What type of cell divison occurs in each type of reproduction?

A
  • Sexual Reproduction uses Meiosis to produce gametes which fuse during fertilization
  • Asexual reproduction uses mitosis to produce clones
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7
Q

SB3b - Define the term genome

A

The entire genetic material of an organism

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8
Q

SB3b - What is the term for a fertilised egg before and after cell division starts to occurs?

A
  • Before: A zygote
  • After: An embryo
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9
Q

SB3b - What makes gametes different to regular body cells?

A

They are haploid rather than diploid meaning that they contain 1 set of 23 chromosones.

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10
Q

SB3b - What process is used for division of gamete cells, and how does this differ from mitosis?

A

Meiosis:

  • The gamete ‘making’ cell is diploid.
  • Once it has divided in the same way as it would in mitosis, it divides once more without replicating the DNA producing haploid daughter cells.
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11
Q

SB3c - Describe the hydrogen bonding between Adenine/Thymine and Guanine/Cytosine

A
  • A/T form two hydrogen bonds while C/G form three hydrogen bonds.
  • This explains why each of them have pairs and A can’t bond with C for .
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12
Q

SB3c - Describe the lab extraction of a precipitate of peas DNA.

A
  • We mash up some peas then put them into a beaker containg a solution of detergent and salt, then mix well.
  • The detergent will break down the cell membranes to release the DNA
    The salt will cause the DNA to clump together
  • We then filter the mixture to get the froth and large, insoluble bits of cell out.
  • Then, we gently add some ice-cold ethanol to the filtered mixture.
  • The DNA will start to come out of the solution as it’s not soluble in cold ethanol. It will appear as a stringy white precipitate, that can be fished out with a galss rod.
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13
Q

SB3c - Describe the structure of DNA.

A
  • A double helix structure with nuecloetides.
  • Each nucleuotide contains a phosphate group and a sugar.
  • This forms a sugar phosphate backbone.
  • They also have bases which form complementary base pairs and joined together by weak hydrogen bonds.
  • The bases are adenine guanine thymine and cytosine with A being complimentary to T and C being complimentary to G.
  • The DNA forms a polymer because it is many nuceuotides joined together.
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14
Q

SB3c - How many genes do humans roughly have?

A
  • 20,000
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15
Q

SB3c - What are starch, proteins and cellulose polymers of?

A
  • P: Polymer of amino acids
  • S: Polymer of glucose
  • C: Polymer of glucose
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16
Q

SB3c - Describe how DNA strands are held together

A

Parts of DNA have very slight electrical charges - a slightly negatively charged part of one base attracts a slightly positive charged part of another base. This forms a weak force of attraction called a hydrogen bond.

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17
Q

SB3c - What is a gene and why do genes differ between people?

A
  • The order of bases form a gene.
  • Everyone has a slightly different order of bases (except identical twins) meaning that they all have different genesd.
  • Since DNA and genes are passed down along family, this information can be used to find out if people are related.
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18
Q

SB3c - What is a gene?

A

A section of DNA that contains the code instructions for a protein

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19
Q

SB3d - Descibe the process of translation.

A
  • Translation is the second stage of protien synthesis and follows transcription
  • The mRNA attaches to ribocomes in the cytoplasm
  • The ribosome moves along the mRNA three bases at a time (a triplet of bases is called a codon)
  • At each codon, a complemantary tRNA molecule, the anticodon, (that codes for a specific amino acid) joins opposite to it.
  • Eventually, all the amino acids join up to from a polypeptide chain
  • This chain will then fold up to form a protein
20
Q

SB3d - Describe the process of transcription.

A
  • Transcription is the first stage of protien synthesis in which RNA is created inside the nucleus
  • RNA polymerase attaches to the non-coding binding site of the DNA
  • This causes the strands of DNA to unzip. One strand acts as a template.
  • Complementary nucleotides attach to the template strand EXCEPT Instead of T attaching to A, Uracil attaches to A
  • The nucleotides join up to form a polymer of mRNA (RNA Polymerase)
  • The mRNA leaves the nucleus through nuclear pores
21
Q

SB3e - Describe how different bases create different proteins

A
  • A triplet of bases forms a codon.
  • Each codon codes for a different amino acid.
  • Different orders and collections of amino acids will form different proteins
22
Q

SB3e - What is a mutation and what are the two types of causes for this?

A
  • A mutation is a change in the sequence of bases in a gene.
  • This can be caused by DNA not being copied properly or by enviromental factors (such as radiation)
23
Q

SB3e - Where along a strand of DNA would a mutation be most harmful?

A
  • In the non-coding site.
  • This is because this site decides when proteins and processes should/should not take place.
  • A mutation in this could lead to repeated rapid mitosis leading to a cancerous tumor, or a lack of a required protien.
24
Q

SB3f - Describe’s Mendel’s observation and conclusion through his experiment about characteristics of tall and short plants.

A

After breeding tall and short plants together, he noticed that:

  • In the first generation of offspring, all the plants were tall
  • Despite having both tall parent plants, the second generation of offspring contained some plants that were short
  • This meant that characteristics inherited by offspring are not just a blend of parent’s characteristics
  • Also that there were ‘factors’ (now know as alleles) which affect this outcome and that one was dominant over the other
25
Q

SB3f - What were Mendel’s laws of inheritance?

A
  1. Each gamete receives only one factor for a characteristic
  2. The version of a factor that a gamete receives is random and does not depend on the other factors in the gamete
  3. Some versions of a factor are more ‘powerful’ than others and always have an effect on the offspring
26
Q

SB3f - Why was Mendel’s work largely ignored?

A
  • Scientists did not see how ‘factors’ could explain the many variations in characteristics
  • It didn’t fit with Darwin’s theory of evolution
27
Q

SB3g - How is an allele chosen to be visible in the phenotype?

A
  • There are dominant alleles (represented by capital letters) and recessive alleles.
  • In any heterozygous case, the dominant allele will be visible in the phenotype.
  • The only way a recessive allele can be visible is if both alleles present are recessive.
28
Q

SB3g - What is the difference between heterozygous and homozygous.

A
  • Homozygous: Both the allelles are the same
  • Heterozygous: Both the alleles are different
29
Q

SB3g - What is the phenotype?

A

The physical characteristic

30
Q

SB3g- What is a genotype?

A

The genetic material of an organism, represented by letters

31
Q

SB3g - What is monohybrid inheritance?

A

The inheritance of 1 characteristic

32
Q

SB3h - Explain how the chance of have a boy or girl baby is equal.

A
  • Females have XX chromosones;
  • Males have XY chromosones.
  • The mother has XX and the father has XY.
  • The means that if you draw a punnet square:

X Y

X XX XY

X XX XY

  • Thus the chances are 50/50
33
Q

SB3h - What determines the sex of a human?

A
  • Sex is determined by the sperm the fertilises the egg - whether it carrys an X or a Y chromosome
34
Q

SB3h - What diagram can be used to determine the chance of inheriting a certain characteristics?

A

Punnet squares.

35
Q

SB3i - Define coodominance, using blood as an example.

A
  • A pair of alleles inherited that are both dominant alleles.
  • For example, your blood group can be A, B, o or AB. in this case, o is recessive while A and B are both dominant and so if the AB alleles are inherited, they will both be present in the phenotype giving you AB blood type.
36
Q

SB3i - Explain why a male is more likely to inherit certain genetic disorders.

A

Since males have a Y chromosome which is missing regions, if a recessive allele is present in the X chromosone, but that area isn’t present in the Y chromosome, then the male will get the disease without having to have two recessive alleles.

37
Q

SB3i - How is a Y chromosone different to an X?

A

A Y chromosone is missing regions that are present on an X chromosone.

38
Q

SB3i - Why is a son guarenteed to inherit a recessive sex-linked genetic disorder if his mother has it?

A
  • If it is sex-linked, that area isn’t present on the Y chromosone (which he’d inherit from his father) and so only the mother’s genes matter.
  • Thus if it is a recessive disorder, the mother must have two of this and is guarenteed to pass this on to her son
  • Meaning her son will inherit the recessive allele and won’t be able to inherit a dominant allele to counter it.
39
Q

SB3j - Explain how variation in height is both envionmental and genetic.

A
  • Your capacity to grow is based off the alleles you inherit form your parents and increase the chance of you being tall/short.
  • However your diet will alsoaffect your growth and so it is affected by genetic and environmental factors.
40
Q

SB3k - If you plot the frequency of a variable with continuous variation in a species on a graph, what will it look like?

A
  • It will be a normal distribution (bell-shaped) curve.
  • The most common value is in the middle of the whole range and the further away from this, the fewer individuals have this value.
41
Q

SB3j -What are the advantages / disadvantages of the Human Genome Project?

A

Advantages

  1. Alerting people that they are at risk of certain diseases - people may be able to change their lifestyle to reduce this risk
  2. Distinguishing between different forms of diseases
  3. Allows doctors to tailor treatment for some diseases to the individual where alleles affect how their respond to the treatment

Disadvantages

  1. People who are at risk of certain diseases may be discriminated against when applying for work or life insurance
  2. It may not be helpful to tell someone they are at risk for a condition which there is no cure.
42
Q

SB3j - What is variation and what is it caused by?

A

The differences in the characteristics of a population - this is caused by mutations.

43
Q

SB3j - What was the Human Genome Project?

A
  • The human genome project was a project that was carried out to try to map and identify all of the genes in a human.
44
Q

SB3k - Name the two types of factor affecting variation giving examples of a factor and its variation.

A
  • Environmental factors: Effects from your surroundings. e.g. water and light content will affect plant growth
  • Genetic factors: Effects from your alleles and mutations. e.g, natural hair colour is based off the alleles you inherit form your parents
45
Q

SB3k - What is the difference between discontinuous and continuous variation?

A
  • Discontinuous variation is variation in something that has a limited amount of possible values (e.g. number of leaves)
  • Continuous variation is variation in something that has possible values that could be measured to an infinite degree of accuracy (e.g leaf length)
46
Q

SB3i - What are the different blood types and their possible genotypes?

A

A - IaIa IaIo

B- IbIb IbIo

AB- IaIb

O- IoIo

Edexcel GCSE Biology (9-1) (11 decks)

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