Download Unit 7 Heredity PPT

CHAPTER 11
INTRODCUTION
TO GENETICS
?
Father
Grandfather
Grandmother
Mother
Genetics =
A branch of Biology that studies Heredity
1800’s
Gregor Mendel =
Father of Genetics
1857
Garden Pea Plant
Pea plants are available in many varieties with distinct heritable
features (characters) with different variants (traits).
Sexual Reproduction
Male Gamete = Pollen
(stamens)
Female Gamete = Egg
(pistil/carpal)
Pollen
Controlled fertilization
Artificial cross-pollination
(hybridize)
Monohybrid Cross
= One Trait
“Height”
Tall Pea x Short Pea
T = Dominant
t = Recessive
TT x tt
“Homozygous
Dominant”
“True Breeding” = Homozygous
X
“Homozygous
Recessive”
Generations
P1 = Parent Plants
-True breed Tall x True breed Short
TT
x
tt
F1 = First Generation (children)
Genotype = Tt (Heterozygous) 4:4 100%
Phenotype = Tall 4:4 100%
100%
F2 = Second Generation (grandchildren)
Tt x Tt
Genotype:
1 TT (Homozygous Dominant)
1:4 25%
2 Tt (Heterozygous)
2:4 50%
1 tt (Homozygous Recessive) 1:4 25%
Phenotype
Tall 3:4 (75%)
75%
Short 1:4 (25%)
25%
Gene = a segment of DNA located on the
chromosomes
Alleles = different gene forms
(tall or short)
Dad Mom
 Locus
Tall or Short
Diploid = 2n
2 alleles determine a Trait:
Mother’s + Father’s = Trait
What happened in the F1?

Alleles: Tall = Dominant (T)
Short = Recessive (t)
Dominant = Trait Observed
Recessive = Trait that disappeared
Genotype Phenotype
TT = Tall
Tt = Tall
tt = Short
Can’t always know
an organisms
genotype by
looking at its
phenotype?
Homozygous
Dominant
Homozygous
Recessive
tt
TT
T
t
Tt
Heterozygous
Change of colors to follow the parental alleles:
F1
Tt x Tt
Combination of Letters/Alleles?
F2
3 Tall and 1 Short
TT
Tt
Tt
tt
Similar
3 to 1 ratios
among F2
offspring when
crossed for
other traits
1st LAW OF HEREDITY
“Law of Segregation” =
– The 2 alleles for each trait must separate
when gametes (sperm/egg) are formed.
-A parent passes on, at random, only one allele
for each trait to each offspring
A
aa

Segregation
Random
Fertilization
Law of Probability
“Rules of Chance”
“Odds”
Numerator = winner
Denominator = # horses
1/12
20:1 5%
1:12 “odd”
10:1 10%
8% “chance”
2:1 50%
Probability?
“Chance” of getting a tail?
“Chance” of getting snake eyes on two dice?
“Chance” of getting a boy?
Male: Female
XY XX
½
1:2 odd Boy
1:2 odd Girl
50% chance
Survey Large Number
1:1
Punnett Square
= used to predict and compare the genetic
variations that will result from a cross
If you know the genotypes of Parents,
you can use a PS to predict the
genotypes/ phenotypes of Offspring
Monohybrid Cross =
Cross for one trait
P
p
Genotype =
PP (1:4) 25%
Pp (2:4) 50%
pp (1:4) 25%
P
P P
P p
Phenotype =
Purple (3:4) 75%
White (1:4) 25%
p
P p
p p
Punnett Square Rules:
1.
2.
3.
4.
5.
Make the square/ squares
Place the parents genotype (letters) on outside of square.
Fill in the individual squares
Ratio/ Percentage of Genotype (letters)
Ratio/ Percentage of Phenotype (look-like)
Dihybrid Crosses:
Crossing for 2 characteristics/ traits
•Seed Shape and Seed Color
•Shape =Round was Dominant to Wrinkled
•Color = Yellow was Dominant to Green
Round Yellow Seeds
Wrinkled Green Seeds
x
RRYY
RRYY
rryy
rryy
F1?
RrYy
F1 = All plants Round Yellow Seeds
RrYy
F2?
RrYy
RrYy
Round Yellow
Round Green
RrYy
Wrinkled Yellow
Wrinkled Green
The presence of one specific
allele for one trait has no impact
on the presence of a specific
allele for the second trait.
The two pairs of alleles
segregate independently
of each other.
Four classes of gametes
(RY, Ry, rY, and ry) would be
produced in equal amounts.
RY
Ry
RrYy
rY
ry
ND
2
LAW OF HEREDITY
• Law of Independent Assortment =
genes for different traits are
inherited “independently” of each
other.
•RrYy = the R and r will separate as well
as the Y and y.
•Alleles can recombine in 4 different ways.
HUMAN PHENOTYPES
COMPLETE DOMINANCE
Widow’s Peak = Dominant
Clockwise = Dominant
Cleft = Dominant
Dimples = Dominant
Mid-Digital Hair = Dominant
Left Crossing Right = Dominant
Hitchhiker Thumb =
Recessive
Bent Little Finger = Dominant
Right Handed = Dominant
Free = Dominant
Roll Tongue = Dominant
PTC Taste = Dominant
Right Leg on Top = Dominant
Shorter Big Toe = Dominant
PATTERNS OF HEREDITY
EXTENDING
MENDELIAN GENETICS
INCOMPLETE DOMINANCE
Flower color
of snapdragons
Heterozygote
CODOMINANCE
Two alleles affect the phenotype in separate, distinguishable ways.
Dominant alleles do not somehow subdue a recessive allele
Shorthorn Red
Shorthorn Roan
Shorthorn White Recessive
MULTIPLE ALLELES
HUMAN BLOOD TYPES
Three alleles: IA, IB, and i
Which dominant?
Codominant?
4
A and B are completely dominant over i
A and B
6
place type A oligosaccharides on the
surface of their red blood cells
Type?
B
Type?
AB
Type?
Neither
Antibodies present in blood = proteins
If the donor’s blood has an A or B factor that is foreign to the recipient,
antibodies in the recipient’s blood will bind to the foreign molecules,
cause the donated blood cells to clump together, and can kill the recipient.
Universal donor?
O
Universal recipient?
AB
Polygenic Inheritance
More than one gene determines
the trait
Quantitative Characters
= an either-or classification is impossible
Characters vary in the population
along a continuum (in gradations)
Sub-Saharan
African
Indian
Southern
European
Northern
European
Skin pigmentation
At least 3 genes involved
(A, B, C)
A dominant over a
B dominant over b
C dominant over c
“Bell Curve/ Normal Distribution”
aabbcc =
very light
AaBbCc =
intermediate
AABBCC =
very dark
Environmental Factors =
Cool 30o C = Female
Warm 34oC = Male
Environmental Influences = Age
Check Fetus for Genetic Disorders
When you contemplate all that
can occur in the pathway from genotype
to phenotype =
His work was “impressive” indeed
MENDELIAN INHERITANCE IN HUMANS
Pedigree
= “Family Tree”
Studying humans:
1 generation = ~20 years
Few offspring
Not moral to study
Follow certain traits through family histories
Understand past and predict the future
• YouTube - I'm My Own Grandpa
YouTube - I'm My Own GrandpaRay Stevens ( with family tree
diagram)