Unit 6 - Inheritance, Variation & Evolution Flashcards
What is sexual reproduction?
● Type of reproduction.
● Involves the production of gametes by meiosis.
● A gamete from each parent fuses to form a zygote.
● Genetic information from each gamete is mixed so the
resulting zygote is unique.
What are gametes?
● Sex cells (sperm cells and egg cells in
animals, pollen and egg cells in flowering
plants).
● Haploid (half the number of chromosomes).
What is meiosis?
● Form of cell division involved in the formation of
gametes (non-identical haploid cells) in reproductive
organs.
● Chromosome number is halved.
● Involves two divisions.
What must occur prior to meiosis?
Interphase - copies of genetic
information are made during this
process.
What happens during the first stage of
meiosis?
● Chromosome pairs line up along the cell equator.
● The pair of chromosomes are separated and move to
opposite poles of the cell (the side to which each
chromosome is pulled is random, creating variation).
● Chromosome number is halved.
What happens during the second stage
of meiosis?
● Chromosomes line up along the cell equator.
● The chromatids are separated and move to opposite
poles of the cell.
● Four unique haploid gametes are produced.
Why is meiosis important for sexual
reproduction?
● It increases genetic variation.
● It ensures that the zygote formed at
fertilisation is diploid.
Describe fertilisation and its resulting
outcome
Gametes join together to restore the normal
number of chromosomes and the new cell then
divides by mitosis (which increases the number
of cells).
As the embryo develops, cells differentiate.
Describe the circumstances in which
Malarial parasites reproduce sexually
and asexually
Sexual reproduction in the mosquito.
Asexual reproduction in the human host.
Describe the circumstances in which
fungi reproduce sexually and asexually
Asexual reproduction by spores.
Sexual reproduction to give variation.
Describe the circumstances in which
plants reproduce sexually and asexually
Sexual reproduction to produce seeds.
Asexual reproduction by runners (e.g.
strawberry plants) or bulb division (e.g.
daffodils).
What is DNA?
A double-stranded polymer of
nucleotides, wound to form a double
helix.
The genetic material of the cell found in
its nucleus.
Define genome
The entire genetic material of an organism.
Why is understanding the human
genome important?
The whole human genome has been studied and is
important for the development of medicine in the future.
● Searching for genes linked to different types of disease.
● Understanding and treating inherited disorders.
● Tracing human migration patterns from the past.
What is a chromosome?
A long, coiled molecule of DNA that
carries genetic information in the form of
genes.
How many chromosomes do human
body cells have?
46 chromosomes (23 pairs)
How many chromosomes do human
gametes have?
23 chromosomes
Define gene
A small section of DNA that codes for a
specific sequence of amino acids which
undergo polymerisation to form a protein.
What are alleles?
Different versions of the same gene.
What is a dominant allele?
A version of a gene where only one copy
is needed for it to be expressed.
What is a recessive allele?
A version of a gene where two copies
are needed for it to be expressed.
What is meant when an organism is
homozygous?
When an organism has two copies of the
same allele (two recessive or two
dominant).
What is meant when an organism is
heterozygous?
When an organism has two different
versions of the same gene (one
dominant and one recessive).
What is the genotype?
The genes present for a trait
What is the phenotype?
The visible characteristic.
How are dominant alleles represented in
a punnett square?
They are represented using uppercase
letters.
How are recessive alleles represented in
a punnett square?
They use the lowercase version of the
same letter as the dominant allele.
Draw a Punnett square for a cross
between a homozygous recessive blue
eyed female (bb) with a heterozygous
brown eyed male (Bb)
Bb, Bb
bb, bb
Draw a Punnett square for a cross
between a homozygous dominant red
flower (RR) with a homozygous
recessive white flower (rr)
Rr, Rr
Rr, Rr
Draw a Punnett square for a cross
between two heterozygous cystic fibrosis
carriers (Ff)
FF, Ff
Ff, ff
PKU is a recessive condition. Two
heterozygous parents (Pp) have
offspring. Predict the proportion of
offspring that will have PKU.
75% chance of normal phenotype
25% chance of PKU phenotype
What is the problem with single gene
crosses?
Most characteristics are controlled by
multiple alleles rather than just one.
What is an inherited disorder?
A disorder caused by the inheritance of
certain alleles.
Give 2 examples of inherited disorders
● Polydactyly (having extra fingers or toes) -
caused by a dominant allele.
● Cystic fibrosis (a disorder of cell
membranes) - caused by a recessive allele.
How are embryos screened for inherited
disorders?
During IVF, one cell is removed (from an 8 cell
embryo) and tested for disorder-causing
alleles. If the cell doesn’t have any indicator
alleles, then the originating embryo is
implanted into the uterus.
What are the ethical issues concerning
embryo screening?
● It could lead to beliefs in society that being disabled or having a
disorder is less human or associated with inferiority.
● The destruction of embryos with inherited disorders is seen by
some as murder as these would go on to become human beings.
● It could be viewed as part of the concept of designer babies as it
may be for the parents convenience or wishes rather than the
child’s wellbeing.
What are the economic issues
concerning embryo screening?
● Costs of hospital treatment and medication
will need to be considered if it is known that
a child will have an inherited disorder and
financial support explored if necessary.
What are the economic issues
concerning embryo screening?
● Costs of hospital treatment and medication
will need to be considered if it is known that
a child will have an inherited disorder and
financial support explored if necessary.
What are the social issues concerning
embryo screening?
● Social care for children with inherited disorders may
need to be considered if parents are unable to provide
care.
● If an embryo is found to have an inherited disorder and
is terminated, this can prevent a child and its parents
from potential suffering in the future due to the disorder.
What is gene therapy?
The insertion of a normal allele into the
cells of a person with an inherited
disorder to functionally replace the faulty
allele.
What are the ethical concerning gene
therapy?
● Some people believe that it is going
against and ‘playing God’.
● The introduced genes could enter sex
cells and so be passed to future
generations.
What are sex chromosomes?
A pair of chromosomes that determine sex:
● Males have an X and a Y chromosome
● Females have two X chromosomes
Why does the inheritance of a Y
chromosome mean that an embryo
develops into a male?
Testes development in an embryo is
stimulated by a gene present on the Y
chromosome.
A couple have a child. Using a punnett
square, determine the probability of
having offspring that is female.
50% chance of female (XX)
What is a sex-linked characteristic?
A characteristic that is coded for by an
allele found on a sex chromosome.
Why are the majority of genes found on
the X chromosome rather than the Y
chromosome?
The X chromosome is bigger than the Y
chromosome so more genes are carried on it.
Why are men more likely to show the
phenotype for a recessive sex-linked trait
than women?
● Many genes are found on the X chromosome that have no
counterpart on the Y chromosome.
● Women (XX) have two alleles for each sex-linked gene whereas men
(XY) often only have one allele ∴ only one recessive allele is required
to produce the recessive phenotype in males.
Haemophilia is a recessive X-linked
condition. A carrier female and a normal
male have a son. What is the probability
of the child having haemophilia?
50% chance of
haemophilia (XhY)
What is variation?
Differences in the characteristics of
individuals in a population is called
variation.
What are the causes of variation within a
species?
● Genetics
● Environment
● A mixture of both of the above
What is genetic variation?
● Variations in the genotypes of organisms of
the same species due to the presence of
different alleles.
● Creates differences in phenotypes.
What creates genetic variation in a
species?
● Spontaneous mutations
● Sexual reproduction
What is a mutation?
A random change to the base sequence
in DNA which results in genetic variants.
They occur continuously.
State the three types of gene mutation
● Insertion
● Deletion
● Substitution
How may a gene mutation affect an
organism’s phenotype?
● Neutral mutation does not change the sequence of amino acids.
Protein structure and function same. No effect on phenotype.
● Mutation may cause a minor change in an organism’s phenotype e.g.
change in eye colour.
● Mutation may completely change the sequence of amino acids. This
may result in a non-functional protein. Severe changes to phenotype.
What is the consequence of a new
phenotype caused by a mutation being
suited to an environmental change?
There will be a rapid change in the
species.
What is evolution?
● A gradual change in the inherited traits
within a population over time.
● Occurs due to natural selection which may
result in the formation of a new species.
Outline the theory of natural selection
All species of living things have evolved from simple life forms that
first developed more than 3 billion years ago.
1. Genetic variation exists due to spontaneous mutations.
2. Selection pressures (e.g. competition, disease) exist.
3. Random mutation gives an organism a selective advantage.
4. Organism is better adapted to the environment and survives.
5. Organism reproduces, passing on its beneficial alleles.
6. Frequency of advantageous alleles increase.
How do two populations become
different species?
When their phenotypes become different
to the extent that they can no longer
interbreed to produce fertile offspring.
What is selective breeding?
The process by which humans artificially select
organisms with desirable characteristics and
breed them to produce offspring with similar
phenotypes.
Outline the main steps involved in
selective breeding
- Identify a desired characteristic e.g. disease resistance.
- Select parent organisms that show the desired traits and
breed them together. - Select offspring with the desired traits and breed them
together. - Process repeated until all offspring have the desired traits.
Outline the main steps involved in
selective breeding
- Identify a desired characteristic e.g. disease resistance.
- Select parent organisms that show the desired traits and
breed them together. - Select offspring with the desired traits and breed them
together. - Process repeated until all offspring have the desired traits.
Give examples of characteristics
selected for in selective breeding.
● Disease resistance in crops
● Higher milk or meat production in animals
● Gentle nature in domestic dogs
● Large flowers
What is the main advantage of selective
breeding?
Creates organisms with desirable features:
● Crops produce a higher yield of grain
● Cows produce a greater supply of milk
● Plants produce larger fruit
● Domesticated animals
Other than in agriculture, where else is
selective breeding useful?
● In medical research
● In sports e.g. horse racing
Outline the disadvantages of selective
breeding
● Reduction in the gene pool (which becomes especially
harmful if sudden environmental change occurs).
● Inbreeding results in genetic disorders.
● Development of other physical problems e.g. respiratory
problems in bulldogs.
● Potential to unknowingly select harmful recessive alleles.
What is genetic engineering?
● The modification of the genome of an organism by the insertion
of a desired gene from another organism - genes from
chromosomes of humans and other organisms can be ‘cut out’
and transferred to cells of other organisms.
● Enables the formation of an organism with beneficial
characteristics.
Give an example of uses for genetically
modified plants.
● Disease resistance
● Produce larger fruits
What is a use for genetically modified
bacteria cells?
To produce human insulin to treat
diabetes mellitus.
Describe the benefits of genetic
engineering
● Increased crop yields for growing population e.g.
herbicide-resistance, disease-resistance.
● Useful in medicine e.g. insulin-producing bacteria, anti-thrombin
in goat milk, possibility to overcome some inherited disorders
(being explored in medical research).
● GM crops produce scarce resources e.g. GM golden rice
produces beta-carotene (source of vitamin A in the body).
Describe the risks of genetic engineering
● Long-term effects of consumption of GM crops unknown.
● Negative environmental impacts e.g. reduction in biodiversity, impact
on food chain, contamination of non-GM crops forming ‘superweeds’.
● Late-onset health problems in GM animals.
● GM seeds are expensive. LEDCs may be unable to afford them or
may become dependent on businesses that sell them.
What is the name for crops that have
had their genes modified?
Genetically modified (GM) crops e.g.
those modified to be resistant to insect
attack and herbicides.
What is Bacillus thuringiensis (Bt)?
● Insect larvae are harmful to crops.
● Bt is a bacterium which secretes a toxin
that kills insect larvae.
How is genetic engineering used to
protect crops against insects?
● The gene for toxin production in Bt can be
isolated and inserted into the DNA of crops.
● Bt crops now secrete the toxin which kills any
insect larvae that feed on it.
What are the benefits of Bt crops?
● Increased crop yields (fewer crops damaged).
● Lessens the need for artificial insecticides.
● Bt toxin is specific to certain insect larvae so is
not harmful to other organisms that ingest it.
What are the risks of Bt crops?
● Long term effects of consumption of Bt crops
unknown.
● Insect larvae may become resistant to the Bt
toxin.
● Killing insect larvae reduces biodiversity
Describe the process of genetic
engineering
- DNA is cut at specific base sequences by restriction enzymes to
create sticky ends. - Vector DNA cut using the same restriction enzymes to create
complementary sticky ends. - Ligase enzymes join the sticky ends of the DNA and vector DNA
forming recombinant DNA. - Recombinant DNA mixed with and ‘taken up’ by target cells.
What is a vector?
A structure that delivers the desired gene
into the recipient cell e.g. plasmids,
viruses.
State two kinds of evidence used to
show evolution.
● Fossils
● Antibiotic resistance in bacteria
How are fossils formed?
● Parts of organisms that have not decayed due to
conditions needed for decay being absent.
● Parts of organisms that have been replaced by
minerals as they decayed eg. bones.
● Traces of organisms are preserved, covered in
sediment and becoming rock.
Why are there few traces of early
life-forms left behind?
They are mostly soft-bodied.
How do fossils act as evidence for
evolution?
Scientists can identify the ages of the
fossils and use them to show how
organisms change over time.
What do branches in evolutionary trees
indicate?
Where speciation has occurred.
What is extinction?
Where there are no individuals of a
species still alive.
State the factors that may lead to
extinctions.
● New disease
● Predation
● Competition
● Changes to the environment
● Catastrophic events
What enables bacteria to evolve quickly?
The fast rate of their reproduction.
Outline the process of antibiotic
resistance bacteria evolving.
● Mutations occur in bacteria producing genetic variation.
● Certain strains are resistant to antibiotics and are not
killed when the antibiotic is applied.
● Resistant strains survive and reproduce.
● Over time, the population of the resistant strains increase.
Outline the process of antibiotic
resistance bacteria evolving.
● Mutations occur in bacteria producing genetic variation.
● Certain strains are resistant to antibiotics and are not
killed when the antibiotic is applied.
● Resistant strains survive and reproduce.
● Over time, the population of the resistant strains increase.
Why are resistant strains of bacteria
dangerous?
People have no immunity to them and
there is no effective treatment.
State an example of a resistant strain of
bacteria.
MRSA.
What can be done to reduce the rate of
development of antibiotic resistant
bacteria?
● Refrain from inappropriately prescribing
antibiotics eg. for viral diseases.
● Patients should complete the prescribed course of
antibiotics.
● Restrict agricultural uses of antibiotics.
Why is it difficult to keep up with
emerging resistance strains?
Developing antibiotics have a high cost
and take a long time to develop.
What are the classes of organisms as
determined by Carl Linnaeus?
Kingdom, phylum, class, order, family,
genus, species.
Which features are living creatures
traditionally classified by?
By their structure and characteristics.
What is the binomial system of naming
organisms?
Genus name followed by species name.
Why were new classification models
proposed?
● Developments in microscopy allowed better
examination of internal structures.
● Improvement in understanding of
biochemical processes.
State the three domains
● Archaea
● Eukarya
● Bacteria
Which organisms belong in the domain
Archaea?
Bacteria, usually living in extreme
environments.
Which organisms belong in the domain
Bacteria?
Bacteria.
Which organisms belong in the domain
Bacteria?
Bacteria.
Which kingdoms belong in domain
Eukarya?
● Plants
● Animals
● Fungi
● Protists
How are evolutionary trees created?
By examining the DNA of different
species and analysing how similar the
sequences are.
