B6 - Inheritance, Variation, And Evolution Flashcards
What is DNA?
What is a gene?
DNA = Polymer made up of two strands that form a double helix.
Gene = Section of DNA that codes for a characteristic.
Each gene codes for a particular sequence of amino acids which are put together to a make a specific protein
What is a genome?
What is the human genome project and its uses?
Genome = The entire genetic content of an organism.
The human genome has sequenced the whole human genome.
Uses:
• Medicine
• Search for genes linked to different diseases
• Understand inherited disorders + treatments
• Trace human migration patterns in the past
What is sexual reproduction?
Requires 2 parents
Uses meiosis to create gametes
Fusion of gametes
Creates variation
What is asexual reproduction?
Requires 1 parent
Offspring are clones (genetically identical)
Happens by mitosis
What is meiosis?
Cell division that produces 4 genetically different gametes
What is the process of meiosis?
Mitosis:
1. Parent cell replicates it’s DNA
2. The membrane breaks down
3. Chromosomes line up in the centre of the cell
4. One set of chromosomes is pulled at each end of the cell
5. Nucleus divides
6. 2 daughter cells identical to original are produced
Meiosis:
7. Second division (same steps)
8. 4 genetically different gametes are produced
What is classification?
What are the main levels of classification?
Why is classification used by scientists?
Classification = the process of grouping living organisms based on their similarities and differences
Kingdom, phylum, class, order, family, genus, & species
The classification system is based on shared characteristics, including physical features, genetic similarities and evolutionary relationships which helps scientists study and compare different organisms.
What is the binomial system?
Example?
It is used to give species a two part Latin name which includes genus & species
Humans are classed as homosapien (genus: homo & species: sapiens)
Why has the classification system changed over time?
Our understanding of genetics & evolution has advanced - how traits are inherited, DNA, etc
The original method was limited as it was based on physical characteristics & didn’t account for genetic differences between species
Scientists began to use genetic information to help classify organisms more accurately
What is an allele?
What is a genotype?
What is a phenotype?
Allele
= a version of a gene
Genotype
= combination of alleles
Phenotype
= physical appearance
What does dominant mean?
What does recessive mean?
What does homozygous mean?
What does Heterozygous mean?
Dominant = a stronger allele (only one needed)
Recessive = a weaker allele (both needed)
Homozygous = 2 of the same alleles
Heterozygous = one of each allele
GENDER
Allele
Genotype
Phenotype
Homozygous
Heterozygous
Allele - x or y
Genotype - xx or xy
Phenotype - female or male
Homozygous - xx
Heterozygous - xy
What are the 2 phenotypes for eye colour?
🤎 Brown (dominant allele: B)
🩵 Blue (recessive allele: b)
Genotype - phenotype
BB - brown eyes
Bb - brown eyes
bb - blue eyes
What is cystic fibrosis?
• type of allele
• affects
Caused by a recessive allele
Affects cell membranes
The body produces too much thick sticky mucus in
• pancreas - enzymes don’t work as well
• airways - lung infections & breathing difficulties
What is the genotype for cystic fibrosis?
What is a carrier?
FF = normal
Ff = carrier
ff = cystic fibrosis
A carrier has one allele for the disease so can pass it in to the next generation
What is polydactyly?
• type of allele
• affects
What is the genotype for polydactyly?
Caused by a dominant allele
Extra digits
DD = polydactyly
Dd = polydactyly
dd = normal
What is embryo screening?
1) during IVF, embryos are fertilised in a lab & implanted into uterus
2) before implantation a few cells can be removed from the embryo and the genes can be analysed
3) DNA can also be taken from an embryo in the uterus
4) some genetic diseases can be detected by analysing amniotic fluid
5) results of tests can lead to embryos being destroyed or pregnancies being terminated
What are the arguments for and against embryo screening?
For:
• Reduce suffering
• Save money on treatment
• There are laws controlling it
Against:
• Implies people with genetic defects are inferior
• Expensive (for NHS)
• May lead to choosing desirable characteristics
What is a mutation?
Organisms of the same species have differences - both genetic (inherited) & environmental
Mutation
= a change in DNA that can be inherited (not necessarily a good or bad thing)
How does a mutation happen?
What can this lead to?
• A gene codes for a sequence of amino acids that make up a protein
• If a mutation produces a change in the sequence of amino acids, a different protein could be made
Evolution by natural selection
(Charles Darwin)
What is evolution?
When a species becomes more adapted for their environment due to mutations, increasing chances of survival
Over millions of years
What is the process of evolution?
- mutations cause variation
- organisms that are better suited to the environment survive & reproduce (organisms that are not suited to the environment die)
- the better adapted organisms can pass on their genes to the next generation
- over time beneficial characteristics become common (= evolution)
What is speciation?
Members of the same species can reproduce fertile offspring
Speciation
= development of a new species
• This happens when members of a population become so different (due to variation) that they can no longer breed to produce fertile offspring
What is extinction?
What are the causes of extinction?
All members of a species are no longer alive (e.g. dodo).
Due to - change in environment,
predators, disease, lack of food, catastrophic event, etc.
What is the evidence for evolution?
Fossils
= remains do plants & animals found in rocks
Formed in 3 ways:
1) bones & teeth are replaced by minerals
2) cast or impression in clay (burrow, footpaths)
3) preservation in a place without decay - e.g. amber, glaciers, peat bogs (pete marsh)
Why do scientists not know if evolution is true?
When life began, no one was around d so we have ideas about it but no one actually knows
Many early life forms were soft bodies & fossils were destroyed by geological activity
How does evolution cause antibiotic resistance?
1) mutation causes variation
2) some bacteria are resistant to an antibiotic (not killed)
3) these bacteria can reproduce & pass on their resistance to the next generation
4) overtime the number of resistant bacteria increases
What is selective breeding?
When humans artificially select the plants or animals that are going to breed so that the genes of a particular characteristic remain in the population
Why is selective breeding done?
Characteristics can be chosen for their usefulness or appearance:
• disease resistance in food crops
• animals which produce more meat or more milk
• dogs with a good temperament
• plants with big/unusual flowers
What is the process of selective breeding?
- Select those which have the desired characteristics
- Breed them with each other
- Select the best offspring and breed them together
- Continue over several generations until all offspring have the characteristic
What are the issues with selective breeding?
• Reduces the gene pool
• Breeding closely related animals is inbreeding
• More chance of organisms inheriting genetic defects
What does DNA do?
DNA (deoxyribonucleic acid)
Carries instructions for how our bodies develop, work, & stay healthy
Makes living things unique & functional
Is the code that determine how we look
What was the understanding of DNA in the early 1950s?
Scientists knew genes (which carry information about how living things develop & function) are located on chromosomes inside cells
Who was Rosalind Franklin?
What did she contribute to the understanding of DNA structure?
Skilled X-ray crystallographer
Conducted detailed X-ray diffraction experiments on DNA fibres
Produces high quality images of the DNA molecule structure
Data suggested a helical structure
Who proposed the double helix model of DNA?
