STUDY OF HEREDITY DEVELOPED BY GREGOR MENDEL

Mendelian Genetics

Mendel’s Three Laws

Law of Dominance

Law of Independent Assortment

Law of Segregation

Genetics- study of heredity Trait- a characteristic that can be passed

from parent to offspring. Gregor Mendel – “the father of modern

genetics” used pea plants to study how traits were passed on among generations.

Applied mathematics to make statistics on how traits are passed along.

Why Pea Plants?

Mendel chose pea plants for 3 reasons: The structure of the pea flower The presence of distinctive traits Rapid reproduction cycle

He was able to isolate and control variable.- Cut anthers and only pollinated with desired pollen

Purebred- an organism that possesses identical alleles for a particular trait.

-homozygous (same alleles)- receives the same genetic traits from both parents

Hybrid- an organism that possesses different alleles for a particular trait.

-heterozygous (different alleles)

Study Mendel’s experiment from page 132

P = parentalF1 = filial (offspring) first generationF2 = second generationWhich trait is dominant?Chartreuse is dominant.

Genes- section of a chromosome that code for a specific trait.

Mendel called them “elements”1. allele- a distinct form of a gene (ex: brown

hair)2. Dominant allele- form of a gene that is always

fully expressed when two genes are present.3. Recessive allele- form of a gene that is not

expressed when paired with a dominant allele.

Genotype- the genetic makeup of an organism

Bb TT Ll

Phenotype- the outward expression of a trait ( an organism’s appearance)

Brown Tall Long haired

6.3

Probability-Predicting the likelihood of an event or outcome.

Using fractions, percentages, or ratios.

1/2 50% 1:1

Probability in Biology

Used to predict the phenotypes and genotypes of offspring in breeding experiments.

Can even predict the numbers of kinds offspring before fertilization takes place.

Scientists use a tool to make these predictions.

Punnett square

Punnett square- a grid for organizing genetic information. Shows probabilities, not actual results.

The study of the inheritance of only one trait at a time. - monohybrid cross

Cross a yellow pea plant with a green pea plant. (Purebred Cross)

Use a Punnett square, show genotypic ratios and phenotypic ratios.

Yellow x greenYY x yy

Genotype

Phenotype

Cross a heterozygous yellow pea plant with a heterozygous yellow pea plant. Monohybrid cross

Use a Punnett square, show genotypic ratios and phenotypic ratios.

Turn in your book to page 138 Figure 6.8.

Hybrid Cross

F1 Yellow vs F1 Yellow

Yy x Yy

Genotype

Phenotype

Two Traits

Apply the same rules of probability.The inheritance of two traits at the same time

- dihybrid crossCross two heterozygous round, heterozygous

yellow pea plants.Punnett square 4 x 4.Use a Punnett square, show genotypic ratios

and phenotypic ratios.

Dihybrid Cross

RrYy x RrYy Genotype

Phenotype

Test Cross

If dominant, how do you know whether it is homozygous or heterozygous?

By doing a test cross.Test cross- crossing the organism with an

unknown genotype with a homozygous recessive organism.

If the unknown genotype is heterozygous, Yy, about 50% the offspring should show the recessive phenotype.

If the unknown genotype is homozygous, YY, 100% the offspring will show the dominant phenotype.

Figure 6.10 shows this.

How do you know if the plant is a heterozygous or homozygous tall wheat plant?

Tall wheat plant x short wheat plant

F1Genotypes

Phenotypes

Test Cross- Practice Problems

Test Cross Examples

Ability to roll tongue x inability to roll tongueWhat is the genotype of the parent with the

ability to roll their tongue, if they have 2 children that can roll their tongue and 2 children that cannot?