View Full Version : Two questions about genetics

11-16-2002, 02:17 PM
My first question is whether it's possible for two people to have the same biological parents, without being more genetically related to each other, than to any other person.

We spilt mum's 46 chromosomes into part 1 and part 2, with 23 chromosomes in each part, different to any other chromosome of the other part, and do the same with dad's chromosomes as well.

The most likely thing to happen when the parents have a baby is that the baby has chromosomes from both of the parts from the parents. But there's a small chance that the baby has got, for example, it's mum chromosomes from her part 1 only, and it's dad chromosomes from his part 2 only.

Then these parents could have a second baby, which has got it's mum chromosomes from her part 2 only, and it's dad chromosomes from his part 1 only.

If so, these two babies wouldn't be sharing any chromosome. It would of course be working the other way too, with the same chance, that the babies share every chromosome, and thus are as much related to each other as identical twins.

Am I right here, or have I missed something? If I'm right, could anyone please calculate the odds for one of these things happening for two babies with the same parents?

My second question is whether there's an outside chance that a homozygot brown eyed parent and a homozygot blue eyed parent can have a blue eyed baby, which would require that baby to be homozygot blue eyed.

Sometimes something goes wrong when a sperm cell or an egg cell is created. Instead of getting 23 chromosomes, one of them could, for example, get 24. That's why a baby with downs syndrome is born has got 47 chromosomes.

Then I thought the blue eyed homozygot parent could have an extra of the chromosome where the gene for eye colour is located, and the brown eyed
homozygot could be missing the chromosome where the gene for eye colour is located.

Could this lead to a healthy, blue eyed homozygot baby, or would complications occur here due to inbreeding, and do you then think such a baby at least could survive?

11-16-2002, 10:43 PM
My first question ..........

.............ther as identical twins.

>> you have to take into consideration of that fact that the DNAs in the homologus chromosomes are crossing over during metaphase1(not sure about the exact pahse, but i think this is the one), which creats a HUGE variation in the two replicated chromosomes. This happens everytime a egg or sperm is formed, so, it's not that the chromosomes are pulled apart and create two sets of chromosomes that are same everytime, they are VERY different, :. its hard for two childern borm from the same parents at two different times be identical twins.

Am I right here......

......... homozygot blue eyed.

>> a homozygous dominant parent and a homozygous recessive parent will never create a offspring with a recessive phenotype(blue eye).

B - Dominant. for eye color(brown)
b - Recessive. for eye color(blue)
Parents : BB , bb

GAMETES: Parent1: B B | Parent2: b b

B | B
b| Bb | Bb |
b| Bb | Bb |

NO bb, therefor all heterozygous dominent for eyecolor(brown)

Sometimes something goes wrong when a sperm cell ..........

............could survive?

>> There will be problems when down syndrom occurs and when the baby is born(sometimes the fetus do survive) with an extra set of chromosomes, s/he will show some abnormality in their phenotype structure(EG: characteristic faces, tongues eyelids and would be developmntally chalaged physically and mentally) But your idea about having the blue eye is very interesting and i do see some possibilities of it having some truth.... thigns like that are possible(when the dominent gene is missing, the recessive takes over IE. sexlinked color blindness)

i would've probably been able to tell u somethings more if i lisened in my bio class, but, since i dodn't i guess that's all from me..