Studied by 2 people
state advantages of asexual reproduction
populations can be increased rapidly
can exploit suitable environments quickly
more time and energy efficient
reproduction completed much quicker than sexual reproduction
don’t need to waste time finding a mate
state disadvantages of asexual reproduction
limited genetic variation within populations
population is vulnerable to changes in condition (may only be suited for one habitat)
disease is likely to affect the whole population
state advantages of sexual reproduction
increases genetic variation
species can adapt to new environments due to variation
disease is less likely to affect the whole population
state disadvantages of sexual reproduction
takes time and energy to find a mate
difficult for isolated members of the population to reproduce
describe meiosis
cell division
producing four daughter cells
each with half the number of chromosomes
resulting in the formation of genetically-different haploid gametes
state what a DNA polymer is made of
two strands coiled
to form a double helix
linked by a series of complementary base pairs
joined together by weak hydrogen bonds and nucleotides
that consist of a sugar and phosphate group
with one of the four different bases attached to the sugar
state complementary DNA base pairs
A+T
G+C
genome definition
entire DNA of an organism
gene definition
section of a DNA molecule
that codes for a specific protein
explain how DNA can be extracted from fruit
mash the fruit and mix into a beaker containing a solution of detergent and salt
filter the mixture into a test tube
gently add ice-cold ethanol to the filtrate by pouring slowly down the side of the test tube
DNA will appear as a stringy, white precipitate
the precipitate can be extracted using a glass rod
explain why detergent is used in the extraction of fruit DNA
breaks down the cell membranes
causing fruit cells to release their DNA
explain why salt is used in the extraction of fruit DNA
salt causes the fruit DNA to stick together
explain why ice-cold ethanol is used in the extraction of fruit DNA
ethanol causes the DNA to precipitate
explain how order of bases in a gene decides the order of amino acids in the protein
each gene acts as a code for making a specific protein
gene = triplet of bases
amino acids are made in the number and order
dictated by the number and order of base triplets
amino acid molecules join together in a long chain to make a protein molecule
proteins are then folded into their correct shape
to make them functional
describe the stages of protein synthesis (transcription)
occurs in the nucleus of the cell
part of a DNA molecule unwinds
when hydrogen bonds between complementary base pair breaks
this exposes the gene to be transcribed
RNA polymerase binds to a region of non-coding DNA in front of the gene
RNA polymerase makes a complementary copy of the code from the gene
by building mRNA
mRNA leaves the nucleus via a pore in the nuclear envelope
describe the stages of protein synthesis (translation)
occurs in the cytoplasm of the cell
after leaving the nucleus, mRNA attaches to a ribosome
cytoplasm contains free molecues of tRNA
tRNA have anticodons at one end
and a region where a specific amino acid can attach at the other
tRNA bind with their specific amino acid and bring them to the mRNA on the ribosome
anticodons on tRNA pair with complementary codons on the mRNA
2 tRNA fit onto the ribosome at one time, bringing the amino acid they are each carrying side by side
a peptide bond is formed between the 2 amino acids (polypeptide)
process continues until a ‘stop’ codon on the mRNA is reached
this acts as a signal for translation to stop
and the amino acid chain is complete
the chain will then fold into a protein
state what anticodons are
a triplet of unpaired bases
explain the role of ribosomes in protein synthesis
ribosomes read the code on the mRNA in groups of 3
each triplet of bases on the mRNA code for a specific amino acid
ribosomes translate the sequence of bases
into a sequence of amino acids
state what RNA polymerase is
enzyme
state what mRNA is
single-stranded nucleic acid molecule
explain how genetic variation in non-coding DNA of a gene can affect phenotype
RNA polymerase attaches to a non-coding section of DNA
if this region has a mutation, the ability of RNA polymerase to bind there is affected
causing less mRNA to be transcribed
and less protein that the gene codes for will be synthesised
phenotype is affected by how much protein is produced
even if the coding region of DNA is completely normal
explain how genetic variation in coding DNA of a gene can affect phenotype
mutations in the coding region of DNA cause the gene to code for
a different sequence of amino acids
amino acid sequences are highly specific
and form specific shapes and types of proteins
change in sequence of amino acids may affect the shape of the protein
and thus change its function
meaning a change in pheenotype can be caused
describe gregor mendel’s work
mendel studied how characteristics were passed on between generations of plants
in his first experiment, he crossed a tall pea plant with a dwarf pea plant
in his second experiment, he crossed two tall pea plant offspring
he observed that the inheritance of each characteristic is determined by
‘hereditary units’ that are passed onto descendants unchanged
mendel discovered that the tall unit in pea plants was dominant
describe gregor mendel’s conclusions
characteristics are determined by hereditary units
and hereditary units are passed unchanged from parents to offspring
offspring receive one hereditary unit from each parent
hereditary units can be dominant or recessive
explain why understanding inheritance before mendel’s work was difficult
DNA, genes and chromosomes
had not been discovered yet
explain why there are differences in inherited characteristics as a result of alleles
alleles are different version of the same genes
difference in inherited characteristics arise due to variation in alleles
chromosome definition
thread-like structure of DNA
carrying genetic information
in the form of genes
located in the nucleus
allele definition
different versions of the same gene
dominant definition
allele that is always expressed
if at least one copy is present
recessive definition
allele only expressed
only if two copies are present
homozygous definition
if two alleles are the same
heterozygous definition
if two alleles are different
genotype definition
combination of alleles
that control each characteristic
phenotype definition
observable characteristics
gamete definition
sex cells
zygote definition
fertilised egg cell (ovum)
explain monohybrid inheritance
inheritance of characteristics
controlled by a single gene
state how monohybrid inheritance can be investigated
punnett squares
family pedigrees
explain how punnett squares work
genetic diagram that shows
the possible combinations of alleles
that could be produced in offspring
ratios of combinations can be worked out from this
explain how family pedigrees work
trace the pattern of inheritance
of a specific phenotype/genotype
through generations of a family
can be used to work out the probability that a family member will inherit a genetic disorder
describe how the sex of offspring is determined at fertilisation using genetic diagrams
sex is determined by an entire chromosome pair
females have XX sex chromosomes
males have XY sex chromosomes
only a male can pass on a Y chromosome
so the male is responsible for determining the sex of the child
punnett squares of the parents chromosome pair can be used
to determine the ratio of the offspring’s sex
describe the inheritance of the ABO blood groups
inheritance of blood groups is an example of codominance
three alleles determine blood group inheritance instead of two
alleles IA and IB are both codominant
they are both dominant to IO
IA results in production of antigen A in the blood
IB results in production of antigen B in the blood
IO results in no antigens being produced in the blood
codominance definition
both alleles within a genotype are expressed
state what phenotype IAIA produces
A
state state what phenotype IAIO produces
A
state what phenotype IBIB produces
B
state what phenotype IBIO produces
B
state what phenotype IAIB produces
AB
state what phenotype IOIO produces
O
explain how sex-linked genetic disorders are inherited
sex-linked genetic disorders are usually caused by an X chromosome allele
males are more likely to be affected by X-linked recessive disorders
as they do not have a dominant X chromosome to mask the affects
a female with a masked recessive allele is a carrier
and has a 50% chance of passing it to her offspring
if the offspring is male, he’ll have the disease
what are most phenotypic features a result of
multiple genes
rather than single gene inheritance
describe the influence of genetic variation on phenotype
meiosis creates genetic variation between gametes
meaning each gamete carries significantly different alleles
during fertilisation, any male gamete can fuse with a female gamete
to form a zygote
random fusion of gametes at fertilisation also creates genetic variation
between zygotes
zygotes eventually grow and develop into adults
with differing expressed phenotypes
describe the influence of environmental variation on phenotype
environmental factors such as
accidents, climate, diet, culture and lifestyle
can cause differences in phenotypes such as
scarring (accidents), eating too much (weight gain),
raised in a different country (different language)
plant in shade (grows taller)
which are acquired characteristics
state the outcomes of the human genome project
mapped and identified
all the genes in the human genome
state the applications of the human genome project within medicine
information about DNA can be helpful
for forensic science
tracing human migration patterns
and understanding and treating genetic disorders
state what causes genetic variation
genetic mutation
state the degree of variation within a population of a species
extensive
state the effect most genetic mutations have on phenotype
none
state the effect some genetic mutations have on phenotype
small
state the effect few genetic mutations have on phenotype
significant
