Lecture 23 Evolution And Development

Question 1

Two perspectives on developmental evolution

Answer 1

Phenotypic
genetic

Question 2

Phenotypic

Answer 2

Adult morphs seen as modifications of timing, rates, and fates of development (quantitative genetics)

Question 3

Genetic

Answer 3

Reductionist approach, identifying genes responsible for development, led to rethinking homology concepts (population genetics)

Question 4

Phenotypic examples (3)

Answer 4

Allometry
Isometry
Heterochrony

Question 5

Allometry

Answer 5

Change in the relative growth of morphological structures, e.g., neoteny, acceleration

Question 6

Isometry

Answer 6

Uniform growth, no changes in shape (rate is the same through growth)

Question 7

Heterochrony

Answer 7

Changes in relative timing of developmental events

Question 8

Mode of developmental changes (2)

Answer 8

Paedomorphosis
Peramorphosis

Question 9

Paedomorphosis

Answer 9

Gonads mature quickly and a sexually reproductive “juvenile” is produced
Adult looks like juvenile of common ancestor

Question 10

Progenesis

Answer 10

(early development), truncation of ancestral growth period leads to retention of juvenile characters

Question 11

neoteny

Answer 11

(slowed development, allometric decrease) reduced rate of development leads to retention of juvenile characters

Question 12

Paedomorphosis (2)

Answer 12

Progenesis
Neoteny

Question 13

Peramorphosis

Answer 13

An additional stage is added to the end of developmental sequence (Terminal Addition). A former adult form now becomes a juvenile stage.
Juvenile descendants look like adult of ancestor

Question 14

Hypermorphosis

Answer 14

(extended development), extensions of ancestral growth period leads to exaggerated adult characters

Question 15

Acceleration

Answer 15

(allometric increase), increased rate of development leads to exaggerated adult characters

Question 16

Peramorphosis (2)

Answer 16

Hypermorphosis
Acceleration

Question 17

Genetic (2)

Answer 17

Homeotic genes and development

Question 18

Home/Hox genes code for

Answer 18

Transcription factors
Regulatory genes that provide positional information

Question 19

Hox genes are

Answer 19

Clustered together on chromosomes and their arrangement is highly conserved among animals phyla

Question 20

Deep homology

Answer 20

Where growth and differentiation are controlled by regulatory genes that are homologous and deeply conserved across a wide range of species even if the subsequent organization and function of those structures is not homologous

Question 21

Examples of Deep homology “Segmentation/vertebral identity”

Answer 21

Scr, Antp, Ubx expression in arthropods determines main body part boundaries
Hox expression in mice determines number of vertebrae

Question 22

Example deep homology limbs

Answer 22

“sticky-outeys”
How limbs are made is conserved

Question 23

Deep homology example eyes

Answer 23

Pax-6, Mammalian gene Pax-6 and the Drosophila gene eyeless are homologous, and both are expressed in developing eyes, despite the fact that the eyes are so different in construction

Question 24

Pax-6

Answer 24

Can induce eye formation in Drosophila, even on other segments and structures (make eyes)
This a “basic” eye (simple photoreceptor) may have evolved only once, but once that initial structure evolved, improvements in function occurred repeatedly