help with genetics? phenotype and genotype...?

Question

can someone help me answer these questions...Im quite confused and could you please briefly explain it?

1. If offspring exhibit a 3:1 phenotypic ratio, what are the genotypes of the parents?

2. If the F2 generation consists of 90 long-winged flies to 30 vestivial-winged flies, what was the phenotype of the f1 flies?

and could you also explain in simple way what x-linked are?

oh i see...thanks ecolink :) really appreciate it

Answer 1

Phenotype means the form of the trait that shows in the individual -- like long-winged, colorblind, red-eyed, etc. Think "phenotype=form" and match the f sounds at the beginning of the words.

Genotype means the combinations of alleles an individual has, or what the genes say -- like Rr or RR.

If the genotype is homozygous, the alleles match: RR or rr.
(Think homozygous = same-o-zygous)

If the genotype is heterozygous, the alleles are different: Rr or rR.
(Think heTerozygous = differenT with the emphasis on the T in the words.)

1. Whenever the offsprings' phenotype is in a 3:1 ratio, then that means the parents of that generation were both heterozygous, like Rr x Rr.

2. 90 long: 30 vestigial is the same as 3:1. So the F1 must have been all heterozygous, like Rr. Same reason as answer number 1. Your teacher is just trying to get you to see that parents that are all heterozygous produce offspring in a 3:1 ratio, whether it's the original parents making the F1 or the F1 individuals producing the F2.

X-linked means that the gene for the trait is on the X-chromosome. Therefore, in fruit flies and in people, the females have two copies of these genes because the females have two X-chromosomes. The males have only one copy of these genes because the males have only one X-chromosome and one Y-chromosome.

When recessive traits are X-linked, a female has to have two copies of the recessive allele (or form of the gene) in order to show the trait. That isn't very likely if the allele is fairly rare. The males only need one copy of the recessive allele to show the trait because the Y-chromosome doesn't have an allele for that trait. It's sort of like the Y doesn't have any opinion on that matter.

White eyes is an X-linked trait in fruit flies.
Color blindness and hemophilia are X-linked traits in people.

Answer 2

Really simply put, the phenotype of an organism is going to be the physical characteristic it is exhibiting. The genotype is the genetic make-up of that organism.

So if you have a boy with recessive genes for eye color 'bb' and he has blue eyes, his PHENOTYPE is blue eyes and his GENOTYPE is 'bb'.

X-linked what? X-linked traits are characteristics of an organism for which the genes are located on the X-chromosome. You might be referring to a lot of the genetic disorders that are x-linked. When a female bares a male child, she gives that child one X-chromosome, and his father gives him a Y. If the mother is a 'carrier' for a certain disorder (meaning she has one X-chromosome that is 'normal' and one that carries the genetics for the disorder) and she gives her son an effected X-chromosome, the male child will have the disorder. This is referring to a recessive x-linked disorder, which is commonly seen in males (for instance, color-blindness).

Answer 3

the achieveable genotypes for deep-lobed leaves are DD and Dd. the achieveable genotype for shallow-lobed leaves is dd. The pass is here: Dd x Dd this could yield a three:a million phenotypic ratio (3 deep and a million shallow) The genotypic ratio is a million:2:a million (a million DD, 2 Dd, a million dd)