For recording of genetics problems we have simple rules, but adherence to them will greatly facilitate the understanding of genetics of the studied traits. TOPIC:
When breeding females guppi with a black tail and the males who had a red tail in all F1 fish were in the red-tailed black. In the F2 was splitting into 4 phenotypic classes, one (blue) was new.
Explain and define the splitting of parental genotypes.
ANALYSIS:
1. Parents are recorded as follows:
First written sign PP (parents), then the signs of a female, the "x" and symptoms male. In doing so, the words male and female fall, because it is clear that the female on the left and right - male.
For example,
PP black red tail x tail
So the female with a black tail crossed with red tail male.
If the known genes, we can write the following designation of the genes, for example:
PP black red tail x tail
aaVV and AAbb
In this example, the color of each tail is indicated by two genes - A and B, but different alleles - dominant (AA and BB - it is genotype) and recessive (aa and bb).
We assume that these are autosomal genes and will not be the difference in phenotype between males and females. Thus, in both sexes have the same phenotype in the F1 and the same splitting in the F2.
After recording signs parents can bring pictures of fish (if available).
2. Progeny of first generation is recorded as a F1.
In our case:
F1 red-black
Aa Bb
3. The second generation (hybrid F1xF1) is written as F2, etc. (F3, F4 ...).
Consequently, to draw the lattice Pinneta (see below), we obtain the following splitting of F2:
F2 AABB AABb AAbb AaBB AaBb Aabb aaBB aaBb aabb,
which is made 4 color-type tail
(AABB AABb AaBB AaBb) - red-black
(aaBB aaBb) - black tail
(AAbb Aabb) - red tail
aabb - blue (new phenotype)
genotypes in the ratio 4: 2: 2: 1 and phenotypes 9: 3: 3: 1.
Now, explain the option, when these genes are sex chromosomes - X and Y.
Record condition of the problem we need in another way:
PP black red tail x tail
XAXA Xa YB
Get
F1 XAXa (female) XAYB (males)
red-tail black black tail
In the F2 cleavage will be, respectively, as follows:
F2 (XAXA XAXa)
all females with a black tail
XAYB
males with red and black tail
[B] X [/ b] aYB
males with a red tail
When analyzing a crossover (crossover with the homozygous recessive form, which is the analyzer, since only one type of gamete with the recessive allele) - written Fa (analysis), back when (when crossing the progeny with one parent) - Fr (return).
