Download sex chromosomes

Objective: 1)
Provide an
example for
codominance,
incomplete
dominance, and
multiple alleles.
2) Define
karyotype.
SOME TRAITS THAT ARE DOMINANT INCLUDE:
HITCHHIKER’S THUMB, ALMOND-SHAPED EYES,
THICK LIPS, HAIR ON MIDDLE SECTION OF
FINGER.
.
Human Traits: autosomal
Oval dominant, square recessive
1. Shape of face (probably polygenic)
2. Cleft in chin
No cleft dominant, cleft recessive
3. Hair curl (probably polygenic)
Assume incomplete dominance
Curly:
Wavy:
Straight: homozygous
4. Hairline
Widow peak dominant, straight hairline
recessive
5. Eyebrow size
Broad dominant, slender recessive
6. Eyebrow shape
Separated dominant, joined recessive
7. Eyelash length
Long dominant, short recessive
8. Dimples
Dimples dominant, no dimples recessive
9. Earlobes
Free lobe dominant, attached recessive
homozygous
heterozygous
10. Eye shape
Almond dominant, round recessive
11. Freckles
Freckles dominant, no freckles recessive
12. Tongue rolling
Roller dominant, nonroller recessive
13. Tongue folding
Inability dominant, ability recessive
14. Finger mid-digital hair
Hair dominant, no hair recessive
15. Hitch-hiker's thumb
Straight thumb dominant, hitch-hiker thumb
recessive
16. Bent little finger
Bent dominant, straight recessive
17. Interlaced fingers
Left thumb over right dominant, right over
left recessive
18. Hair on back of hand
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19. Tendons of Palmar Muscle
Hair dominant, no hair recessive
Two tendons dominant, three tendons
recessive
INCOMPLETE DOMINANCE: THE PHENOTYPE OF
THE HETEROZYGOUS CONDITION IS A CROSS
BETWEEN THE DOMINANT AND RECESSIVE
TRAITS.
EXAMPLE: IN CARNATIONS, R=RED
r=WHITE
RR= RED CARNATION
Rr= PINK CARNATION
rr= WHITE CARNATION
CODOMINANCE: THE PHENOTYPES OF BOTH
ALLELES ARE EXPRESSED IN A HETEROZYGOUS
INDIVIDUAL.
EXAMPLE:
IN CHICKENS, B= BLACK FEATHERS, W=
WHITE FEATHERS
BB = BLACK FEATHERS
BW = BLACK AND WHITE FEATHERS
WW = WHITE FEATHERS
MULTIPLE ALLELES: SOMETIMES MORE THAN 2
ALLELES CONTROL A TRAIT.
3 ALLELES DETERMINE PIGEON FEATHER
COLOR
Occurs when one gene controls the expression of a
second gene.
In mice, one gene controls whether the mouse will
have coloration (dominant) or albinism/white
(recessive). IF coloration is dominant, THEN a
second gene will determine if the mouse will be
brown or black.
Pleiotropy is a condition that occurs when 1 gene
controls many phenotypes.
A classic example of pleiotropy is the human disease
PKU (phenylketonuria). This disease can cause
mental retardation and reduced hair and skin
pigmentation, and can be caused by a mutation in a
single gene that codes for an enzyme (phenylalanine
hydroxylase) that converts the amino acid
phenylalanine to tyrosine, another amino acid.
One trait or phenotype is controlled by many genes.
For example between 4 to 10 genes control human
height.
Genes linked to
human height:
ZBTB38, HHIP,
CDK6, HMGA2,
GPR126, ADAMTSL3,
GDF5, LCORL,
EFEMP1, and
HIST1H1D
AUTOSOMES: THERE ARE 22 PAIRS OF
HOMOLOGOUS CHROMOSOMES (TOTAL
CHROMOSOMES =44)
SEX CHROMOSOMES: 1 PAIR OF CHROMSOMES
THAT DETERMINE THE SEX OF AN
ORGNANISM. SOME TRAITS ARE CONTROLLED
BY GENES LOCATED ONLY ON THE SEX
CHROMOSOMES (EXAMPLE: COLOR BLINDNES
AND HEMOPHILIA).
YOUR CHROMOSOMES
ORGANIZED AS A KARYOTYPE
(CHROMOSOME MAP)
YOUR
CHROMOSOMES
DURING METAPHASE
SEX-LINKED TRAITS: TRAITS CONTROLLED BY
GENES LOCATED ON THR SEX CHROMOSOMES.
X = FEMALE SEX CHROMOSOME
Y = MALE SEX CHROMOSOME (SMALLER THAN
X AND DOES NOT CONTAIN AS MANY GENES)
THOMAS HUNT MORGAN DISCOVERED TRAITS
LINKED TO SEX CHROMOSOMES. HE FIRST
NOTICED THIS IN FRUIT FLY EYE COLOR.
MORGAN’S 1ST EXPERIMENT:
X
FEMALE
Xr
Y
XR
XRXr
XRY
XR
XRXr
XRY
MALE
OFFSPRING: ALL
RED EYES