Science of
                                                              Key Concepts*

             Informational Transfer of the physical characteristics
             of cells and organisms from generation to generation.


Heredity studies how the FORM [morphology] and APPEARANCE  [phenotype]
       of an organism as
established by its genes & as influenced by the environment.

     Should one look at the genetic ancestry of a prospective mate ????             

Essence of heredity... 
of the thousands of known different species, each reproduces itself, faithfully,
       yielding progeny that belong to the SAME species, i.e., the parent organism hands
       down information specifying, in exacting detail, the characteristics of its offspring.

       The phenomena of Heredity is a central definition of Life...
       it is the ability of cells to faithfully copy its DNA instructions into
identical progeny
       passing traits
of parents or ancestors to offspring, while allowing genetic variations.


        a genetic pedigree













Two aspects of heredity: we observe patterns & analyze mechanisms...
the essence of the Scientific method)
    Mendelian Genetics -  (observes patterns of appearance - PHENOPTYPES)

Quantitative analysis of inheritance of morphological characters in organisms...
                 we'll look at experiments which established the basic principles & laws
                 that predict the pattern of inheritance from generation to generation

often done with a genetic pedigree

    Molecular Genetics -
  (molecular mechanisms of the appearance - GENOTYPES
           physical properties of molecules (DNA & RNA & proteins) provide the
                 molecular mechanisms that affect the observed patterns of inheritance.

                             Central  Dogma  of  Molecular  Biology 
DNA --> transcription --> RNA -- translation --> Protein










ENDELIAN   GENETICS...                         
Mendel Museum - Mendel's Legacy    

Gregor Johann Mendel was an Augustinian monk (later abbot) at the 
                the Abbey of St. Thomas in Brno (today part of the Czech Republic)

Mendel did his experiments between 1856 & 1863 breeding 29,000
Psium sativum pea plants...

flowering*sweet pea can produce progeny via self pollination* & cross pollination*
                Mendel made experimental crosses between true breeding parents 
                for a single genetic character (morphological trait)
                with 2 different phenotypes (appearances)

      Mendel's 7 TRUE BREEDING morphological traits in pea plant via genetic crosses

the design of a typical Mendelian experimental  MONOHYBRID  CROSS...
         generation                  experimental genetic cross
        Parental       round seed     x    wrinkled seed   [ true breeding
            F1            round seed     
[ x  themself - self-pollinate]

            F2         3
* seed  to  1 wrinkled* seed   
  another example of monohybrid cross using flower color in peas*   







Mendel described his observations in terms of Particulate Inheritance

Physical characters are discernible as   "PARTICLES"   or   "FACTORS",  which are:
       -  discrete entities with own integrity                       
  (no blending of traits)
       -  a trait is preserved through inheritance 
               (over many generations)
       -  a trait occurs within the individual in PAIRS          (now known as diploid)

       -  some particles mask expression of others            (round masks wrinkled in F1

 Law of Mendelian Segregation...   his hypothesis:  
when gametes are formed... 
               -  2 particles of inheritance in an individual SEGREGATE from each other
               -  each progeny  receives 1 particle (in a gamete) from each parent











Current Interpretation of Mendel's Particulate Inheritance Hypothesis... 


        - Mendel's particles are GENES...  entities definable in
molecular terms [a DNA segment]
- we represent the different forms of a trait by alphabetic symbols =  A & a, B & b,  etc...  

        - a trait (as shape) can have different morphological forms...  each called an ALLELE
               allele - a DNA gene segment which codes for different form of a similar protein, 
                           that governs that gene's phenotype 
(round,  wrinkled purple, etc...)
alleles occur on chromosomes at a specific place = a 

        - some alleles mask expression of others = DOMINANT & RECESIVE allelic traits
               geneticists use upper case = dominant   and   lower case = recessive trait  
                    recessive  -  trait that disappears in the F1 generation (a is masked by A)
                    dominant  -  trait that does not disappear in the F1 (wild type A is dominant to a)
    - each individual possesses [only] 2 alleles for one specific trait, thus 3 combinations...
                                         RR  -   homozygous dominant   (only 1 allele = round)
                                         Rr   -   heterozygous               (dominant allele = round)
                                         rr    -   homozygous recessive  (both alleles to be wrinkled)

animation of Mendel's monohydrid cross with Punnett Squares*    









          Mendelian Monohybrid Genetic Cross   &   Meiosis







round phenoytpe






         gametes (4)

          x  haploid






    (R is expressed
      r is not)


makes 4 gametes 

but, show only 2 different


  Punnett Square

  lists the probabilities of
    offspring genotypes


flower color* 



  Results of a Monohybrid Cross...         
PHENOTYPE   (APPEARANCE)           3 round   to    1 wrinkled 


(ALLELE MAKEUP)         1  (RR)    to    2 (Rr)  to  1 (rr)    


Mendel's hypothesis [that the F1 is Aa] is scientifically testable... 
- his premise [a testable hypothesis]... hypothesized F1 should be a heterozygote [Rr]
          (2 particles segregate & each gamete receives 1 particle of each type from each parent)

- a testable experiment:  we can do a Testcross/Backcross*
                    a cross of unknown F1 genotype [RR or Rr] to homozygous recessive [rr]...
                    since 2 recessive alleles are necessary to see the recessive phenotype
                    one can easily see if the recessive is present in the unknown genotype.

prediction   1:1 ratio
r r

   if  F1  heterozygote

R Rr Rr

r rr rr

prediction  all the same
r r
   if  F1  homozygote R Rr Rr

either  RR   or   rr           

R Rr Rr






ndel wrote a 2 part scientific paper on Experiments on Plant Hybridizations
He read part 1 to the Natural History Society of Brno on Feb.,  8, 1865
                                                                           and part 2 on March 8, 1865.

         He published his results in 1866; but they were largely ignored.

   The true value of Mendel's experiments was his approach to the scientific method...

                1.  his experimental results were given numerically

                2.  he used statistical analyses

                3.  he used large sample sizes

                4. he followed his results for several generations

                5. he used an inquiry based approach... &   did experimental test crosses...

These are the hallmarks of the scientific method in genetics and
   clearly established that traits are not blended, but separate distinct characters.













The predominant theory of inheritance of the 19th century was blended inheritance, where the inherited characteristics of progeny is the average of the parents' values of that characteristic.
Blended Inheritance   vs.   Incomplete Dominance    -   snapdragons*
            can it still be explained by Mendel's Law's?    Yes        -   incomplete dominance of traits*
          - yes. neither gene is dominant,   i.e., alleles do NOT MASK expression of the other.

 Mendel's Law of Independent Assortment 
       Different genes sort independently from one another during progeny reproduction.
      a dihybrid cross demonstrates principle of  Independent Assortment
            dihybrid crosses involves 2 characters or traits, that result in...
                               new combinations of traits, not exhibited by either parent.
                                        parentals     -  progeny look like parents
                                 non-parentals     -  progeny don't look like either parent


                                         DOMINANT         RECESSIVE
                flower color             W = red                w = white
                seed color                G = green             g =

           P1         WWGG         x        wwgg                   true breeding [homozygous]
           F1         WwGg    c     (x   WwGg self cross)  what's the progeny phenotypes










 F2      phenotypes                   
flower color    seed color              ratio

parental  red          green      9 of 16

     non-parental white      green      3 of 16     9:3:3:1

     non-parental red yellow     3 of 16

parental  white       yellow     1 of 16

            Each trait alone    red (3)       =  12 of 16   white (1)          =  4 of 16
                       3:1             green (3)   =  12 of 16   yellow (1)        =  4 of 16

►   New Combinations NOT SEEN in the parents appear because the..
[flower/seed color] SORT INDEPENDENT
               - these traits  are distributed to progeny independent of each other
               - thus, the genes must occur on
different chromosomes
         animation of independent assortment

                 -  a dihybrid cross*      (animation of dihybrid crossview@home)
          some sample Genetics Problems*in new tab                                                               



Rediscovery of Mendel's hypotheses:

  1900 - Hugo deVries, Carl Correns & Erich von Teschermak, were botanists who
             studied heredity and all reference Mendel's earlier works.

1902-1903  Walter Sutton & Theodor Boveri
      analyzed spematogenesis and oogenesis, especially in grasshopper & sea urchins  
      and described chromosomes & observed MEIOSIS and noted...
              -  hereditary traits are carried in sperm & egg cells
              -  on chromosomes
              -  chromosomes obey
Mendel's laws
                  >  chromosomes occur in pairs, as do Mendel's "particles"   (homologs)
                  >  chromosomes segregate at meiosis, as do the  "particles"
                           via Mendel's
Law of Segregation  (homologs/chromatids separate)
                  >  chromosomes sort independently  of each other
                           via Mendel's Law of Independent Assortment  -
fig 15.4 (laws)

   Sutton and Boveri propose Chromosomal Theory of inheritance, which states that
      genes are found at specific locations on chromosomes and that the behavior of
      chromosomes during meiosis
involves segregation, independent assortment, and
      occasionally, linkage of genes.









CHROMOSOMAL INHERTIANCE & LINKAGE... Golden Age of Mendelian Genetics (1910-1930)

Thomas Hunt Morgan... Columbia Univ. geneticist - fruit fly*     [Calvin Bridges]
     working on fruit flies in what was known as the "Fly Room"; he mapped genes, and
     linked heredity traits to specific loci on chromosomes&  observed
sex determination.

Morgan's research group recognized 2 types of
NIH site

1. AUTOSOMES - the non-sex chromosomes (44 homologs + 2 sex chromosomes)
* - photographic map of a species chromosomes (1956 by J.H. Tjio)
NCBI Human karyotype gene map good reference web site


 2. SEX Chromosomes* (X & Y) - show different structural morphology
        were 1st described by
Natalie Stevens in 1905 in meal worms.

Sex determination*-> heterogametic sex (xy) & homogametic sex (xx)

        SEX LINKED Recessives*    when a gene trait is carried only on an X chromosome.
          Xa Xa   vs.   Xa Y    
No corresponding Y trait thus...    HEMIZYGOUS (males)
                                           ex:  red green colorblindness (males = 8% and females 1%)
                           other SLRs:  hemophilia, 
albinism,  myopia,  Duchenes' M.D.
            a sample problem
*try @ home
       Read about the story of The Fly Room of Thomas Hunt Morgan & his protégé (Calvin Bridges).














Autosomal Linkage
...  Linked Genes & crossing over allowed mapping of gene loci.
two traits are carried on a single chromosome   ___R__Y__
       -  thus they do not sort independently;  but, how do we know if they are linked?

generation genotype phenotype

parental RRYY  x   rryy round/yellow   x  wrinkled/green




TESTCROSS * RYry   x  ryry round/yellow   x  wrinkled/green
     for recessives (ry - linked or not) all gametes will have same alleles* 

if linked

           if not linked

      F1         ry 

RY RYry    (RrYy) 

ry ryry 
Ry  Ryry    (Rryy)

rY rYry     (rrYy)

ry  ryry     (rryy)

               1 : 1

             1 : 1 : 1 : 1

         genes occur at a specific locus* &  are linear along chromosomes
              which allowed for Genetic mapping or linkage maps to indicate
              the relative order of genes on a chromosome.
                                                                   Sturtevant,A.H. J. Exp.Zool. (1913) 14:43-59.






















Human Genetic examples 

   Pedigree Analysis*

   Pedigree Symbols


 Pedigree drawing software

Some Examples of Human Genetic Traits...
    -  Widow's peak*  &   free ear lobes*,   &   tongue roll*   &   a cross with Freckles*,   
    -  Blood Groups
* - 4 phenotypes O, A, B, and AB  
                                                          due to RBC surface carbohydrates

    -  Sex linkage - trait carried on X-chromosome 
                              red-green colorblindness, Duchene muscular dystrophy, &

There are some 7,000 chromosomally inherited Mendelian diseases known... 
       Generally of two major forms:
           - Inborn Errors of Metabolism - defective enzymes due to recessive mutations
           - Mistakes of Meiosis -  due to abnormal chromosome structures,  such as...
                as numerical
(Down's syndrome) or structural abnormalities (deleted portions)









Inborn Errors of Metabolism -  mutations = non-functional enzymes       [genes & diseases
PHENYLKETONURIA - [PKU]     pp                                1/10,000 births
       disfunctional phenylalanine hydroxylase on chromosome 12
           PHE  --x-->   tyrosine    --> -->   degraded & excreted
               toxic accumulation -->  blood/brain barrier    mental retardation
               In U.S. a PKU screening test is required all newborns 24–72 hours after birth.
               PHE is essential (dietary only) aa, so
* is treatable by dietary restriction  

TAY SACHS                tt
                           1/300,000 births 
       defective (hexosaminidase-A) enzyme 
-->  high ganglioside fats in nerves  -->  fatal
              Ashkenazic Jewish ancestry shows an incidence of 
1/ 3,600 births   1/30 is Tt 
                Founder Effect
- in populations a very small breeding size recessives can be high 

SICKLE CELL              ss        
pic*                1/6,000 births
              defective beta globin polypeptide of Hb    -
DNA Learning Center video
              a  single nucleotide change = improper folding of Hb --> clogs capillaries

in 1998 - 1st umbilical cord blood stem cell transplant in children - Keone Penn update  
                      in 2014 - stem cell bone marrow transplants reverse Sickle cell in adults   
                      in 2023 - gene editing drug (Casgevy) cuts in a particular gene that can reactivate the production
                                    of fetal hemoglobin, which dilutes the faulty red blood cells caused by sickle cell disease.













Chromosomal Abberations  -
chromosomal mistakes of Meiosis & Ploidy...

  ANEUPLOIDY is a chromosomal aberration due to a variation in chromosome #
     monosomy - 1 less       disomy = normal (diploid)       trisomy + 1 more than normal 

* forms trisomies where some or all cells have an extra chromosome
Common trisomies*  =   trisomy 21*- Down Syndrome - frequency vs. age* 
Other ex: 
     4 common types of structural changes - animation*  figure 15.14 
                                   1) deletions - chromosome fragment without centromere is lost
                                   2) duplications - a segment is repeated...

                                   3) inversions - a segment reverses is linear sequence
                                   4) translocations - both segments moves from one chromosome to another. 

[Gk: eu-true  &  genos-race, stock, kin] social improvement of human genomes. 
     Eugenics movements aim to improve Humans, often via selective breeding or non-breeding
     Historically... proposed to be done by elimination of "inferior" genes in the populations...
             [ex:  forced sterilizations of the mentally ill - in U.S. in 1950 over 1,526 individuals 
                     were sterilized by legal statutes].
  Amniocentesis -  fetal diagnosis
* -   biochemical and cytological analysis of the
                                                           amniotic fluid surrounding a fetus for genetic abnormalities.  

                                                       preimplantation tests  &  Umbilical Cord Banking

Human Chromosome Map:  of human diseases, disorders, & syndromes.   

  back        next lec - Molecular Genetics              Sample Genetics Problems            

   copyright c2024     - 
       Charles Mallery,     - Biology 150, Department of Biology,   U. of Miami,  Coral Gables, FL
















Ex: Aneuploidy of SEX chromosomes: (in > non-disjunction of XX)

X X 





  X0      X   or    Y Y0     XXX   X   or   Y   XXY


   Turner syndrome
   1/5000 births
90% abort -
   appears female
   often sterile TSS

                               dies           triple X
                                                 1/1000 births
                                                 no visible symptoms
                                                 may be sterile
                                                 developmental issues

   1/2000 births
    appears male



Sex & Sports



     F1 parents of a F1 testcross  :  RYry   x   ryry 
             linked on same chromosome            not  linked
on different chromosomes
                 ____R__Y___                    ____R____     ____Y___    
     F1         ____r__y___                     ____r____      ____y___     

 * for the recessive parent: makes no difference whether genes are linked or not
____r__y___          or       ___r___  &  ___y___              

F1 gametes   Linked
      2 kinds gametes =
      2 progeny types (parentals)

F1 gametes:  not-linked
4 kinds gametes =
4 progeny types -
(parentals & non-parentals_
____R__Y___ ___R___
____R__Y___ ___R___
____r__y___ ___r___
____r__y___ ___r___











  AB Ab aB ab
Ab AABb AAbb AaBb Aabb
aB AaBB AaBb aaBB aaBb
ab AaBb Aabb aaBb aabb







                                                                    9 : 3 : 3 : 1

 Easy - How many are Homozygous for one allele and Heterozygous for the other allele?
 Harder - How many are wrinkled & yellow?






















a  Mendelian  anomaly ?

[BARR Body*]

   Genomic Imprinting...
The phenotype expressed can open depend upon whether
         the allele (autosomal) comes from the 
 or   parent.
                    - often occurs during gamete formation
                    - either
  gamete or gamete is silenced
                    - zygote expresses only 1 of the 2 alleles & it is passed to all progeny cells
                    - within a given species imprinted genes are always either maternal or paternal


            ex:  1)  gene for insulin-like growth factor (Igf2)
                               - only the paternal allele is expressed  
C7e - fig 15.17a
                               - ratio anomalies occur when mutant allele is passed
C7e - fig 15.17b
                  2)  most other imprinted genes are involved in embryonic development,
                           where presence of only one allele of some genes is tolerated


           cause:  seems likely to be methylation of CYS nucleotides of the affected allele
                         that results in heterochromatinization (inactivation)


Gene Interactions...
and    Mendelian ratio anomalies
Complementary Genes - genes are mutually dependent to show phenotype
   Purple flower color   requires a color protein  &  a protein complement
            P         PPCC x ppcc                         both required for phenotype
            F1             PpCc

            F2      9    P_C_      purple
                      3    ppC_      white            a  9 : 7  ratio
                      3    P_cc      white                                   not 9:3:3:1   ¥
                      1     ppcc    
* - works in similar fashion: often involves B = melanin gene (water soluble pigment)
        where a gene at one locus modifies the phenotype (C = deposits pigment) of gene
        at a second locus (black or brown pigment) and results in an altered dihybrid ratio...
        one loci controls whether pigment is made & other loci deposits (produces) color.
                9 B_C_               3 bbC_                  3 B_cc     1 bbcc          9:3:4
                   black                  brown                          white


Polygenic [Quantitative Trait] Inheritance        
        2 or more genes affect 1 phenotype
           usually with quantitative characters,
                 with a continuous scale of measurement...
                  - heightweight
* (a  polygenic*model of wheat color), etc...

     1 gene influences many phenotypic traits...
                    - a mutant defect in collagen gene = multiple morphological deformities...
                              collagen is a
main component of cartilage, ligaments, tendons, bone and teeth.

                    - sickle cell gene results in many physiological disorders due to key
                                            metabolic role that gene plays in physiology of blood







      Independent assortment of non-linked genes


           Link between GENOTYPE - PHENOTYPE  (round vs. wrinkled)

genotype RR Rr rr

phenotype  (seeds)

round round wrinkled
starch content high median  low
starch grains numerous median few
(reducing) sugar low median high
Starch (glycogen) branching enzyme high median low


thus : dominant allele R of the seed shape gene codes for a normal
                  starch branching enzyme*  ---->     branched starch (amylopectin).
                            The recessive allele is the result of a transposon insertion into normal gene
                            producing a non-functional STARCH-BRANCHING enzyme and a reduction
                            in starch synthesis which results in an accumulation of free sucrose that leads
                            retention of water and seed swelling.
                            Starch is
non-hydgroscopic (doesn't absorb water), but sugar is hygroscopic,
                            so fresh seed water content 
(both RR &
Rr)  keeps it round; but when seed is
                            harvested and dries out greater water loss from rr seed appears
                            in the dry seed state


 Molecular causes of some of Mendel's Other Traits...

    in 1990 - the gene for wrinkled seed was determined to be due to
                         the starch branching enzyme
UDP-glucose (glycogen) phosphorylase 

                   the recessive is caused by a
g* insertion of nucleotides     
                   into the starch branching enzyme's coding region   

    in 1997 - in the pea plant (& in the plant Arabidopsis) a gene called   Le
                            which controls stem length (mutants are shorter) was identified.

                            the gene codes for the enzyme: GA3b-hydroxylase, which converts
                                 two precursors of
Gibberellic Acid into active GA3b,
                                GA3b is a plant hormone that promotes stem growth & fruit set.

            The recessive is due to defective gene coding of GA3b-hydroxylase.


Autosomal Mapping...

      Let's do an actual F1 testcross of known linked genes;
                 we predict 50:50 progeny... both parental types;
;  we get following results...  NOT  1 :[RYry & ryry],  but rather we get...

  round & yellow         41.5%     R_Y_    parental phenotype
                      wrinkled & green      41.5%      rryy      parental phenotype
                      round & green           8.5%      R_yy     non-parental phenotype
                      wrinkled & yellow      8.5%       rrY_      non-parental phenotype 
17% of progeny = non-parentals) 

       -  crossing over during meiosis will allow one to MAP POSITIONS of genes.
              mapping is the frequency (%) of cross over exchange of genes that 
                             is proportional to relative distance between the 2 genes





    or homologous recombination... the process by which two
     non-sister chromatids, paired up during synapsis of meiosis 1,
     exchange equal distal portions of their chromosomal DNA
Would XO be greater between the A-B locus or the A-C locus?

A             B                                     C

 a              b                                     c


Frequency (%) of crossover exchange...
[exchange of chromatids pieces of a homologous pair during synapsis at a chiasma]...
   i.e., the % of non-parental produced from a cross of linked genes.
is proportional to relative distance
between 2 linked genes

is GREATER the FARTHER apart
2 genes are

Relative distance is measured as...

   1% crossover frequency   =   % non parentals
and   1 map unit of map distance is
   1%  CrossOver Freq  =  1  centiMorgan

 above CO Freq   8.5% + 8.5% = 17%

R/Y = 17 map units (centi-Morgans) from each other


   Let's determine the GENE MAP for the genes   R  [shape],  [color]  &   X 

   1. Genes R & Y revealed 17% CO frequency of exchange (above)
           thus genes  R  and  Y  are 17 map units (centiMorgans) apart
   2.  now,  genes  R  and  X  reveal 5% crossover frequency [
X is 5 CM from R ]
thus, genes  Y and  X  could reveal either a 12% or 22%  CO frequency???

      X   5cm  .    5cm    X                                2. RRXX  x  rrxx  -->  RXr -> testcross
              R                 17cm         Y            but 5% are R_xx & rrX_ are nonparentals

              R   5cm     X    12cm         Y 

       5cm  R                17cm         Y     3. YYXX  yyxx --> YXyx    =  % ?
                                                                                                                              nonparentals  =  12%   or  22%
  genes occur at specific loci* &  are linear along chromosomes
a common mapping problem*

ALKAPTONURIA         aa       A. Garrod in 1908                     1/200,000 births
       homogentisic acid oxidase --x-->
*  [urine oxidizes black & causes ochronosis]
                    1st suggestion that mutant genes can make mutant proteins
                    and this disease is due to a defective enzyme/protein.


                      reciprocal :  non-homologous chromosomes exchange piecec7 fig 15.17
                      large portion of chromosome 22 with small tip of 9
                     non-reciprocal :  one chromosome transfers a segment without exchange

                                      Downs's syndrome (5% of cases) small piece of 21 to 14

     Aneuploidy, criminal inheritance, and eugenics????
           XYY syndrome  
       a 1966 study of Pennsylvania prison found 5 were XYY, a statistical
                  anomoly, thus genetic myth of criminal violence & XYY's.

           Richard Speck tested for XYY "supermale karyotype" to get leniency by courts,
                  pleading insanity via XYY.   He was tested and found to be XY.