Mendel & Genetics
Review Powerpoint
Gregor Mendel, the father of genetics.
Genetics is the study of…
heredity
Define Heredity.
The passing on of traits from one generation to
the next.
Where is genetic information stored?
DNA
Specifically, in each individual’s DNA on
chromosomes that contain many genes.
What did Mendel study to understand
inheritance?
Common garden pea plants
Why did he choose pea plants?
1--Fast growing with many offspring = quick
results
2—Sexually Reproduce and male as well as
female reproductive organs in each plant
3—Traits come in a dichotomy—only two
forms.
Like tall and short or green and yellow
What did Mendel call true breeding?
Plants that come from a long line of plants that
show the same trait
When he crossed two true-breeding plants with
opposite traits, he called this what?
The “P” cross for Parental generation
What two individuals did Mendel
cross in the P generation?
True-breeding Tall and Short pea plants
Genotypes?
Tall = TT
Short = tt
What resulted in the F1 generation?
Pea plants that were…
Phenotypes?
All TALL
Genotype?
All “Tt”
What was Mendel’s next step?
He crossed two F1 plants.
What results did he get?
The F2 generation
What interesting ratio did he find?
They were 3:1 (dominant to recessive)
What is the Law of Segregation?
1--Individuals must have two copies of genetic
information for every trait– one from each
parent
2—each copy is passed randomly
3—One of these copies (alleles) can mask the
expression of the other, ie. Dominant alleles
can mask recessive alleles when both are
present
What is the Law of
Independent Assortment?
 Alleles of different genes separate independently of
one another during gamete formation
 What does that mean?
 The allele a parent gives for one trait does not affect
what he/she gives for another trait so you can have
many different combinations of traits given to the egg
or sperm
What are alleles?
Different forms of the same gene for a trait
When an individual has two of the same allele,
the genotype is called…
Homozygous
When there are two different alleles, it is…
Heterozygous
What is the difference between genotype and
phenotype?
Genotype is
the type of genes or alleles
Phenotype is
What is looks like--The physical appearance
of the organism
Monohybrid vs. Dihybrid
Mono hybrid: a cross when there is just
one trait involved, ex.
Height: Tt X tt
Di hybrid: Two traits are involved, ex.
The horse’s coat and gait are crossed
FFGg X Ffgg
Sex-linked Inheritance
 Autosomes are chromosomes not on the.. X or y
chromosomes
 Sex-linked characteristics are always on…
 The X-chromosome
 Give an example of a sex-linked condition
 Hemophilia
 Why does it occur more in males?
 Males only inherit 1 X-chromosome so there is a
better chance they would express (whether its
dominant or recessive) the condition.
Contrast a Punnett Square and a
Pedigree
A Punnett Square is…
 a grid that predicts the types of possible
offspring from a cross
A Pedigree is..
A diagram that shows a family tree and
how traits pass from generation to
generation
Pedigree or Punnett Square?
Is this a monohybrid or dihybrid cross?
Modes of Dominance:
 1--Complete dominance…
 One allele is completely dominant over the
recessive and the recessive is masked in a
heterozygous individual
 2--Incomplete dominance..
 The dominant does not completely mask the
recessive and the heterozygous phenotype is a
blend of the two- an intermediate variation.
 There are three possible phenotypes.
More modes of inheritance
 3-- Co dominance..
 More than one genotype is dominant and when two of
these are together, they form another phenotype
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4– Multiple alleles..
These traits have 3 or more alleles
Example of both codominance and multiple alleles..
blood types. How many blood types are possible?
Four-- They are..
A, B, AB, and O
Modes of Inheritance cont.
5-- Polygenic Inheritance: traits that are..
 controlled by multiple genes pairs.
This makes many variations of color and
trait possible
What are characteristics controlled by
multiple pairs of alleles?
Human hair and eye color