Intro to Genetics

Mendel

Mendel (Father of Genetics)Studied the inheritance of traits in pea plantsDeveloped the laws of inheritanceMendel's work was not recognized until the turn of the 20th century

Gregor Gregor MendelMendel

(1822-1884)(1822-1884)

InheritanceInheritance

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.

Pare

nt

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 PracticeGenotype 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 chicken produce a black and white chicken

Incomplete Dominance

Codominance

• Two alleles are expressed (multiple alleles) in heterozygous individuals.

• Example: blood type

• 1. type A = IAIA or IAi• 2. type B = IBIB or IBi• 3. type AB= IAIB

• 4. type O = ii