Transcript Section 1 Mendel`s Legacy Chapter 9 Mendel`s Experiments

Chapter 9
Fundamentals of Genetics
Table of Contents
Section 1 Mendel’s Legacy
Section 2 Genetic Crosses
Chapter 9
Section 1 Mendel’s Legacy
Objectives
• Describe how Mendel was able to control how his pea plants
were pollinated.
• Describe the steps in Mendel’s experiments on true-breeding
garden peas.
• Distinguish between dominant and recessive traits.
• State two laws of heredity that were developed from Mendel’s
work.
• Describe how Mendel’s results can be explained by scientific
knowledge of genes and chromosomes.
Chapter 9
Section 1 Mendel’s Legacy
Gregor Mendel
• The study of how characteristics are transmitted from
parents to offspring is called genetics.
Chapter 9
Section 1 Mendel’s Legacy
Gregor Mendel, continued
• Mendel’s Garden Peas
– Mendel observed characteristics of pea plants.
– Traits are genetically determined variants of a
characteristic.
– Each characteristic occurred in two contrasting
traits.
Chapter 9
Section 1 Mendel’s Legacy
Gregor Mendel, continued
• Mendel’s Methods
– Mendel used cross-pollination techniques in
which pollen is transferred between flowers of two
different plants.
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Experiments
• Mendel bred plants for several generations that were
true-breeding for specific traits and called these the P
(Parental) generation.
• Offspring of the P generation were called the F1
(First Filial ) generation.
• Offspring of the F1 generation were called the F2
(Second Filial) generation.
Chapter 9
Section 1 Mendel’s Legacy
Three Steps of Mendel’s Experiments
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Experiments
Click below to watch the Visual Concept.
Visual Concept
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Results and Conclusions
• Recessive and Dominant Traits
– Mendel concluded that inherited characteristics
are controlled by factors that occur in pairs.
– In his experiments on pea plants, one factor in a
pair masked the other. The trait that masked the
other was called the dominant trait. The trait that
was masked was called the recessive trait.
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Results and Conclusions, continued
• The Law of Segregation
– The law of segregation states that a pair of
factors is segregated, or separated, during the
formation of gametes.
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Results and Conclusions, continued
• The Law of Independent Assortment
– The law of independent assortment states that
factors for individual characteristics are distributed
to gametes independent of one another.
– The law of independent assortment is observed
only for genes that are located on separate
chromosomes or are far apart on the same
chromosome.
Chapter 9
Section 1 Mendel’s Legacy
Support for Mendel’s Conclusions
• We now know that the factors that Mendel studied
are alleles, or alternative forms of a gene.
• One allele for each trait is passed from each parent
to the offspring.
Chapter 9
Section 1 Mendel’s Legacy
Mendel’s Conclusions
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Visual Concept
Chapter 9
Section 2 Genetic Crosses
Objectives
• Differentiate between the genotype and the phenotype of an
organism.
• Explain how probability is used to predict the results of genetic
crosses.
• Use a Punnett square to predict the results of monohybrid and
dihybrid genetic crosses.
• Differentiate a monohybrid cross from a dihybrid cross.
Chapter 9
Section 2 Genetic Crosses
Genotype and Phenotype
• The genotype is the genetic makeup of an organism.
•
The phenotype is the appearance of an organism.
Chapter 9
Section 2 Genetic Crosses
Probability
• Probability is the likelihood that a specific event will
occur.
• A probability may be expressed as a decimal, a
percentage, or a fraction.
Chapter 9
Section 2 Genetic Crosses
Calculating Probability
Click below to watch the Visual Concept.
Visual Concept
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Monohybrid Crosses
• A Punnett square can be used to predict the
outcome of genetic crosses.
• A cross in which one characteristic is tracked is a
monohybrid cross.
Chapter 9
Section 2 Genetic Crosses
Punnett Square with Homozygous Cross
Click below to watch the Visual Concept.
Visual Concept
Chapter 9
Section 2 Genetic Crosses
Monohybrid Cross
of Heterozygous
Plants
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Monohybrid Crosses, continued
• Complete dominance occurs when heterozygous
individuals and dominant homozygous individuals are
indistinguishable in phenotype.
TT (Homozygous Dominant)---Tall
Tt (Heterozygous)---Tall
tt (Homozygous Recessive)---Short
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Monohybrid Crosses, continued
• Incomplete dominance occurs when two or more
alleles influence the phenotype and results in a
phenotype intermediate between the dominant trait
and the recessive trait.
• Intermediate Color is a
blend of Parental Traits
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Monohybrid Crosses, continued
• Codominance occurs when both alleles for a gene
are expressed in a heterozygous offspring. Both
Parental Traits appear together.
• Example: Roan Cow or Horse. There are equal
amounts of white hair and red hair blending
together to give a color that is a combination of
the two.
Chapter 9
Section 2 Genetic Crosses
Predicting Results of Dihybrid Crosses
• A cross in which two characteristics are tracked is a
dihybrid cross.
Chapter 9
Section 2 Genetic Crosses
Dihybrid Crosses
Dihybrid Punnett Square
• Homozygous
round and
yellow with a
heterozygous
yellow and
round
• RRYY with
RrYy
• Offspring are all
round and
yellow
RY
RY
RY
RY
RY
RRYY
RRYY
RRYY
RRYY
Ry
RRYy
RRYy
RRYy
RRYy
rY
RrYY
RrYY
RrYY
RrYY
ry
RrYy
RrYy
RrYy
RrYy
Dihybrid Punnett Square
• Homozygous
wrinkled and
green with a
heterozygous
yellow and round
• rryy with RrYy
• 4 round yellow,
4 round green,
4 wrinkled yellow,
4 wrinkled, green
ry
ry
ry
ry
RY
RrYy
RrYy
RrYy
RrYy
Ry
Rryy
Rryy
Rryy
Rryy
rY
rrYy
rrYy
rrYy
rrYy
ry
rryy
rryy
rryy
rryy
Chapter 9
Section 3 Genetics
Gene Linkage
• Gene Linkage- genes that are located on the same
chromosome are inherited together.
• These genes travel together during gamete
formation.
• This is an exception to the Mendelian Principle of
Independent Assortment because linked genes do
not segregate independently.
Chapter 9
Section 3 Genetics
Multiple Allele
• Multiple Alleles- exist for a particular trait even though
only two alleles are inherited.
Ex. Three alleles exist for blood type (A, B, and O),
which result in four different blood groups.
Blood Type (Phenotype)
Genotype
Type A
AA and AO IAIA or IAi
Type B
BB and BO IBIB or IBi
Type AB
AB
I AIB
Type O
OO
ii
Blood Type Crosses
Type O mother and Type AB father
i
i
Homozygous Type A mother and
Homozygous Type B father
IA
IB
IAi
IB i
IA
IAi
IB i
IA
50% blood type A
50% blood type B
IB
IB
IAIB
IAIB
IAIB
IAIB
100% type AB
ABO and Rh Blood Type
Frequencies in the United States
Blood Type Frequencies in the US
ABO Type
Rh Type
How Many Have It
O
positive
37.4%
O
negative
6.6%
A
positive
35.7%
A
negative
6.3%
B
positive
8.5%
B
negative
1.5%
AB
positive
3.4%
AB
negative
.6%
44%
42%
10%
4%
Chapter 9
Section 3 Genetics
Polygenic Traits
• Polygenic Traits are traits
that are controlled by two or
more genes. These traits
often show a great variety of
phenotypes.
Ex. Skin Color
• Mendel’s principles of genetics did not explain
that many traits are controlled by more than one
gene.
Sex Determination
• Remember that humans have 22 pairs of autosomes and
1 pair of sex chromosomes
• These sex chromosomes determine the gender of the
offspring
– XX is a female
– XY is a male
• Each offspring gets an X from the
mother and either an
X or a Y from the father----Male determines
the sex of the offspring
Sex Determination
• Predicting the sex of the offspring can be done using
a Punnett Square
• Each time a male gamete fertilizes a female gamete,
there is a 50% chance for either sex
Chapter 9
Section 3 Genetics
Sex-Linked Traits
• Sex-Linked Traits result of genes that are carried on
either the X or the Y chromosome.
• This is an exception to Mendel’s principle of
independent assortment , which does not explain
sex-linked traits.
• Males: XY
Females: XX
• In humans, the Y chromosome carries very few
genes, the X chromosome contains a number of
genes that affect many traits. Sex-linked genes are
expressed differently form an autosomal gene.
Chapter 9
Section 3 Genetics
Sex-Linked Traits (continued)
• If a gene is linked on the X chromosome (X-linked):
Female offspring will inherit the gene as they do all
other chromosomes X from the father and X from the
mother).
Male offspring will inherit the gene on their X
chromosome, but no on the Y chromosome.
Since males have on X chromosome, they express
the allele whether it is dominant or recessive, there is
no second allele to mask the effects of the other
allele.
Predicting Sex-Linked Traits
• The chances that an offspring will have a sex-linked trait can be
predicted using a Punnett Square
Chapter 9
Section 3 Genetics
Sex-Linked Traits (continued)
Sex-Linked Crosses
Colorblindness is a recessive sex-linked trait. Use XN for the normal allele and
Xn for the colorblind allele
Heterozygous Normal mother
Colorblind mother and Normal father
and Colorblind father
Xn
Xn
XN
Y
XNXn
X nY
XN Xn
X nY
Xn
Y
XN
XNXn
XN Y
Xn
X nX n
X nY
Normal daughters (carriers)
50% Normal daughters and sons
Colorblind sons
50% colorblind daughters and sons
DOMINANT AND RECESSIVE CHARACTERISTICS
Characteristics in the left-hand column dominate over those characteristics listed in the right-hand column.
eye coloring
vision
hair
facial features
appendages
other
DOMINANT TRAITS
brown eyes
farsightedness
normal vision
normal vision
normal vision
dark hair
non-red hair
curly hair
full head of hair
widow's peak
dimples
unattached earlobes
freckles
broad lips
RECESSIVE TRAITS
grey, green, hazel, blue eyes
normal vision
nearsightedness
night blindness
color blindness*
blonde, light, red hair
red hair
straight hair
baldness*
normal hairline
no dimples
attached earlobes
no freckles
thin lips
extra digits
fused digits
short digits
fingers lack 1 joint
limb dwarfing
clubbed thumb
double-jointedness
immunity to poison ivy
normal pigmented skin
normal blood clotting
normal hearing
normal hearing and speaking
normal- no PKU
normal number
normal digits
normal digits
normal joints
normal proportion
normal thumb
normal joints
susceptibility to poison ivy
albinism
hemophilia*
congenital deafness
deaf mutism
phenylketonuria (PKU)
Chapter 9
Section 3 Genetics
Pedigree- is a chart constructed to show an inheritance
pattern (trait, disease, disorder) within a family
through multiple generations. Through the use of a
pedigree chart and key, the genotype and phenotype
of the family members and the genetic characteristics
(dominant recessive, sex-linked) of the trait can be
tracked.
Chapter 9
Section 3 Genetics
Chapter 9
Section 3 Genetics