Download Intro to Genetics

Intro to Genetics
Mendel
Mendel (Father of Genetics)
Studied the inheritance of traits in pea
plants
Developed the laws of inheritance
Mendel's work was not recognized until
the turn of the 20th century
Gregor Mendel
(1822-1884)
Inheritance
Mendel stated that physical
traits are inherited as
“particles”
Mendel did not know that the
“particles” were actually
Chromosomes & DNA
Vocabulary
 Trait:- any characteristic that can be
passed from parent to offspring
 Heredity: - passing of traits from
parent to offspring
 Genetics: - study of heredity
 Purebred: one that always produces
offspring with the same form of a trait
as the parent. (homozygous)
• Hybrid: has both forms of a trait
(heterozygous)
More Vocabulary
 Alleles - two forms of a gene (dominant
& recessive)
 Dominant - stronger of two genes
expressed in the hybrid; represented by
a capital letter (R)
• Recessive - gene that shows up less
often in a cross; represented by a
lowercase letter (r)
• Homozygous and purebred = BB
• Heterozygous and hybrid= Bb
Eight Pea Plant Traits
•
•
•
•
•
•
•
•
Seed shape --- Round (R) or Wrinkled (r)
Seed Color ---- Yellow (Y) or Green (y)
Pod Shape --- Smooth (S) or wrinkled (s)
Pod Color --- Green (G) or Yellow (g)
Seed Coat Color ---Gray (G) or White (g)
Flower position---Axial (A) or Terminal (a)
Plant Height --- Tall (T) or Short (t)
Flower color --- Purple (P) or white (p)
Generations
P-Generation (Parents)
F1 Generation (1st Generation of
Offspring)
F2 Generation (2nd Generation of
Offspring)
Punnett Squares
• The gene
combinations that
might result from a
genetic cross can be
determined by
drawing a diagram
known as the punnett
square.
Parent 2
Parent 1
Try these: Tt x TT, Bb x bb, TT x
tt , and Bb x Bb
Genotype and Phenotype
• Genotype is an organisms genetic
makeup. For example Bb or BB or bb
• Phenotype is the physical
characteristics or what they look like.
For example if we were talking about
eye color, the phenotype would be blue
or brown eyes.
• If B =brown eyes and b= blue eyes
– Bb=would have brown eyes
– BB= brown eyes
– bb = blue eyes
Let’s Practice
Genotype or phenotype
•
•
•
•
•
BB
Brown
Blonde
Bb
bb
•
•
•
•
•
Blue
Tt
Tall
Tt
Short
Beyond Dominant and Recessive Alleles
• Some alleles are neither dominant or
recessive, and many traits are
controlled by multiple alleles or
multiple genes.
• Incomplete dominance: one allele is
not completely dominant over another.
A red flower crossed with a white
flower, produce pink flowers.
(blending)
• Codominance: Both alleles contribute
to the phenotype of the organism.
Black chicken crossed to a white
Incomplete Dominance
Codominance
• Two alleles are expressed (multiple
alleles) in heterozygous individuals.
• Example: blood type
•
•
•
•
1.
2.
3.
4.
type
type
type
type
A
B
AB
O
=
=
=
=
IAIA or IAi
IBIB or IBi
I AI B
ii