Download Modeling Mendel*s Laws

Modeling Mendel’s Laws
Who Was Gregor Mendel?
• Gregor Mendel, an Austrian monk, is known
as the “Father of Genetics”.
• He was the first person to use mathematics of
probability to explain heredity and to trace
one trait for several generations.
Inheriting Traits
• During meiosis, a pair of chromosomes separates
and the alleles move into separate cells.
• Each chromosome now contains one gene for each
trait.
EXAMPLE: One chromosome may have the allele for
dimples and the other may have the allele for no
dimples.
What are Genotype and Phenotype?
• Gregor Menel recognized that an organism
could pass traits on to their offspring, that
were not outwardly visible in the parent.
• Example: Two parents might have blonde hair,
but their child might have brown hair.
What are Genotype and Phenotype?
• Mendel had actually discovered the difference between
genotype and phenotype.
• Genotype: the particular set of alleles or version of a gene
that codes for a trait
a. Heterozygous: An organism with two alleles for one trait
that are different: Example: Tt
b. Homozygous: An organism with two alleles for one trait
that are the same. The organism can be Homozygous
Dominant (TT) or Homozygous recessive (tt)
What are Genotype and Phenotype
Alleles: the different forms of a trait that a gene
may have:
Examples: tall or short, blue eyes or brown,
dimples or no dimples
What are genotype and phenotype?
Phenotype: The way an organism looks and
behaves as a result of its genotype.
What is Dominance?
Dominant Allele: The stronger allele.
It will cover up or dominate the other allele
and it is always expressed in the way an
organism looks.
It is represented by a capital letter
EXAMPLE: T for tall
B for brown hair
What is Dominance?
Recessive Allele: The weaker allele.
It may seem to disappear if the other allele is
dominant. The only way it can show up in the way
an organism’s appearance is if two recessive alleles
are inherited for a trait.
Always represented by a lower case letter.
EXAMPLE: t for short b for blond hair
What is Dominance?
Punnett Squares
Probability helps you predict the chance that
something will happen.
To figure probability, we use a punnett square.
A punnett square helps you predict the chance an
organism will inherit a certain trait.
a. Uppercase letters = dominant alleles,
always written first.
b. Lowercase letters = recessive alleles
Gregor Mendel
P1 Generation: Parent Generation
F1 Generation: Children of parent generation
F2 Generation: Grandchildren of parent
generation or
What is Dominance?
EXAMPLE: Let T = tall allele t = short allele
An organism gets one gene from each parent.
If the organism got the following allele combinations:
TT = two dominant alleles, person would be tall
Tt = one dominant and one recessive, person would be tall
because the dominant gene covers up the recessive one
tt = two recessive alleles, person would be short
Punnett Squares
Example: Let the P1 generation alleles be TT and tt.
TT x tt gives the following results:
100% of offspring will be tall
0% will be short
T
Tt
t
T
Tt
t
T
TTt
Tt
Punnett Squares
Suppose the P1 generation was Tt x Tt
T
TT
t
Tt
T
Tt
tt
t
The probabilities from this cross would be:
75 % tall
25% short
Mendel’s Law of Dominance
• Some alleles are dominant and others are recessive.
AN organism with at least one dominant allele for a
gene coding for a particular trait will exhibit the
dominant form of the trait.
• An organisms will only express the recessive trait if
no dominant alleles are present
Mendel’s Law of Segregation
• During gamete formation, the alleles for each
gene separate from each other, so that each
gamete carries only one allele for each gene.
• NOTE: This is due to meiosis. When the cells
divide in meiosis, the chromosome number is
reduced from diploid to haploid, so each
gamete has only one copy of the gene for a
trait.
Mendel’s Law of Segregation
Mendel’s Law of Segregation
• If segregation of allele’s fails to happen, the
chromosomes will not separate properly, and
nondisjunction occurs.
• The result is gametes may have an extra or a missing
chromosome.
Mendel’s Law of Independent Assortment
• Genes of different traits can segregate independently
during the formation of gametes.
• If corn color and taste are on separate genes, this law
is the reason you could have yellow corn that is
sweet or purple corn that is sweet. The genes for
color and taste separate independently of each
other.