6. Conclusion: From 3, 4, and 5 we can conclude that organisms with the traits that make them more likely to survive and reproduce will produce offspring with those traits,
Are traits always passed on to the next generation? Suppose there was a person born with blue eyes for the first time and suppose these blue eyes were helpful to survival and reproduction. Does this mean that this trait is automatically going to be passed on? Could his or her offspring have brown eyes?
I'm not sure just how many genes control eye color in humans, but if we assume that thee are just two, B for brown and b for blue. We know that blue eyes are recessive, so in order to be expressed, the person must be homozygous recessive. here's a punnet square to help demonstrate: the cross BB * bb
being "BB" is homozygous dominant. being "bb" is homozygous recessive. all the offspring (the ones in the boxes) are Bb and this is known as being heterozygous. no offspring will have blue eyes, but will have the trait. if the cross is Bb * bb, half of the offspring will express the trait for blue eyes, and all will carry it. Try this cross on your own, using the same format of the square below.
__|_b__|__b__| B | Bb | Bb | __|____|_____| B | Bb | Bb | __|____|_____|
abe: cleaned up the format of the post. abe2: punnet squares are evil to format. abe3: i give up formatting it This message has been edited by kuresu, 05-12-2006 12:30 PM
This message has been edited by kuresu, 05-12-2006 12:32 PM
This message has been edited by kuresu, 05-12-2006 12:32 PM
This message has been edited by AdminAsgara, 05-12-2006 11:46 AM
This message has been edited by AdminAsgara, 05-12-2006 11:47 AM
That would rather depend on why that person had blue eyes. If the basis of his blue eyes was genetic then a classical genetic analysis like Kuresu has done will tell you the likelihood of the gene being passed on and whether or not the trait was expressed in the progeny would depend on the nature of the trait, i.e. if it was reccessive/dominant etc....
If the basis was not genetic, i.e. environmental or epigenetic, then the trait might very well be lost from the progeny, although there are a number of examples of epigenetic inheritance of traits, such as in agouti mice(Morgan et al., 1999).
Actually, what you are talking about is simply shared parental genetic representation in the offspring of diploid species.
Sexual recombination refers specifically to the rearrangement of genes on individual chromosomes that occurs during the formation of gametes in meiosis because of the phenomenon of 'crossing over'. Your sperm don't carry an exact single copy of each one of your chromosomes, but each carries a unique mix of alleles from the two copies.
The consequence of this process is called 'independent assortment' of alleles - genes are inherited independent of their (temporary) association with other genes on the same chromosome. It means that even though you have half the genes from your mother and half from your father they are all mixed up in completely different chromosomal combinations when the chromosomes of the gametes segregate, even though each allele retains its specific locations on a chromatid.
Violations of this general rule do occur, and 'two locus' effects can be detected when disportionate numbers of either 'coupling gamates' or 'repulsion gametes' can be demonstrated. This is refered to as a 'linkage disequilibrium' and was once hypothesized to indicate incipient 'supergene' formation.
I thought he meant that the trait was definitely going to be passed on, but it might be recessive, which I assume means that it might turn up in the phenotype in later generations.
That was the case in the example I used. Try a cross between two heterozygotes, in this case that would be Bb * Bb. the resutls are: BB, Bb, Bb, bb.
BB is homozygous dominant, and neither carries the blue-eye gene or expresses it. Bb is heterozygous, and while not expressing blue eyes they do carry that gene. bb is homozygous reccesive and does carry the gene as well as express it.
As to the second part of what you said, that much is true.
Since mutation occurs randomly, albeit not with equal probability on all portions of the genome, the odds are that we all carry a number of mutations that occurred during the formation of the gametes that gave rise to us when they formed a zygote. Fortunately, most of these probably have little or no effect on our fitness or we wouldn't be here.
BB is homozygous dominant, and neither carries the blue-eye gene or expresses it
OK, so it's very possible for a "positive" trait to disappear within one generation, in which case it would have no evolutionary significance, correct? But we could even say that it could extend for a few generations and then disappear. But I guess the more generations it got passed down, the more likely it would be to become permanent (since more indivduals would possess it), other conditions being equal.
Since mutation occurs randomly, albeit not with equal probability on all portions of the genome, the odds are that we all carry a number of mutations that occurred during the formation of the gametes that gave rise to us when they formed a zygote.
So any mutations that have evolutionary significance occur during conception, when the strand from one double helix meshes with a strand from that of the mate, and what happens is that they don't all mesh properly?
quote:so it's very possible for a "positive" trait to disappear within one generation
Not entirely ture. As in the case of the blue-eye example that you started. Given the condition that I assumed (blue is reccesive), it would get passed down to the offspring, based off of statistical probability. Now, if those offsrping carrying the gene were killed before they could pass on the new gene, and they were the only ones with the mutation that lead to that gene, then yes, it is possible to wipe out a positive trait in a single generation.
Not entirely ture. As in the case of the blue-eye example that you started. Given the condition that I assumed (blue is reccesive), it would get passed down to the offspring, based off of statistical probability
So some of the offspring MUST have the trait, just not all of them?