4 Development

growth

growth

depends on: cell size, cell division, apoptosis; proportions change during developmentc

maternal loading

cell development; the mother loads regulatory factors asymmetrically into the egg

asymmetric cell division

cell development; regulatory factors are localized to one side before cell division

cell-cell signaling

cell development; cells induce each other to turn On/Off genes

cells

have to be born different from each other or they have to be induced to develop differently

observations

find it, move it, lose it: determine the sequence of events

• Dyes: follow cell movements, cell lineages

• Antibodies: track expression patterns

• In situ hybridizations: track expression patterns

loss-of-function

find it, move it, lose it: determine necessity of factors

• Mutants or specific inhibitors of gene expression

• Specific inhibitors of protein activity

• Destruction of a portion of embryo

gain-of-function

find it, move it, lose it: determine sufficiency of factors

• Hypermorphs/overexpression

• Transplantations

gene replacement/gene addition

we can

• Modify the germ cells to generate transgenic offspring

• Modify a patient’s stem cells in the lab and reintroduce them

• Infect the patient with a virus that will genetically modify specific populations of cells in the body.

genetic engineering

methods:

1. Restriction enzymes and ligation:

   1. Enzymes isolated from various strains of bacteria cut DNA at specific sequences.  Ligase will paste sequences together.

2. Gibson cloning:

   1. PCR can be used to generate overlapping fragments of DNA that can be joined seamlessly together.

3. CRISPR:

   1. A system adapted from bacteria can easily be adapted to cut any DNA sequence in a genome.

transgenics

methods:

1. Plasmid vectors:

   1. We can introduce DNA into small, stable circles that bacteria will copy

2. Viral vectors:

   1. We can introduce DNA into genomes of viruses that can be used to infect host cells.

3. Homologous recombination:

   1. We can introduce DNA into host cell chromosomes at specific sites.

4. CRISPR:

   1. We can introduce DNA into host cell chromosomes at specific sites via copying from a template.

DNA

when inserted into the genome:

1. It can function unpredictably in new context nearby regulatory sequences fusion with other genes

2. It can interrupt important genes

3. It can turn neighboring genes ON or OFF.

germ line gene therapy

treatment not just for the patient, but all future generations

• Method 1: genetically modify a germ cell or fertilized egg

• Method 2: modify ES cells and create a chimera that is comprised of modified-genome cells

stem cells

cells that never terminally differentiate: they do not fully specialize and they continue to divide

embryonic stem cells/es cells

stem cells that are pluripotent: they can form any tissue except placenta

therapeutic human cloning

1. Remove the nucleus from an egg and replace it with the nucleus of any somatic cell from the patient. The egg now has two copies of every gene.

2. Scientists  “activate” the egg to induce embryonic development. The embryo is harvested to produce ES cells that are genetically identical to the patient. These cells can be used to produce cells and tissues the patient needs.

• One problem: if the patient had a genetic disease, so will the ES cells that were cloned from the patient. Genetic engineering of the ES cells is necessary in these cases.

reproductive human cloning

• Identical twins are clones of each other.

• To clone an adult, remove the nucleus from a donor egg and replace it with the nucleus of a cell from the person you want to clone. Activate the egg to induce development. At the blastocyst stage, implant the embryo in a surrogate’s uterus.

hermaphrodites

organisms in which both gonads appear

pseudohermaphrodites

organisms in which the sex of the gonad does not correlate with the external phenotype

sry

determines sex in mammals

• sex-determining region of the Y; found by examining Y-deletions and translocations

quickening

when the mother first detects the movements of the fetus. For many people, this is an important milestone in the pregnancy. It often occurs in the fifth month of pregnancy.

viability

when, if a fetus were born, it could survive. This is an important criterion in interpreting Roe v. Wade. Medical improvements have pushed viability (though not likelihood of healthy outcomes) as far back as 20-21 weeks post-fertilization. Lung development is generally not complete until the end of pregnancy.