Many biological processes involved in growth, reproduction and dynamic homeostasis include temporal regulation and coordination.

2E

Temporal regulation• a type of regulation of gene expression in which a gene is only

expressed at a specific time in development; for example, genes that are only expressed in the light or during flower development

Cell differentiation• 1. Cell differentiation results from the expression of

genes for tissue-specific proteins, and the induction of transcription factors during development results in sequential gene expression. Cell differentiation also results from specific silencing of gene expression• Transcription factors are proteins that determine what genes are

turned on or off in the genome of an organism

• 2. Explain an example of specific silencing of gene expression• Homeotic genes determine developmental patterns and

sequences in organisms. A homeotic gene is one of a series of “master switch” genes that determine the form of segments developing in the embryo.

• Homeotic genes contain a sequence of DNA known as a homeobox, which encodes a segment of 60 amino acids within the homeotic transcription factor protein. If a mutation occurs in the homeobox of any of the homeotic genes, an organism will not develop correctly.

• For example, in fruit flies (Drosophila), mutation of a particular homeotic gene results in altered transcription, leading to the growth of legs on the head instead of antenna; this is known as the antennapedia mutation.

• 3. Genetic transplantation experiments support the link between • Gene expression• Mutations• Development of the organism

• Programmed cell death (apoptosis) plays a role in normal development and differentiation.

• 4. Give 2 examples of how plants respond to interactions• Photoperiodism and Phototropism

• Organisms respond to changes in their environment through behavioral and physiological mechanisms.

• • Photoperiodism and phototropism in plants • Define Photoperiodism

• Long-day plants• Short-day plants• Define Phototropism

• Photoperiodism - physiological reaction of organisms to the length of day or night. It occurs in plants and animals - amount of uninterrupted darkness is what determines the formation of flowers on most types of plants

• Phototropism - directional growth of organisms in response to light (plants and some fungi

• If the long night of late fall is artificially interrupted by a flash of light – the clover will bloom, not the cocklebur

9

FIG 41.6

• Coleoptile - A protective sheath enclosing the shoot tip and embryonic leaves of grasses

• 5. Give 2 examples of how animals respond to interactions– circadian rhythm– seasonal responses

• 6. List 3 animal behaviors triggered by environmental cues– Hibernation– Migration– Estivation (dormancy of an animal during hot or

extremely dry periods)

• 7. Photoperiodism occurs in plants due to changes in critical night length.

• 8. Cooperation and communication within or between populations contributes to the survival of individuals and the population.

Essential knowledge 2.E.1: Timing and coordination of specific events are necessary for the normal development of an organism, and these events are regulated by a variety of mechanisms.

Stems cells and Differentiation

• https://www.youtube.com/watch?v=rXVdSajL08E

• a. Observable cell differentiation results from the expression of genes for tissue specific proteins.

• b. Induction of transcription factors during development results in sequential gene expression

Read Induction can lead to cell differentiation on pg 377-378 and summarize

• Induction – change in cell fate due to interaction with an adjacent cell. Induction occurs when one cell type produces signal molecules that induce gene expression in neighboring target cells. – In frogs, cells from animal and vegetal poles do not

develop into mesoderm when isolated. • Blastomeres (one of the cells of the of a blastula)from one

pole (end) of the embryo(the “animal pole” or yolk-poor hemisphere) develop features of the ectoderm. Blastomeres from the opposite pole (“vegetal pole” or yolk-rich hemisphere) develop features of endoderm

• In tunicates, signaling of the growth factor FGF induces mesoderm development.

1. Homeotic genes are involved in developmental patterns and sequences

• Define Homeotic genes– one of a series of “master switch” genes that

determine the form of segments developing in the embryo.

2. Embryonic induction in development results in the correct timing of events

• Read Cells become determined prior to differentiation & tracking determination pg 375-376 and summarize– The process of determination commits a cell to a

particular developmental pathway prior to its differentiation. This is not visible, but can be tracked experimentally. Determination is due to differential inheritance of cytoplasmic factors or cell-to-cell interactions.

– Embryonic induction in development results in the correct timing of events

• 3. Temperature and the availability of water determine seed germination in most plants.

• What are the two factors that most commonly lead to seed germination? Correct temperature and the availability of water

4. Genetic mutations can result in abnormal development.

• Describe three ways that mutations in genes can lead to abnormal development– To function correctly, each cell depends on thousands of proteins to

do their jobs in the right places at the right times.– Sometimes, gene mutations prevent one or more of these proteins

from working properly. – By changing a gene’s instructions for making a protein, a mutation

can cause the protein to malfunction or to be missing entirely. – When a mutation alters a protein that plays a critical role in the

body, it can disrupt normal development or cause a medical condition.

– A condition caused by mutations in one or more genes is called a genetic disorder.

5. Genetic transplantation experiments support the link between gene expression and normal development.

• 6. Genetic regulation by microRNAs plays an important role in the development of organisms and the control of cellular functions

c. Programmed cell death (apoptosis) plays a role in the normal development and differentiation.

• Define apoptosis– the process of programmed cell death; used to

produce planned and orderly elimination of cells that are not destined to be present in the final tissue

• http://www.youtube.com/watch?v=fKyljukBE70

• http://www.youtube.com/watch?v=gaK0VPV9NlE

Read Programmed cell death is a necessary part of development and summarize

• Apoptosis, programmed death of cells, removes structures once they are no longer needed