Mendelian Genetics10.2 and 10.3

The Father of GeneticsGregor Mendel-

Austrian Monk and Plant breeder

Used pea plants to study how traits were inherited(heredity)

Mendel was the first person to trace the characteristics of successive generations of a living thing (pea plants).

Because of his work he is regarded as the ‘father of genetics’

(1823-1884)

Experiments with Pea Plants

Why Peas?

Quick reproductive cycle Self-pollinating

He studied simple traits, traits that occurred in only one of two possible

variations.

Mendel’s Experiment Gregor Mendel performed cross-pollination

in pea plants.

Flower colorSeed colorPod colorSeed texturePod TextureHeightFlower Placement

Mendel’s ExperimentMendel cross pollinated a plant with green seeds and plant with yellow seeds. The F1 generation was all yellow.Mendel allowed the F1 generation to self- fertilize The F2 generation was in a 3:1 ratio of yellow to green seeds

Mendel’s ExperimentMendel concluded that there was two forms

of the trait for seed color in pea plants. Yellow and green

He called these different forms of the trait alleles

From his experiment he determined some forms of a trait were dominant to others. E.g. yellow is dominant to green

Homozygous and HeterozygousDominant allele = Capital Letter (A)Recessive allele = lower case letter (a)

Homozygous= two of the same alleleHomozygous dominant (AA)Homozygous recessive (aa)

Heterozygous = two different alleles for a trait(Aa)

Genotype vs. PhenotypeGenotype Phenotype

Allele pairObservable trait

(physical features)

Mendel’s LawsLaw of Segregation-two alleles for each

trait separate during meiosis.

Law of Independent assortment- Random distribution of alleles occurs during gamete formation

Monohybrid Crosses

Only 1 trait is looked at.

Ex: Pod color is the only trait being looked at

Punnett Squares

Is a toolHelps us keep track of crossesAllow us to predict possible offspring

outcomes

Let’s PracticeRed flowers are dominant over white flowers

What possible offspring would the following crosses produce?

Rr x rrRR x rrRr x RrRr x RR

In guinea pigs dark fur (D) is dominant over light fur (d). What are the genotypes and phenotypes of each of the following crosses?

Dd X ddDD X DdDd X DdDD X dd

Punnett Square PracticeBrown eyes is dominant to blue

eyes. Show a cross between two heterozygous parents.

What are the genotypic and phenotypic ratios?

Homozygous dominant: Heterozygous: Homozygous Recessive

Brown hair is dominant to red hair. Two parents who are heterozygous want to know the probability of having a child with red hair. What is their probability?

In a family a heterozygous father and a homozygous recessive mother for the trait of freckles. If freckling is a dominant trait, what is the probability that each child is heterozygous?

Dihybrid Crosses

Following 2 traits instead of one.

When two heterozygous parents are crossed, their offspring are in a 9:3:3:1 phenotypic ratio

Short tails are dominant to long tails and Black fur is dominant to brown fur.SsBb X SsBb

PolyploidyOne or more extra sets

of chromosomes.Always lethal in

humansEarthworms and

goldfish can sometime be polyploidy.

Wheat (6n), oats (6n), sugar cane (8n)