How can a trait skip a generation?

[kateaugu]

i cant seem to find in anywhere in my book and i kinda want to know

[taiga]

A cumulation of recessive genes.

Assume A = dominant, B= recessive

grandpa and grandma are BB and AB respectively, so mum perhaps ends up being AB. Grandma and Mum have the recessive genes but none of them will actually have it displayed in their characteristics. Grandpa does display that trait though.

Mum ends up having a baby with another AB (dad), and the baby ends up being BB, hence displays the recessive B gene.

Hence the trait has skipped a generation in the sense that neither mum or dad show the trait.

I think if you draw a punnet square or something you can show how it happens.

(waiting for someone who has actually studied biology to confirm)

[slothpomba]

This is a fairly simple question if you think about the principals behind it. Let me explain.

First however, let's assign the alleles some symbols.

T - is the dominant allele (Upper case is always dominant by convention)
t - is the recessive allele (lower case is always recessive by convention)

P1: TT x tt (Parental generation, one parent is homozygous dominant for the trait in question, the other is homozygous recessive.)

You can draw up a punnet square if you wish to find out the probabilities of which alleles the kids will have but due to one parent being homozygous recessive, all children will have one dominant allele and one recessive allele. Since they have one dominant allele, they all show the dominant phenotype. We'll pretend dominant T produces black hair and recessive t red hair. So, in this case, all children have one dominant T allele, so, all have black hair.

F1: Tt, Tt, Tt, Tt

Now, we'll select one of the heterozygous children - Tt.

This person is in the 2nd generation, one of their parents had black hair (TT), the other parent had red hair (tt).

They are heterozygous for this trait. They have black hair but they also carry one allele for red hair, as shown above (Tt).

This child later goes onto marry another person(from another family) who is either heterozygous or homozygous recessive for this trait.

Case 1: Heterozygous partner
P:Tt x Tt
F1:TT/Tt/Tt/tt

25% chance of the child being homozygous recessive for the trait (tt) and thus displaying the recessive trait after 'skipping' a generation.

Case 2:Homozygous partner
P:Tt x tt
F1:Tt/Tt/tt/tt

50% chance of child being homozygous recessive for the trait (tt) and displaying the recessive trait after 'skipping' a generation.

[Markkiieee]

This is a fairly simple question if you think about the principals behind it. Let me explain.

First however, let's assign the alleles some symbols.

T - is the dominant allele (Upper case is always dominant by convention)
t - is the recessive allele (lower case is always recessive by convention)

P1: TT x tt (Parental generation, one parent is homozygous dominant for the trait in question, the other is homozygous recessive.)

You can draw up a punnet square if you wish to find out the probabilities of which alleles the kids will have but due to one parent being homozygous recessive, all children will have one dominant allele and one recessive allele. Since they have one dominant allele, they all show the dominant phenotype. We'll pretend dominant T produces black hair and recessive t red hair. So, in this case, all children have one dominant T allele, so, all have black hair.

F1: Tt, Tt, Tt, Tt

Now, we'll select one of the heterozygous children - Tt.

This person is in the 2nd generation, one of their parents had black hair (TT), the other parent had red hair (tt).

They are heterozygous for this trait. They have black hair but they also carry one allele for red hair, as shown above (Tt).

This child later goes onto marry another person(from another family) who is either heterozygous or homozygous recessive for this trait.

Case 1: Heterozygous partner
P:Tt x Tt
F1:TT/Tt/Tt/tt

25% chance of the child being homozygous recessive for the trait (tt) and thus displaying the recessive trait after 'skipping' a generation.

Case 2:Homozygous partner
P:Tt x tt
F1:Tt/Tt/tt/tt

50% chance of child being homozygous recessive for the trait (tt) and displaying the recessive trait after 'skipping' a generation.

+1