Introduction to Genetics

Heredity and Mendel’s Peas

Mrs. Stewart

Honors Biology

Central Magnet School

Standards:

CLE 3210.4.1 Investigate how genetic information is encoded in nucleic acids.

CLE 3210.4.2 Describe the relationships among genes, chromosomes, proteins, and hereditary traits.

CLE 3210.4.3 Predict the outcome of monohybrid and dihybrid crosses.

Objectives:

Differentiate between characteristics and traits

Analyze Mendal’s principle of dominance

Predict genotype based on phenotype Analyze characteristics and traits in

this classroom

Decide with your partner

What is heredity?

Why do family’s look alike?

Heredity & Genetics

Heredity - The transmission of characteristics from parents to offspring

Genetics – the study of heredity

Genes – Segments of DNA that code for a characteristic

Characteristics vs. Traits

Characteristic – a heritable feature Example: flower color, plant height

Trait – a genetically determined variant of a characteristic Example: purple flower color vs white Now referred to as “Alleles”

Dogs Tell your cats two examples of

characteristics that can be inherited from human parents to offspring.

Cats Give your dogs an example of

traits/alleles (variations) for the characteristics he/she listed.

Gregor Mendel (1822-1884)

“Father of Genetics”

Austrian Monk

Studied characteristics & traits in pea plants Have only 7 chromosomes Can cross pollinate or self pollinate

Gregor Mendel’s Peas• “Self pollination”-

Pollen from the plant fertilizes its own eggs• Similar to asexual

reproduction. • “True-breeding” -

produce identical new plants.• “Purebreds”

Mendel’s Peas• “Cross-pollination”• Remove male parts

from true breeding plant, pollinate it with pollen from a plant with different traits.

• Produce “hybrids”• Genetically

different

Mendel’s Observations

Characteristics

Seed shape

Seed color

Seed coat color

Pod shape

Pod color

Flower position

Plant height

Traits/Alleles

wrinkled or smooth

yellow or green

white or grey

smooth or constricted

green or yellow

axial or terminal

tall or short

Alleles

We use letters to represent the different variations

Capital Letters = Dominant allele Lowercase letters = recessive allele Example: T = tall plant, t = short plant Most genes have two or more variations

(alleles)

Important Vocabulary Terms HETEROzygous:

(DIFFERENT) have different alleles Example: Tt

HOMOzygous : (SAME) have the same

alleles. Example: TT or tt

HYBRID = offspring of heterozygous parents

PUREBRED (true-breeding) = offspring of homozygous parents – will produce offspring identical to parent traits

Generations• The parent

generation

• The first generation

• The second generation

Dominance

• Tall height “masks” the effects of short height.• Tall is “dominant”; Short is “recessive”.

(P) – Purebred Tall x Purebred Short

F1 – All tall (hybrids)

F2 – 3:1 ratio tall:short

Principle of Dominance

some variations (traits/alleles) are dominant over others

Dominant traits will mask or hide the presence of a recessive trait

Recessive traits are hidden/masked by a dominant allele

Principle of Dominance – UFC style

Only one can win

•Matt Hughes = Recessive

•BJ Penn = Dominant

Genotype VS. Phenotype

GENOTYPE: actual combination of alleles (genes) inherited from parents. (One from MOM, and one from DAD.) Example: Tt, TT or tt

PHENOTYPE: physical appearance/expression of the trait. Example: Tall plant or short plant

Cats and Dogs (think – pair – share)

Phenotype Widows Peak or straight

hair line

Genotype Ww, WW or ww

Cats And Dogs

The dominant trait is “gray” fur, and the recessive trait is “white” fur. Lets use the following alleles: Gray is G. White is g.

If a bunny is heterozygous gray: What is the genotype? ______________

If a bunny is homozygous white: What is the genotype? ______________

If a plant is homozygous gray: What is the genotype? ______________

Gg

gg

GG

Principles of Dominance

Predictable patterns of dominant and recessive only apply to single gene traits

Example: gene for hairline has 2 alleles – widow’s peak (W) or straight hairline (w) Possible Genotypes: WW, Ww or ww

Dominance VS. Commonality

Does dominant mean most commonly occurring?

No Examples:

Polydactyl – having 6 fingers Achondroplasia – Dwarfism O blood type (recessive)

Group Activity

Inventory of Traits

Dogs and Cats

Predict you and your partners possible genotypes for the phenotypes listed in traits activity.

Objectives:

Differentiate between characteristics and traits

Analyze Mendal’s principle of dominance

Predict genotype based on phenotype Analyze characteristics and traits in

this classroom