Genetics Flashcards
Describe the advantages of asexual reproduction
Rapid reproductive cycle (can colonise new areas rapidly) , only one parent needed (no need to wait for mate).
Describe the disadvantages of asexual reproduction
No genetic variation- if conditions become unfavourable the whole population is affected (e.g. a disease or a new predator)
Describe the advantages of sexual reproduction
Genetic variation- population can adapt to selection pressures- species can evolve
Describe the disadvantages of sexual reproduction
Takes more time and energy- organisms have fewer offspring in their lifetime. Mates are needed.
How are gametes produced?
By meiosis
Describe meiosis
- Cell duplicates its DNA (1 arm of each X-shaped chromosome is a copy of the other)
- First division:
- Chromosomes line up in pair along the centre of the cell (1 chromosome in each pair is from the organism’s mother and one from its father)- The pairs are pulled apart so each new cell has only one copy of each chromosome- some of the father’s and some of the mother’s go into each cell creating genetic variation
- Second division:
- chromosomes line up along the centre of the cell, arms of chromosomes are pulled apart
- 4 haploid daughter cells are produced
Why are haploid gametes needed for sexual reproduction?
so the offspring has the right number of chromosomes
What is an organism’s genome?
all of its DNA
What is a gene and where are they found?
A section of DNA on a chromosome that codes for a particular protein.
Where is DNA found in a eukaryotic cell?
in the nucleus
What are the bases of DNA and how are they paired?
Adenine-thymine, cytosine-guanine
Describe the structure of DNA
DNA strands are polymers made up of nucleotide (1 sugar, 1 phosphate- alternating, forming a ‘backbone to DNA strands-, 1 base, A, T, C or G) monomers. A DNA molecule is made up of 2 strands of DNA coiled together in a double helix. Complementary base pairs are joined by weak hydrogen bonds.
Describe how DNA is extracted from strawberries.
Mash strawberries and put them in a beaker containing a mix of detergent (breaks down cell embranes to release DNA) and salt (makes DNA stick together). Filter mixture to remove froth and lumps. Gently add ice-cold alcohol to the mixture. DNA is insoluble in ice-cold alcohol so will appear as a white precipitate which can be removed with a glass rod
Where are proteins made?
In the cell cytoplasm by ribosomes
How is the shape of a protein determined?
the way the amino acid chain folds up
How is the order of amino acids in a protein determined?
The order of bases in a gene (each amino acid is coded for by a sequence of 3 bases in the gene- a base triplet)
What happens during transcription?
RNA polymerase (an enzyme) binds to a region of non-coding DNA in front of a gene. The 2 DNA strands unzip and RNA polymerase moves along 1 strand. It uses coding DNA in the gene to make mRNA using complementary base pairing (mRNA uses uracil, U, instead of thymine, T) The mRNA molecule moves out of the nucleus and joins with a ribosome.
What happens during translation?
Amino acids are brought to the ribosome by tRNA. The order in which amino acids are brought matches the order of base triplets (codons) in mRNA. Part of the tRNA’s structure is complementary to the codon for the amino acid ( an anticodon), making sure the amino acids are brought to the ribosome in the correct order. Amino acids are joined by the ribosome making a polypeptide (protein)
What is a mutation?
A rare, random change to the base sequence of DNA in an organism that can be inherited.
How do mutations occur?
during reproduction of cells, producing genetic variants. In non-coding areas of DNA, affecting the binding of RNA polymerase, affecting how much RNA is transcribed and therefore how much protein is produced
What are the effects of mutations on amino acid sequences?
The genetic variant may code for a different sequence of amino acids, changing the shape of the final protein.
who discovered the basis of genetics?
mendel
how was breeding pea plants used to determine the basis of genetics?
tall pea plants bred with dwarf pea plants produced tall pea plants (tall gene is dominant). the offspring bred together produced a mix of each ( 3:1 ratio).
What is an allele?
An allele is a different version of a gene which helps to determine your phenotype (physical characteristics).
