SB3 - Genetics ✓ Flashcards Preview

Edexcel GCSE Biology > SB3 - Genetics ✓ > Flashcards

Flashcards in SB3 - Genetics ✓ Deck (33)
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SB3a - What is the difference asexual and sexual reproduciton?

  • 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


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

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


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


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


  • Time consuming from fertilisation to birth


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


  • Very quick and takes up very little energy
  • No need to find a mate


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


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

  • Before: A zygote
  • After: An embryo


SB3b - What makes gametes different to regular body cells?

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


SB3b - Use the words genome, DNA, polymer, chromosones to define each other.

  • DNA is a molecule containing instructions for an organism. The DNA of an organism is its genome.
  • The human genome is made of many molecules each containing a chromosone.
  • DNA is used to code for and create protiens which are polymers.


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


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


SB3c - Describe the structure of DNA.

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


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

  • 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 .


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

  • 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.


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

  • P: Polymer of amino acids
  • S: Polymer of glucose
  • C: Polymer of glucose


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

  • Thoroughly mash up some peas
  • Make a solution of salt water and detergent without making it soapy
  • The detergent will break down the cell surface membranes and membranes around the nucleus
  • Mix the mash into the solution
  • Place the beaker containing this mixture in a water bath at 60 degrees for 15 minutes
  • Pour some of the filtrate into a boiling tube and add two drops of the protease enzyme (to break down proteins)
  • Tilt the tube slightly and let some ice cold ethanol run down the side of the tube slowly
  • Leave for a few minutes. The ethanol will cause the DNA to precipitate


SB3d - Describe the process of transcription.

  • 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.
  • Complemantary neucleotides 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


SB3d - Descibe the process of translation.

  • 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 (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


SB3e - Describe how different bases create different protiens.

  • 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 protiens


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

  • 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)


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

  • In the non-coding site.
  • This is becuase this site decides when protiens 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.


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

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


SB3g - What is the difference between heterozygous and homozygous.

  • Homozygous: Both the allelles are the same
  • Heterozygous: Both the alleles are different


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

  • There aredominant 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 visibel is if both alleles present are recessive.


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

Punnet squares.


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

  • 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



  • Thus the chances are 50/50


SB3i - Define coodominance, using blood as an example.

  • 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.


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

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


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

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


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

  • 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.


SB3j - What was the human genome project and did this: 1) reveal about the similarities in genes between peopl 2) do to help reduce risk of disorders 3) Help in treatment of diseases

  • The human genome project was a project that was carried out to try to map and identify all of the genes in a human.
  • Surprisingly, it revealed that despte all the visible variations, human all share around 99% of the same genes.
  • This was incredibly useful as it could be sued to identify genes that increase risk of cancer and other diseases/disorders.
  • It also shows which medication a person woul not be able to take making treatment more efficient and effective.


SB3j - What is variation?

The differences in the characteristics of a population.


SB3j - Name the two types of factor affecting variation giving examples of a factor and its variation.

  • 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