Question
Topic – 7.4 Population Genetics
(a) – Topic – 7.4 Population Genetics
(b) – Topic – 4.5 Cell Cycle
(c) – Topic – 7.9 Phylogeny
(d) – Topic – 8.7 Disruptions in Ecosystems
Researchers study mechanisms that enable or prevent speciation.
(a) Describe a post-zygotic mechanism that prevents gene flow and thus enables speciation.
New genes can evolve from noncoding regions of DNA. It is not until certain regulatory elements are present in the DNA that a noncoding region becomes a new, functional gene that encodes a protein. These regulatory elements include a promoter, a 5′ untranslated region (UTR) followed by a start codon, and a 3′ UTR following a stop codon (Figure 1).
Researchers studied the evolution of the family of antifreeze-glycoprotein (AG) encoding genes in Gadidae, a family of marine fish known as cods. When present in the fish, these glycoproteins reduce the freezing temperature of the fish. The researchers compared genomic sequences in nine cod species and one non-cod fish species, B. brosme. They recorded the presence or absence of the elements of functional ag genes as well as ag-like sequences that are similar to a functional gene but have undergone mutation and do not contain all the elements required to enable protein production (Figure 2).
(b) Based on the data in Figure 2, explain how changes to the genome enabled cods to survive and reproduce after a period of freezing temperatures between 10 and 15 million years ago.
(c) Using the template in the space provided for your response, place an “X” on the phylogenetic tree to represent the origin of the functional ag gene.
(d) Based on Figure 2, explain how genetic differences among the species in the Gadidae family determine the habitats in which they can survive.
▶️Answer/Explanation
5(a) Describe a post-zygotic mechanism that prevents gene flow and thus enables speciation.
• The offspring do not survive (long enough to reproduce)/cannot (successfully) reproduce.
5(b) Based on the data in Figure 2, explain how changes to the genome enabled cods to survive and reproduce after a period of freezing temperatures between 10 and 15 million years ago.
• (Over time) the addition of the promoter/ag repeat sequences/ 3′ UTR/regulatory elements led to emergence of new genes/ag genes/functional gene products (that prevent freezing).
5(c) Using the template in the space provided for your response, place an “X” on the phylogenetic tree to represent the origin of the functional ag gene.
• An X is placed anywhere along the colored L-shaped line in the figure.
5(d) Based on Figure 2, explain how genetic differences among the species in the Gadidae family determine the habitats in which they can survive.
• Species with the functional ag gene/antifreeze glycoprotein are able to live in colder water/lower temperatures (than are species without the functional gene).