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ceruleanbat2Lv1

28 Sep 2019

1. The vertebral column typical of snakes is very similar tothat in most fishes. The fish vertrebral column would be consideredancestral to that of the snake but that found in snakes issecondary derived. Characterize the vertebral columns in both ofthese groups and explain what is meant by a secondarily derivedcharacteristic.

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Patrina SchowalterLv2

28 Sep 2019

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[Animal Biology]

Part A. The coral snake and the king snake have similar coloration, but the coral snake is venomous whereas the king snake is not. Assume that the ancestors of the king snakes had a simpler color pattern that did not resemble that of the coral snake. Explain how the king snake may evolved to resemble the coral snake via natural selection. In your answer be sure to discuss all of the points describing evolution by natural selection.

Part B. Imagine you are developmental biologist interested in the evolution of giraffe necks. How would you approach this challenge, what would you expect to find with respect to how the giraffe got its neck at the genetic level?

magentaplatypus975

1. Consider the following eight statements about vertebrae. Which four of the following eight statements are TRUE? Choose all four correct answers.

(a) In Actinopterygii, Chondrichthyes, and some Amphibia (and one unusual taxon of Lepidosauria), the vertebrae have centra which surround the notochord.

(b) Some vertebrae have processes such as spines that function as sites for muscle attachment.

(d) In tetrapods, the vertebrae have processes called zygapophyses that function as specialized sites for articulation with the ribs.

(e) Vertebrae arise from sclerotome epimere mesoderm.

(f) All extant vertebrate taxa have vertebrae.

(g) Some vertebrae have hemal arches which protect blood vessels (such as the dorsal aorta).

(h) Vertebrae have neural arches which protect the notochord.

2. While walking through the halls of the Biosciences building, you find a single vertebra lying on the floor. You notice that it does not have zygapophyses. It has an amphicoelous centrum, and it has both a neural arch and a hemal arch. This vertebra is completely ossified. Identify to which vertebrate taxon this vertebra belongs, and to which region of the vertebral column.

(a) caudal region - Petromyzontida

(b) thoracic region - Aves

(d) trunk region - Actinopterygii

(e) caudal region - Actinopterygii

(f) caudal region - Amphibia

(g) caudal region - Chondrichthyes

3. You are doing a study on the diet of polar bears. While examining the scat (droppings) of a large polar bear, you find a single vertebrae. You need to identify this vertebra to determine what this polar bear has been eating. Polar bears are known to eat mammals, birds, and some fish (Actinopterygii). This vertebra has a heterocoelous centra and it has no articulation sites for ribs. It also has an odontoid process. To which of these three vertebrate taxa, and to which region of the vertebral column does this vertebra belong?

(a) synsacral region - Aves

(b) cervical region - Mammalia

(d) cervical region - Aves

(e) caudal region - Actinopterygii

(f) thoracic region - Mammalia

4. Which four of the following eight statements about the skeleton are TRUE? (Choose all four correct options.)

(a) Bone is a tissue that is able to withstand large tensile forces but not large compressive forces.

(b) An important role of the vertebral column in actinopterygii and chondrichthyes is to support the body weight.

(c) in amniotes, the ribs consist of two parts, a costal rib (which articulates with a thoracic vertebra) and a sternal rib (which articulates with the sternum). The mobile joints between the costal and sternal rib, as well as between the costal rib and the vertebra and between the sternal rib and the sternum, make the ribcage flexible such that it can expand during breathing.

(d) A vertebral column with procoelous centra would have a greater range of mobility than a vertebral column with acoelous centra.

(e) In all extant vertebrate taxa, the vertebral column provides axial structural support, as well as support for locomotion.

(f) In many mammals, ligaments and muscles attaching to the neural spines of vertebrae help to stabilize the vertebral column and pull it into a stable arch, which helps to efficiently bridge the body weight to the legs.

(g) In tetrapods, the pectoral girdle is firmly fused to the vertebral column to allow for efficient transfer of locomotive forces from the forelimbs to the axial skeleton.

(h) In chondrichthyes, actinopterygii, sarcopterygii, and some tetrapods, the vertebral column acts as a firm but flexible rod on which muscles pull to produce lateral undulations of the body for locomotion.

5. Consider the following eight statements about the form and function of the appendicular skeleton. Which four of the following eight statements are TRUE? (Choose all four correct options.)

(a) In sharks (Chondrichthyes), the pectoral and pelvic fins are mainly used for propulsion - to propel the body forward through the water.

(b) The tips of fins are supported by fin rays, thin rods which support a webbing of skin (and sometimes also connective tissue) - this increases the surface area of the fin

(c) The fleshy fins of sarcopterygii are not very maneuverable, and are used only to stabilize the body by preventing roll, pitch, and yaw when swimming rapidly.

(d) In both actinopterygii and chondrichthyes, the pectoral girdle attaches directly to the back of the skull while the pelvic girdle is embedded in the muscle of the body wall.

(e) In both sharks (Chondrichthyes) and actinopterygii, the pectoral and pelvic fins provide stability while swimming by preventing roll, pitch, and yaw.

(f) In male chondrichthyes, the pelvic fins have special extensions called claspers that are used to transfer sperm to females during copulation for internal fertilization.

(g) Petromyzontida and myxinoidea have paired pectoral and pelvic fins that are used to provide stability while swimming, as well as for steering.

(h) The main functions of girdles are to provide attachment sites for the muscles of the appendages (paired fins or limbs) and to stabilize the appendages.

6. Consider the following statements related to the appendicular skeleton and terrestrial locomotion of tetrapods. Which three of the following six statements are CORRECT? (Choose all three correct options.)

(a) In tetrapods with erect limb posture, the limbs are positioned directly under the body, while in tetrapods with sprawled limb posture, the limbs are positioned to the sides of the body.

(b) In terrestrial tetrapods, the distal ends of the humerus and femur are rotated such that the digits are oriented in line with the direction of travel, increasing both tractive and propulsive forces during terrestrial locomotion.

(c) Tetrapods with digitigrade foot posture have relatively longer limbs than tetrapods with plantigrade foot posture, such that they have a greater stride length.

(d) When terrestrial tetrapods are walking or running, the recovery stroke of the limbs involves the limb touching the ground while the propulsive stroke of the limbs involves the limb being lifted and moving from posterior to anterior.

(e) In tetrapods with sprawled limb posture, the dorsal elements of the pectoral girdle (such as the scapula) are much larger than the ventral elements of the pectoral girdle (such as the clavicle and corocoid).

(f) When walking or running, tetrapods with erect limb posture use an overarm swing for the recovery stroke, which is relatively slow.

7. You are walking along the beach and find a skeleton in the sand. You notice that the pelvic girdle is not fused to the vertebral column while the pectoral girdle is fused to the skull. The distal ends of the appendages have fin rays. It appears that all muscles controlling the appendages were located within the body wall, not within the appendages. To which vertebrate taxon does this skeleton belong?

(a) Sarcopterygii

(b) Lepidosauria

(d) Amphibia

(e) Actinopterygii

(f) Petromyzontida

8. Your neighbour finds a skeleton while cleaning out the pond in her backyard, and she asks you to identify it. You notice that the vertebrae have zygapophyses and that the centra of the vertebrae are procoelous. The ribs are quite short, and articulate with the vertebrae but not with the sternum. The pelvic and pectoral girdles appear robust and highly ossified, and the pectoral girdle has enlarged ventral elements but relatively small dorsal elements. The appendages each have five digits. Identify this skeleton for your neighbour, and describe to her as much as you can about its style of locomotion, based on this information about its axial and appendicular skeleton. (Choose all three correct options.)

(a) This skeleton is most likely from an amphibian.

(b) This skeleton is most likely from a sarcopterygian.

(d) This animal most likely had sprawled limb posture.

(e) This animal most likely could not support its own body weight using its appendages, and so would not have been capable of terrestrial locomotion.

(f) This animal probably walked with lateral undulations of the body, using the feet as pivot points.

(g) This animal most likely walked with a recovery stroke that used an energetically efficient pendulum-like swing.

(h) This skeleton is most likely from a crocodilian (Archosauria).

Can you tell me what the purpose and hypothesis of this article is please? Its obviously somewhere in the first 2 short paragraphs, but I cant REFINE the purpose. And as for the hypothesis, I know the question they are trying to solve, but im missing where they hypothesized what the outcome would be. Thank you in advance.

Article: Progressive Loss of Function in a Limb Enhancer during Snake Evolution

Distant-acting transcriptional enhancers are a major class of tissue-specific regulatory DNA sequences that has been implicated in morphological evolution in vertebrates. Sequence changes in non-coding regulatory DNA are hypothesized to be a main driver of changes in body shape), but many aspects of this complex inter- play between molecular changes in regulatory sequences and morphological adaptations across the vertebrate tree remain the subject of considerable debate.

In the present study, we utilized a series of recently sequenced snake genomes to study the molecular and functional evolution of a critical limb enhancer in snakes and examine its possible role in limb loss. Our analysis focuses on one of the best-studied verte- brate enhancers, the Zone of Polarizing Activity [ZPA] Regulatory Sequence (ZRS, also known as MFCS1). The ZRS is a limb-specific enhancer of the Sonic hedge- hog (Shh) gene that is located at the extreme distance of nearly one million base pairs from its target promoter. During limb devel- opment, the enhancer is active in the posterior limb bud mesen- chyme, where its activity is critically required for normal limb development in mouse. Single- nucleotide mutations within the ZRS cause limb malformations, such as preaxial polydactyly, in multiple vertebrate species including humans. Surprisingly, we observed that the sequence of this limb enhancer is conserved throughout nearly all examined species in the snake lineage. In basal snakes, which retain vestigial limbs, it is highly conserved, whereas it un- derwent a rapid increase in substitution rate in advanced snakes, in which all skeletal limb structures have disappeared. Consistent with this, we provide evidence that the snake enhancer progres- sively lost its in vivo function as the body plan evolved from basal to advanced snakes. Finally, we identify a specific subset of nucleotide changes within the enhancer that contribute to its functional degeneration in snakes and show in a mouse model that synthetic reintroduction of just one degraded transcription factor binding site is sufficient to recreate the ancestral function and to rescue normal limb formation in vivo.

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