Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
Reptiles and birds share a common ancestor that lived more than 250 million years ago. Even though a lizard and a robin look completely different as adults, their embryos reveal hidden similarities.
When scientists observe reptile and bird embryos under a microscope, both show small skin bumps called placodes that later form epidermal structures. In lizards, these placodes flatten into overlapping scales, while in birds they elongate and branch into feather filaments. This means that feathers and scales are homologous structures - they come from the same embryonic origin, but develop differently.
Modern research has shown that a few key genetic switches control whether placodes form feathers or scales. For example, genes like β-catenin, BMP2, and Sonic Hedgehog (SHH) are activated in similar patterns in both embryos, but at different intensities and times. By adjusting these signals, scientists can even cause chicken embryos to develop scale-like patches, or reptile embryos to form proto-feather structures - proving that both features share a developmental foundation.
These discoveries have major implications for understanding evolution. The fossil record shows that many theropod dinosaurs had feathery coverings, long before birds appeared. When combined with embryological data, these findings show that feathers are simply modified reptilian scales, reshaped through time and development.
By analyzing pictorial and microscopic data from embryonic skin development, students can see how small changes in early development lead to major evolutionary innovations - the difference between walking on land and taking flight.
Graph of Information - Figure 1.
Graph of Information - Figure 2.
Figure 3.
Figure 4.
Using Table 1, compare BMP2 activity and SHH expression between bird and reptile embryos. What pattern do you observe?
According to Table 2, which gene shows the largest difference in activity level between chicken and lizard embryos?
Explain why placodes in reptiles and birds are considered evidence of shared ancestry despite developing into different adult structures.
Using Table 2 and Figures 1–2, what does the consistent difference in gene activity levels suggest about how feathers and scales develop from similar embryonic origins?
Does the embryological and gene-expression data support the claim that feathers and scales are homologous structures?
Claim:
Evidence:
Reasoning:
Based on the reading, which statement best explains how feathers could evolve from reptilian scales?