topic 7 Flashcards
Explain what is meant by the
term phenotype.
- Expression / appearance / characteristic due to genetic
constitution / genotype / allele(s); - (Expression / appearance / characteristic) due to environment;
In genetic crosses, the
observed phenotypic ratios
obtained in the offspring are
often not the same as the
expected ratios.
Suggest two reasons why.
- Small sample size;
- Fusion/fertilisation of gametes is random;
Ignore breeding is random - Linked Genes;
Accept crossing over / sex linkage - Epistasis;
- Lethal genotypes;
Explain what is meant
by codominant alleles.
Both alleles are expressed / shown (in the phenotype).
Explain what is meant by
a dominant allele.
Is always expressed / shown (in the phenotype);
Explain what is meant by
a recessive allele.
Only expressed / shown (in the phenotype) when homozygous /
two (alleles) are present / when no dominant allele / is not
expressed when heterozygous;
In fruit flies, the genes for body
colour and wing length are
linked. Explain what this
means.
(Genes / loci) on same chromosome
Red-green colour blindness
affects more men than women.
Explain why.
- (Gene/allele) is on the X chromosome;
- Females require two alleles/females can be
heterozygous/carriers and males require one allele;
Location of a sex-linked gene
The non-homologous section of an X chromosome
Which statistical test could a
scientist use to determine
whether the observed results
of a genetic cross were
significantly different from the
expected results?
Give the reason for your choice
of statistical test
- Chi squared test;
- Categorical data
Explain one way in which the
behaviour of chromosomes
during meiosis produces
genetic variation in gametes.
Crossing over / exchange of material (between chromatids);
Different combinations of alleles / linkage groups changed / broken;
OR
Independent assortment / alignment of (homologous)
chromosomes;
Different combinations of (maternal and paternal) chromosomes /
alleles;
What does the
Hardy-Weinberg principle
predict?
The frequency / proportion of alleles (of a particular gene);
Will stay constant from one generation to the next / over
generations / no genetic change over time;
Providing no mutation / no selection / population large / population
genetically isolated / mating at random / no migration;
The three principles for marking are:
What feature
What happens to it
Providing . . .
Accept: genotype / explanation of genotype
Accept: alternative wording, e.g. there is no gene flow / genetic drift
for genetically isolated.
What is a gene pool?
All the alleles in a population;
There are nine subspecies of
giraffe. These subspecies
evolved when populations of
giraffe were separated for long
time periods.
Explain how different
subspecies of giraffe may have
evolved from a common
ancestor.
- No interbreeding / gene pools are separate / geographic(al)
isolation;
Accept: reproductive isolation as an alternative to no interbreeding. - Mutation linked to (different) markings/colours;
- Selection/survival linked to (different) markings/colours;
- Adapted organisms breed / differential reproductive success;
Note: ‘passed on to offspring’ on its own is not sufficient for
reproduction. - Change/increase in allele frequency/frequencies;
Lord Howe Island in the
Tasman Sea possesses two
species of palm tree which
have arisen via sympatric
speciation. The two species
diverged from each other after
the island was formed 6.5
million years ago. The flowering times of the two species are different.
Using this information, suggest
how these two species of palm
tree arose by sympatric
speciation.
- Occurs in the same habitat / environment / population;
- Mutation/s cause different flowering times;
- Reproductive separation / isolation
OR
No gene flow
OR
Gene pools remain separate; - Different allele/s passed on / selected
OR
Change in frequency of allele/s - Disruptive (natural) selection;
- Eventually different species cannot (inter)breed to produce
fertile offspring;
Explain how resistance to an
antibiotic could become
widespread in a bacterial
population following a gene
mutation conferring resistance
in just one bacterium.
- frequent use of antibiotic creates selection pressure / antibiotic
kills bacteria; - bacteria with mutation / resistance have (selective) advantage
over others / described; - (survive to) reproduce more than other types pass on
advantageous allele / mutated allele in greater numbers; - frequency of (advantageous) allele increases in subsequent
generations; - frequency of resistant types increases in subsequent generations;
