Topic 3 - Genetics Flashcards
Sexual reproduction
Genetic information of 2 organisms is combined to produce offspring which are genetically different to either parent,
Gametes
Reproductive cells: sperm and egg -haploid (23 chromosomes)
Fertilisation
The gametes fuse to produce a fertilised egg known a zygote. The zygote has a full set of chromosomes. The zygote then undergoes cell division to form an embryo
Embryo characteristics
Inherits characteristics from both parents as it received a mixture of chromosomes (therefore genes).
Production of gametes
Meiosis
Meiosis
Produces haploid cells which aren’t genetically identical. Only occurs in reproductive organs.
Meiosis Division 1
Cell duplicates DNA forming an X-Shaped chromosome. Chromosomes line up at equator. One chromosome from each pair came from the organisms mother and the other from the father. The pairs are pulled apart. Each new cell with have a mixture of the mother’s and father’s chromosomes. This mixture allows for genetic variation.
Meiosis Division 2
Chromosomes line up, arms of chromosomes are pulled apart. 4 haploid daughter cells are produced these are gametes, all genetically different.
Asexual reproduction
Using mitosis to produce genetically identical cells.
Sexual reproduction process
Meiosis resulting in genetically different haploid gametes which fuse to form a diploid cell at fertilisation.
Advantages of asexual reproduction
Produces lots of offspring very quickly as for short reproductive cycle. Eg. Bacteria - E. coli.
This allows them to populate and colonise areas very rapidly.
Only one parent is required so can reproduce when conditions are favourable eg. Aphids in the summer when food is plentiful
Sexual reproduction advantages
Creates genetic variation allowing different characteristics meaning if conditions change some individuals will have the characteristics to survive. This is natural selection and evolution.
Asexual reproduction disadvantages
No genetic variation. So if environment changes the whole population is vulnerable. Eg. Black Sigatoka is a disease affecting banana plants. All banana species are vulnerable.
Sexual reproduction disadvantages
Takes more time and energy so fewer offspring are produced in lifetime because mates must be found requiring energy and time. Eg. Male Bowerbirds build structures of twigs to impress females.
2 parents are needed for sexual reproduction, if an individual is isolated this is an issue. Eg. Polar Bears are independent and may walk 100 miles to find a mate.
Nucleotide
The monomer of DNA
DNA structure
A double helix sugar-phosphate backbone with complimentary nucleotides connected with a weak hydrogen bonds.
Base pairs
Adenine -> Thymine
Cytosine -> Guanine
Chromosomes
Long coiled up molecules of DNA. Found in the nucleus of eukaryotic cells.
Gene
Section of DNA which codes for a certain protein
Genome
All the DNA of an organism
Extract DNA
Mash the fruit.
Add:
Detergent - break down nucleus
Salt - Makes DNA stick together
Filter the mixture and remove froth and insoluble bits.
Add ice-cold ethanol to draw out the DNA as its not soluble in alcohol. A white precipitate will form. Remove with glass rod,
DNA controls
The production of proteins
Proteins are made up of
Amino acids in a polypeptide chain. They can have different orders and have a specific shape which defines its function.
Base triplet
Each amino acid is coded in a sequence of 3 bases in the gene (DNA)
Non-coding regions
Don’t code for any amino acids although still involved in protein synthesis.
Genome
All DNA within an organism including non-coding.
Genetic variation by mutation
If a mutation happens in a gene it can code for a different sequence of amino acids therefore proteins. This effects the phenotype, it may be positive or negative. Can also occur in non-coding regions.
Ribosomes
Make proteins in the cytoplasm
Transcription
- RNA polymerase (enzyme) binds to the non-coding DNA.
- RNA polymerase unzips the DNA and moves along the strands of DNA placing mRNA.
- Coding DNA is used as a template. Base pairings ensure mRNA is complimentary to the gene.
- Once a stop gene is reached the mRNA moves out of nucleus and joins with Ribosomes.
Purpose of transcription
DNA found in the nucleus (as it’s so big) must pass over genetic material to ‘ribosomes’ to construct proteins. ‘Messenger RNA’ is used (single strand and shorter). ‘Uracil’ is used instead of ‘thymine’.
Translation
- Amino acids brought to the ribosome by tRNA.
- tRNA has an ‘anticodon’ which is complimentary for the amino acid. This ‘anticodon’ on the tRNA (acts as the original coding side) matches the base triplet on the mRNA. This pairing ensures amino acids are in the correct order.
- Amino Acids are joined together with a peptide bond forming a polypeptide chain (protein)
Transcription and mutation
If a mutation occurs on the non-coding side it can affect RNA polymerase’ ability to bind to it. This affects how much is transcribed therefore how much protein is produced affecting the end phenotype.
Mendel’s experiment
- Mendel crossed 2 pea plants of different heights
-tall pea and -dwarf pea
The offspring all produced were ALL TALL PEA - He bred 2 of these tall offspring together (from the last generation) and 3 tall pea plants were produced for every 1 dwarf pea plant.
T - Dominant - Tall
t - recessive - dwarf
Mendel’s 3 conclusions
- Characteristics were determined by “hereditary units” (genes).
- Hereditary units are passed on to the offspring unchanged from both parents.
- Hereditary units can be dominant or recessive.
Mendel’s work in society
He was cutting edge and took time for people to understand his work.
It is now understood today that “hereditary units” are genes but scientists at the time didn’t know of DNA or genes.
His work wasn’t significant until after his death that he explained the mechanism of inheritance.
