Genetics Flashcards
What are some advantages of sexual reproduction? (3)
- Produces genetic variation, means that if the environment changes, it is likely that one of the offsprings will be resistant to this change and survive, decreasing the chance of this species becoming extinct.
- It allows us to use selective breeding to produce offsprings with desirable characteristics.
- This speeds up natural selection.
What are some disadvantages of sexual reproduction?
- Organisms need to find and attract mates which takes more time and energy then asexual reproduction, so organisms produce fewer offspring in their lifetime.
- Two parents are needed. This can be a problem if individuals are isolated.
What are some advantages of asexual reproduction? (3)
- Only one parent is needed.
- Uses less energy and is faster as organism do not need to find a mate.
- In favourable conditions, a lot of offsprings can be produced in a short period of time
What are some disadvantages of asexual reproduction?
- There’s no genetic variation between offspring in the population. So, if the environment changes and conditions become unfavourable the whole population may be affected.
What is meiosis?
Cell division that produces 4 genetically different haploid gametes. This is important for asexual reproduction.
What are the steps of meiosis? (4)
- The cell makes copies of its chromosomes, so it has the double amount of chromosomes.
- The cell divides in two cells, which each cell having half the amount of chromosomes (46).
- The two cells divide again into four cells, with each cell having 23 chromosomes.
- These cells are called gametes as they are all genetically different from each other, because the chromosomes are shuffled up during the process, resulting in random chromosomes ending up in different cells.
What is DNA?
A double-stranded polymer of nucleotides, that wound up together to form a double helix.
What are DNA nucleotides made up of? (3)
- common sugar
- phosphate group
- one of four bases (adenine, thymine, cytosine and guanine)
Describe how nucleotides interact to form a DNA molecule (3)
- Sugar and phosphate molecules join together to form a sugar-phosphate backbone in each DNA strand.
- Base connected to each sugar.
- Complementary bases pairings joined by weak hydrogen bonds.
What is the genome?
All of the genetic material of an organism.
What is a gene?
A short section of DNA that codes for a specific protein.
Describe the method used to extract DNA from a fruit (6)
- Place a piece of fruit in a beaker and crush it.
- Add detergent and salt and mix.
- Filter the mixture and collect the liquid in a test tube.
- Pour chilled ethanol in the test tube.
- DNA precipitates forming a white solid.
- Use a glass rod to collect the DNA sample.
Why is detergent added to the crushed fruit?
It disrupts the cell membrane, releasing the DNA into the solution.
Why is salt added to the crushed fruit?
Salt encourages the precipitation of the DNA.
Why is chilled ethanol added to the fruit solution rather than water?
DNA is insoluble in ethanol, encouraging its precipitation.
Explain the importance of the order of bases in a section of DNA?
It decides the order of amino acids in the protein which fold to produce specifically shaped proteins such as enzymes.
Describe the process of transcription (5)
- Proteins are made in the cell’s cytoplasm by ribosomes. DNA is found in the nucleus and can’t move out of it as its really big.
- An enzyme called RNA polymerase binds to region of non-coding in front of a gene.
- The two DNA strands unzip and the RNA polymerase moves along one of the strands of DNA.
- It uses the coding DNA in the gene as a template to make the mRNA . Base pairing between the DNA and RNA ensures that the mRNA is complementary to the gene.
- Once made, the mRNA molecule moves out of the nucleus through the nuclear pores and joins with a ribosome.
Describe the process of translation (3)
- Once the mRNA is bounded to a ribosome, the protein can be assembled. Amino acids are brought the ribosomes by another RNA molecule called transfer RNA (tRNA).
- The order in which the amino acids are brought to the ribosome matches the order of the base triplets in mRNA. Base triplets in mRNA are known as codons.
- The amino acids join together to form a polypeptide, known as the protein.
What is non-coding DNA?
DNA which does not code for a protein, but instead controls gene expression.
Describe how genetic variants in the non-coding DNA of a gene can affect the phenotype
It influences the binding of RNA polymerase and alters the quantities of proteins produced.
Describe how genetic variants in the coding DNA of a gene can affect the phenotype
It alters the sequence of amino acids and therefore the activity of the protein produced.
Describe Mendel’s experiment (2)
- In one experiment, Mendel breaded two pea plants of different heights - a tall pea plant and a dwarf pea plant. The offspring produced were all tall pea plants.
- In another experiment, he then bred two of these tall offspring together. He found that when the offspring from the first cross were crossed with each other. Three tall offspring were produced for every one dwarf overall. In other words he produced a 3:1 ratio of tall: dwarf plants.
What were Mendel’s three important conclusions?
- Characteristics in plants are determined by hereditary units.
- Hereditary units are passed on to offspring unchanged from both parents, one unit from each parent.
- Hereditary units can be dominant or recessive-if any individual has both the dominant and the recessive unit for a characteristic, the dominant characteristic will be expressed.
What does the term chromosome mean?
A long, coiled molecule of DNA, that carries genetic information in the form of genes.
What does the term allele mean?
A version of a gene.
What does the term homozygous mean?
If both alleles for one gene are the same.
What does the term heterozygous mean?
If the alleles are different in a gene.
What does the term genotype mean?
The alleles in the organism.
What does the term phenotype mean?
An organism observable physical characteristics.
What is monohybrid inheritance?
The inheritance of a single gene.
What are codominant alleles?
Alleles that equally contribute to an organisms phenotype.
Describe codominance in blood groups
A and B are codominant and gives the blood group AB.
What is a sex-linked characteristic?
A characteristic that is coded for by an allele on a sex chromosome.
What are the two causes of variation within species?
Genetic variation - different characteristics as a result of mutation and sexual reproduction.
Environmental variation - different characteristics caused by an organisms environment.
What is the Human Genome Project?
Their aim was to understand the function of every gene in the human genome.
How can the results of the Human Genome Project be applied to medicine? (3)
- Enables scientists to understand how lifestyle factors interact with genes.
- Disease-causing alleles identified more rapidly and the appropriate treatments prescribe earlier on.
- Scientists can predict an individuals response to drugs.
What is a mutation?
A random change in the base sequence of DNA that may result in genetic variants.
How may a gene mutation affect an organisms phenotype? (3)
- Neutral mutation does not change the sequence of amino acids, the protein function and structure, thus the phenotype remains the same.
- Mutation may cause a minor change in an organisms phenotype e.g. eye colour.
- Mutation may completely change the sequence of amino acids, which may result in a non-functional protein, causing severe changes to the phenotype.
