Single-gene inheritance - Some genes discovered by observing segregation ratios

7 important questions on Single-gene inheritance - Some genes discovered by observing segregation ratios

What is one general aim of genetic analysis today?

To dissect a biological property by discovering the set of single genes that affect it.

Mutant alleles can be either dominant or recessive, depending on their action; so the question of dominance needs to be considered in the analysis. What is the standard procedure?

To cross the mutant with wild type.

Type of grid showing gametes and gametic fusions.

A Punnett square
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1:1 ratio
The ratio is the same within males and females, within the bounds of sampling error. From these results, the “short wings” mutant was very likely produced by a dominant mutation. Note that, for a dominant mutation to be expressed, only a single “dose” of mutant allele is necessary; so, in most cases,when the mutant first shows up in the population, it will be in the heterozygous/homozygous state.

Heterozygous

Are dominant mutations represented by uppercase letters or words?

Yes

Sometimes, the severity of a mutant phenotype renders the organism sterile, unable to go through the sexual cycle. How can the single-gene inheritance of sterile mutants be demonstrated?

In a diploid organism, a sterile recessive mutant can be propagated as a heterozygote and then the heterozygote can be selfed to produce the expected 25 percent homozygous recessive mutants for study. A sterile dominant mutant is a genetic dead end and cannot be propagated sexually, but, in plants and fungi, such a mutant can be easily propagated asexually.

What if a cross between a mutant and a wild type does not produce a 3 :1 or a 1:1 ratio, but some other ratio?

Such a result can be due to the interactions of several genes or to an environmental effect.

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