BIO 101 -- GENERAL BIOLOGY
MENDELIAN INHERITANCE
I.
II.
III.
INTRODUCTION
A. Living things
1.
Reproduce
2.
Adapt
B.
Genetics
1.
Blueprint for reproduction
2.
Means of adaptation: Mutations = alleles
a.
translocation
b.
deletion
c.
inversion
d.
duplication
MENDELIAN GENETICS
A. Mendel used scientific method
B.
Monohybrid inheritance
P  F1  F2
1.
Mendel's Law of Segregation
a.
Each organism has 2 factors (alleles) for each trait
b.
Factors (alleles) segregate (separate) during formation of
gametes
i.
Each gamete carries one factor (allele)
c.
Fertilization = zygote with 2 factors (alleles) for each trait
(1 from each P)
2.
Dominant / recessive trait (allele)
a.
Gene = section of DNA with enough code to make one
protein. Each protein contributes to a trait that is inherited.
b.
Allele = one version of a gene. It shows a particular trait.
3.
Genotype / phenotype
Testcross determines genotype of dominant phenotype
a.
Heterozygous
b.
Homozygous
C.
Dihybrid inheritance
1.
2 traits, each trait having 2 factors (alleles)
2.
Mendel's Law of Independent Assortment
Each pair of factors segregates independently of every other pair of
factors. All possible combinations of factors can occur in gametes.
VARIATIONS ON MENDEL'S LAWS
A. Incomplete dominance (Codominance)
1.
red + white  pink
B.
Multiple alleles
1
Ex: blood type
C.
D.
E.
IV.
V.
AA
AB
BB
AO
BO
OO
Polygenic inheritance
1.
Trait controlled by several genes
2.
Results in range of characteristics on bell shape curve intermediate
genotype most abundant
Epistasis
1.
interaction among the products of two or more genes
Pleiotropy
1.
positive or negative effects on 2 or more traits owing to expression
of alleles at a single gene locus
2.
effects may or may not emerge at the same time
CHROMOSOME THEORY OF INHERITANCE
A. Developed in early 1900's
1.
Behavior of chromosomes in mitosis described in 1875
2.
Meiosis described in 1887
3.
1902 - Group headed by Thomas Morgan observed parallel
behavior of genes & chromosomes
B.
Concluded genes on chromosomes
C.
1950’s – structure of DNA discovered.
CHROMOSOME SEX DETERMINATION
A. Paired chromosomes same = autosomes
B.
All are autosomes except: sex chromosomes
XX = Human Female
XY = Human Male
VI.
VII.
HUMAN GENETIC DISORDERS
A. X-linked recessive genetic disorders
1.
Carriers = females only (faulty recessive gene masked by normal
dominant gene)
2.
Trait shows in males more often than females
B.
Autosomal recessive genetic disorders
C.
Autosomal dominant genetic disorders
D. Incompletely dominant genetic disorders
SUMMARY
A. Mendel's Law of Segregation
experiments with monohybrid crosses showed:
2
F1 resembled 1 of the parents
F2 1/4 showed traits of the other P
factors segregated into the gametes
1 dominant / 1 recessive
B.
Mendel's Law of Independent Assortment
Dihybrid cross
1.
2.
C.
4 phenotypes in F2
all possible combinations of alleles occur in gametes
Exceptions to Mendel's laws
1. Incomplete dominance
2. Multiple alleles
3. Polygenic inheritance
4. Epistasis
5. Pleiotropy
D.
HOMEWORK
1. Practice Punnet Squares.
3