On the paper write :
1. your
name
(first
last)
Take
out
a and
blank
sheet of paper
2. The date today (5-5-03)
3. The letter of the correct answer to the following question
While viewing stained onion root tip cells you notice that
distinct chromosomes cannot be observed in most of the
cells. This is because most of the cells …..?
A.)
were destroyed while preparing the slide
B.)
must be in interphase (G1, S, G2)
C.)
are undergoing mitosis.
D.)
are undergoing meiosis.
Asexual and Sexual Reproduction
•
Genetically identical cells are produced from
a single parent cell by mitosis.
 Fission or Budding
•
Sexual reproduction occurs when new
individual is formed through union of two sex
cells (gametes).
 Produce zygote.
 Haploid gametes formed by meiosis in sex
organs (gonads).
Asexual and Sexual Reproduction
•
Different Approaches to Sex
 Parthogenesis - Virgin birth
- Exclusive
- Switching

Sexual Reproduction
-
monoecious / dioecious
Hermaphroditism - Both Sex organs
Sexual Reproduction
•
Sex Determination
 In some organisms, environmental
conditions can determine sex of offspring.
- In mammals, sex is determined early in
embryonic development.
 Embryonic gonads are indifferent.
 Y chromosome produce males.
Animals: Sex Determination
Plant Life Cycle
Alternation of
generations
Alternation of generations in Gynosperms
Alternation of generations in angiosperms
Comparison between Animal and Plant life
cycles
•
•
•
Plants gametes divide
so individuals are
haploid or diploid
Animals individuals
are diploid and
gametes are haploid
Patterns of Inheritance
Pattern of inheritance
hypotheses

heredity – the tendency for traits to be
passed from parent to offspring



“blending” hypothesis – the genetic material of
the parents mixes in a manner similar to blending
paint.
Lamark’s inheritance of acquired characteristics.
example a giraffe's neck
Mendel’s inheritance of characteristic traits
Mendelian Genetics
 Who
was Gregor Mendel?
Monk studied science and
mathematics at University of
Vienna.
Worked with garden peas to
study heredity.
Many varieties available
Infrequent version of a trait
Small and easy to grow
What were Mendel’s experiments?
Mendel performed simple test
crosses
 Parent
generation
P2
P1 X

First Filial generation
F1

Second Filial generation
F2

In each generation he recorded the phenotype of
each individual and the number with each
phenotype
How did Mendel derive his
rules?




Used pea plants to
control parental
crosses
Chose only characters
that were present or
not present.
Started parental cross
with true-breeders
Crossed two truebreeders of different
varieties –
hybridization cross
Mendel’s first observation:
Alleles show dominance
 Dominance: One allele controls the phenotype

Dominant phenotype is given by two
genotypes:
Homozygote and heterozygote: RR and Rr

Recessive phenotype is given by one
phenotype:
Homozygote: rr

Dominant phenotype is given by two
genotypes:
Homozygote and heterozygote: RR and
Rr
 Gene – a discrete unit of heredity
 Allele – alternate forms of a gene when expressed result
in variation within traits
 Phenotype – the physical trait expressed
 Genotype – the alleles present





Somatic cells have two alleles of each
gene but gametes have only one allele
Alleles of each gene segregate during
gamete formation
Principle of allele segregation is
Mendel’s first rule
Parent =
Gametes =
Rr
1/2 R
1/2 r
 Segregation
followed by random gamete fusion
produces the observed numerical ratios of
genotypes
 Dominance gives the observed ratios of
phenotypes
How do scientists predict the probability
of inheritance?
Punnett Squares
Punnett Squares can be used to visualize
crosses between two individuals.
 Possible gametes of individual are listed along
horizontal side. And possible gametes of the other
individual are listed along the vertical side.
Genotypes of potential offspring are represented by
cells within square.
Frequency expressed as probability.
Genotype
Rr
ovule produced with one
allele R
and one
allele r
Genotype
rr
pollen produced with
one
allele r
and one
allele r
Punnet’s Square
r
R
r
r
Rr
rr
Rr
rr
Second Law Independent Assortment
Genes located on
different
chromosomes are
inherited
independently of one
another.
Dihybrid Crosses
YyRr heterozygous
YR Yr
yR
yr
YR
YY RR
YY Rr
Yy RR
Yy Rr
Yr
YY Rr
YY rr
Yy Rr
Yy rr
yR
Yy RR
Yy Rr
yy RR
yy Rr
yr
Yy Rr
Yy rr
yy Rr
yy rr
YyRr heterozygous
Parental heterozygous cross
phenotypic ratio?
9
YY RR
YY Rr
Yy RR
Yy Rr

Yellow round seeds
(any with Y or R)
Yellow wrinkled
3 seeds
(any with Y and
rr)
YY Rr
YY rr
Yy Rr
Yy rr
Yy RR
Yy Rr
yy RR
yy Rr
3
yy rr
Green round seeds
(any with yy and
1 R)
Yy Rr
Yy rr
yy Rr
Green wrinkled
seeds
(any with yy and
Incomplete
Dominance
 Some alleles produce
a heterozygote
phenotype that is
intermediate between
those of the parents.
Multiple Alleles
Often each allele has its own effect and the alleles
are considered codominant.
Human ABO Blood type
Type A individuals only galactosamine
Type B individuals add only galactose
Type AB individuals add both sugars
Type O individuals add neither sugar
Rh Blood Group
Rh cell surface marker
Epistasis
Epistasis - Interaction between products of two
genes where one gene modifies the other gene’s
phenotypic expression.
Emerson - To produce pigment, a Zea mays plant must
possess at least one functional copy of each enzyme gene.
Epistasis
Sex Linkage

A trait determined by a gene on the sex
chromosome is said to be sex-linked.

In Drosophila, sex is determined by the number of copies
of the x chromosome.
Eye color gene is carried on
the X chromosome
What alleles will the
sperm have?
What alleles will the
eggs have?
XR
XR
Y
X RX R
X RY
Xr
X RX r
X rY
Heterozygous for
red eye color
Offspring
phenotypes
All females
have red eyes
½ of the males
have white
eyes and ½ the
males have
red eyes
Mutations in Human Heredity
Mutations are accidental changes in genes.
 Rare, random, and usually result in recessive
alleles.
Pedigrees used to study heredity.
 Hemophilia - Inherited condition where blood is
slow to clot or does not clot at all.
Only expressed when individual has no copies of the
normal allele.
Royal Hempohilia - Sex-linked
Sickle-Cell Anemia

Sickle-Cell Anemia is a recessive inherited
disorder in which afflicted individuals have
defective hemoglobin, and thus are unable
to properly transport oxygen to tissues.


Heterozygotes usually appear normal.
Homozygotes have Sickle-Cell, but are resistant
to malaria.
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Other Disorders

Tay-Sachs

Incurable heredity disorder which causes brain to
deteriorates.


Nonfunctional form of hexosaminidas A enzyme.
Huntington’s Disease

Inherited condition caused by dominant allele
causing progressive brain deterioration.

Symptoms usually develop late in life.
Genetic Counseling and
Therapy

Process of identifying parents at risk of
producing children with genetic defects and
assessing genetic state of early embryos.



Amniocentesis
Ultrasound
Chorionic Villi Sampling
Pedigree Analysis
Mendel’s laws allow us to analyze the genetic
information in family records (pedigrees)
From this we can determine the nature of alleles
that control traits. From this we can:
deduce whether the trait is dominant or recessive
deduce whether the trait is sex linked
deduce the genotypes of members of the family
predict the phenotypes of future offspring
deduce the genotypes of parents from their offspring
phenotypes


In a pedigree, each
individual is represented by
a symbol
The shape, color, and
location of the symbol carry
information about the sex
and phenotype of the
individual

A dominant allele has a different pattern of inheritance:
Aa
Aa
Trait A
dominant
Only a a for recessive trait
expression so both
parents have to have a
recessive allele