Genetics Chapter 6 & 7

Gregor Mendel Austrian Monk who tended plants at a monastery in 1865

Gregor Mendel By experimenting with pea plants he was the first to correctly identify patterns of inheritance.

Gregor Mendel The methods he used forms the basis of our modern genetics. Known as the “Father of Genetics”

Mendel’s Experiment

A pure strain is a group that always exhibit the same trait. Crossing Pure Strains A pure strain is a group that always exhibit the same trait.

An example is a group of pea plants that are always tall. Crossing Pure Strains An example is a group of pea plants that are always tall.

Mendel called his pure strains the P1 generation (parents). Crossing Pure Strains Mendel called his pure strains the P1 generation (parents).

He pollinated a pure tall plant with a pure short plant Crossing Pure Strains He pollinated a pure tall plant with a pure short plant

All the offspring were tall!!! He called them the F1 Generation

Crossing Pure Strains The offspring are the F1 Generation If all of the F1’s were tall Then the short trait seemed to disappear

Crossing Pure Strains This happened with every cross that he did. Green X Yellow = All green Round X Wrinkled = All round

He called the trait that showed up dominant. Crossing Pure Strains He called the trait that showed up dominant.

The trait that disappeared was called recessive. Crossing Pure Strains The trait that disappeared was called recessive.

Cross of F1’s Next Mendel crossed two of the F1 tall plants.

Cross of F1’s Out of all offspring, 75% were tall and 25% were short. This happened with every trait (green,yellow, round, wrinkled)

F2 Generation

As a result of the pea plant experiments Mendel learned that: 1. One factor may mask another. The dominant factor may mask the recessive factor. The dominant is represented by a capital letter (T). Recessive is lowercase (t).

Mendel also learned that 2. Every offspring has 2 factors that make up a trait. One coming from each parent. These factors are called alleles.

Mendel’s Laws

Law of Segregation A parent passed on at random only 1 allele for each trait to each offspring.

Law of Segregation Example: A mother’s egg can only carry a T for tall or a t for short. Even though her genotype is Tt.

Law of Independent Assortment Genes for different traits are inherited independently of each other.

Law of Independent Assortment Example: Plant height and seed color are not linked.

Punnett Squares An English biologist named Punnett came up with a short hand way of finding proportions: the Punnett Square

A monohybrid cross involves 1 trait. Punnett Squares A monohybrid cross involves 1 trait. Example: Gg x gg (pea plant color)

Punnett Squares A dihybrid cross involves 2 traits. Ex: TTGG x ttgg (pea height and color)

Punnett Squares A homozygous (purebred) individual has 2 alleles that are the same. Example: TT, tt

Punnett Squares Homozygous Dominant = TT (pure strain tall) Homozygous Recessive = tt (pure strain short)

Punnett Squares A heterozygous (hybrid) individual has 2 alleles that are different. Example: Tt (hybrid tall)

Punnett Squares The way an organism physically looks is it’s phenotype. The gene combinations an organism contains is it’s genotype.

Punnett Squares Example of phenotype: brown eyes Example of genotype: Bb

Genetic Traits and Disorders

Polydactyly

Hitchhiker’s Thumb

Widow’s Peak

XYY Syndrome

Sickle-Cell Anemia

Polygenic Eye Color

The End