component 2 exam errors Flashcards
) In a cross between two individuals with the genotype DdEe, where the genes D and E are on the same chromosome, the offspring showed four different types of phenotype.
The phenotype of some of the offspring was far more common than expected and some phenotypes
were very rare. Explain these observations.
this occurred due to crossing over in meiosis, as alleles were exchanged between chromosomes.
crossing over is however very rare, so phenotypes that came about due to it were very rare as well
incomplete linkage
genes were further apart on the same chromosome
recombinants were equal in number
In terms of insect pollination , how is the effective transfer of pollen ensured ?
Effective transfer of pollen is ensured when the anther and the stigma touch the same part of the insect
How is self pollination avoided
By the anther and the stigma maturing at different times
Function of the generative male nucleus
For fertilisation
Function of the tube nucleus
It controls the growth of the pollen tube
Features of a wind pollinated flower
Small petals
They have no nectar
That have feathery stigmas
They are not scented
Petals are dull
State how the production of pollen grains has enabled flowering plants to adapt to terrestrial life
Pollen tube delivers male gametes to the egg
This stops the risk of dehydration of gametes
Leads to the formation of a tough exine or outer wall
Part of the flower that develops into the testa
Integuments
Part of the flower that develops into the embryo plant
Zygote
Why is a wheat grain considered more as a fruit than as a seed
Because seeds only have testas , but the grain has an endosperm and embryo
A fruit retains the ovary wall unlike a seed , which is what a wheat grain does
Explain why events taking place in the embryo sac of a wheat flower are described as double fertilisation
One nucleus fuses with the ovum , and the other fuses with the polar nuclei
The first forms the zygote and the second forms the triploid endosperm nucleus
genetic drift
a process of random fluctuations in the frequency of alleles in a populations
founder effect
type of genetic drift that occurs when a small group of individuals separates from a larger population to establish a new colony
when organisms of the same species are put in different habitats over a long period of time, explain why they eventually evolve into separate species
they are geographically isolated
so over time, they develop adaptations that prevent them from successfully breeding with the original population
courtship behaviour
suggests pieces of evidence that can be used to identify organisms of the same species
they share the same gene pool
similar behavior
similar genetic profile
similar morphology
similar proteins
suggest possible isolating mechanisms
mechanical isolation
courtship behavior
behavioral isolation
dogs and foxes have different number of chromosomes
rare cases of mating between both species to produce a “dox” has been recorded. The dox is never sterile, give the reasons for this sterility
chromosomes are not homologous
so they cannot form bivalents during prophase 1 of meiosis
meiosis does not occur
so they cannot produce gametes
uterus wall also known as
uterus lining is also known as the
myometrium
endometrium
suggest why only one functional female gamete is produced as a result of meiosis
polar bodies are produced
functional gametes retain most of the cytoplasm, which acts as a food store for the zygote until implantation occurs
blastocyst
hollow ball of undifferentiated cells that the zygote divides to form
state how the secondary oocyte usually prevents polyspermy and suggest a reason why there is an increased risk of polyspermy with IVF
the cortical reaction occurs to form a fertilization membrane, thereby preventing the entry of any more sperm
secondary oocyte that is taken from the Graafian follicle during IVF is immature, so it cannot form a fertilization membrane
the developing embryo is not transferred into the uterus until three days after IVF. explain why this delay is needed using your knowledge of fertilization and implantation
to allow the cleavage to form
if the embryo is put into the uterus immediately, the endometrium would not be fully developed
trophoblastic villi will not have developed so HCG will not be produced
so the embryo would not implant
give two reasons why there must be a barrier between fetal and maternal blood systems
what serves as this barrier
to protect the foetus from the mother’s immune system
protection against differences in pressure in the mother’s blood
serves as a barrier against toxic substances in the mother’s blood
the placenta
suggest how pressure differences in the uterine arteries and the intervillous space allow the placenta to carry out its function
pressure differences force materials through the capillaries in the placenta
