Topic 3 - Genetics Flashcards
Give examples of the advantages of asexual reproduction
-Only one parent is needed
-Time and energy efficient as you don’t need a mate
-Faster than sexual reproduction
-These factors allow for the population to increase rapid when conditions are favourable
Give examples of the disadvantages of asexual reproduction
-It does not lead to variation in a population so the species may only be suited to one habitat and could be susceptible to one disease/selection pressure
Give examples of the advantages of sexual reproduction
-It produces variation in offspring. This means that the species
can adapt to new environments due to variation, which gives them a survival advantage and a disease is less likely to affect all the individuals in a population
-Humans can speed up natural selection through selective breeding, which can be used, for example, to increase food production
Give examples of the disadvantages of sexual reproduction
-Time and energy are needed to find a mate
-It is not possible for an isolated individual
Explain the role of meiotic cell division
Meiosis produces four haploid, non-identical sex cells, or gametes which are all genetically different.
These fuse to form a diploid fertilised egg cell during fertilisation.
Meiosis produces sperm and egg cells in animals, and pollen and egg cells in plants.
Describe DNA
DNA is a polymer made up of two strands coiled to form a double helix. These strands linked by a series of complementary base pairs which are joined together by weak hydrogen bonds. It is made up of nucleotides that consist of a sugar and phosphate group with one of the four different bases attached to the sugar.
(A - T and G - C)
Describe the genome
The entire DNA of an organism
Describe a gene
A section of a DNA molecule that codes for a specific protein
Explain how DNA can be extracted from a fruit
*Crush the fruit - to break down the cell wall
* Add salt water - clumps the DNA together
* Add detergent - breaks down cell and nuclear membrane
* Filter - to remove insoluble material and separate out cell contents
* Add cold ethanol - cold slows down enzyme activity which will break the DNA apart and ethanol to precipitate the DNA out
Pick the DNA apart
*You will see strands of DNA with bubbles in them at the boundary between the filtrate and the chilled ethanol
Explain how the order of bases in a section of DNA decides the order of amino acids…
-Each group of three bases (codons) codes for one particular amino acid.
-The amino acid molecules join together in a long chain and fold to make a protein molecule. The number and sequence of amino acids determines which protein is produced.
-Therefore, it is the order of bases in the DNA that determines which proteins are produced
(There are also non-coding parts of DNA that do not code for proteins)
Describe transcription
The enzyme RNA polymerase breaks the hydrogen bonds between 2 DNA strands, exposing the bases. One DNA strand becomes the template strand. mRNA is made with complementary base pairs to the template DNA strand. The mRNA moves out of the nucleus into the cytoplasm.
Describe translation
The mRNA moves to the ribosomes. The anticodon on the tRNA molecule binds to a codon (3 bases) on the mRNA by a complementary base pairing. The tRNA molecule carries a specific amino acid. Peptide bonds formed between amino acids to produce a polypeptide chain.
Define transcription
The process in which a copy of DNA is made
Define translation
Where amino acids are joined together to make a polypeptide chain, following the sequence.
Describe the stages of protein synthesis
-RNA polymerase binds to non-coding DNA located in front of a gene
-RNA polymerase produces a complementary mRNA strand from the coding DNA of the gene
-the attachment of the mRNA to the ribosome
-the coding by triplets of bases (codons) in the mRNA for specific amino acids
-the transfer of amino acids to the ribosome by tRNA
-the linking of amino acids to form polypeptides
Describe how genetic variants in the non-coding DNA of a gene can affect phenotype
Enzyme RNA polymerase binds to non-coding DNA and a change in the order of bases in this non-coding DNA can affect the amount of RNA polymerase that can bind to it. This means the enzyme is less likely to bind and so less protein is produced. If less protein is produce this can affect the phenotype of the organism.
Describe how genetic variants in the coding DNA of a gene can affect phenotype
A genetic variant will alter the sequence of bases and therefore may change the sequence of amino acids which alters the final structure of the protein produced.
Describe the work of Gregor Mendel in discovering the basis of genetics
He carried out breeding experiments on pea plants and in 1886 came to the conclusion that:
-Offspring have some characteristics that their parents have because they inherit ‘hereditary units’ from each.
-One unit is received from each parent. -Units can be dominant or recessive and cannot be mixed together.
Why did people struggle to understand Mendel’s work?
Because it wasn’t until the 20th century that genes and chromosomes were discovered.
Explain why there are differences in the inherited characteristics as a result of alleles
Different alleles code for different forms of the same protein. An allele that codes for a damaged form of a protein can cause illness. This leads the protein being folded incorrectly and causing the illness.
Explain the term chromosome
A structure found in the nucleus which is made up of a long strand of DNA
Explain the term gene
A section of DNA that codes for a protein
Explain the term allele
Different versions of the same gene
Explain the term dominant
AN allele that is always expressed, even if there is just one copy
