1. NİŞANTAŞI ÜNİVERSİTESİ
GENERAL BIOLOGY
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2. Fraternal and Identical Twins
Fraternal “twins” from separate eggs are not any more genetically alike than other siblings.
Twin and Adoption Studies
To assess the impact of nature and nurture, how do we examine how genes make a difference within the same environment?
study traits of siblings vs. identical twins
see if the siblings vary more than twins
Identical twin: Same sex only
Fraternal twin: Same or opposite sex
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Fraternal twins are more alike than other siblings, however, in the home environment they share. They are raised at the same time in their parents’ lives, with the same number and age of siblings.
Even identical twins, though, can have biological differences, if they have separate placentas (this happens in about one out of three times) and thus get different nourishment.
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3. Identical vs. Fraternal Twins
Twin and Adoption Studies
How do we find out how the same genes express themselves in different environments?
We can study the traits of identical twins as they grow up, or if they were raised separately (e.g., the Minnesota Twin Family Study).
Studies of twins in adulthood show that identical twins are more alike than fraternal twins in:
personality traits such as extraversion (sociability) and neuroticism (emotional instability).
behaviors/outcomes such as the rate of divorce.
abilities such as overall Intelligence test scores.
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Instructor: In these and related studies, not only are identical twins more alike than fraternal twins, but fraternal twins are more alike than random strangers even though random strangers are also raised in different environments.
Question for the students, in this slide and the next: which factor is being controlled here, and which factor is varying? [Answer: presumably, these studies are done on twins raised at first together, then having some adult time apart; if fraternal twins have more differences than identical twins, the only factor which has varied is the level of genetic similarity.]
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4. Studies of Identical Twins Raised Apart
Given the evidence of genetic impact on how a person turns out, does parenting/nurture make any difference?
Does the home environment have any impact?
Similarities found in identical twins despite being raised in different homes:
personality, styles of thinking and relating
abilities/intelligence test scores
attitudes
interests, tastes
specific fears
brain waves, heart rate
Studies have been performed with adopted children for whom the biological relatives are known.
Findings: Adopted children seem to be more similar to their genetic relatives than their environmental/nurture relatives.
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Instructor: There are cases in which identical twins are separated at birth through adoption but are later found to be twins. The Minnesota Twin Family Study is the biggest example of this.
Again, I suggest asking the students: which factor is being controlled here, and which factor is varying?
Sidebar: Another critique is that the environments or “nurture” may be more similar for twins than for a pair of unrelated people because they look identical and thus are treated more similarly.
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5. Searching for Parenting Effects: Biological vs. Adoptive Relatives
Despite the strong impact of genetics on personality, parenting has an influence on:
religious beliefs
values
manners
attitudes
politics
habits
Automatic animation.

6. NİŞANTAŞI ÜNİVERSİTESİ ©
kaynaklar
James W. KALAT (2015). Biological Psychology (Vol. 12). Cengage Learning
Kenneth R. Miller, Joseph S. Levine (2001) Prentice Hall:Biology
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