CHAPTER 11
Introduction to Genetics
Genetics- the scientific study of heredity
Gregor Mendel
Gregor Mendel’s work
Fertilization- sexual reproduction, union of male
and female reproductive cells
True-breeding- to produce offspring that are
identical to the parents in characteristics
Gregor Mendel’s work
Cross-pollination- taking the sperm cells from one
plant and joining them with the egg cells of
another plant
Gregor Mendel’s work
Trait- specific characteristic
P generation- Parental generation
F1 generation- offspring of first generation
F1 “first filial”
Hybrids- offspring of
parents with different traits
Conclusions
1. Biological inheritance is determined by factors
that are passed from one generation to the next
Genes- chemical factors that determine traits
ex: the gene for plant height
Alleles- different forms of a gene
ex: the short allele and the tall allele
Conclusions
2. Principle of dominance
some alleles are dominant and some are recessive
Segregation
What happened to the traits of the P generation that
disappeared in the F1 generation?
Segregation
F2 generation- the F1
generation self-pollinated
Segregation
The gametes (sex cells)
contain only one of the traits.
The gametes separate the
traits and recombine them
in the offspring
11-2 Probability and Punnett Squares
• Probability- the likelihood that a particular event
will occur
Punnett Squares
• Can be used to
predict and
compare the
genetic
variations that
will result
from a cross
• Homozygous- two identical alleles for a
particular trait. Ex: TT or tt
• Heterozygous- two different alleles for a
particular trait. Ex: Tt
• Phenotype- physical characteristics
• Tall plants or short plants
• Genotype- genetic makeup
• TT, tt, or Tt
• Can two organisms have the same phenotype but
a different genotype?
Probabilities predict averages
• Increasing the number of
offspring yields results
closer to the predicted
averages
11-3 Exploring Mendelian Genetics
• Independent Assortment
• Does the segregation of one pair of alleles affect
the segregation of another pair of alleles?
• Round Yellow X Wrinkled Green
Round Yellow X Wrinkled Green
• All the F1 generation were round yellow
• Which traits are dominant?
ry
ry
ry
ry
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
F2 generation, RrYy X RrYy
RY
RY
Ry
rY
ry
Ry
rY
ry
F2 generation, RrYy X RrYy
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
F2 generation, RrYy X RrYy
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
• Round Yellow
F2 generation, RrYy X RrYy
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
• Round Yellow
• Round Green
F2 generation, RrYy X RrYy
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
• Round Yellow
• Round Green
Wrinkled Yellow
F2 generation, RrYy X RrYy
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
• Round Yellow
Wrinkled Yellow
• Round Green
Wrinkled Green
9: 3: 3: 1 Ratio
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
• Round Yellow
Wrinkled Yellow
• Round Green
Wrinkled Green
Independent Assortment
RY
RY
Ry
rY
RRYY RRYy RrYY
ry
RrYy
Ry
rY
ry
RRYy
RrYY
RrYy
Rryy
rrYy
rryy
RRyy
RrYy
Rryy
RrYy
rrYY
rrYy
• Genes for different traits can segregate
independently during the formation of gametes.
Beyond Dominant and Recessive Alleles
• Incomplete Dominance
R
W
W
R
Beyond Dominant and Recessive Alleles
• Incomplete Dominance – neither allele is
dominant
R
R
W
RW
RW
W
RW
RW
Beyond Dominant and Recessive Alleles
• Incomplete Dominance – neither allele is
dominant
R
R
W
W
Beyond Dominant and Recessive Alleles
• Incomplete Dominance – neither allele is
dominant
R
W
R
RR
RW
W
RW
WW
Beyond Dominant and Recessive Alleles
• Codominance- both alleles contribute to the
phenotype
• Ex: Brown mated with white creates a mixture of
brown and white (roan)
Beyond Dominant and Recessive Alleles
• Multiple Alleles- genes that have more than two
alleles
• Ex: Human blood types
• Blood phenotypes: A, B, AB, O
Phenotype
Genotype
Genotype
Type A
IA IA
IA i
Type B
IB IB
IB i
Type AB
IA IB
Type O
ii
• Polygenic TraitsPhenotype is controlled
by many different genes
• Ex: Skin color is
controlled by at least
three different genes
Thomas Hunt Morgan
• Fruit Flies (Drosophila melanogaster)
• Ideal for genetics experiments:
• Reproduce quickly
• Large # of offspring
• Small in size
Nature vs. Nurture
• Which has a greater influence on an organism, the
DNA or the environment?
Nature vs. Nurture
Phenotype often depends on genes and the
environment.
• Humans:
• Height- nutrition
• Strength- exercise
• Skin color- exposure to sunlight
• Intelligence- experience
11-4 Meiosis
Chromosome Number
Fruit Fly has 8 chromosomes
4 from father
4 from mother
Homologous chromosomes- same type of
chromosome
The 4 chromosomes from the male parent are
homologous to the 4 chromosomes from the
female parent.
Diploid vs. Haploid
• Diploid- a cell that contains two sets of
homologous chromosomes. 2N
• Fruit flies: 2N= 8
Humans: 2N=46
Most adult cells are diploid.
Haploid- a cell that contains one set of chromosomes. N
Fruit flies: N= 4
Humans: N=23
Gametes (sex cell: sperm, egg) are haploid.
Phases of Meiosis
• Meiosis- the process of the number of
chromosomes per cell is cut in half in the
production of daughter cells by the separation of
homologous chromosomes
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Phases of Meiosis
Interphase I
Prophase II
Prophase I
Metaphase II
Metaphase I
Anaphase I
Anaphase II
Telophase I
Telophase II
Cytokinesis
Cytokinesis
Phases of Meiosis
Interphase I
2N
Prophase I
Metaphase I
Anaphase I
Telophase I
Cytokinesis
2N
4N
2N
Prophase II
2N
2N
Metaphase II
Anaphase II
Telophase II
Cytokinesis
N
N
N
N
Phases of Meiosis
Interphase I
2N
Prophase I
Metaphase I
Anaphase I
Telophase I
Cytokinesis
2N
4N
2N
Prophase II
2N
2N
Metaphase II
Anaphase
II
Telophase II
Cytokinesis
N
N
N
N
Phases of Meiosis
Interphase I
2N
Prophase I
4N
Metaphase I
Anaphase I
Telophase I
Cytokinesis
2N
2N
• Tetrad- a structure of two homologous
chromosomes, 4 sister chromatids
• Occurs during Prophase I
• Crossing over- process of exchanging portions of
sister chromatids
• Crossing over creates
many unique
combinations of
gamete cells.
Sperm production
2N
2N
N
N
2N
N
N
4N
Egg production
2N
2N
N
N
2N
N
N
4N
Polar Body
Polar Body
Polar Body
Zygote Formation
• Egg and Sperm join together to form a zygote
• Egg= N
• Sperm= N
• Zygote = 2N
11-5 Linkage and Gene Maps
TT
Tt
TT
TT
TT
t t
TT
TT
Tt
Tt
T
T
T
T
T
t
T
t
TT
tt
TT
TT
TT
tt
tt
tt
T
T
T
T
t
t
t
t
TT
tt
T
T
t
Tt
Tt
t
Tt
Tt
Tt
Tt
Tt
Tt
Tt
T
t
T
t
Tt
Tt
Tt
Tt
T
t
T
t
Tt
T
t
T
TT
Tt
t
Tt
tt
It is really the
chromosomes that
get sorted not the
individual genes in
meiosis
T
t
T
T
T
t
t
T
t
t
What if there are
two trait on one
chromosome?
What if there are
two trait on one
chromosome?
Those traits would
be inherited
together.
For fruit flies, body
color and wing size
are linked. Those
genes are on the
same chromosome.
G
N
g
n
Do not find these
combinations:
G
n
g
N
G
N
g
n
Is it possible to find
these combinations
if the genes are
linked?
G
n
g
N
G
N
G
N
g
n
g
n
If the genes are
linked, crossing
over can occur.
G
N
g
n
This helps create
genetic diversity.
G
n
g
N
Alfred Struvenat developed gene maps
• The further apart two genes are on a chromosome,
the more likely they are to cross over.
• A gene map shows the frequency at which genes
cross over and therefore their relative position on
the chromosome.