Download Chp11

Heredity / Genetics
Early explanations for heredity?
Gregor Mendel published 1865
Consequences of a monk proposing the nature of heredity?
Early 1900’s accuracy recognized
Grew up on a farm
Educated in mathematics (probability) & science
Why
garden
pea plant?
P1 - Pure Breeding homozygous F1
seeds
phenotypes
F2
phenotypes
Round x
wrinkled
All round
5,474 round
2.96 : 1
1,850 wrinkled
Yellow x
green
All yellow
6,022 yellow
2,001 green
3.01 : 1
All gray
705 gray
224 white
3.15 : 1
Full x
constricted
All full
882 full
299 constrict
2.95 : 1
Green x
yellow
All green
428 green
152 yellow
2.82 : 1
Axial x
terminal
All axial
652 axial
207 terminal
3.14 : 1
All long
787 long
277 short
2.84 : 1
Gray x white
pods
stem
Long x short
F2 ratio
Explanation
Experimentation led to four basic conclusions:
Concept of Unit Characters:
Traits are controlled by factors that occur in pairs
Law of Segregation:
This says that of a pair of characteristics (e.g. blue and brown eye color) only one
can be represented in a gamete.
Principle of Dominance
One factor in a pair may mask the expression of the other
Dominant factor vs. Recessive factor
Law of Independent Assortment
Different pairs of factors are passed to offspring independently of each other.
The result is that new combinations of genes present in neither parent
are possible. (flip two pennies & two nickels)
Gene for yellow seeds (Y), gene for green (y)
P1 = Pure bred cross - YY x yy
x
y
y
Y
Yy
Yy
Y
Yy
Yy
x
Y
y
Y
YY Yy
y
yY
yy
Essential Terms
•Homozygous vs Heterozygous
•Dominant vs Recessive
•Phenotype vs Genotype
•Ratio
•Alele
•Hybrid
•Monohybrid Cross
•Dihybrid Cross
•P1. F1. F2
•Punnet Square
•Pedigree
•Gamete
•Probability
•Product Rule
Human examples of Mendelian Traits
Listed below are human traits that reveal dominance & recessiveness All traits listed are the dominant phenotype
•Tongue Curling
•Widow’s Peak
•Free Ear lobe
•Brown Pigmented Iris
•Hitch Hikers Thumb (45 degree angle)
•Shorter Big Toe (shorter in length than second toe)
•Mid Digital Hair
•Freckles
•Rh Factor
•PTC taster
•Left Thumb Over Top Right - (When Interlocking Fingers of both hands)
•Short Palmar Muscle (Two tendons back of thumb to wrist is dominant, three is recessive)
What about combinations of characteristics?
Law of Independent Assortment
different pairs of alleles are passed to offspring independently of
each other. The result is that new combinations of genes present in
neither parent are possible.
If we took two coins what is the probability of flipping
one head and one tail? To determine this we must
1. realize that the outcome of one does not influence the
outcome of the other. (Independent assortment).
2. Determine all of the possible outcomes
x
H
T
H
HH HT
T
TH HH
Head & Head = (1/2 x 1/2)
Head & Tail = 2(1/2 x 1/2)
Tail & Tail = (1/2 x 1/2)
When Mendel looked at combined characteristics:
Flower position (axial & terminal) and stem length (long & short)
Pure bred axial flower_round seed producing plant crossed with
pure bred terminal flower_wrinkled seed producing plant
AARR x aarr = all offspring AaRr
F1 all axial flower round seed producing plants (F1 hybrids)
F2 parents (AaRr x AaRr)
Gametes from AaRr
(independent assortment)
AR , ar or Ar, aR
Axial_round = 9/16
Axial_wrinkled = 3/16
Terminal_round = 9/16
Terminal_wrinkled = 1/16
x
AR
ar
Ar
aR
AR
AARR
AaRr
AARr
AaRR
ar
AaRr
aarr
Aarr
aaRr
Ar
AARr
Aarr
AArr
AaRr
aR
AaRR
aaRr
AaRr
aaRR
Product Rule:
The chance of two random events happening simultaneously is equal
to the sum of their separate probablilities
Two coins both heads = 1/2 x 1/2 = 1/4
Pair of dice both coming up 6 = 1/6 x 1/6 = 1/36
One di and one coin coming up with a head and a six = 1/2 x 1/6 = 1/12
AaRr x AaRr the chance for getting AaRr = 1/2 x 1/2 = 1/4
Thc chance for getting AARr = ?
Phenotypic Ratio? (A_R_, A_rr, aaR_, aarr)
x
A
a
x
R
r
A
AA
Aa
R
RR
Rr
a
aA
aa
r
rR
rr
AaRrCcDd x AarrCcdd
AarrCcDd?
AARrCcDD?
Non-Mendelian patterns of inheritance
Incomplete Dominance:
Hybrids produce a trait that reveals a
blend of both aleles
R = red W = white
RR = red
WW = White
RW = Pink
Co-Dominance
Hybrids reveals trait of both aleles
R = red W = white
RR = red
WW = White
RW = Roan (red & white colors)
Polygenic inheritance
Multiple pairs of genes all influencing one trait
Yao Ming 7’5”
Earl Boykins 5’5”
Many pairs of genes
influence the height of a
human. Efficiency of
the digestive system,
circulatory system, and
endocrine system - each
being controlled by
many pairs of genes will all impact height.
Multiple Aleles
Traits in which within a population there exists more than two
forms of a gene.
Human blood type - RBC surface proteins must be compatible when
initiating a transfusion. Some people have A proteins on their RBC’s,
others have B proteins., and others have neither.Within the human
population there exists three forms of the gene that controls surface
proteins on RBC’s.
Alele A (makes A proteins) Alele B (makes B proteins) Alele i (makes neither A or B)
Four main blood types: (phenotypes) A - B - AB - O
Genotypes:
•AA, Ai - blood type A
•BB, Bi - blood type B
•AB - blood type AB
•ii - blood type O
Ai x Bi ?
Sex Linkage
Most animal species have a special
pair of chromosomes that
determine gender. In humans 22
pairs of autosomes and 1 pair of
sex chromosomes
Two types - X (large and has genes that
control non gender related traits)
Y (small and only promotes
the formation of male genitalia)
XX = female
XY = male
X
Y
X
XX
XY
X
XX
XY
XX x XY
Sex linked traits are traits
controlled by genes on the X
chromosome. Females have two,
males have only one. Females can
carry but not show defective sex
linked traits. Males CAN NOT be
carriers.
Duchene’s Muscular Dystrophy
Color Blindness
Hemophilia
Duchene’s Muscular Dystrophy
Color Blindness
Hemophilia
Duchene’s Muscular Dystrophy
Color Blindness
Hemophilia
Duchene’s Muscular Dystrophy
Color Blindness
Hemophilia
Duchene’s Muscular Dystrophy
Color Blindness
Hemophilia