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Genetics
A study of inheritance
Gregor Mendel
• Father of modern
genetics
Gregor Mendel
• Father of modern
genetics
• Researched with
pea plants
Gregor Mendel
• Father of modern
genetics
• Researched with
pea plants
• Developed ideas of
dominance and
trait segregation
Phenotype
• Phenotype
– Physical
characteristics
Genotype
• Phenotype
– Physical
characteristics
• Genotype
– Genes we inherit from
our parents
Phenotype
Notice the similarities:
– Facial structure
Phenotype
Notice the similarities:
– Facial structure
– Eyes
Phenotype
Notice the similarities:
– Facial structure
– Eyes
– Smile
Phenotype
Notice the similarities:
–
–
–
–
Facial structure
Eyes
Smile
Ears
Phenotype
Notice the similarities:
–
–
–
–
–
Facial structure
Eyes
Smile
Ears
Nose
Phenotype
Notice the similarities:
–
–
–
–
–
–
Facial structure
Eyes
Smile
Ears
Nose
Neck
Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:
•Height - short or TALL
Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:
•Height - short or TALL
•Seed color - green or YELLOW
Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:
•Height - short or TALL
•Seed color - green or YELLOW
•Seed shape - wrinkled or ROUND
Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:
•Height - short or TALL
•Seed color - green or YELLOW
•Seed shape - wrinkled or ROUND
•Seed coat color - white or GRAY
Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:
•Height - short or TALL
•Seed color - green or YELLOW
•Seed shape - wrinkled or ROUND
•Seed coat color - white or GRAY
•Pod shape - constricted or SMOOTH
Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:
•Height - short or TALL
•Seed color - green or YELLOW
•Seed shape - wrinkled or ROUND
•Seed coat color - white or GRAY
•Pod shape - constricted or SMOOTH
•Pod color - yellow or GREEN
Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:
•Height - short or TALL
•Seed color - green or YELLOW
•Seed shape - wrinkled or ROUND
•Seed coat color - white or GRAY
•Pod shape - constricted or SMOOTH
•Pod color - yellow or GREEN
Mendelian Genetics
We will work with the following three:
•Height - short or TALL
•Seed color - green or YELLOW
•Seed shape - wrinkled or ROUND
•Seed coat color - white or GRAY
•Pod shape - constricted or SMOOTH
•Pod color - yellow or GREEN
•Flower position - terminal or AXIAL
Mendel's Four Hypotheses
• 1) There are alternative forms of “heritable
factors” (what we now call genes).
– Alternative forms are called alleles. In our flowers we
have two alleles for color, purple and white.
• 2) Each individual inherits two copies of these
alleles. These may be two of the same (e.g., two
alleles for purple), or two different ones (one for
white, one for purple).
– - if an individual has two of the same alleles, it is
termed “homozygous”
– - if an individual has two different alleles, it is
“heterozygous”.
Mendel's Four Hypotheses
• 3) If the two alleles are different (the
individual is a heterozygote), then one of
– the alleles will determine the individual's
appearance. This is the "dominant“ allele.
– - the other allele essentially has no effect on the
individual, and is called “recessive”.
• 4) a gamete carries only 1 allele for each
trait (because alleles separate from each
other during production of gametes.
Homozygous
• Homozygous
– Homo means "same or common".
– Homozygous means that both alleles
are the same. Genotypes such as
BB, bb, B1B1 are homozygous.
Heterozygous
•
Heterozygous
– Hetero means
"different". Heterozygous means
that the two alleles are not the
same. Thus, genotypes such as Bb,
are heterozygous
Predicting Inheritance
To determine the chances of inheriting a given
trait, scientists use Punnett squares and symbols
to represent the genes.
UPPERCASE letters
dominant genes.
are
used
to
represent
lowercase letters are used to represent recessive
genes.
Predicting Inheritance
For example:
T = represents the gene for TALL in pea plants
t = represents the gene for short in pea plants
So:
TT & Tt both result in a TALL plant, because T is
dominant over t. t is recessive.
tt will result in a short plant.
Remember there are two genes for every trait!
Predicting Inheritance
For example:
Mendels’ Principle of Dominance
T = represents the gene for TALL in pea plants
tSome
= represents
the gene
short inand
pea others
plants are
genes (alleles)
arefor
dominant
recessive. The phenotype (trait) of a dominant gene
will be seen when it is paired with a recessive gene.
So:
TT & Tt both result in a TALL plant, because T is
dominant over t. t is recessive.
tt will result in a short plant.
Remember there are two genes for every trait!
Predicting Inheritance
Let’s cross a totally dominant tall plant (TT) with a
short plant (tt).
Each plant will give only one of its’ two genes to
the offspring or F1 generation.
TT x tt
T
T
t
t
Predicting Inheritance
Let’s cross a totally dominant tall plant (TT) with a
short plant
(tt). “Law” of Segregation
Mendels’
Each plant will give only one of its’ two genes to
Eachoffspring
gene (allele)
from the other so that
the
or F1separates
generation.
the offspring get only one gene from each parent for a
given trait.
TT x tt
T
T
t
t
Punnett Squares
Tt
Tt
The genes from one parent go here.
The genes from the other parent go
here.
Tt
Tt
Punnett Squares
T
T
t
Tt
Tt
t
Tt
Tt
Punnett Squares
T
T
t
Tt
Tt
t
Tt
Tt
Punnett Squares
T
T
t
Tt
Tt
t
Tt
Tt
Punnett Squares
T
T
t
Tt
Tt
t
Tt
Tt
Punnett Squares
T
T
t
Tt
Tt
t
Tt
Tt
Punnett Squares
t
t
T
T
Tt
Tt
Tt
Tt
F1 generation
Interpreting the Results
The genotype for all the offspring is Tt.
The genotype ratio is:
Tt - 4/4
The phenotype for all the offspring is tall.
The phenotype ratio is:
tall - 4/4
Punnett Squares
T
t
??
??
Your
Turn!!
T
??
??
t
Punnett Squares
T
t
T
t
TT
Tt
Tt
tt
F2 generation
Punnett Squares
Next, give the genotype and phenotype
T (F2 generation).
t
ratios of the offspring
T
TT
Tt
t
Tt
tt
Punnett Squares
Genotype ratio: TT - 1
T
t
T
TT
Tt
t
Tt
tt
Punnett Squares
Genotype ratio: TT - 1, Tt - 2
T
t
T
TT
Tt
t
Tt
tt
Punnett Squares
Genotype ratio: TT - 1, Tt - 2, tt - 1
T
t
T
TT
Tt
t
Tt
tt
Punnett Squares
Genotype ratio: TT - 1, Tt - 2, tt - 1
T
t
T
TT
Tt
t
Tt
tt
Phenotype ratio: Tall - 3
Punnett Squares
Genotype ratio: TT - 1, Tt - 2, tt - 1
T
t
T
TT
Tt
t
Tt
tt
Phenotype ratio: Tall - 3, short - 1
Punnett Squares
This is a monohybrid T
cross. We worked
with
t
only one trait. The height of the plant.
T
TT
Tt
t
Tt
tt
Punnett Squares
This is a monohybrid T
cross. We worked
with
t
only one trait. The height of the plant.
T
TT
Tt
t
Tt
tt
Nondisjunction
• Nondisjunction is the failure of
chromosome pairs to separate properly
during meiosis or mitosis.
• Examples of Nondisjunction:
• A. Down's Syndrome: 47 chromosomes with 3
#21 chromosomes.
• B. Triple-X Syndrome: 47 chromosomes caused
by 3 X chromosomes.
– Can cause women to be taller
• C. Klinefelter's Syndrome: 47 chromosomes
caused by 2 X chromosomes and 1 Y
chromosomes.
– Men are unable to have children
• D. Turner's Syndrome: 45 chromosomes with 1
X chromosome (caused by the absence of one of
the X chromosomes or a Y chromosome).
– Women can not have children and may be shorter.