Heredity  

8th  Grade  

What  do  you  think?  

•  What  do  you  think  the  Father  looked  like?  •  Orange  with  8ger  stripes  •  How  do  you  Know?  •  The  baby  ki>en  has  orange  and  8ger  stripes  

DNA  

•  A cell uses a code in its hereditary material. The code is a chemical called deoxyribonucleic acid, or DNA

•  It contains information for an organism’s growth and function.

•  DNA is stored in cells that have a nucleus. •  When a cell divides, the DNA code is copied

and passed to the new cells.

•  In this way, new cells receive the same coded information that was in the original cell.

•  .

•  In a DNA model, each side of the ladder is made up of sugar-phosphate molecules

•  The rungs of the ladder are made up of other molecules called nitrogen bases.

•  Most of your characteristics, such as the color of your hair, your height, and even how things taste to you, depend on the kinds of proteins your cells make.

•  DNA in your cells stores the instructions for making these proteins.

•  Proteins build cells and tissues or work as enzymes.

•  Proteins are made of chains of hundreds or thousands of amino acids.

•  Changing the order of the amino acids makes a different protein.

•  The instructions for making a specific protein are found in a gene which is a section of DNA on a chromosome.

•  Each chromosome contains hundreds of genes.

•  Each  chromosome  pair  has  the  same  genes.    

•  The  genes  are  lined  up  in  the  same  order  on  both  chromosomes.    

•  In many-celled organisms like you, each cell uses only some of the thousands of genes that it has to make proteins.

•  Each cell uses only the genes that direct the making of proteins that it needs.

•  For example, muscle proteins are made in muscle cells but not in nerve cells.

•  If DNA is not copied exactly, the proteins made from the instructions might not be made correctly.

•  These mistakes, called mutations, are any permanent change in the DNA sequence of a gene or chromosome of a cell

•  Outside factors such as X rays, sunlight, and some chemicals have been known to cause mutations.

3  types  of  Muta8ons  

•  Not all mutations are harmful. They might be helpful or have no effect on an organism.

•  A  muta8on  is  harmful  if  it  reduces  an  organism’s  chance  for  survival  and  reproduc,on.  

• Whether  or  not  a  muta8on  is  harmful  depends  partly  on  the  organism’s  environment.    •  For  example,  a  white  lemur  may  not  survive  in  the  wild,  but  the  muta8on  has  no  effect  on  its  ability  to  survive  in  a  zoo.  

•  Helpful  muta8ons,  on  the  other  hand,  improve  an  organism’s  chances  for  survival  and  reproduc8on.    

•  An8bio8c  resistance  in  bacteria  is  an  example.    

•  An8bio8cs  are  chemicals  that  kill  bacteria.  Gene  muta8ons  have  enabled  some  kinds  of  bacteria  to  become  resistant  to  certain  an8bio8cs—that  is,  the  an8bio8cs  do  not  kill  the  bacteria  that  have  the  muta8ons.    

•  The  muta8ons  have  improved  the  bacteria’s  ability  to  survive  and  reproduce.  

•  If the mutation occurs in a body cell, it might or might not be life threatening to the organism.

•  If a mutation occurs in a sex cell, then all the cells that are formed from that sex cell will have that mutation.

•  Mutations add variety to a species when the organism reproduces  

•  Genes control the traits you inherit

•  Without correctly coded proteins, an organism can’t grow, repair, or maintain itself.

•  A change in a gene or chromosome can change the traits of an organism.

•  If three copies of chromosome 21 are produced in the fertilized human egg, Down’s syndrome results. •  Individuals with Down’s syndrome can be short,

exhibit learning disabilities, and have heart problems.

•  Eye color, nose shape, and many other physical features are some of the traits that are inherited from parents.

•  An organism is a collection of traits, all inherited from its parents

•  Heredity is the passing of traits from parent to offspring.

•  Generally, genes on chromosomes control an organism’s form and function.  

•  The different forms of a trait that a gene may have are called alleles  

•  When a pair of chromosomes separates during meiosis, alleles for each trait also separate into different sex cells.

•  Every sex cell has one allele for each trait.

•  The study of how traits are inherited through the interactions of alleles is the science of genetics  

Mendel  Ponders  (not  in  notes    lets  just  think  about  it)  

•  A  scien8st  by  the  name  of  Mendel  no8ced  differences  about  pea  plants.  

•  What  differences  do  you  think  pea  plants  could  have?  

•  He  no8ced  some  were  tall,  some  short,  some  produced  yellow  seeds,  some  produced  green  seeds.  

•  These  are  call  traits  or  characteris8cs.  

Mendel  

•  Gregor Mendel began experimenting with garden peas in 1856.

•  Mendel made careful use of scientific methods, which resulted in the first recorded study of how traits pass from one generation to the next

•  Mendel was the first to trace one trait through several generations.

•  He was also the first to use the mathematics of probability to explain heredity.

•  Each time Mendel studied a trait, he crossed two plants with different expressions of the trait and found that the new plants all looked like one of the two parents

•  He called these new plants hybrids because they received different genetic information, or different alleles, for a trait from each parent  

•  An organism that always produces the same traits generation after generation is called a purebred.

•  Tall plants that always produce seeds that produce tall plants are purebred for the trait of tall height.

• 

First  the  Basics  

•   The  flower’s  petals  surround  the  pis8l  and  the  stamens.    

•  The  pis,l  produces  female  sex  cells,  or  eggs.    •  The  stamens  produce  pollen,  which  contains  the  male  sex  cells,  or  sperm.    

•   A  new  organism  begins  to  form  when  egg  and  sperm  join  in  the  process  called  fer,liza,on.    

•  Before  fer8liza8on  can  happen  in  pea  plants,  pollen  must  reach  the  pis8l  of  a  pea  flower  through  pollina,on.    

•   Pea  plants  are  usually  self-­‐pollina,ng,  meaning  pollen  from  a  flower  lands  on  the  pis8l  of  the  same  flower  

•  Mendel  developed  a  method  by  which  he  cross-­‐pollinated,  or  “crossed,”  pea  plants.    

•  To  cross  two  plants,  he  removed  pollen  from  a  flower  on  one  Plant.  He  then  brushed  the  pollen  onto  a  flower  on  a  second  plant.    

Meet  the    Parents  

•  What  are  their  characteris8cs?  •  One’s  short;  One’s  tall  

F1  -­‐Genera8on  

•  What  do  you  no8ce  about  the  first  genera8on  compared  to  the  P  genera8on?  

•  They  are  all  tall?  

•  When  the  plants  in  the  F1  genera8on  were  full-­‐grown,  Mendel  allowed  them  to  self-­‐pollinate.  

•  What  do  you  no8ce?  

•  In  all  of  Mendel’s  crosses,  only  one  form  of  the  trait  appeared  in  the  F1  genera,on.    

•  However,  in  the  F2  genera,on,  the  “lost”  form  of  the  trait  always  reappeared  in  about  one  fourth  of  the  plants.    

•  In his experiments, Mendel used pollen from the flowers of purebred tall plants to pollinate by hand the flowers of purebred short plants.

•  This process is called cross-pollination

•  He found that tall plants crossed with short plants produced seed that produced all tall plants.

Dominant  and  Recessive  Alleles  

•  Mendel  reasoned  that  individual  factors,  or  sets  of  gene8c  "informa8on,"  must  control  the  inheritance  or  traits  in  Peas.    

•  The  factors  that  control  each  trait  exist  in  pairs.  The  female  parent  contributes  one  factor,  while  the  male  parent  contributes  the  other  factor.      

•  One  factor  in  a  pair  can  mask,  or  hide,  the  other  factor.  The  tallness  factor,  for  example,  masked  the  shortness  factor.  

•  Mendel called the tall form the dominant factor because it dominated, or covered up, the short form.

•  He called the form that seemed to disappear the recessive factor.

Genes  and  Alleles    

•  The  word  gene    is  used  for  the  factors  that  control  a  trait.  

•  Alleles  (uh  LEELZ)  are  the  different  forms  of  a  gene.    

•  The  gene  that  controls  stem  height  in  peas,  for  example,  has  one  allele  for  tall  stems  and  one  allele  for  short  stems.  

•  Each  pea  plant  inherits  two  alleles  from  its  parents-­‐one  allele  from  the  egg  and  the  other  from  the  sperm.    

•  A  pea  plant  may  inherit  two  alleles  for  tall  stems,  two  alleles  for  short  stems,  or  one  of  each.    

•  A  dominant  allele  is  one  whose  trait  always  shows  up  in  the  organism  when  the  allele  is  present.    

•  A  recessive  allele  is  hidden  whenever  the  dominant  allele  is  present.  A  trait  controlled  by  a  recessive  allele  will  only  show  up  if  the  organism  does  not  have  the  dominant  allele.  

•  Many human genetic disorders, such as cystic fibrosis, are caused by recessive genes.

•  Some recessive genes are the result of a mutation within the gene.

•  Such genetic disorders occur when both parents have a recessive allele responsible for this disorder.

•  Because the parents are heterozygous, they don’t show any symptoms.

Lets  look  at  some  allele’s  

•  Gene8cists  use  a  capital  le>er  to  represent  a  dominant  allele  and  a  lowercase  version  of  the  same  le>er  for  the  recessive  allele.      

•  Probability is a branch of mathematics that helps you predict the chance that something will happen.

•  Mendle studied almost 30,000 pea plants over a period of eight years.

•  A handy tool used to predict results in Mendelian genetics is the Punnett square.

•  In a Punnett square, letters represent dominant and recessive alleles

•  An uppercase letter stands for a dominant allele

•  A lowercase letter stands for a recessive allele

•  They show the genotype, or genetic makeup, of an organism.

•  The way an organism looks and behaves as a result of its genotype is its phenotype  

Examples  

•  Most cells in your body have two alleles for every trait.

•  These alleles are located on chromosomes within the nucleus of cells.

•  An organism with two alleles that are the same is called homozygous – Ex=  TT  or  >  

•  An organism that has two different alleles for a trait is called heterozygous – Ex= Tt  

•  Which  is  heterozygous?  •  Which  is  homozygous?  

Which  is  Heterozy?    Which  is  Homozy?  

Mul8ple  Alleles  

•  Many traits are controlled by more than two alleles.

•  A trait that is controlled by more than two alleles is said to be controlled by multiple alleles.

•  Traits controlled by multiple alleles produce more than three phenotypes of that trait.

•  Blood type in humans is an example of multiple alleles that produce only four phenotypes

•  The alleles for blood types are called A, B, and O.

Blood  Type  

•  AB=  AB  •  A=  AA  or  AO  •  B=BB  or  BO  •  O=  OO  

•  In  addi8on  to  the  A  and  B  an8gens,  there  is  a  third  an8gen  called  the  Rh  factor,  which  can  be  either  present  (+)  or  absent  (  –  ).  In  general,  Rh  nega8ve  blood  is  given  to  Rh-­‐nega8ve  pa8ents,  and  Rh  posi8ve  blood  or  Rh  nega8ve  blood  may  be  given  to  Rh  posi8ve  pa8ents.  

•  The  universal  red  cell  donor  has  Type  O  nega8ve  blood  type.  

•  The  universal  plasma  donor  has  Type  AB  blood  type.  

WWW.redcrsossblood.org    

•  Blood  Types  and  the  Popula,on  •  O  posi8ve  is  the  most  common  blood  type.  Not  all  ethnic  groups  have  the  same  mix  of  these  blood  types.  Hispanic  people,  for  example,  have  a  rela8vely  high  number  of  O’s,  while  Asian  people  have  a  rela8vely  high  number  of  B’s.    

WWW.redcrsossblood.org    

The  mix  of  the  different  blood  types  in  the  U.S.  popula8on  is:  

 

WWW.redcrsossblood.org    

•  Polygenic inheritance occurs when a group of gene pairs acts together to produce a trait

•  The effects of many alleles produces a wide variety of phenotypes.

•  Your height and the color of your eyes and skin are just some of the many human traits controlled by polygenic inheritance.

•  It is estimated that three to six gene pairs control your skin color.

•  The environment also plays an important role in the expression of traits controlled by polygenic inheritance  

Gender  and  Alleles  

•  Each egg produced by a female normally contains one X chromosome.

•  Males produce sperm that normally have either an X or a Y chromosome.

•  When a sperm with an X chromosome fertilizes an egg, the offspring is a female, XX.

•  A male offspring, XY is the result of a Y-containing sperm fertilizing an egg.

•  An allele inherited on a sex chromosome is called a sex-linked gene.

•  Color blindness is a sex-linked disorder in which people cannot distinguish between certain colors, particularly red and green.

•  This trait is a recessive allele on the X chromosome.

•  Because males have only one X chromosome, a male with this allele on his X chromosome is color-blind.

•  A color-blind female occurs only when both of her X chromosomes have the allele for this trait.