HSC Biology Question Thread

[inescelic]

Thanks, that helped alot.
I wasn't too sure if the dot point wanted me to draw a model as you said or link this process to an analogy.

Good to hear
Your model would most definitely be a drawing as this biological concept is way too unique to compare it with anything else to be an analogy.
Also, keep in mind that this dot point will usually be testing biological skills e.g. reliability, validity, advantages and disadvantages of models. Thus, you should note that you researched and found the diagrams from which you based model from reputable sources (e.g. from a scientific institution) and that you compared a variety of sources for reliability.

[cnimm2000]

Hey guys
Could i get an explanation on why sex-linked genes don't produce simple mendelian ratios

[Potatohater]

Hey guys
Could i get an explanation on why sex-linked genes don't produce simple mendelian ratios

So sex linked inheritance depends on the sex of the offspring. Since the X chromosome is longer than the Y chromosome, characteristics carried on the X chromosome may not be masked by the Y. Let's say the allele in question is recessive, if it were inherited by a girl she would need this allele on both chromosomes for it to be expressed in the phenotype. If the offspring were a boy, he would only need one copy of the allele, on his only X chromosome, for it to show. Therefore the inheritance of sex linked traits does not follow simple Mendelian ratios. I hope that made sense, if not just let me know and I'll attempt to explain in another way.

*AN suggestion: we should have some sort of drawing feature thing so that I could draw pedigrees and punnet squares to explain genetics Q's *

[AngelWings]

Hey guys
Could i get an explanation on why sex-linked genes don't produce simple mendelian ratios

For organisms under the XY sex determination system (e.g. humans or Drosophila melanogaster [fruit/ vinegar fly]), females have two X chromosomes (XX), whereas males only have one and fill the other with a Y chromosome (XY) when they inherit sex chromosomes. This means that the presence of the Y chromosome makes an organism male under this system. Each of these sex chromosomes has alleles - these are known as sex-linked alleles (sometimes referred to as X-linked alleles). This is usually denoted as a superscript letter beside a capital X or Y as appropriate, such as X^wX^w for a white eyed female, where 'w' is the white eye allele. Why it doesn't produce normal Mendellian ratios is because the progeny's sex will impact how much of the genetic info will be shown (but this isn't the end of the story, more on that below).

What do I mean by this? For sex-linked traits with the XY system, male progeny are hemizygous (This basically means it only shows up one copy from its parents.); they'll display whatever trait their mother gave them (they need an X chromosome to live) and automatically receive the Y chromosome their father had (because where else can they get a Y chromosome to become male?). The Y chromosome is often considered 'too small to have visible effect' ("gene-poor") and thus, Dad's genes don't show up in the male progeny's phenotype.

Mendellian ratios would show that both sexes of the progeny will be the same (female + males show Mum + Dad's info). Under sex-linked ratios, females will show both Mum + Dad's info (since they have 2 X chromosomes and inherit these equally from the parents), but males will only show Mum's (hemizygous). This difference causes the observed ratio differences.

The best example I can give you is on this link right here, which includes the research of Thomas Hunt Morgan on Drosophila melanogaster (the experiment that essentially discovered the existence of sex-linked alleles).

Some more helpful links: Sex-linked inheritance
See halfway down the page under "Inheritance of Sex Linked Traits"

NOTE: I got beaten by Potatohater, but I thought the links might be useful, so I'm posting anyway. Also, I know I explained it in a convoluted manner, but I hope it made sense. Since genetics is my major, I tend to have a more technical background.

[cnimm2000]

So sex linked inheritance depends on the sex of the offspring. Since the X chromosome is longer than the Y chromosome, characteristics carried on the X chromosome may not be masked by the Y. Let's say the allele in question is recessive, if it were inherited by a girl she would need this allele on both chromosomes for it to be expressed in the phenotype. If the offspring were a boy, he would only need one copy of the allele, on his only X chromosome, for it to show. Therefore the inheritance of sex linked traits does not follow simple Mendelian ratios. I hope that made sense, if not just let me know and I'll attempt to explain in another way.

*AN suggestion: we should have some sort of drawing feature thing so that I could draw pedigrees and punnet squares to explain genetics Q's *

For organisms under the XY sex determination system (e.g. humans or Drosophila melanogaster [fruit/ vinegar fly]), females have two X chromosomes (XX), whereas males only have one and fill the other with a Y chromosome (XY) when they inherit sex chromosomes. This means that the presence of the Y chromosome makes an organism male under this system. Each of these sex chromosomes has alleles - these are known as sex-linked alleles (sometimes referred to as X-linked alleles). This is usually denoted as a superscript letter beside a capital X or Y as appropriate, such as X^wX^w for a white eyed female, where 'w' is the white eye allele. Why it doesn't produce normal Mendellian ratios is because the progeny's sex will impact how much of the genetic info will be shown (but this isn't the end of the story, more on that below).

What do I mean by this? For sex-linked traits with the XY system, male progeny are hemizygous (This basically means it only shows up one copy from its progeny.); they'll display whatever trait their mother gave them (they need an X chromosome to live) and automatically receive the Y chromosome their father had (because where else can they get a Y chromosome to become male?). The Y chromosome is often considered 'too small to have visible effect' ("gene-poor") and thus, Dad's genes don't show up in the male progeny's phenotype.

Mendellian ratios would show that both sexes of the progeny will be the same (female + males show Mum + Dad's info). Under sex-linked ratios, females will show both Mum + Dad's info (since they have 2 X chromosomes and inherit these equally from the parents), but males will only show Mum's (hemizygous). This difference causes the observed ratio differences.

The best example I can give you is on this link right here, which includes the research of Thomas Hunt Morgan on Drosophila melanogaster (the experiment that essentially discovered the existence of sex-linked alleles).

Some more helpful links: Sex-linked inheritance
See halfway down the page under "Inheritance of Sex Linked Traits"

NOTE: I got beaten by Potatohater, but I thought the links might be useful, so I'm posting anyway. Also, I know I explained it in a convoluted manner, but I hope it made sense. Since genetics is my major, I tend to have a more technical background.

Thanks guys for the great explanation

[kaustubh.patel]

Hey bio lovers I'm having some trouble understanding enantiostasis i know an example of estuarine fish counter acting the increase in salt water by decreasing their pH but i dont get the reasoning behind this, any help is appreciated thank you.

[Opengangs]

Hey,
So homeostasis is the process whereby am organism maintains their internal environment from a relatively stable environment. There may be sudden changes in the environment from time to time but it is generally stable.

On the other hand, some organisms live in an environment where it is constantly changing. Mangroves that live in estuaries have to constantly cope with the changes in salt levels as they live in an environment where the tide meets the stream.

At high tide, there are increased salt levels while at low tide there are decreased levels of salt. Thus, homeostasis will not be efficient. This is where enantiostasis comes into play.

Enantiostasis is the process whereby they keep a relatively stable physiological and metabolic function against the constant changes within the external environment. They do this by either conforming to the external environment (osmoconformers), that is their temperature is proportionate to the external environment or they maintain their own temperature regardless of external stimuli (osmoregulators).

[mickinimaj]

Would the change in kangaroo teeth (from (ancient to modern) count as mac or mic evolution
If so, what would be the explanation

[Natasha.97]

Would the change in kangaroo teeth (from (ancient to modern) count as mac or mic evolution
If so, what would be the explanation

Hi!

I'd probably say that it is classified as microevolution, as no new species are formed as a result of the change in kangaroo teeth

[cnimm2000]

Would the change in kangaroo teeth (from (ancient to modern) count as mac or mic evolution
If so, what would be the explanation

Just to add onto what Jess1113 said:
Here is a summary of the criteria, to help you differentiate if it is a result of macro-evolution or micro-evolution:
Macro-evolution:
Takes place over millions of years and results in the arising of new species (even larger groups such as families and orders)
Micro-evolution
Takes place over shorter periods of times and results in changes within the population, but doesn’t reproduce new species.

[mickinimaj]

what would be the reason for why maintaining body temeprature in mammals count as feedback system?

[markkhodair]

Hey! This is probably a dumb question, but in our exams, are we ever allowed to talk in 1st/2nd person? Would "our body requires and wants to maintain a balance of water and salt, therefore, it passively reabsorbs and secretes water until we reach that balance." suffice? Or would that be illegible and we have to write "the human body requires and wants to maintain a balance of water and salt, therefore, it passively reabsorbs and secretes water until it reaches that balance."? I'm sorry if this is a dumb question I probably most likely know that we can't write in 1st/2nd person but I've gone blank. Thank you!!

[Potatohater]

Hey! This is probably a dumb question, but in our exams, are we ever allowed to talk in 1st/2nd person? Would "our body requires and wants to maintain a balance of water and salt, therefore, it passively reabsorbs and secretes water until we reach that balance." suffice? Or would that be illegible and we have to write "the human body requires and wants to maintain a balance of water and salt, therefore, it passively reabsorbs and secretes water until it reaches that balance."? I'm sorry if this is a dumb question I probably most likely know that we can't write in 1st/2nd person but I've gone blank. Thank you!!

Sure you can write in 1st/2nd person so long as you are getting the point across clearly and concisely, so that 1st example is totally acceptable

[Natasha.97]

what would be the reason for why maintaining body temeprature in mammals count as feedback system?

Hi!

One of the key focuses of this topic (MaB) is organisms and their enzymes. Enzymes function best at certain temperatures/pH/concentrations etc. Mammals have feedback mechanisms in place so that if the body temperature is below optimum, a series of actions will take place resulting in the return to the optimum temperature and vice-versa. An example is included below:

- Stimulus: Hot room
- Skin receptors detect change in temperature, and an impulse is transmitted along sensory neurone to the brain
- The brain transmits a response along the motor neurone to the effector (sweat gland)
- Sweating and vasodilation occurs to return the body back to normal temperature

Hope this helps

[markkhodair]

Hey! What are some examples of halophytes who use salt avoidance mechanisms rather than salt tolerance? Thank you!