Inheritance, Variation and Evolution Flashcards
Types of reproduction
- sexual
- asexual
Sexual reproduction
Genetic information from 2 organisms (father + mother) fusing to produce offspring genetically different from parents
What do the mother and father produce in sexual reproduction
Gametes
Gametes
Sex cells
Male gamete
Sperm cell
Female gamete
Egg cell
How many chromosomes in a human gamete
23
Fertilisation
Egg from mother + sperm from father fuse together to form a zygote (fertilised egg) with full number of chromosomes (46)
What kind of reproduction do flowering plants use
Sexual
How do flowering plants reproduce
Pollen (containing male gametes) from a plant carried to another plant’s egg cell
Why does sexual reproduction lead to variety in offspring
There is mixing of genetic information
Asexual reproduction
1 parent cell divides by mitosis to form 2 genetically identical cells (to each other and parent cell) - clone
What organisms reproduce asexually
- bacteria
- some plants
- some animals
What does meiosis produce
Gametes
How many cell divisions happen in meisosis
2 rounds
Where does meiosis happen in humans
Reproductive organs - ovaries + testes
Meiosis STAGE 1
- before division
- cell duplicates genetic info
- 2 armed chromosomes formed - 1 arm exact copy of other arm
- chromosomes arrange into pairs
Meiosis STAGE 2
- first division
- chromosomes line up in centre of cell
- pairs pulled apart
- each new cell has 1 copy of each chromosome
- some of father’s + mother’s chromosomes in each cell
Meiosis STAGE 3
- second division
- chromosomes line up in centre of cell
- arms pulled apart
- 4 gametes - 23 chromosomes in each
- gametes genetically different from other as chromosomes shuffled up during meiosis - each gamete gets half at random
What happens after gamete fusion
- resulting cell divides by mitosis many times to produce copies of itself in embryo
- embryo develops - cells differentiate, specialised cells eventually make up whole organism
Chromosomes
Long molecules of DNA
How are chromosomes usually found
In pairs
What does DNA stand for
deoxyribonucleuic acid
DNA
Chemical all genetic material is made up of
What does DNA contain
Coded information - instructions to put organism together and make it work
Where is DNA found
Nucleus of animal + plant cells
Structure of DNA
Polymer made up of 2 strands coiled together in shape of double helix
Gene
Small section of DNA that codes for a particular sequence of amino acids, put together to make a specific protein
How do genes code
Tell cells what order to put amino acids together in
How many amino acids are used to make proteins in humans
20
How many proteins are found in humans
Thousands
What determines what type of cell a cell will be
What proteins it produces - determined by DNA
Genome
Entire set of genetic material in organism
Has the complete human genome been worked out
Yes
How is understanding the human genome important for medicine
- scientists can identify genomes linked to different types of disease
- know genes linked to inherited disorders - could develop effective treatments
How can understanding human genome be used to trace past human migration patterns
- modern humans descended from common ancestor from Africa
- as different populations migrated away from Africa, developed tiny differences in their genome
- investigate differences - work out when new populations split off + route they took
Which chromosomes determine your sex
23rd pair
Types of 23rd chromosome pair
- XY
- XX
XY chromosome
Y chromosome causes male characteristics
XX chromosomes
XX combination allows female characteristics to develop
Probability of sperm getting X/Y chromosome in meiosis
50%
What chromosome do all egg cells have
X
How to find probability of getting a boy or girl
Draw a genetic diagram
Genetic diagrams
Models used to show all possible outcomes when different genes/chromosomes crossed together
Types of genetic diagrams
- Punnett square
- genetic cross
- family trees
How to use Punnett square to find probability of having boy or girl
- put possible gametes from one parent down side, other parent’s at top
- male parent - sperm with X chromosome OR sperm with Y chromosome
- female parent
- egg with X chromosome OR egg with Y chromosome
- fill in boxes to make pairs of letters
How to use genetic cross diagram to find probability of having boy or girl
- parent chromosome pairs at top - XX + XY
- middle circles show possible gametes - X X X Y
- crossed lines show all ways X and Y chromosomes could combine
- possible combinations of offspring shown in bottom circles
What are characteristics controlled by
Single gene or several genes interacting
What are most characteristic controlled by
Multiple genes interacting
Alleles
Different versions of a gene that exist
How are alleles represented in genetic diagrams
A letter
How many alleles of each gene are there in the body
2 - 1 in each chromosome in a pair
Homozygus
When organism has 2 alleles for particular gene that are the same
Heterozygus
When organism has 2 alleles for a particular gene which are different
Types of allele
- dominant
- recessive
Dominant allele
Allele in heterozygus gene that determines what characteristic is present
How are dominant alleles shown in genetic diagrams
Capital letter
Recessive allele
Other allele in homozygus gene that doesn’t determine what characteristic is present
How are recessive alleles shown in genetic diagrams
Lower case letters
When does organism display recessive characteristic
When both alleles for particular gene are recessive
When does organism display dominant characteristic
When both alleles for particular gene are dominant OR 1 dominant allele + 1 recessive allele
Genotype
All genes + alleles an organism has
Phenotype
Characteristic determined by alleles, result of genotype
Carrier
Someone unaffected by an inherited disorder but can pass the allele on through reproduction
Inherited disorders
- cystic fibrosis
- polydactyly
What causes cystic fibrosis
Inheriting 2 recessive alleles
Cystic fibrosis
- genetic disorder of cell membranes
- body produces much thick sticky mucus in air passages + pancreas
How many people carry recessive cystic fibrosis allele
About 1 in 25
What causes cystic fibrosis carriers
Inheriting 1 recessive allele
What must parents be for child to have chance of having cystic fibrosis
Both have disorder OR are carriers
What causes polydactyly
Inheriting a dominant allele
Polydactyly
Genetic disorder where baby is born with extra fingers/toes
How are embryos screened for genetic disorders
- DNA taken from embryo and tested
- could then decide to terminate pregnancy
How are IVF embryos screened for genetic disorders
- before being implanted into womb:
- cell removed from each embryo - genes analysed
- embryos with bad alleles destroyed
Reasons for embryonic screening
- helps stop suffering
- treating disorders after birth expensive for government
- laws to stop it going too far - parents can’t decide sex of baby (unless for health reasons)
Reasons against embryonic screening
- suggests people with genetic disorders ‘undesirable’ - could lead to prejudice
- more people may want embryo screened for desirable ones - e.g- blonde boy
- expensive
Types of variation
- genetic
- environmental
What causes genetic variation
Caused by differences in genotype
Environmental variation
Caused by interactions with condition phenotype lives in - e.g- plant grown on sunny windowsill grows luscious + green
What determines most variation
Mixture of genetic + environmental factors
Mutation
Rare, random change in organism’s DNA that can be inherited
When do mutations occur
They are continuously occuring
What does mutation cause
Altered gene, producing genetic variant (different form of gene)
Effects of most mutations on phenotypes
no effect
Why do most mutations not affect phenotype
Most genetic variants have little/no effect on protein gene codes for
Example of variation having small influence on phenotype
- eye colour controlled by more than 1 gene
- mutation in 1 changes eye colour slightly
Example of variation having dramatic effect on phenotype
- gene coding for a protein that controls salt + water movement in/out of cells can become mutated
- leads to cystic fibrosis
What can cause rapid change in species
- environment changes
- new phenotype makes individual more suited to environment
Theory of Evolution
All of today’s species have evolved from simple life forms that started developing over 3 billion years ago
Darwin’s theory of evolution
Evolution by natural selection
Survival of the fittest
Organisms with most suitable characteristics for environment would be more successful competitors and more likely to survive
What happens to unsuccessful organisms in an environment
Death
What happens to successful organisms in an environmnt
Survival
What happens to surviving organisms in an envronment
Reproduction
What causes evolution
Beneficial characteristics become more common in genotype, species changes
Selective breeding
Humans artificially selecting plants/animals to breed so particular characteristics remain in population
What features are selectively bred
- useful
- attractive
Examples of selectively bred useful characteristics
- animals that produce more meat/milk
- crops with disease resistance
Examples of selectively bred attractive characteristics
- domestic dogs with gentle nature
- decorative plants with big/unusual flowers
Process of selective breeding
- select existing stock with desired trait
- breed them together
- select best offspring with desired trait
- breed them together
- continue process over several generations - desired trait will get stronger, then all offspring will have trait
Other name for selective breeding
Artificial selection
Problem with selective breeding
Reduces gene pool - number of different alleles in population as farmer selects similar plants/animals (inbreeding)
Problem with inbreeding
Higher chance of inheriting harmful genetic defects when gene pool limited
Problem with reduced gene pool
All closely related stock likely to be killed by new disease
What is genetic engineering
Process of transferring gene responsible for desirable from one organism’s genome to another so it also has desired characteristic
Process of genetic engineering
- useful gene cut from organsism’s genome using restriction enzyme
- insert gene into vector by ligase enzyme
- vector (usually plasmid/virus) with gene taken up by cell
- cell multiplied
Examples of genetic engineering
- bacteria modified to produce human insulin to treat diabetes - vector-plasmid
- crops have been modified to be resistant to disease or to produce bigger/better fruits
How to make organism develop with genetically engineered gene
Transfer gene in early stages of development - e.g- egg/embryo
Risks of genetic engineering
Changing organism’s genome may accidentally create unplanned problems, passed on to future generation
Pros of genetically modified crops
- characteristic can increase yield
- crops could be engineered to contain missing nutrient in developing nations
- being grown in some places without problems
Genetically modified crops
Crops that have had genes modified
Cons of genetically modified crops
- may affect number of wild flowers, affecting number of insects - reducing farmland biodiversity
- may not fully understand effects of eating them on humans
- transplanted genes may get out into natural environment
Fossils
Remains of organisms from many thousands of years ago which are in rocks
What can fossils tell us
How much/little organsisms have evolved over time
Ways fossils form in rocks
- gradual replacement by minerals
- casts and impressions
- preservation
What kind of fossils form by gradual replacement by minerals
Things like teeth/bones don’t decay easily, can last long time when buried
How does gradual replacement by minerals form fossils
- replaced by minerals as they decay
- forms rock-like substance shaped like original part
How do casts and impressions form fossils
- organism buried in soft material like clay
- clay hardens + organism decays, leaving cast of itself
OR - footprints can be pressed into material when soft
- leaving impression when it hardens
How does preservation form fossils
- places where no decay happens
- because of problems with decay microbes
-glaciers - too cold to work
-peat bogs - too acidic
-tar pits - no oxygen/moisture so can’t survive
Why can’t scientists be certain about how life began on Earth
- many early life forms soft-bodied - left few traces behind
- few traces left behind mainly destroyed by geological activity
Why can bacteria evolve rapidly
They reproduce at a fast rate
How do bacteria become antibiotic resistant
- mutations of bacterial pathogens produce new strains
- causes variation - some strains are antibiotic resistant, some aren’t
- those that aren’t die
- those that are survive
- those that survive reproduce, passing on gene for antibiotic resistance
- bacteria have evolved to be antibiotic resistant
How to reduce rate of development of antibiotic resistant strains
- doctors shouldn’t prescribe antibiotics inappropriately - for non-serious or viral infections
- patients should complete full course of antibiotics to kill all bacteria so none survive to mutate to be resistant
- restrict use of agricultural antibiotics - resistant bacteria can spread from animals to humans
Why is it difficult to keep up with new antibiotic resistant bacteria strains
Development of new antibiotics costly + slow
MRSA
- antibiotic resistant
- difficult to get rid of
- often affects people in hospital
- can be fatal if enters bloodstream
Classification
Organising living organisms into groups
Traditional classification system
Linnaean system (Carl Linnaeus)
Linnaeun classification system
- kingdom
- phylum
- class
- order
- family
- genus
- species
How did Linnaeus name organisms
- binomial system
- Genus
- species
Why classification systems changes over time
- improved knowledge of biochemical processes taking place inside organisms
- improved microscopes - improved knowledge of internal structures of organisms
Newer classification system
3 domain system (Carl Woese)
How are organisms grouped in 3 domain system
- split into 3 domains
- domains subdivided into kingdom, phylum, class, order, family, genus, species
3 domains
- archaea - primitive bacteria, usually living in extreme conditions
- bacteria - true bacteria
- eukaryota - broadly includes protists + fungi + plants + animals
What do evolutionary trees show
- evolutionary relationships
- how scientists think species are related to each other
- show common ancestors and relationships between species
How are evolutionary trees developed
- living organisms - current classification data
- extinct organisms - fossil data
Extinction
When there are no remaining individuals of a species still alive
Factors causing extinction
- environment changing too quickly
- new predator killing all
- new disease killing all
- can’t compete with new species for food
- catastrophic event
