Topic 6- Inheritance, Variation and Evolution Flashcards
what’s a gene
small section of dna found on a chromosome
what is DNA made of
polymer, 2 strands coiled up in shape of double helix
chromosomes come in…
pairs (usually)
where is DNA found
nucleus of animal and plant cells
in long structures called chromosomes
what does DNA contain
coded info
all the instructions for an organism to work
what is DNA
the chemical that all of the genetic material in a cell is made up of
what are chromosomes?
long molecules of DNA
give examples of asexual reproduction in certain species of plants
bulbs
runners
how do ‘runners’ work
theyre asexual
stems grow horizontally on the surface of soil away from plant
at various points along the runner, new plants form, identical to original plant
what do sexually produced spores do
introduce variation- often produced in response to unfavorable change in environment to increase survival
what do a-sexually produced spores do
form fungi that are generally identical to parent fungus
what are fungi spores
things released by fungus which can become new fungi when they land in a suitable place
when does a parasite to asexual reproduction
in the human host
when does a parasite do sexual reproduction
in the mosquito
advantages of asexual reproduction
- only one parent needed
- less energy- dont need to find a mate
- faster
- many identical offspring can be produced in favourable conditions
advantages of sexual reproduction
- variation in offspring
- survival advantage
- natural selection- bettera dapted to environment, better chance of survival and will breed successfully
- selective breeding
as an embryo starts to develop, the cells start to…
differentiate into the different types of specialised cells that make up a whole organism
after the gametes(sperm and egg)have fused, what happens
the new cell divides by mitosis to copy itself into the embryo.
what happens in meiosis
1- cell duplicates genetic info
2- this forms two armed chromosomes, the chromosomes arrange into pairs
3- FIRST DIVISION- pairs line up in centre of cell
4- pairs pulled apart- each new cells has one copy of each chromosome, some fathers, some mothers
5- SECOND DIVISION- chromosomes line up again in centre. Arms pulled apart
6- produces 4 genetically different gametes
what does meiosis produce
gametes
cells which have half the normal number of chromosomes
humans reproduce…
sexually
what reproduces asexually
bacteria, some plants, some animals
what does asexual reproduction happen by, and how?
MITOSIS- an ordinary cell makes a new cell by dividing in two
what happens in asexual reproduction
ONE parent
No gamete fusion or mix of chromosomes
No genetic variation between parent and offspring
They’re clones/genetically identical
what type of cells does asexual reproduction produce?
gentically identical
whats a flowers version of sperm
pollen
what does the mixture of genetic info produce
variation in the offspring
what is fertilisation
egg meets sperm
what does the offspring contain
a mixture of parents genes
what happens to the sperm and egg
the egg and sperm cell fuse together (fertilisation) to form a cell with the full number of chromosomes
1/2 mothers 1/2 fathers
how many chromosomes does each gamete contian
23 chromosomes (half the number in a normal cell)
what are gametes and how are they produced in sexual reproduction
gametes are sperm and the egg
produced by meiosis
what happens in sexual reproduction
genetic info from 2 organisms (m and d) is combines to produce offspring which are genetically different to either parent
what type of cells does sexual reproduction produce
genetically different
what is a mutation
a random change in the genetic code
they sometimes can be inherited
give examples of proteins and their function
enzymes (biological catalysts)
hormones- carry messages around the body eg. insulin regulated blood sugar levels
structural proteins- physically strong eg. collagen strengthens ligaments and cartilage
what happens when the chain of amino acids in made into proteins
it folds into a unique shape which allows the protein to perform a task
how are proteins made
by using a molecule called MRNA
the MRNA acts as a messenger between the DNA and the ribosome
the correct amino acids are brought to the ribosomes in the correct order by carrier molecules
where are proteins made
in the cytoplasm on tiny structures called ribosomes
what carries the code to the ribosomes
mRNA
what do the parts of DNA that don’t code for proteins do
switch genes on and off
control whether or not a gene is expressed (used to make a protein)
what join together to make various proteins depending on the order
amino acids
how many bases in a gene codes for an amino acid
3
what does the order of bases in a gene determine
the order of amino acids in a protein
describe complimentary base pairing
A pairs with T
G pairs with C
explain how the sugar and phosphate molecules alternate
one of 4 different bases, A,T,G,C joins to each sugar
each base links to a base on the opposite strand in the helix
what dose the sugar and phosphate molecule in the nucleotides form
a ‘backbone’ to the DNA strands
what does each nucleotide consist of
1 sugar molecule
1 phosphate molecule
1 base
what is DNA
polymer made of lots of repeating units called nucleotides
why is the human genome really important for scientists
to identify genes linked to disease
knowing which genes link to inherited diseases- develop effective treatments
trace migration
what is a genome
entire set of genetic material in an organism
what does DNA also determine
what proteins in the cell produces eg. haemoglobin, keratin
this determines what type of cell it is eg. red blood, skin cell
how many amino acids are there
20
what dose each gene code for
a particular sequence of amino acids which are put together to make a specific protein
what happens if there’s a mutation in the non-coding DNA
then it can alter how genes are expressed
describe two wasy a mutation can affect the shape of a protein
if the enzymes ACTIVE SITE changes shape, the substrate can’t bind to it
structural proteins loose strength
how does a mutation affect a protein
most only change it to a small extent
some can seriously affect a protein and CHANGE ITS APPEARENCE.
what do mutations do
change DNA base sequence
Change shape of amino acid
changes in protein
when can mutations occur
spontaneously eg.chromosome doesn’t replicate properly
when exposed to certain substances or certain types of radiation, chances increase
what are the three different types of mutation
insertions, deletions, substitutions
what is insertion
where a new base is inserted into the DNA base sequence where it shouldnt be, which has a knock on affect, changing multiple amino acids
what is deletion
when a random base is DELETED form the DNA base sequence
what is substitution
when a random base in the DNA base sequence is changed to a different base
characteristics are controlled by a single gene
fur colour
in mice; and red-green colour blindness in humans
what are alleles
different versions of genes
what’s genotype means
the combination of alleles you have
whats your phenotype
the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.
when are dominant and recessive alleles expressed
A dominant allele is always expressed, even if only one copy is present.
A recessive allele is only expressed if two copies are present (therefore
no dominant allele present).
If the two alleles present are the same the organism is
homozygous
if the alleles are different they are
heterozygous.
what are most characteristics a result of
multiple genes interacting, rather
than a single gene.
how many pairs of chromosomes do the human body cells contain
Ordinary human body cells contain 23 pairs of chromosomes
How many pairs control characteristics only
22 pairs
how many of the pairs carries the
genes that determine sex.
one
• In females the sex chromosomes are…
the same (XX)
• In males the chromosomes are…
different (XY)
some disorders are caused by the
inheritance of what?
certain alleles
What disorder is caused by a dominant
allele.
Polydactyly (having extra fingers or toes)
What disorder is caused by a recessive allele
Cystic fibrosis (a disorder of cell membranes)
FOR embryo screening
helps stop suffering
treating disorders costs the government and the taxpayers a lot of money
laws to stop it going too far
AGAINST embryonic screening
implies the baby is less worthy of life- prejudice
lead to designer babies
screening is expensive
what were mendel’s three main conclusions about heredity
- characteristics in plants are determined by hereditary units
- hereditary units are passed on to offspring unchanged from both parents, one unit from each parent.
- hereditary units can be dominant or recessive- if an individual has both the dominant and the recessive unit for a characteristic, the dominant characteristic will be expressed.
what is variation
Differences in the characteristics of individuals in a population
how is genetic variation caused
when there is a combining of genes form two parents- no two of the species are genetically identical
which characteristics are determined only by genes in animals?
hair and eye colour, blood group, inherited disorders
what is environmental variation
when the environment causes differences between members of the same species
what is variation due to
- the genes they have inherited (genetic causes)
- the conditions in which they have developed (environmental causes)
- a combination of genes and the environment.
what effect does mutations have on the phenotype
most have
no effect on the phenotype; some influence phenotype; very few
determine phenotype.
If the new phenotype is suited to an environmental change, what can it lead to?
a relatively rapid change in the species.
what is evolution
all of today’s species have evolved form simple life forms that first started to develop over 3 bn yrs ago
what does the theory of evolution by natural selection state
that all species of
living things have evolved from simple life forms that first developed
more than three billion years ago.
what’s speciation (new species being formed)
when two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring
what did darwin conclude
Individual organisms within a particular species show a wide range of
variation for a characteristic.
• Individuals with characteristics most suited to the environment are
more likely to survive to breed successfully.
• The characteristics that have enabled these individuals to survive are
then passed on to the next generation.
why was Darwin’s theory only gradually accepted
• the theory challenged the idea that God made all the animals and
plants that live on Earth
• there was insufficient evidence at the time the theory was published
to convince many scientists
• the mechanism of inheritance and variation was not known until
50 years after the theory was published.
what is extinction
when no individuals of a new species remain
why do species become extinct
the environment changes too quickly- e. destruction of habitat
new predator kills them all (humans hunting)
new disease kills them all
can’t compete for food
catastrophic event (eg. volcano, collision with an asteroid)
What was Lamarck’s ideas
-changes that an organism aquires during its lifetime will be passed on to its offspring
why was Lamarck’s hypothesis eventually rejected
experiments didnt support it
why was Darwin’s hypothesis eventually accepted
fossil evidence, discovery of bacteria evolution and it provided an explanation of how organisms born with beneficial characteristics can pass them on
what does selective breeding involve
choosing parents with the desired
characteristic from a mixed population. They are bred together. From the
offspring those with the desired characteristic are bred together. This
continues over many generations until all the offspring show the desired
characteristic.
what is selective breeding
humans breed plants and animals for particular genetic characteristics.
how long has selective breeding been around
Humans have been doing this for thousands of years since they first bred food crops from wild plants and domesticated animals.
name some desired characteristics in selective breeding
- Disease resistance in food crops.
- Animals which produce more meat or milk.
- Domestic dogs with a gentle nature.
- Large or unusual flowers.
what can selective breeding lead to
‘inbreeding’ where some breeds are
particularly prone to disease or inherited defects (reduction in the gene pool)
how does genetic engineering work
• enzymes are used to isolate the required gene; this gene is inserted
into a vector, usually a bacterial plasmid or a virus
• the vector is used to insert the gene into the required cells
• genes are transferred to the cells of animals, plants or
microorganisms at an early stage in their development so that they
develop with desired characteristics.
why have plant crops been genetically engineered
to be resistant to diseases or to produce bigger better fruits.
why have bacterial cells been genetically engineered
to produce useful
substances such as human insulin to treat diabetes.
give a simple definitiion for genetic enginerring
genes from the chromosomes of humans and
other organisms can be ‘cut out’ and transferred to cells of other
organisms.
what are GM crops made to be
resistant to insect attack or to herbicides
Give some examples of worries for Genetic engineering
long term effects- changing an organisms genes may accidentally create unplanned problems, which could get passed on to the future generations
Pros of genetic engineering
increase yield
foods with specific nutrients in- ‘golden rice’
already being grown in some places perfectly fine
Cons of genetic engineering`
Could affect no. of wild flowers and therefore the population of insects- reducing farmland biodiversity
Some people feel the effects of eating GM crops on
human health have not been fully explored.
transplanted genes may get out into the natural environment - could lead to ‘superweed’ variety
What is modern medical research is exploring the possibility of
genetic modification to overcome some inherited disorders.
what two ways can plants be cloned by
tissue culture and cuttings
what is tissue culture
using small groups of cells from part of a plant to grow
identical new plants.
This is important for preserving rare plant species
or commercially in nurseries.
what is the method of ‘cuttings’
method used by gardeners to produce
many identical new plants from a parent plant.
explain Embryo transplants
splitting apart cells from a developing animal
embryo before they become specialised, then transplanting the identical
embryos into host mothers.
What is Adult cell cloning
• The nucleus is removed from an unfertilised egg cell.
• The nucleus from an adult body cell, such as a skin cell, is inserted
into the egg cell.
• An electric shock stimulates the egg cell to divide to form an embryo.
• These embryo cells contain the same genetic information as the adult
skin cell.
• When the embryo has developed into a ball of cells, it is inserted into
the womb of an adult female to continue its development.
What are some issues of cloning
reduced gene pool- fewer different alleles in a population- may be no allele in population to fight off a specific disease
cloned animals might not be as healthy as normal ones
humans may be cloned in the future- unsuccessful attempts could lead to disabled children
positive things about cloning
leads to more knowledge of development of embryo and age-related disorders
preserve endangered species
what are fossils
‘remains’ of organisms from millions of years ago, which are found in rocks.
how can fossils be formed
- from preservation in a place where decay cannot happen
- parts of the organism are replaced by minerals as they decay
- from casts and impressions
why cant scientists be certain
about how life began on Earth
Many early forms of life were soft-bodied, so
have left few traces behind. Few traces have been mainly destroyed by geological activity
what is a species
a group of similar organisms that can reproduce to give fertile offspring
which two ways lead to speciation
Natural selection and isolation
what is isolation
where populations of a species are separated
Eg. floods and earthquakes can cause physical barriers
conditions on either side will be different eg. climate
different characteristics will become more common in each population due to NATURAL SELECTION
Explain how natural selection leads to speciation
each population has genetic variation and a wide range of alleles
better adapted animals have better chance of survival, therefore have better chance to breed successfully
‘good’ alleles will pass on to the next generation
EVENTUALLY THE TWO SIDES CAN NO LONGER BREED WITH EACH OTHER
what is Alfred Wallace famous for
- came up with the idea of natural selection
- worked with Darwin- prompted Darwin to publish ‘On the Origin of Species’- 1859
- provided evidence- relalised species had ‘warning colours’
How does antibiotic resistance work?
Mutations of bacterial pathogens produce new strains.
Some strains might be resistant to antibiotics- so are not killed.
They survive and reproduce, so the population of the resistant strain increases.
The resistant strain will then spread because people are not immune to it and there is no effective treatment.
Why can bacteria can evolve rapidly?
because they reproduce at a fast rate.
give an example of a superbug which is not resistant to bacteria
MRSA
how can we reduce antibiotic resistant strains?
- do not prescribe antibiotics inappropriately
- patients should complete their course of antibiotics
- agricultural use of antibiotics should be restricted
What is the system developed by Carl Linnaeus
where living things are classified into groups depending on their structure and characteristics
Name the order of the classification system
kingdom, phylum, class, order,
family, genus and species
Why were new models of clamssification made
Evidence of internal structures became more developed due to improvements in microscope.
Andthe understanding of biochemical processes progressed.
What did Carl Woese do
proposed the three domain system,
- archaea (primitive bacteria usually living in extreme environments)
- bacteria (true bacteria)
- eukaryota (which includes protists, fungi, plants and animals).
how does the binomial system work
first part- genus
second part-species
Eg. Homo-Sapien
How are Evolutionary Trees used by scientists
method used by scientists to show how they
believe organisms are related.
They use current classification data for living organisms and fossil data for extinct organisms.
