SB3 - Genetics ✓ Flashcards Preview

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

Flashcards in SB3 - Genetics ✓ Deck (46)
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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 daughter plant until it is well develpoed.


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

  • when they couldn't find a mate
  • when they are very well adapted to a new environment
  • when they needed to reproduce qucikly


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


  • 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


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


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 environments


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


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

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


SB3b - Define the term genome

The entire genetic material of an organism 


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 - 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 same way as it would in mitosis, it divides once more without replicating the DNA producing haploid daughter cells.


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

  • 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. 


SB3c - Describe the structure of DNA.

  • 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.


SB3c - How many genes do humans roughly have?

  • 20,000


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

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


SB3c - Describe how DNA strands are held together

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.


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 is a gene?

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


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, 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


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.
  • 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


SB3e - Describe how different bases create different proteins

  • 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


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 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.


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


SB3f - What were Mendel's laws of inheritance?

  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


SB3f - Why was Mendel's work largely ignored?

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


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

  • 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.


SB3g - What is the difference between heterozygous and homozygous.

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


SB3g - What is the phenotype?

The physical characteristic


SB3g- What is a genotype?

The genetic material of an organism, represented by letters