Development Homework #2 is due 10/17 Bonus #1 is due 10/24

So, Smoking during pregnancy may have indirect and/or direct affects on fetal development, and these affects may manifest themselves in adults.

Correlation of weight (BMI)% Biological siblings34 Parents and children living together26 Identical twins reared together80 Identical twins reared apart72 Fraternal twins reared together43 Adopted children and parents 4 Unrelated children living together 1 Correlation of weight and relatedness

Nature and Nurture: Are traits coded for by genes fixed while traits coded for by the environment are under our control?

Fig 12.1 Developmental mutants of Drosophila melanogaster

Vertebrate Development: from zygote to adult

Besides adding cells, development can involve cell death.

CB Development of a mouse paw: yellow areas show dying cells

Early embryo development

Totipotent: ability to differentiate into any cell-type

Totipotency is limited to early stages of animal development

Mature, differentiated plant cells are totipotent

Why do cells lose totipotency?

Gene expression can be controlled at many points between DNA and making the final proteins. Changes in the various steps of gene expression control when and how much of a product are produced.

Why change gene expression? Different cells need different components Responding to the environment Replacement of damaged/worn-out parts

DNA packaging fluctuates… genes being expressed are unpackaged, genes not needed are tightly packaged.

Normally DNA is loosely packaged During mitosis DNA is tightly packaged as chromosomes and individually visible box 2.1

DNA packaging fluctuates… Some of the tight packaging of DNA is irreversible.

Irreversible packaging of DNA partially explains the loss of totipotency.

Stem cells still have totipotency

Embryonic Stem Cells are totipotent Adult Stem Cells are pluripotent (only form some cell types)

Fig 12.2 Developmental information can be encoded by both genetic and non-genetic information.

What genetic mechanisms regulate/allow development?

All humans are female for the first nine weeks of development

Down’s Syndrome is caused by an extra chromosome 21.

Too much information disrupts normal development.

Flower parts: Complexity from a few simple genes 4 whorls of a flower

CB Each whorl expresses a specific combination of three genes

Changing expression of A, B, or C genes changes organ identity CB 21.20

Development Homework #2 is due 10/17 Bonus #1 is due 10/24