genetics - clutch ch.14 genetic control of...

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GENETICS - CLUTCH

CH.14 GENETIC CONTROL OF DEVELOPMENT

CONCEPT: STUDYING THE GENETICS OF DEVELOPMENT

● Scientists use many different ______________________- to study development □ Developmental research focuses on four main questions

- What genes control development, and at what point in development are they expressed?

- Where are these genes expressed?

- How are these genes regulated?

- What happens if these genes are defective?

□ Scientists use many different model organisms to study development

- These include: yeast, plants, fruit flies (drosophilia) worms (C. elegans) and mice

- These organisms are chosen because they grow easily, rapidly reproduce, and are genetically similar

EXAMPLE:

● Development begins with a zygote, which is a _______________________ egg □ This cell is totipotent, which means it can develop into any cell type

□ Determination is the process through which a cell becomes committed to its fate (cell type, death, etc…)

- Mosaic determination is when each cell in an organism has a pre-determined fate (C. elegans)

- Regulative determination is when cells can regulate their fates according to their environment (humans)

□ Variable gene activity hypothesis states that determination is controlled through activating/inactivating genes

- Gene activation/inactivation occurs at different times and in different cell types

GENETICS - CLUTCH


EXAMPLE:

PRACTICE:

1. During early development, human cells determine their differentiated fates based on the environment. What term describes this phenomenon?

a. Totipotent b. Mosaic determination c. Regulative determination d. Variable gene hypothesis

Two Embryonic Cells

One is destroyed

Mosaic Development

Regulative Development

Normal DevelopmentAbnormal Devleopment

GENETICS - CLUTCH


2. True or False: The variable gene activity hypothesis states that cell differentiation and determination is controlled through differences in gene activation or inactivation.

a. True b. False

3. If an embryonic cell is damaged in an organism that undergoes mosaic determination, will the offspring produced develop normally or abnormally?

a. Normal development b. Abnormal development

GENETICS - CLUTCH


CONCEPT: DEVELOPMENTAL PATTERNING GENES

● The first __________________ to development is to determine the front, back, top, and bottom of an organism □ The anterior (front/head) and posterior (back) are determined first

□ The dorsal (top) and ventral (bottom) are determined second

□ Many different genes determine the positioning (patterning) of these locations

- Maternal effect genes are maternal genes found within the egg. These genes are active first

- Zygotic genes are the embryo’s genes that control later development

EXAMPLE:

● Segmentation genes control the development of specific ____________________ of an organism □ Maternal effect genes control development first

-Highter bicoid concentrations form anterior

- Higher nanos concentrations form posterior

□ Gap genes are zygotic genes that divide the embryo into body segments (ex: giant, krüppel)

□ Pair-rule genes are zygotic genes that result in pairs of segments (ex: even-skipped)

□ Segment-polarity genes determine the anterior/posterior location in each segment (ex: wingless)

□ The concentration of each gene, activates the next set of genes

- Bicoid concentration activates gap. Gap activates pair-rule, and pair-rule activates segment-polarity

GENETICS - CLUTCH


EXAMPLE:

● Homeotic genes (HOX) controls organ development in each previously _____________________ segment □ These genes contain a homeobox of 180bp with homeodomain that binds DNA (helix-turn-helix)

- Allows for HOX genes to act as transcription factors

□ In Drosophilia there are two clusters of HOX genes

- Antennapedia (ANT-C) has five genes which control head and anterior thorax development

- Bithorax (BX-C) has three genes for posterior thorax and abdominal development

□ HOX genes are extremely well conserved

- Some animals have more HOX gene clusters than fruit flies (ex: mice have four)

EXAMPLE:

GENETICS - CLUTCH


Plant Development

● Plants contain their own __________________________ of homeotic genes □ In Arabidopsis there are three classes of HOX genes called Class A,B,and C

- Class A forms the sepals

- Class A and B form the petals

- Class B and C form the stamen

- Class C form the carpels

EXAMPLE:

GENETICS - CLUTCH


PRACTICE:

1. Which genes are the first genes that control patterning of the offspring during early development? a. Anterior genes b. Maternal effect genes c. Zygotic genes d. Dorsal genes

2. Areas with higher bicoid expression will develop into which body pattern? a. Anterior b. Posterior c. Dorsal d. Ventral

GENETICS - CLUTCH


3. Activation of the segmentation genes occurs in which of the following orders? a. Maternal effect à gap à segment polarity à pair rule b. Gap à maternal effect à pair rule à segment polarity c. Maternal effect à gap à pair rule à segment polarity d. Segment polarity à pair rule à gap à maternal effect

4. Which of the following HOX clusters are responsible for forming the abdominal in Drosophila development? a. Segment polarity b. Antennapedia c. Bithorax d. Pair rule

GENETICS - CLUTCH


5. In Arabidopsis, which class of HOX genes are responsible for forming the plant carpels? a. Class A b. Class B c. Class C d. Class B and C

GENETICS - CLUTCH


CONCEPT: EARLY DEVELOPMENTAL STEPS

● Fertilization is the ______________________ step of development 1. In fruit flies, after fertilization there are 13 nuclear divisions that occur without cell division

- 9th division: Nuclei begin to migrate to one side of the embryo

- 10th division: Nuclei at posterior pole are enclosed in membranes – become primordial germ cells

2. During interphase of the 14th division the blastoderm layer of embryonic tissue is created

- The blastoderm is one cell deep and forms ~3 hours after fertilization

3. Gastrulation begins, which forms the three major germ layers

- Endoderm: Will form the lining of the gut

- Mesoderm: Will form inner tissues, like blood cells, muscles, etc…

- Ectoderm: Will form the outer layer of the organism (skin, nervous system, teeth)

4. Segmentation begins after ____________________________

- Anterior-posterior formation and HOX genes

EXAMPLE:

bicoid

nanos

Blasoderm

PrimordialGerm Cells

GENETICS - CLUTCH


Cell-Cell Interactions

● Proper development is entirely dependent on cells ___________________ to signals from other cells or their environment □ During very early development, different cellular regions must respond differently to the same molecule

- If the egg itself is asymmetric, then different egg regions promote development differently

- Ex: Drosophila eggs have nurse cells, which express bicoid, only at the anterior end

- If the egg is symmetric, then fertilization via sperm controls asymmetry

- Ex: C. elegans determine anterior/posterior based on the side the sperm enters the egg

EXAMPLE:

□ During later development, cells must be able to respond to different ___________________

- Juxtracrine signaling is when a ligand attached to one cell can bind a receptor on another cell

- Paracrin signaling is when the ligand from one cell is secreted, and then binds receptor on another cell

□ Often, a ligand binding to a receptor initiates a cell signaling cascade

Asymmetric Egg Symmetric Egg

DeterminesAsymmetry

DeterminesAsymmetry

GENETICS - CLUTCH


EXAMPLE: Notch Signaling Pathway

PRACTICE:

1. Which of the following is not a germ layer formed during gastrulation? a. Endoderm b. Mesoderm c. Exoderm d. Ectoderm

GENETICS - CLUTCH


2. Which of the following characteristics describes the blastoderm embryonic tissue? a. Contains 13 cells b. Is one cell layer deep c. Will develop into primordial germ cells d. Forms outer later of the organism

3. True or False: Gastrulation occurs after segmentation a. True b. False

GENETICS - CLUTCH


4. True or False: Patterning of asymmetric eggs is first controlled through contact with sperm. a. True b. False

GENETICS - CLUTCH


genetics - clutch ch.14 genetic control of...

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