Question

Maternal effect genes are a special class of genes that have their effect in the reproductive organs of the mutant. They are interesting because the mutant organism may appear phenotypically normal, and it is the progeny that express detectable differences, and they do so whether the progeny have inherited the mutant gene or not. The first maternal effect gene identified was the gene controlling shell coiling in the water snail Lymnaea peregra. Alleles of this maternal effect gene are non-lethal and have a dominant recessive relationship. The dominant allele D results in a right-handed coiling pattern called dextral and the recessive allele d results in a left-handed pattern called sinistral.

1. A cross was made between male dextral and female sinistral snails. All of the progeny of the sinistral snails were found to have dextral coiling. List all possible genotypes of the sinistral parent of the cross? (2 pts)

                                   

Snails are hermaphroditic animals that possess both male and female reproductive organs. Assume that the progeny of the sinistral snail described in the previous question produced offspring without mating. Assume further that 50% of this progeny was dextral and 50% was sinistral.

2. Based on the information provided, what are the correct genotypes of the dextral and sinistral parents described in the previous question? (2 pts)

Genotype of dextral parent:

Genotype of sinistral parent:

Use the information below to answer questions 3 – 4.

Maternal effect genes have now been identified in several species including humans. Many of these genes are functional during embryogenesis where they are required for axial positioning. Female animals bearing mutations in maternal effect genes required for axial positioning are usually sterile.

The encroachment of human populations into the South American rain forests has revealed many formerly unknown species. A geneticist discovered a maternal effect gene in a new species of fly which controls the formation of head and thorax segmental development. The progeny of female flies bearing at least one copy of the dominant allele m⁺ were found to develop normally. However, the allele m had a lethal penetrance of 28%. In a mating experiment performed by the geneticist a female fly with the genotype mm was mated with a male fly with the genotype m⁺m. Assume that after mating the female laid 408 eggs.

3. How many eggs are expected to produce viable offspring? All calculations must be shown to receive full points. (2 pts)

     

4. How many of the progeny can be expected to be females with the genotype mm? (5 pts)

Answer 1

this is due to maternal affect

The f1 progeny genotype is Dd but its phenotype is sinistral because mother phenotype is also sinistral this is due to maternal effect