Transcript Genetic Engineering and The Human Genome

The Human
Genome: Beyond
Dominant and
Recessive
Ch. 14
Learning Goals




Explain how flower color can be an incomplete
dominant trait.
Compare autosomal and sex chromosomes .
Describe the cause of Down Syndrome.
Defend why Calico cats are never males.
A. Human Chromosomes



22 pairs of autosomes or non sex chromosomes
for a total of 44.
1 pair of sex chromosomes for a total of 2.
Males ( 44 + XY) and females (44 + XX) = 46
autosome
sex chromosome
autosome
sex chromosome
Karyotype: pictures of chromosomes,
can be used to study our chromosomes.
Male or female?
B. Beyond Dominant and Recessive:
: textbook pages 272-273
1. Incomplete Dominant: The heterzygous
condition results in a “blending” of the
phenotypes.
•Red flower = RR
white flower = WW
• pink flower= RW
•2. Co-dominance: the heterozygous condition
results in “both “ phenotypes being expressed.
•White chicken= WW Black chicken = BB
‘black and white spotted chicken = BW

3. Multiple alleles = more than two alleles
available for the trait.
Rabbits have different alleles for coat color.

C = brown

cch = gray
ch = black and white
c =albino
4. Polygenic Traits: many traits are responsible for
the phenotype.
 Skin color in humans has many variations, due
to many genes that control this trait .
C. Autosomal recessive Disorders

Most genetic disorders are caused by autosomal
recessive alleles, on chromosome 1 to 22.
Tay-Sacs: causes nervous system breakdown. No
treatment, fatal. genotype-= cc
 Albinism: no pigment, no cure. genotype= aa
 Polydactlysim: more than five fingers/toes.
genotype = pp

***both recessive alleles present!!!!

YouTube - White Negros - South Africa
D Autosomal dominant disorders

Huntington’s : causes brain cells to waste
away. Genotype: HH or Hh

Dwarfism : shorter limbs, normal mental
development.
genotype DD or Dd
***one dominant allele needs to be present.
Little People Big World
E. Sex-Linked Disorders



Disorders located on the X and Y Chromosome.
Males have one X chromosome and thus all
inherited X-linked traits are expressed in males.
ex. XcY (male, colorblind)
XcX (female, not colorblind)
Disorders include : Colorblindness ( see shades
of gray) , Hemophilia (can”t clot blood), and
Duchennes Muscular Dystrophy (muscular
break down) .
Color blind Test
F. Hemophilia: Queen Victoria
Hemophilia is an X-linked recessive disorder. It causes
the inability to clot blood ( blood can not stop
bleeding).
Queen Victoria was a carrier for this mutation. She had a
mutation that occurred and passes it off to 3 of her
nine children.
X X = normal female
X Xh = female carrier , not a hemophiliac
XhXh= female with hemophilia
Xh Y = male with hemophilia
Queen Victoria’s Pedigree
G. X- Chromosomes Inactivation







Females have two X chromosomes….in Calico cats the
alleles for black fur and orange fur both present and
are randomly turned on and off, resulting in these
blotches of color. All calico patterned cats are female!
XoXb= calico female
XoXo= orange female
XbXb= black female
XoY=orange female
XbY=black male
*b=black, o=orange
H . Non –Disjunction : caused
chromosomal disorders.

Nondisjunction occurs when chromosomes fail to
separate_____ during meiosis.
Meiotic Nondisjunction at Meiosis I Animation




The result is an abnormal number of chromosomes.
Down Syndrome – Extra chromosome at position 21.
AKA Trisomy 21 . Total chromosome = 47 !
Turner’s Syndrome – a female with only one X
chromosome Total chromosome = 45
Klinefelters’ syndrome – In Males too many X
chromosomes. Ie. XXXXXY or XXY.
Total chromosome = 47 or 50
What does this person have?
Turner Syndome
Klinefelter
Downs Syndrome
Summary 5-7 sentences

Cornell questions on the side/comments