Biology Unit 4 Questions Megathread

[nooshnoosh95]

can someone explain the difference between incomplete variation, partial variation and co-dominance?

are they all the same
or does one refer to colours like roan (both red and white hairs on cows present) and another to pink when red flowers are crossed with white flowers?

[Russ]

What is the purpose of a back cross?

Determine allele status of offspring as well as being useful for breeding purposes (ie if you have a particular purebreed and want to keep it that way)

1. What exactly is an Anti-Codon and What is it's purpose?

It is complementary to the codons of mRNA and thus localizes the tRNA, to which it is attached, to the ribosome translating mRNA. Since tRNAs also have amino acids attached, it essentially is used to direct them to the appropriate location in the polypeptide.

2. Can someone explain what is independent assortment and what happens during it?

Independent assortment means that the genes you're considering are not affected by each other during assortment. It's one of Mendel's laws, I forget which, but it basically says that independently assorting genes will be divided randomly between daughter cells in meiosis.

3. An explanation on DNA Hybridisation.

You basically just convert your sample of interest to ssDNA and check to see what complementary sequences will anneal with it and produce dsDNA. This tells you what your original sample was. You can do cool stuff, such as FISH, which makes the hybrid sequences fluorescent and easily visible etc.

4. What is  Chismata Formation?

During meiosis, as the chromosomes line up next to each other, they can exchange genetic material. This is calling "crossing over" but the technical term for the join is a "chiasma'.

or does one refer to colours like roan (both red and white hairs on cows present) and another to pink when red flowers are crossed with white flowers?

Those are codominance and incomplete dominance respectively, but I've never heard of the incomplete/partial variance terms.

[nooshnoosh95]

huge question
in the NOB text book on page 359 it says coding regions (introns) and non-coding regions (exons)
is this a typo
because i thought during dna replication the introns are taken out because they are the non-coding region???
help
btw thanks russ

[Ravit]

yes, that part is a typo:D

[Mr. Study]

Thank you for the answers Russ!

[HERculina]

Helllo
I just finished doing the NEAP 2011 paper, and I got a lot wrong and don't know why
Could you please explain the answers. thanks

[Kaille]

can the d loop in the mtdna only be used to identify recent common ancestors because it mutates so much?

[Drunk]

Helllo
I just finished doing the NEAP 2011 paper, and I got a lot wrong and don't know why
Could you please explain the answers. thanks

1. Sperm cells are made by meiosis, which actually involves crossing over of chromosomes. Independent assortment is attributed to mitosis.

[Russ]

Going very quickly off what i remember, the G1 block would be right at the end before it tried to move on in the cycle. Failing that checkpoint would leave it in permanent G0 and eventually apoptosis.

[HERculina]

Helllo
I just finished doing the NEAP 2011 paper, and I got a lot wrong and don't know why
Could you please explain the answers. thanks

1. Sperm cells are made by meiosis, which actually involves crossing over of chromosomes. Independent assortment is attributed to mitosis.

Isn't independent assortment got to to with homologous chromosomes pairing up --> meiosis?

Going very quickly off what i remember, the G1 block would be right at the end before it tried to move on in the cycle. Failing that checkpoint would leave it in permanent G0 and eventually apoptosis.

Oh ok, but what causes teh G1 block to fail? I would have thought that it wouldn't have cause aren't telomeres a good thing

[HERculina]

can the d loop in the mtdna only be used to identify recent common ancestors because it mutates so much?

Ye, I think that cause it mutates at such accelerated rate (although some areas of mitochondria have a lower muatation rate) it's easier to tell the differences between two closely related genomes. Something like that

EDIT: two more quick questions
1. What's the correct theory now; is it the out-of-africa one or the multiregional hypothesis?
2. QUESTION 17
Today’s wide range of kangaroos evolved from shorter nosed ancestors from thousands of
years ago. The shorter nosed ancestors lived in Australia when the continent was once
covered by forests, from the east to west coast. As the climate became drier, however,
grasslands replaced much of the forest. In response, all of the short-nosed browsing species
of kangaroo independently evolved the longer grazing snouts that we recognise today.
The independent evolution of longer grazing snouts from shorter browsing
snouts in Australian kangaroos is an example of:
A Convergent evolution.
B Parallel evolution.
C Allopatric speciation.
D Divergent evolution.

Why's the answer B? What is parallel evolution?

[WhoTookMyUsername]

yes, independent assortment has nothing to do with mitosis.
It is purely associated with meiosis

[simpak]

Yes, independent assortment occurs during meiosis.  The confusion comes from how poorly worded and explained the question is in itself.  Does it help if I tell you that they might want you to assume all four cells are the product of one meiotic event and not a number of meioses?

[WhoTookMyUsername]

In early hominins (Australopithecus) is the foramen magnum already completely centrally located (very close to modern humans? ) .

AKA

is it incorrect to say a more centrally located foramen magnum is a distinguishing feature between homo sapiens and australoptiehcus?

[HERculina]

^ yep.   

Yes, independent assortment occurs during meiosis.  The confusion comes from how poorly worded and explained the question is in itself.  Does it help if I tell you that they might want you to assume all four cells are the product of one meiotic event and not a number of meioses?

.       Hm but theres no difgerent coloured band things on the chromosomes to highlight that crossing over occured. Why isnt independent assortment right doesnt it result in different chromosomes separating into the four daughter cells