Class Notes (834,986)
Canada (508,846)
Psychology (7,776)
PSYB30H3 (526)
Lecture

Chapter 6- Genetics.pdf

6 Pages
124 Views
Unlock Document

Department
Psychology
Course
PSYB30H3
Professor
Connie Boudens
Semester
Summer

Description
Chapter  6:  Genetics     -­‐Specific  gene  combinations-­‐called  genotypes     Behavioral  genetics:  Which  is  the  study  of  the  genetic  and  environmental   contributions  to  individual  differences  in  personality  and  behavior.     Nature  and  Nurture  as  Allies   -­‐  The  best  characterization  of  the  nature-­‐nurture  issue  is  that  nature  and  nurture   transact.  That  is,  genes  and  environment  can  work  separately,  together,  or  they  may   influence  one  another.   -­‐Certain  environments  have  different  effects  on  people  deepening  on  their  specific   genetic  makeup.  We  call  this  combination  of  nature  and  nurture  a  genotype-­‐ environment  interaction.   -­‐  Yet  another  possibility  is  that  it  may  be  impossible  to  separate  the  effect  of  genes   from  the  effect  of  the  environment.  What  if  people  change  environments  and   environments  change  people,  so  that  we  really  can't  separate  the  impact  of  genes  on   environment?  This  is  called  a  genotype-­‐environment  correlation.   -­‐  In  fact,  some  researchers  advocate  an  even  more  complicated  equation  for   understanding  the  manifestation  of  complex  human  traits-­‐a  concept  known  as   phenotype.     Phenotype  =  Genotype  +  Environment  +  Gene-­‐  environment  correlation  +  Gene-­‐   environment  interaction.      Genes  and  Environment  as  Co-­‐actors   Heritability     Heritability  :(h  ^2)  is  the  amount  of  observed  individual  differences  in  some   characteristic  that  can  be  accounted  for  by  genetic  differences.     -­‐Heritability  refers  to  differences  across  a  group  or  population  of  people-­‐not  to  a   specific  person.  It  is  impossible  to  say  how  much  of  your  height  is  due  to  your  genes.   But,  considering  a  sample  of  people,  like  your  personality  class,  we  can  estimate  that   about  80%  of  the  observed  differences  in  height  is  due  to  differing  genetic  makeup   of  your  classmates  and  20%  is  due  to  differing  environments  your  classmates  were   raised  in,  plus  some  percentage  of  measurement  error.   -­‐  We  cannot  know  what  contributes  more  to  the  personality  of  a  particular  person,   but  we  can  know  how  much  genetics  and  environment  each  account  for  differences   in  a  particular  personality  characteristic  of  this  particular  sample  of  people.   -­‐  Heritability,  therefore,  refers  to  the  inheritance  of  a  particular  trait  in  a  particular   population  at  a  particular  time,  so  sometimes  heritability  estimates  differ  depending   on  the  exact  sample  and  methods  used  by  researchers.       Environmentality     Environmentality  {e2):  Environmentality  estimates  the  extent  to  which  observed   individual  differences  can  be  traced  in  any  way  to  individual  differences  in   environments.   -­‐  Together,  heritability,  Environmentality,  and  measurement  error  account  for  all   the  differences  we  see  among  people  on  a  given  characteristic.       Shared  and  Nonshared  Environments     Shared  environment    :  Includes  aspects  of  the  family  environment  that  are   generally  the  same  for  all  the  children  in  the  household  including  physical,                               psychological,  and  social  aspects.     In  contrast,  the  Nonshared  environment  includes  experiences  that  relatives  have   which  make  them  different  from  one  another.   -­‐  These  may  include  unique  experiences  within  the  family  (e.g.,  being  the  eldest,   being  the  only  boy,  spacing  of  siblings,  differential  parental  treatment),  or  outside   the  family  (e.g.,  peers,teachers,sport,hobbies).     Estimating  Heritability   -­‐  We  estimate  the  heritability  of  a  characteristic  by  seeing  if  people  who  have  similar   genes  show  similar  characteristics.   -­‐  If  a  characteristic  has  a  strong  genetic  component,  then  we  would  expect  identical   twins,  who  share  100%  of  their  genes,  to  be  more  similar  than  strangers  in  that   characteristic.   -­‐  As  you  know,  there  are  two  kinds  of  twins:  identical  and  fraternal.     -­‐Identical  twins,  called  monozygotic  (MZ)  twins,  are  exact  genetic  duplicates  of   each  other.  This  happens  when  a  fertilized  egg,  the  zygote,  splits  into  two  (or  some-­‐   times  more)  identical  part  that  each  go  on  to  develop  into  a  fetus.   -­‐  In  contrast,  fraternal  twins  occur  when  two  zygotes  develop  in  utero  at  the  same   time.  We  call  these  kinds  of  twins  dizygotic  (DZ)  twins.  DZ  twins  result  from  the   fertilization  of  two  different  eggs  by  two  different  sperm  cells,  hence  they  are   genetically  distinct.   -­‐  One  measure  of  heritability,  then,  is  to  calculate  the  correlation  (r)  between  twins   on  a  given  trait  and  compare  the  correlation  between  MZ  twins  and  DZ  twins.  The   exact  formula  is  to  double  the  difference  between  these  correlations  or     h  =  2(mz  – dzr )     -­‐  A  second  way  of  estimating  heritability  is  to  compare  identical  twins  who  have   been  raised  in  separate  environments  .We  call  these  kinds  of  twins  MZA  twins   (monozygotic  twins  raised  apart).  If  such  twins  score  similarly  in  a  trait  such  as   Extraversion,  then  we  know  that  Extraversion  has  a  strong  genetic  component.   2 H =r MZA   -­‐  This  equal  environments  assumption  applies  only  to  similar  treatment  that  is   related  to  the  specific  characteristic  under  study.  For  example,  people  often  dress   their  twins  alike  in  identical  sailor  suits  or  matching  dresses.  This  probably  happens   more  often  to  MZ  twins  than  to  DZ  twins.  If  we  were  studying  something  like  fashion   sense,  then  this  would  violate  our  equal  environment  assumption.  But  unless   wearing  matching  outfits  affects  a  specific  personality  characteristic  like  shyness,   then  this  assumption  still  holds   -­‐  The  double-­‐the-­‐difference  formula  also  assumes  that  twins  are  typical  of  the   population.  We  call  this  the  assumption  of  representativeness.  For  example,  twins   are  often  premature  and  have  a  lower  birthrate  than  single  births.  Twins,  therefore,   may  not  be  representative  of  the  general  population  on  variables  that  are  affected   by  prematurity  or  low  birth  weight.  Again,  this  is  something  researchers  may  test   for,  and  for  the  most  part  this  assumption  holds  as  well.   -­‐  The  rMZA  method  of  estimating  heritability  also  has  its  limitations.  Here,   researchers  assume  that  the  adopted  families  of  each  twin  are  different  from  each   other.  If  the  identical  twins  are  placed  in  similar  environment  this  may  increase  the   similarity  between  the  twins,  artificially  inflating  our  heritability  estimate.  That  is,   twins  may  be  more  alike  on  a  certain  characteristic  due  to  selective  placement   during  the  adoption  process  and  not  to  their  genetics.  Selective  placement  makes  it   impossible  to  see  the  effect  of  genetics  apart  from  the  effect  of  environment  because   it  confounds  the  two.     Heritability  of  Common  Personality  Characteristics   The  variance  in  personality  trait  typically  breaks  down  like  this  :     Observed  differences  in  personality  traits  =  40%  Genetics  +  0%  Shared  environment   +40%  Nonshared  environment  +  20%  Error.   -­‐  Different  forms  of  the  same  gene  are  called  alleles   -­‐  This  concept  of  dominance  explains  the  pattern  of  seeds  Mendel  observed  in   successive  generations.  In  fact,  such  inheritance  patterns  where  one  trait  dominates   over  another  is  called  Mendelian  inheritance  and  Mendel  is  now  known  a  the   founder  of  modern  genetics.   -­‐  Have  researchers  discovered  a  genetic,  yet  noninheritable  means  by  which  the   environment  fundamentally  changes  human  functioning?  Apparently  so.  This   exciting  new  area  of  genetics  research  is  called  epigenetics.   -­‐  We  know  that  a  gene  is  a  sequence  of  DNA  that  codes  for  a  specific  trait.  Genes  are   composed  of  coding  regions  called  exons  and  noncoding  regions  called  introns.   -­‐  For  example,  if  a  disease  was  inherited,  once  we  have  identified  the  exact  gene   involved  in  a  disorder  we  can  diagnose  or  screen  who  had  the  gene.  Researchers   then  will  be  able  to  use  this  information  to  replace  faulty  genetic  code  with  new  and   improved  code  that  had  been  cloned  to  match  a  precisely  as  possible  the  recipient's   genetics  .This  is  called  positional  cloning.           Genes  and  Environment:  A  Dialectical  Synthesis   -­‐  According  to  the  philosopher  Hege
More Less

Related notes for PSYB30H3

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit