B13 - Reproduction Flashcards
How are gametes formed
Meiosis
Meiosis
2n (replicates) 4n (divides) 2n/2n (divides) n/n/n/n
When gametes fuse, the zygote produced has the full number of chromosomes and then undergoes mitosis
Leads to genetic variation.
DNA structure
Double helix of nucleotide polymer chains.
The nucleotide is made of a phosphate, sugar and a base.
The base is either A, T, C or G
Genome definition
All of the DNA in an organism
Size order of things in nucleus - smallest to largest
Allele
Gene
DNA
Chromosome
How do genes code for proteins
A gene is a section of DNA containing instructions to put together amino acids in a particular order to make a protein
What codes for one amino acid
A base triplet (a sequence of 3 bases)
How is a protein synthesised
In the nucleus, a gene on the DNA is copied onto a template molecule (mRNA)
THe mRNA leaves the nucleus and attatches to a ribosome
The template is read (3 bases at a time) and a carrier molecule (tRNA) brings a specific amino acid
The amino acids are joined then the chain folds to create a protein with a specific shape
What does non-coding DNA do
Controls which genes are expressed. This affects which proteins are made by the cell
Mutation possibilities
Nothing
Useful change (natural selection)
Protein that doesn’t function properly is coded - the active site does not fit in the substrate - hormones not able to attatch to receptors on cells p structural protein weakened
Non-coding DNA affect how genes are expressed
Sexual reproduction +
Variation in offspring - means that some of organisms might be suited to survive better than others
Selectively breed plants and animals, and increase food production
Asexual reproduction +
One parent needed so more time and energy efficient
Many identical offspring can make the best use out of good conditions
What is an allele
A form of a gene - can either be recessive or dominant.
Each person has 2 alleles of each gene (one from each parent)
Homozygous dominant
Homozygous recessive
Heterozygous
AA
aa
Aa
Cystic fibrosis
Disorder of cell membranes resulting in thick, stickt mucus. Affects airways + digestive system.
Caused by recessive allele
Polydactyly
Having 1 or more extra fingers or toes. Can be removed by surgery.
Chronic villus sampling
Done between 10-12 weeks
Cells taken from placenta (foetal cells)
Risk of miscarriage/ infection
Aminocentesis
Done between 15-16 weeks
Fluid taken from around foetus (contains foetal cells)
Risk of miscarriage/ infection
IVF/ Embryo screening
Done before embryo is implanted during IVF
Affected embryos destroyed
