Exam 2: #5 Developmental Genetics

Development Overview

Progressive growth of a fertilized egg into an adult organism involves four main types of cellular events:

1. Cell division: making more cells

2. Cell Migration: cells move around

3. Cell differentiation: making specialized cells

4. Cell death (apoptosis) - selective cell loss

Cell death

Important for establishing proper shape

• Maintain organ size and structure

• Remove damage cells

forward genetic screen

method used in gene discovery to identify which genes control a particular phenotype

Start with a normal population of organisms (like fruit flies, yeast, or plants).

1. Induce random mutations in their DNA — this can be done using chemicals, radiation, or insertional mutagenesis.

2. Look for individuals that show an abnormal phenotype — for example, a fly with defective wings or a plant that doesn’t grow properly.

3. Identify which gene is mutated in those abnormal individuals. This step often involves genetic mapping

Reversed genetics

the opposite of forward genetics — it starts with a known gene and studies what happens when that gene is altered or turned off to understand its function.

Gene localization

finding where a specific gene or its RNA is located either within a chromosome (for DNA) or inside a cell or tissue (for RNA).

In Situ Hybridization

a technique used to detect and visualize the location of a specific nucleic acid sequence (DNA or RNA) directly in the cells or tissues

Immunostaining

used to detect specific proteins in cells or tissues using antibodies

• uses antibodies that specifically bind to a target protein. These antibodies are linked to a visible marker (like a fluorescent dye or an enzyme), allowing scientists to see where the protein is located under a microscope.

Body Axis 

Body axis formation = how an embryo establishes its basic body plan

• Anterior–Posterior (A–P) Axis

  • head to tail

  • Maternal effect genes (in Drosophila):

    • Bicoid (anterior): promotes head structures.

    • Nanos (posterior): promotes tail structures.

  • Nurse cells: deliver maternal effect gene products (like bicoid)

Segmentation

• Embryo forms distinct grooves

• Each segment has unique identity and cell fates

Regional Identity

• Regional positional identity driven by morphogen gradients and homeotic genes.

• Homeotic genes: specify the final identity or cell fate of a body region

• Morphogens: proteins that regulate development fate

  • Functions in concentration dependent manner

  • Form gradients between secreting cells and receiving cells

  • Each cell gets different relative combo of morphogen, leads to stripe or spot patterns

Homeotic Genes

Encode transcription factors 

• Homeobox: conserved DNA sequence, binds DNA to regulate gene expression

  • Arrange co-linearly on chromosome in same order as the body regions they control along anterior to posterior

  • Homeotic genes (HOX genes) in vertebrates, 4 clusters in mice

homeotic transformation

when one body part develops into the structure of another due to a mutation in a homeotic (Hox) gene

morphogens

Molecules that convey positional information and promote developmental changes