How can phenotypes be used to predict genotypes in a pedigree?

Answer 1

Phenotype is physical appearance of a character in a living being which depends on their genotype i.e. genetic constituents so by study of phenotype, genotype can be predicted which may or may not be exactly same but definately not wrong because every character can be homozygously dominant or hetrozygously dominant.

Answer 2

It depends on what you are predicting. For example: A man with attached earlobes (ff) and a woman with free earlobes (either FF or Ff, but we'll go with Ff for this example) have a child. What type of earlobes will the child have?

You construct a punnett square with the mother's genotype across the top and the father's down the side. You then fill out the table, as shown:

F f

f Ff ff

f Ff ff

The four boxes that have two alleles each are the possible offspring. Two of the four, or 50%, of the possible children have the genotype Ff - that is, they will have free earlobes. The other two have the genotype ff - that is, they will have attached earlobes. For these two parents, their children have a 50-50 chance of looking like mom or looking like dad. But what if the woman was FF instead? She would still have free earlobes, but she now has two DOMINANT alleles instead of one dominant and one recessive. Now the square looks like:

F F

f Ff Ff

f Ff Ff

All four of the child possibilities have the genotype Ff, or a heterozygous genotype. The couple could only have free-earlobed children.

Some traits depend on the baby's sex. Let's take male-pattern baldness for an example. It is possible to have male-pattern baldness in females, but it is much more common in males. This is because females need two infected alleles to be bald, while men only need one (X's are the only chromosomes that can be infected: females are XX, so they have two copies, but men are XY). Let's take a normal male (XBY) and a normal female whose FATHER was bald (XBXb). Because the woman has an XB allele, she will not show baldness. However, her father WAS bald, so he gave her his Xb allele. Had he given her his other chromosome, his Y, "she" would have been born a "he" instead. Now we construct our square:

XB Xb

XB XBXB XBXb

Y XBY XbY

Let's look at the offspring now. The top row, the row with two X chromosomes, are the possibilities for a daughter. The bottom row, which has one X and one Y, are the possibilities for a son. Let's look first at the daughters. One is XBXb, which makes her a "carrier", that is, that she "carries" the infected baldness allele and could then possibly pass it on to any sons SHE might have. However, neither of the girls is bald. Now let's look at the boys. The first is XBY, with no baldness. The second is XbY. This son WILL be bald. In short, because the trait is sex-linked, in this couple it is impossible for a girl to be bald, but any sons these two have have a 50% chance of losing their hair.

There are others as well, including traits linked with other traits (like albinism) and traits that involve multiple genes (like hair color). However, these are the simple ones.

Hope it helped.

Answer 3

The pedigree will typically show one kind of trait and the affected members of a family. Take a look at if the trait is dominant or recessive first. Once you have that figured out, start to predict the genotypes of the individuals in the pedigree chart. Once you have the genotypes predicted, you can easily predict the phenotypes.

I'll give an example. Lets say that this trait is dominant, and out of the the two individuals in the first row, one is affected and one is not. The one that is not has to be homozygous recessive, but the one that is affected can either be homozygous dominant or heterozygous. To figure this out you have to look at the children... since this is a dominant trait all of the offspring would have to be affected by it in order for the affected parent to be homozygous dominant. If that is not the case, then the parent is heterozygous. Once you have this figured out, you move to the next row and predict their genotype. From that, you get the phenotype. For a dominant trait, homozygous dominant and heterozygous individuals will have this trait, and homozygous recessive individuals not have this trait.

I'm sorry if this sounds a little confusing, it's hard to explain without physically showing you a pedigree chart. Hope this helps!

Answer 4

the answer to this question is phenotype