1. Anamika Datta #MNS-12376005 MS in Biotechnology Summer-2012 BRAC University

2. Dr. M. Mahboob Hossain Associate Professor Department of Mathematics and Natural Sciences BRAC University Dhaka

3. Are Identical Twins always remain same?

4. Scientists have long appreciated the role that environmental factors play in the production of traits in organisms. Environmental factors such as diet, temperature, oxygen levels, humidity, light cycles, and the presence of mutagens can all impact which of an organism's genes are expressed, which ultimately affects the organism's phenotype. For this reason, scientists who study the genetics of model organisms usually seek to minimize environmental influence by maintaining constant environmental conditions for the organisms under study. Nevertheless, even genetically identical organisms exposed to controlled experimental conditions can have different phenotypes, pointing to the power of subtle environmental differences on gene expression.

5. Epigenetics is the study of environmental factors on gene expression in DNA. The variation in phenotype is the result of both genotype – actually the alleles of many genes – and the effects of the environment. Phenotype = Genotype + Environment (i.e. nature and nurture)

6. PROCARYOTES: There are 2 mechanisms by which microorganisms regulate gene expression in response to change in the environment, these are: 1.Mechanisms that involve the rapid “turn on” and “turn off” of gene expression in response to environmental changes. 2. Mechanisms referred to as preprogramed circuits or cascades of gene expression.

8. Eukaryotes: Thousands of genes that are present in the genomes of multicellular eukaryotes are normally expressed in a controlled fashion. Different genes are expressed at different times; some in response to biological signals(i.e. hormones) and others in response to environmental stimuli (i.e. temperature or light).

10. The basic developmental effect of many genes is to control the rate of a specific reaction, a change in temperature can be expected to have widespread effect on development. Transcription of Drosophila hsp70 gene by heat shock:  In temperature below 33 °C, The transcription of hsp70 gene is not occurred.  When temperature exceeds 33 °C, Transcription of hsp70 gene mediated by HSTF, which binds to HSEs.

12. We will look at four examples of the influence of the environment and genotype on phenotype:  Human height  Skin colour  Sex Determination  Cancer

13.  Average human height has risen each generation over the past 150 years.  People in the UK are now on average about 8 cm taller than they were in 1850.  Average heights:

14. Tallness partly determined by Genotype;  Taller men may have more children  Taller people may attract taller people as partners  Children more likely to inherit genes for tallness from two tall parents so more likely than normal to be tall  Tall parents may be more fertile and so have more children So, Genotype determines a potential maximum height

15. Tallness also partly determined by the influence of the Environment  Improved health: More body resources available for growth rather than fighting disease  Better nutrition: More food available, quality of food better so more protein for more growth, calcium and vitamin D, essential for bone growth – probably the most significant factor to enable the full genetic potential (as determined by genotype) to be reached.  Better heating of houses/ better quality and warmer clothing so less energy lost in keeping warm so more energy can be put into growth.

16.  Genotype determines the potential maximum height  Environmental influences determine whether that potential is reached

17.  UV light  skin cells   MSH (melanocyte stimulating hormone)  binds to MSH receptors in membrane of melanocytes  results in activation of transcription and translation of the gene for synthesis of an enzyme called tyrosinase.  Tyrosinase synthesises melanin  melanocytes enlarge, more branched, more MSH receptors, so more melanin and melanosomes produced  darkening of skin

18. Genotype determines number of MSH receptors to determines amount of melanin that can be produced. Environment i.e. amount of UV determines how much melanin is actually produced

19. The temperature at which a crocodile egg is incubated influences the sex of the resulting baby crocodile.  The thermosensitive period (TSP), during which the gonadal tissue is responsive to temperature. When exposed to one range of temperatures, this tissue develops into ovaries; when exposed to a different range, it develops into testes.  Such is the case in the turtle Emys obicularis: at incubation temperatures of 25°C, all such turtles are born male, but at temperatures of 30°C, all are born female.  In particular, expression of the Sox9 gene has been shown to change in response to temperature, with high expression levels at lower temperatures and repressed levels at higher temperatures. Because the transcription factor produced by Sox9 affects a gene that plays a major role in sex determination, the expression of this gene changes when temperature (and therefore Sox9 expression) changes, thus resulting in a specific phenotype of maleness or femaleness.

20. Induction of Cancer Abnormal cell division leads to tumor

21.  Diet  Reproductive and Gynecologic Factors  Environmental pollution  Chemicals & radiation  Unhealthy behavior  Exposure to Mutagens

22. Many Genes, Many Environmental Influences, Many Phenotypes:  The complex interactions of multiple genetic loci with diverse environmental signals suggest that scientists must continue to develop novel methods of studying these situations, such as by simultaneously examining thousands of genes using techniques like microarray technology under different environmental conditions.  While we may never be able to predict an exact phenotype, it is clear that when trying to understand biology and human disease, we must consider interactions of genes and environment in our analysis.