PSYC 3102: Introduction to Behavioral Genetics
Lecture 6
Transcriptional control mechanisms
-Mechanisms that affect the extent to which a gene gets transcribed or not transcribed
1. Methylation – (last lecture)
2. RNA splicing – (last lecture)
Lyonization
 Mary Lyons
 Lyonization is X-chromosome inactivation
 Women inherit XX, men inherit XY
 In the early stages of development, both X’s are active
 Thereafter, one X is randomly inactivated and forms a condensed body in the nucleus called
a Barr body
 All cells produced from a single cell line after inactivation have that same X inactivated
 In some cells the maternal X is inactivated, while in others it is the paternal X
 Lyonization is not 100% complete – not all sections of the Barr body chromosomes are
inactivated
 In many ways, females are a mosaics because different cells may express different alleles of
genes on the X chromosome because of differential inactivation of maternal and paternal X
chromosomes
o Ex. calico cat is black, orange and white
o One parent gives the allele for black fur and the other the allele for orange fur
o Black patches of fur come from active X with the black allele
o Orange patches of fur come from active X with the orange allele
Males only have 1 X, which produces enough copies of the genes
If females have 2 active X, there would be twice as many copies of the genes,
which might be too much
 No one is certain why this happens, but it is believed it is because of dosage compensation
 1 dose of X chromosome genes doesn’t contain much information, nor does the Y
chromosome, only having one X activated is enough
 In order to ensure physiology of males and females remains similar, one of the X
chromosomes should be turned off
Genomic Imprinting (Parental Imprinting)
 Whether a gene is active or not depends on the parent which it is inherited from
 The paternal allele can be inactive and the maternal allele can be active (or vice versa)
 Prader Willi: mom’s genes are turned off, dad’s are mutated
 Angelman Syndrome: dad’s genes are turned off, mom’s genes are mutated
Transcriptional Regulation
 Promoters and Silencers
 A protein or protein complex binds to DNA to enhance or inhibit transcription
 Enhancers usually knock something off DNA and allow other transcription stuff to bind
 Inhibiters usually bind to DNA and prevent other transcription stuff from binding and
starting transcription
 Ex: Lac Operon
o E. Coli adapts to living on lactose, then can switch over to not metabolizing
lactose (E. coli have a system that metabolizes milk, but is turned off when there
is no milk to metabolize in order to save energy)
o When lactose is present, it turns on the genes
o When lactose is absent, it turns them off
o Operon – a series of genes (applies mostly to E. coli systems)
o Regulatory protein – transcription factor that binds to DNA and inhibits or
enhances transcription
Lactose Intolerance
This is a good example of GENE-CULTURE EVOLUTION
 Many cultures throughout history have raised herd animals
 But not all cultures use the milk products of the herd animals
 The evolution of dairy cultures goes along with the prevalence of lactose tolerance and
intolerance
 Cultures without many members with lactose intolerance often developed into dairy cultures
 Dairy products provide another source of food
 This is important in times of famine, one doesn’t have to kill and use up herd animals, it’s a
continuous supply of food
 Therefore lactose tolerance is beneficial in times of famine
Political story behind this as well
 Pres. Lindon Johnson promoted the “Great Society” movement to eradicate poverty
 Developed (with the strong encouragement of the dairy industry) school milk programs
 However, many African American students were lactose intolerant, therefore threw their
milk away
 Genetists testified in Congress
 They then changed the program to include other food supplements
How Watching the Superbowl Changes Gene Expression
Rhesus Monkey Experiment:
 Wilbur and Clyde are two male Rhesus monkeys who have never met
 They are put in a small room together and will compete to establish dominance
 Levels of testosterone are monitored as this occurs
High
Wilbur
Testosterone
Clyde
Low

baseline
introduced
status established
post status
The same phenomena occurs in humans when competing, whether it’s chess or merely being
a fan of a winning or losing team
What does this have to do with genes?
 One of the MOST important transcription factors are HORMONES
Hormones:
 Provide long-distance communication throughout the body
 2 kinds: peptides and steroids
o Steriods are different, they slip through the lipid membrane of the cell and binds
with a receptor
o The hormone-receptor complex acts as a transcription factor and turns gene
expression on or off
 Testosterone is a steroid hormone that enhances or inhibits gene expression depending on the
cell type
 Therefore, levels of testosterone affects gene regulation and expression
 Research in the area of hormones investigates how social situations influence gene regulation
 At the present time there is more direct biochemical evidence of social situations influencing
gene expression than there is evidence for gene expression influencing social situations
 Lemonade!