Embryo Lethal vs Gametophyte lethal I am having a difficulty understanding Gamet

Question

Embryo Lethal vs Gametophyte lethal I am having a difficulty understanding Gametophyte lethality. This is the paragraph in my genetics textbook. Please help me understand what Gametophyte lethality is and how it achieves a 1:1 ratio. Detection in Plants In flowering plants, the effects of lethal alleles can be observed directly. For example, mutation of the RPNla gene that encodes a subunit of the 26S proteosome, a multi-protein complex involved in protein degradation, is an example of a loss-of-function null mutation (rpnla) that results in embryonic lethality in Arabidopsis thaliana and other plant species. In an RPNIa/rpm la x RPNla/rpnla cross, a 3:1 segregation ratio of living seeds (RPNla) to dead seeds (rpn1a/rpnla) can be observed in the fruit. When the living seeds are planted, approximately two-thirds are heterozysous for the lethal allele (RPNla/rpnla) and one-third are homozygous for the wild-type allele (RPNI a/RPN1a) Lethal mutations that result in female gametophytic lethality are also detectable in flowering plants. Consider a plant heterozygous for a female gametophytic allele, FERfer, in which the wild-type FER allele was derived from its mother, and the mutant fer allele came from its father During megasporogenesis, half of all megaspores will inherit the FER allele and the other half will inherit the fer allele. Embryo sacs derived from megaspores inheriting the fer al lele will die, so that only half of all ovules develop into seeds. The alleles segregate in a 1:1 ratio that is observed among the developing seeds in a fruit. Note that the 1:1 ratio is a

Explanation / Answer

Gametophytic lethals are one of the complex factors that maintain the heterozygosity. The gametophytic lethal are lethal in homozygous state and produce only one kind of functional egg. The other egg is carrying the lethal allele and therefore dies. This give 1:1 ratio as only one egg is functional and the other is lethal.

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