Topic 3 - Genetics Flashcards
What is DNA?
The genetic material in the nucleus of most Eukaryotic cells is made from a chemical called DNA.
• DNA is a polymer
• Two strands
• Coiled into twisted ladder
Polymer
A large molecule made from many smaller molecules called monomers.
Chromosomes
A coiled up molecule of DNA. In diploid cells, chromates come in pairs (23).
Genome
The entire DNA of an organism.
XX = female
XY = Male
What is nucleotide and what’s it made up of?
A monomer
• Each nucleotide consists of one sugar molecule, one phosphate molecule and one ‘base’.
• The sugar and phosphate molecules in the nucleotide from a ‘backbone’ to the DNA strands.
• One of 4 different bases joins to each sugar.
Structure of DNA
• Double helix
• Sugar phosphate backbone
• Complimentary base pairing
What is the complimentary base pairing?
A - T
C - G
Held together by weak hydrogen bonds.
Each base links to a base on the opposite strand in the helix.
What is a gene?
• A gene is a section of DNA on a chromosome that codes for a particular sequence of amino acids which form proteins. The sequence of bases in the gene determines what protein is produced.
• Genes control our characterises as they code for proteins that play important roles in what our cells do.
How to extract DNA from fruit cells?
1) Mash kiwi and place in a beaker containing 100cm3 of washing up liquid, salt and water. The detergent will break down the cell membrane and the salt will make the DNA less soluble.
2) Place beaker into a water bath at 60° for 15 minutes - causes the enzymes to denature, then filter the mixture and collect the filtrate in a small beaker.
3) Measure 10cm3 of filtrate into a boiling tube.
4) Add 1 spatula worth of enzyme solution and swirl gently, leave to stand for one minute.
5) Tilt the boiling tube and gently add some ice-cold ethanol to the mixture.
6) The DNA forms a precipitate because its insoluble in cold alcohol.
7) Collect the stringy white substance formed with a glass rod.
Why is salt, water and washing up liquid used?
It breaks down the cell surface membrane and the membrane around the nucleus.
Salt makes the DNA clump together.
Why is enzyme solution used?
Protease/enzymes breaks down proteins in the cell membrane and destroys the enzymes that may break down the dna.
Why is ice cold ethanol used?
To precipitate the dna because dna is insoluble in ethanol.
Why is a pestle and mortar used?
To help break down the flesh/tissue and cell walls.
Why is a hot water bath used?
Denatures the enzymes.
Control variables in practical
• Same volume of solution
• Same mass of kiwi
• Sam fruit age/type
Alleles
Different forms of the same gene. This means that genes for the same characteristic can contain slightly different instructions that creates variations.
• Eye colour
• Skin colour
• Dimples or not
• Ear lobes attached or not
• Tongue roll or not
Heterozygous
Bb
1 dominant
1 recessive
Homozygous dominant
BB
Homozygous recessive
bb
Phenotype
Physical expression of the genotype.
Genotype
The collection of alleles that determine an organisms characteristics.
What is each box worth in a punnet square?
25%
Meiosis
• 4 daughter cells
• Haploid
• 23 chromosomes
• Used for creating sex cells
• Used in sexual reproduction
• Cells are genetically different
Mitosis
• 2 daughter cells
• Diploid
• 46 chromosomes
• Used for growth and repair
• Used in asexual reproduction
• Cells are genetically identical
Human genome project
The human genome project was the name of the international, collaborative research effort to determine the DNA sequence of the entire human genome and record every gene in human beings.
What can the human genome project be used for?
• Prediction and prevention of diseases.
• Testing and treatment for inherited disorders.
• The development of new and improved medicines.
Prediction and prevention of diseases?
Knowing which genes are involved with particular conditions. Doctors can then predict which people are likely to suffer from a particular disease and provide more targeted treatments earlier.
Testing and treatment for inherited disorders?
Inherited disorders are usually caused by the presence of faulty alleles - the human genome project helps us identify these alleles, allowing us to test people for them and provide treatment earlier.
Development of new and improved medicines?
Tailor-making drugs to target specific, known faulty alleles can improve their success rate.
The human genome project can also tell us wether existing medicines will be effective for a patient and how larger dose they will require.
Drawbacks of the human genome project?
1) Increased stress - if someone knew from an early age that they’re susceptible to a nasty brain disease, they could panic every time they get a headache (even if they never get the disease).
2) Gene-ism - people with genetic problems could come under pressure not to have children.
3) Discrimination by employers and insurers - life insurance could become impossible to get if you have any genetic likelihood of serious disease. And employers may discriminate against people who are genetically likely to hey a disease.
Variation
Differences between individual of the same species.
Continuous variation
When there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale. E.g. height, Mass
Discontinuous variation
When there are distinct differences for a characteristic e.g. people are either in blood group A, B, AB or o; can either roll their tongue or not - there are no inbetweens.
Genetic variation
Different characteristics as a result of a mutation and sexual reproduction.
• It can be caused by new alleles arising through mutations.
• Sexual reproduction also causes genetic variation since it results in alleles being combined in lots of different ways in offspring.
Environmental variation
Different characteristics causes by an organisms environment (acquired characteristics).
Mutation
A change in the DNA base sequence.
Causes of mutations
1) Carcinogens (harmful chemicals)
2) Certain types of radiation
Insertions
An extra base is inserted into the sequence.
Substitutions
One of the bases is changed for another random base.
Deletion
One of the bases is deleted from the sequence.
Effects of mutations
• Most mutations have no affect on the phenotype so that it’s appearance or function is not changed.
• Some mutations have a small affect on the phenotype.
• On rare occasions a single mutation will significantly affect the phenotype.
Meiosis
Type of cell division that creates gametes/sex cells.
Male chromosomes
XY
Female chromosome
XX
Egg cell
Only ‘X’ chromosome
Sperm cell
Can either be ‘X’ or ‘Y’ chromosome
Gamete
Reproductive cells
Zygote
Diploid cell that results from the fertilisation between between an egg and a sperm.
