Development Homework 2 is due 1017 Bonus 1

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 and relatedness Correlation of weight (BMI) Biological siblings Parents and children living together Identical twins reared apart Fraternal twins reared together Adopted children and parents Unrelated children living together % 34 26 80 72 43 4 1

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

Developmental mutants of Drosophila melanogaster Fig 12. 1

Vertebrate Development: from zygote to adult

Besides adding cells, development can involve cell death.

Development of a mouse paw: yellow areas show dying cells CB 21. 19

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)

Developmental information can be encoded by both genetic and non-genetic information. Fig 12. 2

What genetic mechanisms regulate/allow development?

All humans are female for the first nine weeks of development

All humans are female for the first nine weeks of development

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

Down’s Syndrome is caused by an extra chromosome 21. Too much information disrupts normal development.

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

Each whorl expresses a specific combination of three genes CB 21. 20

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