genetics Flashcards
meiosis
a type of cell division that produces 4 haploid genetically non-identical gametes/daughter cells
describe the process of meiosis
- chromosomes duplicate so that there is enough for each new cell
- FIRST DIVISION:
- similar chromosomes pair up
- one chromosome in each pair comes from the father and one from the mother
- pairs are pulled apart so each new cell has a copy of one chromosome (a mixture of the mother’s and father’s) - this is important for GENETIC VARIATION
- there are now two cells
- SECOND DIVISION:
- chromosomes line up in the centre of the cells and arms are pulled apart
- each cell divides into two to form 4 genetically non identical daughter cells
sexual reproduction
where genetic information from two organisms is combined to produce offspring which are genetically different from either parent
gamete
haploid sex cells
fertilisation
when a male gamete haploid cell fuses with a female gamete haploid cell to produce a fertilised egg cell/diploid zygote
what happens after fertilisation
the zygote uses mitosis to develop into an embryo
the embryo has characteristics from both parents as it has received a mixture of chromosomes from both mother and father
asexual reproduction
a type of reproduction not involving fertilisation but by mitosis
what are two advantages of sexual reproduction
+ created genetic variation within a population so individuals are more likely to be able to adapt and survive if the environment changes
+ genetic variation can lead to natural selection and evolution so a species becomes better adapted to its environment
what are two disadvantages of sexual reproduction
- two parents are needed which can be a problem if individuals are isolated
- takes more time and energy so fewer offspring are produced in a lifetime
what are two advantages of asexual reproduction
+ can produce lots of offspring quickly so organisms can colonise an area very quickly
+ only one parent is needed so organisms can reproduce when conditions are favourable without having to wait for a mate
what is one disadvantage of asexual reproduction
there is no genetic variation so if an environment changes unfavourably, the whole population may suffer
dna structure
a polymer made of lots of repeating nucleotides forming two strands coiled together in a double helix held together by weak hydrogen bonds
the backbone of a dna strand is made form alternating sugar and phosphate molecules
nucleotide
an organic molecules consisting of one sugar molecule, one phosphate molecule and one base
what are the base pairs
adenine and thymine
cytosine and guanine
chromosomes
long coiled up molecules of DNA
gene
a section of DNA that codes for a particular protein
how would you extract dna from a fruit
1) mash fruit and place in a beaker containing detergent and salt - mix well
- detergent breaks down cell membranes
- salt makes dna stick together
2) filter mixture to remove froth and insoluble parts
3) add ice cold ethanol to mixture
4) a stringy white precipitate will start to form as dna is insoluble in cold ethanol, collect with a glass rod
what is the role of dna in protein synthesis
controls protein synthesis in a cell
- a section of dna coding for a particular protein is a gene
the order of bases controls the order of amino acids
each amino acids is coded for by 3 bases (triplet) which are joined together to form the protein
protein
a chain of amino acids
each protein has its own number and order of this
what are the two stages of protein synthesis
transcription
THEN
translation
what happens in transcription (4)
1) RNA polymerase binds to a region of non-coding DNA in front of a gene
2) 2 dna strands unzip and RNA polymerase moves along one of the strips of DNA
3) the coding DNA is used to make a template to make the mRNA (base pairing ensures the mRNA is complementary)
4) once ready, the mRNA leaves the nucleus through the nuclear membrane and joins with a ribosome
what happens in translation (5)
1) amino acids are brought to the ribosome by tRNA (transfer RNA)
2) the order in which amino acids are brought to the ribosome matches the order of codons in mRNA
3) the tRNA has an anticodon which is complementary to the codon for the amino acid, this pairing makes such amino acids are in the right order
4) amino acids are connected to the ribosome to form the polypeptide/protein
5) the protein folds up to its unique shape
mutation
a rare, random change to an organism’s DNA base sequence that can be inherited
effects of a mutation on coding DNA
affects phenotype by altering the amino acid sequence which may change the shape of the final protein and therefore affect its activity (increasing, decreasing or stopping altogether)
