Unit 6
 Mendelian Genetics
 Chapters 10.2, 10.3
 Chapter 11
Mendelian Genetics
 Chapter 10.2
Explain
 The significance of Mendel’s experiments to the
study of genetics
Summarize
 The law of segregation and law of independent
assortment
Predict
 The possible offspring from a cross using a Punnett
square
Mendelian Genetics
 Mendel explained how a dominant allele can mask
the presence of a recessive allele
How Genetics Began
 1866
How Genetics Began
 1866
 Gregor Mendel
How Genetics Began
 1866
 Gregor Mendel
 Monk
How Genetics Began
 1866
 Gregor Mendel
 Monk
 Plant breeder
Pea plants
 Easy to grow
Pea plants
 Easy to grow
 True-breeding
Pea plants
 Easy to grow
 True-breeding – consistently produce offspring with
only one form of a trait
Pea plants
 Easy to grow
 True-breeding – consistently produce offspring with
only one form of a trait
 Self-fertilization
Genetics
 The science of heredity
The Inheritance of traits
 Mendel noticed
The Inheritance of traits
 Mendel noticed
 Certain traits
The Inheritance of traits
 Mendel noticed
 Certain traits
 Generation after generation
Two true-breeding plants
 P generation
 Removed male organs
 Cross pollinated
F1 Generation
 Seeds grown from P
 Alleles masked
 Allowed to self
pollinate
F2 Generation
 Offspring from F1
 Masked trait reappears
 Almost a perfect 3:1
ratio
Allele
 Traits
 Gene
 Come in pairs
Dominant
 Mendel’s term
 Form of the trait that
appeared in the F1
 Capital
Recessive
 Mendel’s term
 Form of the trait that
was masked in the F1
 Lower case
Homozygous
 Two of the same alleles for a particular trait
 DD
 nn
Heterozyous
 Two different alleles for a particular trait
 Dn
 nD
Genotype
 The organism’s allele pairs
 Dn
 nD
 DD
 nn
Phenotype
 The observable characteristic
 The outward expression of the allele pair
 Dn
 nD  nn  DD -
D
D
n
D
Law of segregation
 Two alleles for each trait separate during meiosis
 During fertilization, two alleles unite
Monohybrid cross
 Cross that involves hybrids for a single trait
Dihybrid cross
 Cross of plants with two or more traits
Dihybrid
 Heterozygous for both traits
Law of independent assortment
 Random distribution of alleles occurs during gamete
formation
 Genes on separate chromosomes sort independently
during meiosis
 9:3:3:1
Punnett Squares
Monohybrid cross
 Take the different types
of alleles from each
parent
 Place in the square
Dihybrid cross
9:3:3:1
 F1 generation is crossed
 Four types of alleles
from the male gametes
 Four types of alleles
from the female
gametes
Probability
 A coin landing on heads – ½
 A coin landing on heads a second time – ¼
 Mendel’s results were not perfect
 Larger the number of offspring the closer
 9:3:3:1
Gene Linkage and Polyploidy
 Chapter 10.3
Main Idea
 The crossing over of
linked genes is a source
of genetic variation
Genetic Recombination
 The new combination of genes produced by crossing
over and independent assortment
Genetic Recombination
 Genetic variation
Independent assortment
 2n
 where n is the number of chromosome pairs
Example
 Pea plants have seven pairs of chromosome
Example
 Pea plants have seven pairs of chromosome
 2n
Example
 Pea plants have seven pairs of chromosome
 2n
 27= 128
 The possible number of combinations after
fertilization is
 128 X 128 = 16,384
Example
 Humans have 23 pair of chromosome
 After fertilization
 223 X 223 = more than a trillion
Example
 Humans have 23 pair of chromosome
 After fertilization
 223 X 223 = more than a trillion
 This doesn’t include the amount of genetic
recombination produced by crossing over
Gene Linkage
 Chromosomes contain multiple genes that code for
proteins
Gene Linkage
 Chromosomes contain multiple genes that code for
proteins
 Genes located close to each other are said to be
linked and travel close together
Drosphila melanogaster
 Fruit Fly
 Gene linkage first studied
 Genes usually travel together during meiosis
 However, sometimes they don’t
Drosphila melanogaster
 Fruit Fly
 Gene linkage first studied
 Genes usually travel together during meiosis
 However, sometimes they don’t
 Scientists concluded that linked genes can separate
during a crossover
Chromosome Maps
Chromosome Maps
 First published in 1913
Chromosome Maps
 First published in 1913
 Fruit fly crosses
Chromosome Maps
 First published in 1913
 Fruit fly crosses
 Not actual chromosome distances
Chromosome Maps
 First published in 1913
 Fruit fly crosses
 Not actual chromosome distances
 Represent relative positions of the genes
Chromosome Maps
 First published in 1913
 Fruit fly crosses
 Not actual chromosome distances
 Represent relative positions of the genes
 Crossing over occurs more frequently between genes
that are far apart
In a cross
In a cross
 Exchange of genes is directly related to the crossover
frequency
In a cross
 Exchange of genes is directly related to the crossover
frequency
 The frequency correlates with the relative distance
between the two genes
In a cross
 Exchange of genes is directly related to the crossover
frequency
 The frequency correlates with the relative distance
between the two genes
 Genes that are further apart would have a greater
frequency of crossing over
Crossover
Polyploidy
 One or more extra sets of all chromosomes in an
organism
Triploid organism
 An organism with 3n chromosome
 Three sets of chromosomes
Triploid organism
 An organism with 3n chromosome
 Three sets of chromosome
 Rare
Triploid organism
 An organism with 3n
chromosome
 Three sets of
chromosome
 Rare
Triploid organism
 An organism with 3n
chromosome
 Three sets of
chromosome
 Rare
 Lethal in humans
Triploid organism
 An organism with 3n




chromosome
Three sets of
chromosome
Rare
Lethal in humans
Plants increase in vigor
and size
Mini Lab 10.2
MAP CHROMOSOMES
Where are genes located on a chromosome?
Where are genes located on a chromosome?
 The distance between
two genes on a
chromosome is related to
the crossover frequency
between them.
Where are genes located on a chromosome?
 The distance between
two genes on a
chromosome is related to
the crossover frequency
between them.
 By comparing data for
several gene pairs, a
gene’s relative location
can be determined.
Get a Piece of paper
 Draw a line
Get a Piece of paper
 Draw a line
 Mark centimeters (1 – 20)
Get a Piece of paper
 Draw a line
 Mark centimeters (1 – 20)
 Label a mark in the center “A”
Model
Gene Pair
Crossover Frequency
AB
3
AC
1
AD
4
BC
2
BD
7
CD
5
Lab
Gene Pair
Crossover
Gene Pair
Crossover
AB
5.5
BF
4.3
AC
6.4
CD
10.9
AD
4.5
CE
2.6
AE
9.0
CF
5.2
AF
1.2
DE
13.5
BC
0.9
DF
5.7
BD
10.0
EF
7.8
BE
3.5
DRAW
 Suppose genes C and D are linked on one




chromosome
And genes c and d are linked on another
chromosome
Assuming that crossing over does not take place
sketch the daughter cells resulting from meiosis
Show the chromosomes and position of the genes
Human Inheritance
CHAPTER 11.1
Basic Patterns of Human
Inheritance
CHAPTER 11.1
California State Standard
3C STUDENTS KNOW HOW TO PREDICT THE
PROBABLE MODE OF INHERITANCE FROM A
PEDIGREE DIAGRAM SHOWING PHENOTYPES
Pedigree
DEFINE
Pedigree
Purebred
Pedigree
 A diagram
Pedigree
 A diagram
 Of a family tree
 showing the occurrence of heritable characters in
parents and offspring over multiple generations.
Human traits
 Follow Mendelian patterns of inheritance
Geneticists
 Scientists who study traits
Geneticists
 Scientists who study traits
 Analyze the traits of offspring in a family
Geneticists
 Scientists who study traits
 Analyze the traits of offspring in a family
 Map them to determine where a trait comes from
Geneticists
 Scientists who study traits
 Analyze the traits of offspring in a family
 Map them to determine where a trait comes from
 Collecting data from family with a trait that can be
traced
Geneticists
 Scientists who study traits
 Analyze the traits of offspring in a family
 Map them to determine where a trait comes from
 Collecting data from a family with a trait that can be
traced
Geneticists
 Scientists who study traits
 Analyze the traits of offspring in a family
 Map them to determine where a trait comes from
 Collecting data from a family with a trait that can be
traced
 The family Pedigree
To make a map
 Need symbols
Male
Female
Start at the beginning
 Mom and Dad
Dad and Mom
Dad and Mom
Dad and Mom
Dad and Mom
Offspring
 Brothers and sisters
Imagine you are a geneticist
 “My name is Scott. My great grandfather Walter had
hairy earlobes (HE), but great grandma Elsie did not.
Walter and Elsie had three children: Lola, Leo, and
Duane. Leo the oldest, has HEs, as does the middle
child, Lola; but the youngest child, Duane, does not.
Duane never married and has no children. Leo
married Bertie, and they have one daughter, Patty.
In Leo’s family he is the only one with HEs. Lola
married John, and they have two children: Carolina
and Luetta. John does not have HEs, but both of his
daughters do.”
Example 2
 Parents of a child with severe sensorineural hearing
loss are referred to the genetics clinic. They indicate
that they have had three children, son, daughter and
another son. The father of these children has two
sisters both of whom have two sons. His parents are
both well. No-one in his family has ever had a child
with hearing loss before. The mother of the three
children has a brother who has one son and one
daughter. Her parents are also well and once again
there is no known history of severed hearing loss in
childhood.
Example 2
 However, her maternal grandfather developed
moderate hearing loss in his sixties. On specific
questioning the mother recalls that her maternal
grandmother was the sister of her husband’s
paternal grandmother.
 Draw a pedigree
Chapter 11.2
 Complex Patterns of Inheritance
Objectives
 Distinguish between various complex inheritance
patterns
 Analyze sex-linked and sex-limited inheritance
patterns
 Explain how the environment can influence the
phenotype of an organism
Dominance
 Heterozygous for a trait
 Dominant trait shows phenotype
 Plant (Tt)
 T = tall
Incomplete Dominance
 Red snapdragons – (RR)
 White snapdragons – (rr)
 Pink snapdragons – (Rr)
Codominance
 Complex inheritance pattern
 Both alleles are expressed
Sickle-cell disease
 Disease affects red blood
cells
 Affects the ability to
transport oxygen
 Change in hemoglobin,
protein
 When heterozygous have
both normal and sicklecell live a normal life
Sickle-cell disease and malaria
 Scientists have discovered
 Distribution of malaria and sickle-cell overlap
 Those with heterozygous sickle-cell are more
resistant to malaria
Multiple Alleles
 Blood groups
 ABO blood types
Multiple Allele
 Color coat of rabbits
 C
 cch
 ch
 c
Epistasis
 One allele hiding the effects of another allele
 Labrador’s coat color is controlled by two sets of
alleles
 The dominant allele E determines whether the fur
will have dark pigment
 EEbb or Eebb – Chocolate brown
 eebb, eeBb or eeBB – Yellow
Sex Determination
 46 chromosomes – 23 pair
 One pair determines gender
 X and Y
 The other 22 pair are autosomes
Dosage Compensation
 Females have 22 pair and one pair of
X chromosomes
 Males have 22 pair and one Y and one X
chromosomes
 X chromosome carries genes necessary for the
development for both females and males
 Y chromosome carries genes necessary for the
development for males
Dosage
 Females get two doses of X
 One of the chromosomes shuts off
 X-inactivation
 Barr bodies – inactive X chromosome
Sex-Linked Traits
 Traits that are controlled by genes located on the X
chromosome
 Female with recessive trait on X would express the
trait on the other X chromosome
Red-green color blindness
XB
Y
XB
XBXB
XBY
Xb
XBXb
XbY
 Mother is carrier
 Father is not color blind
 Only a son
 8% of males are
Environmental influences
 Environment has an influence on phenotype
 Heart disease, diet and exercise
 Sunlight, rainfall and weather
 Temperature with cats and
pigment on fur
Twins
 Scientist study twins to determine the difference of
environment on an individual
Chromosomes & Human
Heredity
CHAPTER 11.3
Karyotype Studies
 Scientists study the whole chromosome
 Pairs of chromosomes are arranged in descending
order
Telomeres
 Protective cap on the chromosome
 Made of protein
 Involved in cancer and aging
Nondisjunction
 Cell division during which sister chromatids fail to
separate properly
 Meiosis I
 Meiosis II
Down syndrome
 Extra chromosome on 21
 Trisomy
 Distinctive facial features
 Mental disabilities
 Short stature
 Heart defects
Nondisjunction in sex chromosomes
GENOTYPE
XX
Female
XO
Turner’s Syndrome
XXX
Nearly normal Female
XY
Male
XXY
Klinefelter’s syndrome
XYY
Nearly normal Male
OY
Results in death
Fetal Testing
 Amniocentesis – diagnosis of chromosome
abnormalities – infection, miscarriage, discomfort
 Chorionic Villus sampling – Diagnosis of
chromosome abnormalities – miscarriage, infection,
limb defects
 Fetal blood sampling – diagnosis of chromosome
abnormalities – risk of bleeding, infection, amniotic
fluid might leak, risk of fetal death