Genetics Flashcards
What is biodiversity
variety of organisms in an ecosystem
What is species diversity
number of different species within an area
Benefits of high species diversity
- stable ecosystem
- each species is less likely to become extinct
How to measure species diversity for an area
- species diversity index
- considers the number of different species and how many individuals there are for each species
- larger species diversity index = larger species diversity
How does deforestation lower species diversity
- decreases plant species diversity
- less variety of habitats
- less variety of food sources
- decreases animal species diversity
How does agriculture/farming reduce species diversity
- deforestation to make space for farm
- selectively breed plants and animals
- use pesticides to kill other species
What is classification
placing organisms into groups
What is hierarchical classification
large groups divided into smaller groups without overlap
What is a species
a group of individuals with similar characteristics that can interbreed to produce fertile offspring
Why are the offspring from 2 different species infertile
offspring will have an odd number of chromosomes so can’t perform meiosis, so cant’t produce gametes
What is phylogenetic classification
species arranged into groups based on their evolutionary origins and relationships
What are 3 ways of comparing relationships between different species
- DNA hybridisation; comparing DNA base sequence
- A A sequence; comparing A A sequence for the same protein
- Protein shape; comparing shape of same protein using immunological technique
What is variation
difference in characteristics between organisms
Two types of variation
- intraspecific; differences between organisms of the same species
- interspecific; differences between organisms of different species
Causes of intraspecific variation
- genetic factors; same genes but different alleles
- environmental factors
Causes of interspecific variation
- genetic; different genes and different alleles
- environmental factors
Name two types of characteristics
- discontinuous
- continuous
Properties of discontinuous characteristics
characteristics fall into certain groups with no overlap based on genetics only
Properties of continuous characteristics
characteristics show a range determined by genetics and environment
What is genetic diversity
number of different alleles of genes in a population
Benefit of high genetic diversity
species able to adapt with changes in the environment
What can reduce genetic diversity
small population size
Describe the principles of natural selection
- random mutation can produce new alleles of a gene
- the new alleles may benefit the possessor, leading to an increased chance of survival and increased reproductive success
- the advantageous allele is passed onto the next generation
- over several generations, the new allele will increase in frequency in the population
Name 2 types of selection
- stabilising
- directional
What is stabilising selection
when the environment favours those with the most common characteristic, so those on the extreme die out; common characteristic increases in proportion
What is directional selection
when the environment favours those with the uncommon, extreme characteristics; overtime, becomes the common characteristic
What is a gene
a section of DNA that codes for a protein
Components of a gene
- intron
- exon
Difference between intron and exon
exon codes for protein, intron doesn’t
- intron = non-coding DNA
- exon = coding DNA
How does a gene code for protein
- gene is made of a sequence of bases
- each 3 bases code for 1 amino acid (triplet code)
- so the sequence of bases determines sequence of triplet codes which determine sequence of amino acids
Properties of triplet code
- degenerate; each amino acid has more than one triplet code
- non-overlapping; each base is only read once
How does a mutation lead to a non-functional enzyme
- change in base sequence
- change in sequence of triplet codes
- change in sequence of amino acids
- change in primary structure
- change in hydrogen, ionic and disulfide bonds
- change in tertiary structure
- change in active site shape
- substrate no longer complementary so no more ES complexes can be formed
How is a protein assembled
by transcription and translation
What is transcription
production of a single stranded complementary copy of a gene (mRNA)
What is translation
use sequence of codons on mRNA to assemble protein (tRNA brings in amino acids)
Define codon
a sequence of three bases on mRNA that codes for a specific amino acid
Define anticodon
a sequence of three bases at one end of a tRNA molecule that’s specific to an mRNA codon
Name differences between DNA and RNA
- DNA, deoxyribose. RNA, ribose
- DNA, thymine. RNA, uracil
- DNA, double stranded. RNA, single stranded
What is mRNA (messenger RNA)
single stranded complementary copy of a gene which carries the code for assembling protein
What is tRNA (transfer RNA)
- single stranded RNA folded over into a clover shape held by hydrogen bonds between bases
- has amino acid on top
- has anticodon at bottom
- anticodon binds to complementary codons on mRNA
Describe the process of transcription
- DNA helicase breaks the hydrogen bonds between complementary bases
- two separate strands are formed, 1 coding, 1 template
- free RNA nucleotides align by complementary base pairing
- uracil is in place of thymine
- RNA polymerase joins adjacent nucleotides by phosphodiester bonds
- this leaves pre-mRNA
- its introns are removed by splicing to form mRNA
Differences between tRNA and mRNA
- tRNA is clover leaf shape, mRNA is linear
- tRNA has hydrogen bonds, mRNA doesn’t
- tRNA has amino acid binding site, mRNA does not
- tRNA has anticodon, mRNA has codon
Describe the process of translation
- mRNA attaches to ribosomes on RER
- tRNA anticodons bind to complementary mRNA codons
- tRNA brings a specific amino acid
- amino acids join by peptide bonds with the use of ATP
- tRNA is released after amino acid joined to polypeptide
- ribosome moves along mRNA to form polypeptide
What does meiosis produce
4 genetically different cells (haploid)
Benefits of meiosis
produces gametes which will be used in sexual reproduction in animals and plants
Name the stages of meiosis
- interphase
- meiosis I
- meiosis II
- cytokinesis
What happens in interphase
- protein synthesis
- DNA replication
- organelle synthesis
What happens in meiosis I
- prophase I; DNA coils to form chromosomes, nucleus breaks down, spindle fibres form
- metaphase I; homologous pair of chromosomes line up at centre of cell and attach to spindle fibre via the centromere
- anaphase I; spindle fibres pull, homologous pair of chromosomes separate to opposite poles via independent assortment
- telophase I; chromosomes uncoil, nucleus reforms (left with 2 nuclei)
What happens in meiosis II
- prophase II; DNA coils to form chromosomes, nucleus breaks down, spindle fibres form
- metaphase II; chromosomes line up at centre of cell and attach to spindle fibres via centromere
- anaphase II; spindle fibres pull, centromere splits, sister chromatids move to opposite end of pole by independent assortment
- telophase II; chromatids uncoil, nucleus reforms (left with 4 genetically different nuclei)
What happens in cytokinesis
cell separates into 4, each receives nucleus and cytoplasm
How does meiosis produce variation
- crossing over
- independent assortment
What is crossing over
homologous pair of chromosomes move towards each other and exchange genetic material
What is independent assortment
produces a mix of alleles from paternal and maternal chromosomes in a gamete
Define proteome of a cell
the full range of proteins a cell can produce
Define genome of a cell
the complete set of genes in a cell
What happens to DNA mass in meiosis
quarters
What happens to chromosome number in meiosis
halves
What is mutation
changes in sequence of nucleotides in a DNA molecule
Name 2 types of mutation
- chromosome mutation
- gene mutation
What causes mutation
random or due to mutagens
What is a chromosome mutation
- homologous pair of chromosomes don’t separate in meiosis, so either inherit one extra or one less chromosome (non-disjunction)
- in plants, inherit more than one diploid set of chromosomes (polyploidy)
What is a gene mutation
a change in the base sequence of DNA
Name 3 types of gene mutation
- substitution; replace one base for another, changes one triplet code
- deletion; removing a base
- insertion; adding a base
What do insertion and deletion cause
frameshift mutations
