Download The Principle of Segregation

Chapter 11 (1 -3) Mendelian Genetics
I.
Heredity- Biological inheritance.
Genetics- the study of heredity
A. Gregor Mendel- an Austrian monk who studied
heredity by working with pea plants.
1. Self-pollination (true-breeding)- seeds
fertilized by the plant that produces them.
(not possible in higher mammals)
2. Cross-pollination – when two plants with a
contrasting trait exchange genetic
information and produce seeds with both of
the parent’s characteristics.
a. Stamen- male, pollen producing part of
the flower
b. Pistil- female, seed (ovaries) containing
part of the flower
II.
Traits – individual genetic characteristics
controlled by one gene
- Genes are chemical factors (DNA segments)
that determine traits for example flower
color or eye color
- Alleles- the two forms of each gene. 1
contributed by father and 1 contributed by
the mother
- Purebred- exhibit the same characteristics
generation after generation (various dog
breeds)
- Hybrid- exhibit a combination of dominant
traits as a result of a cross between two
different parents ( a mutt)
A. The Principle of Dominance states- some
alleles are dominant and others are recessive
- Dominant allele- the gene which expresses
its characteristic
- Recessive allele- the gene whose
characteristic is covered up in the presence
of the dominant gene
B. The Principle of Segregation states- each
allele separates independently during
formation of gametes (sex cells).
III.
Mendel’s experiment- 7 purebred pea plants
bred for seed shape, seed color, pod shape,
flower color, flower position and plant height.
A. Parent plants – P generation- cross pollinate
- Dominant allele- capital letter of dominant
trait- T = tall
- Recessive allele- lower case letter of the
dominant trait- t = short
B. First generation – F1- First Filial – self
pollinate
C. Second generation- F2 – Second Filial
D. Punnett Square – a tool used to predict the
probability or chance that a trait will occur
in offspring of a cross. Expressed in a ratio.
1. Genotype- combination of alleles
2. Phenotype – traits expressed by the
alleles
P= tall (TT) x short (tt)
IV.
V.
VI.
3. Possible Combinations
a. Heterozygous – combination of one
dominant and one recessive allele
b. Homozygous- combination of two of
the same alleles
- TT = Homozygous dominant
- tt = Homozygous recessive
Probability- the chance that a particular event
will occur
A. Each trait segregates independently so
offspring have a 50/50 chance of
inheritance (50% father vs. 50% mother)
B. Past outcomes do not affect future ones
C. An individual outcome is the product of
all the events.
( 1/2 x 1/2 x 1/2 = 1/8 )
Mendel’s Principles
A. Biological characteristics are determined by
inherited genes
B. There are dominant and recessive genes. In
cases when one of each are inherited, the
dominant gene is the one expressed
C. One copy of a gene is inherited from each
parent.
D. Genes segregate independently of one
another in sex cells
Beyond Simple Genetics
A. DiHybrid Cross- Two factor cross.
Each trait assorts independently in
the sex cells of the parent. (9:3:3:1
ratio)
B. Incomplete Dominance- A case where
the heterozygous phenotype is a
blend of two alleles. ( pink coloring in
flowers)
C. Codominance- A case where the
heterozygous phenotype is a
combination of the two dominant
alleles.(coat color in cattle)
D. Multiple Alleles- A case when there
are more than just two alleles of a
single gene. (blood type in humans)
E. Polygenic Traits- Traits that are
controlled by more than one set of
genes. (skin color in humans)