Thanks for sharing questions. I will answer a few of them below
MORE QUESTIONS
Can a mom and dad alleles merge with each other? (for example, Heterochromia)
- your Mom and dad's alleles merge when you do meiosis. That is crossing over.
Why are DNA located in the nucleus?- for protection
How does a chromatid form as it is branching off the DNA strand? - chromatids wind up at the last
part of interphase in mitosis and meiosis.
How much chromatids or genes does one DNA strand produce? - one DNA strand makes one
chromatid
Is an Y Chromatid a piece of an normal chromatid? - a y chromatid is a part of a normal set of DNA in a human.
MUTATION QUESTIONS:
Gene mutations happen when DNA REPLICATION makes a mistake in copying the chromatin. DNA polymerase makes a mistake when your body is exposed to MUTAGENS. a MUTAGEN is anything that causes DNA to make mistakes during replication. For example, UV radiation, or X-rays or smoking, eating a diet heavy in preserved meats... all of these are linked to cancer. These are all EXTERNAL FORCES which cause mutation. Finally, they are discovering that even some viruses can also cause mutation. For example, the human papilloma virus can cause cervical cancer. That is why all of you got the vaccine for HPV when you were young.
CHROMATID AND ALLELE QUESTIONS
"Why does your nucleus contain only one chromatid?"
I'm sorry that my video didn't make this clear. I would like to clarify that
your nucleus contains 46 pieces of chromatin ( like 46 strands of yarn) . And each of these strands can roll up into 46 chromatids (46 balls of yarn). So ONE NUCLEUS would contain 46 chromatids.
But in the nucleus, these 46 strands are IN THE FORM of CHROMATIN, so your cell can access the important information written on the chromatin. When your cell gets ready to replicate and make new cells, it has to bundle up the genetic material into a form that can be transported easily: Then it winds it up into Chromatids. This will be the topic of my next video lesson.
FYI, there ARE alleles at the bottom of chromatids. I did not draw them and now I realize that it make it appear as though there are no alleles down there!
Finally, most human body cells contain a nucleus with 46 chromatin pieces = 46 chromatids.
The exception is your red blood cells.
HOW DO CHROMATIDS BOND TOGETHER
The histones keep the chromatin and chromatids organized so we do not get a big tangle of DNA inside the nucleus.
DOES IT MATTER WHERE THE ALLELE IS LOCATED?
It absolutely matters and in every human, our eye colour allele is located on the SAME CHROMATID! in the SAME SPOT.
Here is a picture. This picture is from a youtube video explaining some of these concepts. Note that she talks about the word Chromatid and refers to it as a "Chromosome". A chromatid is a type of chromosome. I will clarify the difference between these two words in my next video.
This pic is from a youtube video
HOW DO YOU PRODUCE MORE CHROMATIDS
(DOWNS SYNDROME)
Downs syndrome can occur when, during the formation of sperm and egg, the chromatids are sorted into the wrong sperm or egg. For example in our vulcan example, IF SPOCK's sperm production was made a mistake then some of his sperm would be missing a ski, and other sperm will have extra skis. MEIOSIS is the process which sorts out those chromatids, and if the sorting does not go as expected, then some of the sperm or egg would either have less chromatids, or more.
When fertilization happens with an egg with an extra chromatid 21, then Down Syndrome can result. Here is a first person account of someone who lives with Down Syndrome
