Crossing Over, Gene Recombination

Crossing over, as related to genetics and genomics, refers to the exchange of DNA between paired homologous chromosomes (one from each parent) that occurs during the development of egg and sperm cells (meiosis). This process results in new combinations of alleles in the gametes (egg or sperm) formed, which ensures genomic variation in any offspring produced. Crossing Over. Crossing over is a cellular process that happens during meiosis when chromosomes of the same type are lined up. When two chromosomes — one from the mother and one from the father — line up, parts of the chromosome can be switched. The two chromosomes contain the same genes, but may have different forms of the genes. The mother’s form of a gene, let’s say, could be moved to the father’s chromosome, and vice versa. This is a very interesting and important biological activity; different combinations of different gene forms are then potentially passed down to offspring. This genetic variation helps to increase the diversity of a species. And diversity strengthens a species’ ability to respond to changing environments over time, and therefore evolve. Problem: The following is a hypothetical pathway involved in formation of eye color in an insect species. White pigment is converted by product of gene A to vermilion pigment. White pigment is converted by product of gene B to brown pigment. Mix of both vermilion and brown pigments lead to red eye color. Genes A and B are linked and have a map distance of 10 cM. Females with the genotype a a b b are test crossed. Further in these females the two genes are linked in cis. a and b represent wild type alleles, while a and b are null alleles. The progeny of the test cross have individuals with four different eye colors. What is the expected ratio of individuals with eye color red, vermilion, brown and white in the progeny? A) 9:3:3:1 b) 1:1:1:1 c) 9:1:1:9 d) 1:9:9:1 #Genetics #MapUnit #SentiMorgan #crossingover #crossingOver #synapsis #linkedGenes #geneticRecombination #crossingOverInMeiosisI #crossingOverOfChromosomes #homologousChromosomes #nonsisterChromatids #sisterChromatids #MendelianGenetics #ChromosomalCrossover #Genes #FRUITFLYGENETICS #vestigialWings #normalWings #geneticsInFruitFlies #NikolaysGeneticsLessons #ThomasHuntMorgan #fruitFlies #meiosis #recombinantChromosomes #AlfredSturtevant