LECTURE 16

OBSERVABLE PATTERNS OF INHERITANCE

CHARLES DARWIN EXPLAINED HOW NATURAL SELECTION MIGHT
BRING ABOUT EVOLUTIONARY CHANGE

1. INDIVIDUALS VARY IN HERITABLE TRAITS

   a. VARIATIONS THAT IMPROVE CHANCES OF SURVIVING
      AND
REPRODUCING ARE FAVORED
       b. VARIATIONS THAT DON’T IMPROVE CHANCES OF
              SURVIVING AND REPRODUCING BECOME LESS FREQUENT

2. POPULATIONS CHANGE OVER TIME. THIS IS EVOLUTION.

MENDEL’S INSIGHT INTO PATTERNS OF INHERITANCE

GREGOR MENDEL WAS AN AUSTRIAN MONK WHO STUDIED INHERITANCE

1. KNEW AGRICULTURE PRINCIPLES AND PRACTICES
2. KEPT INFORMED ON BREEDING EXPERIMENTS
3. WAS A MEMBER OF THE REGIONAL AGRICULTURE SOCIETY
4. STUDIED MATHEMATICS AT THE
UNIVERSITY OF VIENNA

HE DID BREEDING EXPERIMENTS WITH THE GARDEN PEA (PISUM SATIVUM)

1. FLOWERS ARE SELF-FERTILIZING
       a. PRODUCE BOTH EGG AND SPERM
       b. MAY BE TRUE BREEDING

2. SUCCESSIVE GENERATIONS ARE IDENTICAL TO THE
        PARENTS

3. MAY CROSS FERTILIZE
       a. EGG AND SPERM COME FROM TWO INDIVIDUALS

1. MENDEL MADE "CROSSES" BY TAKING THE STAMENS
       OUT OF ONE TRUE BREEDING FLOWER AND BRUSHING THE
   PISTIL OF THE FLOWER WITH THE STAMENS OF ANOTHER
   TRUE BREEDING FLOWER WITH A CONTRASTING CHARACTER

EXAMPLE: WHITE FLOWERS X PURPLE FLOWERS

RESULT: ALL PURPLE FLOWERS

PURPLE X PURPLE = 3/4 PURPLE & 1/4 WHITE

GENETICS TERMS

1. GENES - UNITS OF INHERITANCE
  a. EACH DIPLOID CELL HAS A
PAIR OF GENES FOR EACH
            TRAIT

2. ALLELES - DIFFERENT MOLECULAR FORMS OF A GENE
      a. EACH DIPLOID CELLS HAS TWO ALLELES FOR EACH
             CHARACTERISTIC
      b. HOMOZYGOUS - BOTH ALLELES ARE THE SAME
      c. HETEROZYGOUS - THE TWO ALLELES ARE DIFFERENT
      d. ONE ALLELE IS EXPRESSED OVER ANOTHER
             1. THE EXPRESSED ALLELE IS DOMINANT
             2. THE NON-EXPRESSED ALLELE IS RECESSIVE
      e. HOMOZYGOUS DOMINANT (AA)
             HOMOZYGOUS RECESSIVE (aa)
             HETEROZYGOUS (Aa)

3. GENOTYPE REFERS TO THE GENES OF AN INDIVIDUAL
        PHENOTYPE REFERS TO THE OBSERVABLE TRAITS OF AN
        INDIVIDUAL

4. GENERATIONS OF A LINEAGE CAN BE REFERED TO AS:
       a. P = PARENTAL GENERATION
       b. F1 = FIRST-GENERATION OFFSPRING
       c. F2 = SECOND-GENERATION OFFSPRING

MENDEL’S THEORY OF SEGREGATION

MENDEL THOUGHT THAT IN EVERY GENERATION A PLANT INHERITS TWO UNITS OF INFORMATION ABOUT A TRAIT; ONE FROM EACH PARENT

HE TESTED THIS THEORY BY DOING A MONOHYBRID CROSS
      a. CROSSED TWO INDIVIDUALS THAT WERE
      TRUE-BREEDING FOR
CONTRASTING CHARACTERS
      b. THE PARENTS ARE HOMOZYGOUS FOR THE CHARACTER
      c. THE OFFSPRING ARE HETEROZYGOUS

PARENTAL GENOTYPES

AA, aa

 

     A      A    
a    Aa     Aa   
      PUNNETT SQUARE

a    Aa     Aa   


TRAITS EXAMINED BY MENDEL

1. SEED SHAPE

2. SEED COLOR

3. POD SHAPE

4. POD COLOR

5. FLOWER COLOR

6. FLOWER POSITION

7. STEM LENGTH

WHEN TWO HETEROZYGOUS F1 INDIVIDUALS ARE CROSSED WHAT HAPPENS?

Aa  X  Aa


     A      a   

A   AA     Aa   

a   Aa     aa   


AA = 1/4

Aa = 2/4 = 1/2

aa = 1/4

TEST CROSSES

A TEST CROSS IS DONE TO DETERMINE THE GENETIC MAKEUP OF AN INDIVIDUAL SHOWING THE DOMINANT CHARACTERISTIC. IS IT HOMOZYGOUS OR HETEROZYGOUS?

ONE PARENT MUST BE HOMOZYGOUS RECESSIVE

A? X aa

 

______A_____?_____

__a_______________

__a_______________

LECTURE 19

INDEPENDENT ASSORTMENT

A- = PURPLE, aa = WHITE
B- = TALL, bb = SHORT
P = AABB X aabb

F1 ALL AaBb

CROSS TWO F1 INDIVIDUALS

AaBb X AaBb

     AB    Ab    aB    ab

AB  AABB  AABb  AaBB  AaBb

Ab  AABb  Aabb  AaBb  Aabb

aB  AaBB  AaBb  aaBB  aaBb

ab  AaBb  Aabb  aaBb  aabb

PHENOTYPIC RATIO:

9 PURPLE, TALL
3 PURPLE, SHORT
3 WHITE, TALL
1 WHITE, SHORT

GENOTYPIC RATIO:

1/16 AABB
2/16 AABb
1/16 Aabb
2/16 aaBB
4/16 AaBb
2/16 Aabb
1/16 aaBB
2/16 aaBb
1/16 aabb

1:2:1:2:4:2:1:2:1

MENDEL’S THEORY OF INDEPENDENT ASSORTMENT

DURING MEIOSIS, THE GENE PAIRS ON HOMOLOGOUS CHROMOSOMES TEND TO BE SORTED INTO ONE GAMETE OR ANOTHER INDEPENDENTLY OF HOW GENE PAIRS ON OTHER CHROMOSOMES ARE SORTED OUT

INDEPENDENT ASSORTMENT LEADS TO A LARGE AMOUNT OF VARIABILITY

MENDEL DETERMINED THAT HEREDITARY MATERIAL IS IN UNITS THAT RETAIN THEIR PHYSICAL IDENTITY FROM ONE GENERATION TO ANOTHER

MENDEL REPORTED HIS RESULTS IN 1865 TO THE BRUNN SOCIETY FOR THE STUDY OF NATURAL SCIENCE

HIS REPORT MADE NO IMPACT AND NO ONE UNDERSTOOD ITS IMPORTANCE

IN 1871 MENDEL BECAME AN ABBOT OF THE MONASTERY AND CEASED HIS EXPERIMENTS

MENDEL DIED IN 1884, NEVER KNOWING THAT HIS WORK WAS THE STARTING POINT OF MODERN GENETICS

KNOW:

HOW TO MAKE GAMETES

HOW TO DETERMINE HOW MANY DIFFERENT GAMETES CAN BE MADE

   COUNT THE NUMBER OF HETEROZYGOUS CHARACTERS.
       NUMBER OF HETEROZYGOTES = n
       2n = NUMBER OF DIFFERENT GAMETES POSSIBLE

EXAMPLE:

AABbCCDdEEFf

 

THE HETEROZYGOUS CHARACTERS ARE:

Bb, Dd, Ff

2n = 23 = 2 x 2 x 2 = 8

THERE ARE 8 POSSIBLE GAMETE COMBINATIONS

AABbCCDdEEFf

LECTURE 20

DOMINANCE RELATIONS

1. INCOMPLETE DOMINANCE

ONE ALLELE IS NOT DOMINANT OVER THE OTHER ALLELE LEADING TO A HETEROZYGOUS PHENOTYPE THAT IS INBETWEEN THE TWO PARENT PHENOTYPES

EX. SNAPDRAGONS

P = RED(WW) x WHITE(ww)

F1 = ALL PINK(Ww)
F2 = PINK(Ww) x PINK(Ww)

    W     w  

W   WW    Ww
______________

w   Ww    ww
______________

THE GENOTYPIC AND PHENOTYPIC RATIOS ARE THE SAME

2. CODOMINANCE

TWO ALLELES, NEITHER BEING DOMINANT OVER THE OTHER BUT BOTH BEING EXPRESSED.

EX. ROAN HORSES

BLOOD TYPES (AB)

ABO BLOOD TYPING

MULTIPLE ALLELIC SYSTEM

THREE ALLELES EXIST IN THE POPULATION

IA
IB
i

IA & IB ARE CODOMINANT

i IS RECESSIVE AND IS MASKED BY IA AND IB

IAIA = TYPE A
IAi = TYPE A
IBIB = TYPE B
IBi = TYPE B
ii = TYPE O

INTERACTIONS BETWEEN GENE PAIRS

TWO ALLELES OF ONE GENE CAN MASK ALLELES OF ANOTHER SO SOME EXPECTED PHENOTYPES MAY NOT OCCUR. THIS IS CALLED EPISTASIS

EXAMPLES: COAT COLOR IN MAMMALS

BLACK, BROWN AND YELLOW COATS OF LABRADOR RETRIEVERS

BLACK (B) IS DOMINANT TO BROWN (b)

E GENE ALLOWS MELANIN TO BE DEPOSITED IN THE HAIR AND ee DOES NOT ALLOW ITS DEPOSIT SO THE HAIR IS YELLOW

P = BBEE x bbee

F1 ALL BbEe

F2 COMBINATIONS POSSIBLE

     BE    Be    bE    be .

BE                        .

Be .                      

bE .                      

be .                      

LESS PREDICTABLE VARIATIONS IN TRAITS

1. CONTINUOUS VARIATION IN POPULATIONS
       a. EYE COLOR RANGES FROM BLACK (MOST MELANIN) TO
      BLUE (LEAST MELANIN)
       b. HEIGHT
              TALL TO SHORT
       c. SKIN COLOR

A BELL SHAPED CURVE IS TYPICAL OF POPULATIONS THAT SHOW CONTINUOUS VARIATION

ENVIRONMENTAL EFFECTS ON PHENOTYPE

COAT COLOR IN HIMALAYAN RABBITS AND SIAMESE CATS

BOTH HAVE THE HIMALAYAN ALLELE (ch) FOR THE HEAT

SENSITIVE VERSION OF AN ENZYME FOR MELANIN PRODUCTION

HOTTER REGIONS OF THE BODY HAVE A LIGHT COLOR BECAUSE

THE ENZYMES FOR MELANIN PRODUCTION ARE NOT FUNCTIONAL. COOLER REGIONS ARE DARKER (TIPS OF EARS, TAIL, AND FEET)

LECTURE 21

CHROMOSOMES AND HUMAN GENETICS

HISTORY

1882 - WALTER FLEMMING OBSERVERED CHROMOSOMES IN A NUCLEUS OF A DIVIDING CELL

1884 - COULD CHROMOSOMES BE THE HEREDITARY MATERIAL?

1887 - AUGUST WEISMANN THAT A SPECIAL DIVISION
       PROCESS THAT REDUCES THE CHROMOSOME NUMBER BY
       HALF BEFORE GAMETES FORM

A CELL’S HEREDITARY MATERIAL IS HALF MATERNAL AND HALF PATERNAL IN ORIGIN

1900 - MENDELS PAPER WAS REDISCOVERED AND RESULTS
       WERE
RECONFIRMED

THE CHROMOSOMAL BASIS OF INHERITANCE

1. GENES ARE UNITS OF INFORMATION ABOUT A HERITABLE
   TRAIT
2. GENES ARE DISTRIBUTED AMONG CHROMOSOMES
3. CELLS THAT GIVE RISE TO GAMETES ARE DIPLOID (2N)
   AND
HAVE HOMOLOGOUS CHROMOSOMES
4. HOMOLOGOUS CHROMOSOMES HAVE THE SAME LENGTH,
   SHAPE AND
GENE SEQUENCE AS EACH OTHER
5. HOMOLOGOUS CHROMOSOMES MAY BE CARRYING IDENTICAL
   OR NONIDENTICAL ALLELES
6. THERE IS NO PATTERN TO THE WAY MATERNAL AND
   PATERNAL CHROMOSOMES LINE UP DURING METAPHASE I
7. GENES CLOSE TOGETHER ON THE SAME CHROMOSOME TEND
   TO STAY TOGETHER BUT GENES FAR APART ARE ABLE TO
   CROSSOVER
8. A CHROMOSOME’S STRUCTURE MAY CHANGE DUE TO
   INSERTION, DELETION OR INVERSION

AUTOSOMES AND SEX CHROMOSOMES

SEX CHROMOSOMES DIFFER IN MALES AND FEMALES

MALES HAVE AN X AND A Y CHROMOSOME

FEMALES HAVE TWO X CHROMOSOMES

THE X AND Y CHROMOSOMES ARE SEX CHROMOSOMES

AUTOSOMES ARE ALL CHROMOSOMES OTHER THAN THE SEX CHROMOSOMES

KARYOTYPE ANALYSIS

KARYOTYPE = THE NUMBER OF METAPHASE CHROMOSOMES AND THEIR

DEFINING CHARACTERISTICS

CHROMOSOMES HAVE A CHARACTERISTIC SIZE, LENGTH AND CENTROMERE LOCATION ALONG WITH BANDING PATTERNS WHEN EXPOSED TO CERTAIN DYES

CONSTRUCTING A KARYOTYPE

1. CELLS ARE CULTURED FOR MANY GENERATIONS
2. DIVISION ARRESTED AT METAPHASE BY THE ADDITION OF
       COLCHICINE
3. CELLS CENTRIFUGED TO SEPARATE CELLS FROM THE
   CULTURE MEDIUM
4. CELLS ARE TRANSFERRED TO A SALINE SOLUTION WHERE
   THEY
SWELL AND MOVE APART AS DO THEIR CHROMOSOMES
5. CELLS ARE DROPPED ONTO A SLIDE WHERE THEY ARE
   FIXED AND STAINED

STAINS - ORCEIN
                      GIEMSA

6. CELLS ARE PHOTOGRAPHED AND ENLARGED SO THAT
   CHROMOSOMES CAN BE CUT OUT AND MATCHED UP
7. AUTOSOMES ARE LINED UP FROM LARGEST TO SMALLEST
        WITH THE SEX CHROMOSOMES LAST

SEX DETERMINATION IN HUMANS

EACH EGG PRODUCED BY A FEMALE HAS AN X-CHROMOSOME

HALF THE SPERM CELLS PRODUCED BY A MALE CARRY AN X-CHROMOSOME AND HALF CARRY A Y-CHROMOSOME

IF AN X-BEARING EGG UNITES WITH AN X-BEARING SPERM THE INDIVIDUAL THAT DEVELOPS WILL BE FEMALE

IF AN X-BEARING EGG UNITES WITH A Y-BEARING SPERM THE INDIVIDUAL THAT DEVELOPS WILL BE MALE

      X    X .

X            .

Y            .

A GENE ON THE Y-CHROMOSOME DETERMINES TESTIS DEVELOPMENT. IF IT IS LACKING, OVARIES WILL DEVELOPE INSTEAD

GENE LOCATION

X-LINKED GENES - SEX-LINKED GENES

X-LINKED - ON X-CHROMOSOME

Y-LINKED - ON Y-CHROMOSOME

LECTURE 22

LINKAGE GROUPS AND CROSSING OVER

WHEN GENES ARE LINKED, THEY ARE ON THE SAME CHROMOSOME

THE CLOSER TOGETHER TWO GENES ARE ON A CHROMOSOME THEY MORE LIKELY THEY ARE TO NOT CROSSOVER.

THE FURTHER APART TWO GENES ARE ON A CHROMOSOME, THE MORE LIKELY CROSSING OVER IS TO OCCUR

EXAMPLE:

GGRR = GREEN, ROUND

ggrr = STRIPED, OBLONG

GGRR x ggrr

F1 = GgRr, ALL GREEN, ROUND

TEST CROSS: GgRr x ggrr

IF THE GENES ARE CLOSELY LINKED, YOU WOULD EXPECT THE FOLLOWING GAMETES:

      GR      gr .

gr               .

gr               .

YOU WOULD EXPECT 1/2 TO BE GREEN, ROUND AND 1/2 STRIPED, OBLONG

BUT, YOU GET:

46 GREEN, ROUND
47 STRIPED, OBLONG
4 GREEN, OBLONG
3 STRIPED, ROUND

WHY? 7% CROSSING OVER OCCURRED

HUMAN GENETIC ANALYSIS

HUMANS ARE DIFFICULT TO WORK WITH GENETICALLY

1. HUMANS LIVE UNDER VARIABLE CONDITIONS
2. HUMANS SELECT THEIR OWN MATES
3. HUMANS REPRODUCE WHEN AND IF THEY WANT
4. HUMANS LIVE AS LONG AS GENETICISTS STUDYING THEM
   SO IT IS DIFFICULT TO STUDY MANY GENERATIONS
5. HUMAN FAMILIES SMALL IN SIZE

THESE PROBLEMS ARE "SOLVED" BY MAKING PEDIGREE CHARTS

SYMBOLS USED ON PEDIGREE CHARTS

MALE

 

FEMALE

 

MARRIAGE/MATING

 

OFFSPRING

 

INDIVIDUALS SHOWING TRAIT BEING TRACKED

 

INDIVIDUAL OF UNKNOWN SEX

 

I, II, III SUCCESSIVE GENERATIONS

HUMAN GENETIC DISORDERS

GENETIC ABNORMALITIES - A RARE OR LESS COMMON VERSION OF A TRAIT THAT IS NOT LIFE THREATENING

GENETIC DISORDERS - AN INHERITED CONDITION THAT LEADS TO MILD TO SEVERE MEDICAL PROBLEMS

PATTERNS OF AUTOSOMAL INHERITANCE

AUTOSOMAL RECESSIVE INHERITANCE

1. IF BOTH PARENTS ARE HETEROZYGOUS:
       a. 1/4 OF THE OFFSPRING ARE HOMOZYGOUS DOMINANT
   AND DON’T HAVE THE CONDITION
       b. 1/2 ARE HETEROZYGOUS FOR THE CONDITION AND CAN
   PASS ON THE CONDITION
       c. 1/4 ARE HOMOZYGOUS RECESSIVE AND EXPRESS THE
   CONDITION

SOME AUTOSOMAL RECESSIVE CONDITIONS ARE:

1. ALBINISM
2. SICKLE-CELL ANEMIA
3. GALACTOSEMIA
4. PHENYLKETOURIA (PKU)

     A    a    .

A     AA   Aa   .

a     Aa     aa .

GENOTYPIC RATIO: 1AA:2Aa:1aa

PHENOTYPIC RATIO: 3 NORMAL:1 AB NORMAL

AUTOSOMAL DOMINANT INHERITANCE

1. THE TRAIT APPEARS IN EVERY GENERATION
2. HOMOZYGOTES EXPRESS TRAIT
3. IF ONE PARENT IS HETEROZYGOUS FOR THE CONDITION
   1/2 OF THE OFFSPRING EXPRESS THE CONDITION AND
   1/2 WILL BE HOMOZYGOUS RECESSIVE AND NOT SHOW THE
   CONDITION

Aa x aa

      A     a    .

a     Aa    aa   .

a     Aa    aa   .

GENOTYPIC RATIO: 1Aa:1aa

PHENOTYPIC RATIO: 1 NORMAL:1 ABNORMAL

AUTOSOMAL DOMINANT CONDITIONS

1. AMYOTROPIC LATERAL SCLEROSIS
2. HUNTINGTON’S DISORDER
3. POLYDACTYLY
4. PROGERIA
5. ACHONDROPLASIA

X-LINKED RECESSIVE INHERITANCE

1. THE RECESSIVE PHENOTYPE SHOWS UP MUCH MORE OFTEN
   IN MALES THAN FEMALES
2. A SON RECEIVES THE GENE FROM THEIR MOTHER

IN FEMALES, BOTH THE MOTHER AND THE FATHER WOULD HAVE TO HAVE THE GENE FOR THE CONDITION FOR THE FEMALE TO HAVE THE CONDITION

IF THE FATHER HAS THE CONDITION, ALL HIS SONS WILL HAVE THE CONDITION AND HIS DAUGHTERS WILL BE CARRIERS OF THE CONDITION

X-LINKED RECESSIVE CONDITIONS ARE:

1. HEMOPHILIA -
       a. MOST ARE MALE
       b. CAUSES EXCESSIVE BLEEDING
       c. AFFECTED MALES LACK THE GENE FOR A CLOTTING
     FACTOR

     XH     X .

X   XHX    XX .

Y   XHY    XY .

1/2 FEMALES CARRIERS
1/2 FEMALES NORMAL

1/2 MALES AFFECTED
1/2 MALES NORMAL

2. DUCHENNE MUSCULAR DYSTROPHY
       a. MUSCLE DEGENERATION
3. RED-GREEN COLOR BLINDNESS

X-LINKED DOMINANT INHERITANCE

1. FAULTY ENAMEL TRAIT

HOMOZYGOUS FEMALES SHOW THE CONDITION
HETEROZYGOUS FEMALES SHOW THE CONDITION

MUTATIONS CAN ALTER THE EXPRESSION OF THE EXPECTED CONDITION

CHANGES IN CHROMOSOME STRUCTURE

1. DELETIONS - LOSS OF A PORTION OF CHROMOSOME

CAN BE CAUSED BY:

a. IRRADIATION
b. VIRAL ATTACK
c. CHEMICAL ACTION

A DELETION FROM CHROMOSOME 5 CAN CAUSE A CONDITION CALLED CRI-DU-CHAT (CAT-CRY)

1. CONSTRICTED ESOPHAGUS
2. MENTAL RETARDATION

2. INVERSIONS AND TRANSLOCATIONS

       INVERSIONS - SEGMENT SEPARATED FROM A CHROMOSOME,
   TURNED AROUND AND REINSERTED

   TRANSLOCATION - THE EXCHANGE OF CHROMOSOME PARTS
   BETWEEN NON-HOMOLOGOUS CHROMOSOMES

WHEN PART OF CHROMOSOME 14 ENDS UP ON CHROMOSOME 8 CANCER CAN RESULT

3. DUPLICATIONS

GENE SEQUENCES THAT ARE REPEATED SEVERAL OR MANY TIMES

MAY GIVE RISE TO THE FRAGILE-X SYNDROME

CHANGES IN CHROMOSOME NUMBER

COME ABOUT BECAUSE OF TOO MANY OR TOO FEW CHROMOSOMES IN A GAMETE

CATEGORIES OF CHANGE:

ANEUPLOIDY - ONE EXTRA OR ONE LESS CHROMOSOME
POLYPLOIDY - THREE OR MORE OF EACH TYPE OF
             CHROMOSOME
     a. COMMON IN PLANTS
     b. LETHAL IN HUMANS

MECHANISMS OF CHANGE:

IRREGULARITIES IN MITOSIS OR MEIOSIS

IRREGULARITIES IN FERTILIZATION

NON-DISJUNCTION - FAILURE TO SEPARATE PROPERLY.

IF A GAMETE WITH ONE EXTRA CHROMOSOME UNITES WITH A NORMAL GAMETE A CELL WITH AN EXTRA CHROMOSOME RESULTS

(2N + 1 = TRISOMY)

IF A GAMETE WITH ONE LESS CHROMOSOME UNITES WITH A NORMAL GAMETE A CELL WITH ONE LESS CHROMOSOME RESULTS

(2N - 1 = MONOSOMY)

CHANGES IN AUTOSOME NUMBER:

TRISOMY 21 = DOWN SYNDROME

SYMPTOMS:

a. MODERATE TO SEVERE MENTAL RETARDATION
b. HEART DEFECTS
c. SHORTER BODY PARTS
d. LOOSE, POORLY ALIGNED JOINTS AND BONES

CHANGES IN SEX CHROMOSOME NUMBER

1. TURNER SYNDROME (XO)
        1 IN 2,500 TO 10,000 NEWBORN GIRLS
2. 75% DUE TO NONDISJUNCTION IN THE FATHER
3. SYMPTOMS:
       a. SHORT STATURE
       b. MOST INFERTILE - DO NOT HAVE FUNCTIONAL
      OVARIES - DO NOT PRODUCE EGGS
                                   - DO NOT PRODUCE SEX HORMONES
                                   - NO BREAST DEVELOPMENT

2. KLINEFELTER SYNDROME (XXY)
       a. 1 IN 500 TO 2,000 LIVEBORN MALES RECEIVE TWO
      X’S AND A Y
       b. NONDISJUNCTION IN THE MOTHER 67% OF THE TIME
       c. SYMPTOMS:

- OCCUR AFTER THE ONSET OF PUBERTY
- TALLER THAN AVERAGE
- STERILE OR SHOW LOW FERTILITY
- TESTIS SMALLER THAN AVERAGE
- FACIAL HAIR SPARSE
- SOME BREAST ENLARGEMENT
- MILD MENTAL IMPAIRMENT

3. XYY

a. 1 IN 1000 MALES HAS ONE X AND 2 Y CHROMOSOMES
b. SOME MILDLY RETARDED, MOST NORMAL
c. AT ONE TIME THOUGHT TO BE MORE PREVALENT IN
   CRIMINALS
D.
  TALLER THAN AVERAGE