3. Mendel's Laws of Heredity
a
is a set of primary tenets that underlie
much of genetics developed by Gregor
Mendel in the latter part of the 19th
century.
a Mendel (1822-1884), an Austrian monk,
was interested in understanding variances
in plants, and between 1856 and 1863
cultivated and tested some 28,000 pea
plants.
4. Mendel used peas...
aThey reproduce sexually
aThey have two distinct, male
and female, sex cells called
gametes
aTheir traits are easy to isolate
5. Mendel crossed them
a Fertilization - the uniting of male
and female gametes
a Cross - combining gametes from
parents with different traits
7. What did Mendel find?
a His experiments brought forth two
generalizations which later became
known as Mendel's Laws of Heredity
or Mendelian inheritance.
8. Rule of Dominance
a The trait that is observed in the
offspring is the dominant trait
(uppercase)
a The trait that disappears in the
offspring is the recessive trait
(lowercase)
9. MENDEL’S LAW OF INDEPENDENT
ASSORTMENT
a Also known as Mendel's Second Law
a The most important principle of
Mendel's law of independent
assortment is that the emergence of
one trait will not affect the emergence
of another.
10. MENDEL’S LAW OF SEGREGATION
a Alternative versions of genes account for
variations in inherited characters. This is the
concept of alleles. Alleles are different versions
of genes that impart the same characteristic.
a For each character, an organism inherits two
genes, one from each parent. This means that
when somatic cells are produced from two
gametes, one allele comes from the mother,
one from the father.
11. a If the two alleles differ, then one, the
dominant allele, is fully expressed in the
organism's appearance; the other, the
segregate during gamete production. This
is the last part of Mendel's generalization.
The two alleles of the organism are
separated into different gametes, ensuring
variation.
12. Words to Know
a Allele: One of two or more forms a gene may
take.
a Dominant: An allele whose expression
overpowers the effect of a second form of the
same gene.
a Gamete: A reproductive cell.
a Heterozygous: A condition in which two alleles
for a given gene are different from each other.
a Homozygous: A condition in which two alleles for
a given gene are the same.
a Recessive: An allele whose effects are concealed
in offspring by the dominant allele in the pair.
13. Dihybrid vs Monohybrid
a Dihybrid Cross - crossing parents who
differ in two traits (AAEE with aaee)
a Monohybrid Cross - crossing parents
who differ in only one trait (AA with
aa)
14. Example of a Cross
Parents: Tall round seeded plant (TTRR) X Dwarf wrinkled
seeded plant (ttrr)
Gametes: TR tr
F1: TtRr (Tall round seeded plants)
When F1 self pollinated: F1 X F1
TtRr(Tall round seeded plants) X TtRr(Tall round seeded
plants)
Gametes: TR Tr tR tr TR Tr tR tr
16. Results of Dihybrid Cross
Examples
Genotype
a 1/16 will be homozygous dominant for both traits (TTRR)
2/16 will be homozygous dominant for height and heterozygous for
shape (TTRr)
2/16 will be heterozygous for height and homozygous dominant for
shape (TtRR)
1/16 will be homozygous dominant for height and homozygous
recessive for shape (TTrr)
4/16 will be heterozygous for both traits (TtRr)
2/16 will be heterozygous for height and homozygous recessive for
shape (Ttrr)
1/16 will be homozygous recessive for height and homozygous
dominant for shape (ttRR)
2/16 will be homozygous recessive for height and heterozygous for
shape (ttRr)
1/16 will be homozygous recessive for both traits (ttrr)
a This is a 1:2:2:1:4:2:1:2:1 genotypic ratio
17. Phenotype
9/16 will be tall and round seeded
3/16 will be tall and wrinkled seeded
3/16 will be dwarf and round seeded
1/16 will be dwarf an wrinkled seeded
a This is a 9:3:3:1 phenotypic ratio.
18. Sources
a http://www.tutorvista.com/biology/dihybrid
-cross-examples
a http://www.hobart.k12.in.us/jkousen/Biology/mendel.htm
a http://www.scienceclarified.com/Ma-Mu/Mendelian-Laws-o
a http://www.scribd.com/doc/12648686/Mendels-Laws-of-He
