Genetics

Punnett Squares

PA State Standards3.3.7.C

Genetics

The study of heredity or the passing on of traits from an organism to its offspring.

In your cells you have chromosomes.These chromosomes contain DNAThis DNA contains all of the information that makes you …YOU!

Gregor Mendel (1822 – 1884)

Mendel was an Augustinian monk who taught natural science to high school students. He was working on pea plants. Mendel is referred to as the father of genetics. His work was so brilliant at the time it took thirty-four years for the rest of the scientific community to catch up to it.

Gregor Mendel (1822 – 1884)

The impact of genetic theory is great. Many diseases are known to be inherited. Determining the probability of passing along a hereditary disease is an important area of study.

Mendel’s Pea ExperimentMendel worked with pea plants.The practical results of Mendel's research has not only changed the way we perceive the world, but also the way we live in it.He wanted to see how certain traits or characteristics were transferred from parent pea plant to offspring.

How did he breed pea plants?

Most flowering plants contain a STAMEN, or the male reproductive structure of the plant. These stamen produce POLLEN, which are the male sex cells (much like sperm cells)

Plant reproduction

Plants also contain a PISTIL, which is the female reproductive structure in a plant.This pistil also contains the female sex cell, the EGG (ovule).

Pollination

Occurs when the pollen lands on top of the pistil of the flower.Pollination produces seeds for the next generation.

Cross pollination

Taking pollen from one plant with a certain trait and placing it on a plant with a different trait. For example, taking pollen from a short plant and placing it on a plant that is tall.

Terms to know…

Alleles each member of a gene pair that determines a specific traitDominant Trait the “more forceful”, the “stronger” of the two traitsRecessive Trait the “less forceful”, the “weaker” of the two traits; this trait seems to disappear when the dominant trait is present

More terms to know…

Homozygous (pure) a trait that has two of the same members of individual genesHeterozygous (hybrid) a trait that has two different members of a genePhenotype the physical appearance of an organismGenotype the actual gene make up of an organism

Dominant Genes (Alleles)

Certain genes are dominant, you only need one of the pair to give you its trait.Dominant genes are represented as capital lettersHave a partner examine your earlobes. If they hang free at the bottom, you are dominant.

(E __ )

Recessive Genes (Alleles)

Other genes are recessive, you need both genes in the pair as recessive to give you the trait.Recessive genes are represented as lower case lettersIf your earlobes are attached, you are recessive.

( e e )

Pure Trait (Homozygous)

Having two identical genes (alleles) for a given trait.Individuals homozygous for a trait always breed true/pure; that is, they produce offspring that resemble them in appearance.

Brown Eyes

BB

Blue Eyes

bb

Hybrid Trait (Heterozygous)

Having dominant and recessive (alleles) for a given trait.Only the dominant trait is expresses in the phenotype.Offspring of heterozygouts can show the trait or the trait can remain recessive.

Brown Eyes

Bb

Detached Ear Lobe

Ee

Genotype

Genotype & Phenotype

The genes of an individual are called its genotype.

Genotype & Phenotype

The genes of an individual are called its genotype.These genes determine what an individual will look like, which is called its phenotype.

Phenotype

Mendel’s experiment

He took two plants that were short and cross pollinated them. In this next generation he discovered that all of the offspring were short.

Mendel’s experiment

He then decided to take a plant that was short and mix it with a plant that was tall. All of the offspring were TALL. There were no short plants.

Mendel’s experimentHe then took one of the offspring he had just worked with (tall and short parent) and allowed this plant to self-pollinate (pollinate itself).The result = some tall and some short plants.The short gene had reappeared. Mendel concluded there must be dominant and recessive genes.

Punnett SquaresThe easiest way to calculate the mathematical probability of inheriting a specific trait is the Punnett Square.In a graphical way you can determine the possible genotypes of the offspring produced. Reginald Punnett

(1875 – 1967)

A true (homozygous) blue eyed father and a true (homozygous) brown eyed mother want to see the probability for their children’s eye color.

1. How can we show this “crossing” of traits?

2. What would be the genotype of the children?

3. What would be the phenotype of the children?

Punnett Squares

Punnett Squares 1

B

B

b b

B b

What would be the genotype of the children?

1. What would be the phenotype of the children?

B b

B b

B b

Genotype: (Bb) Heterozygous 100 %

Phenotype: Brown Eyes 100%

Punnett Squares 2

A true (homozygous) blue eyed father and a hybrid (heterozygous) brown eyed mother want to see the probability for their children’s eye color.

1. What would be the genotype of the children?

2. What would be the phenotype of the children?

Punnett Squares 2

B

b

b b

B b

Genotype(s): Heterozygous (Bb) & Homozygous (bb)

Phenotype: 50% Brown Eyes : 50% Blue Eyes

b b

B b

b b

Punnett Squares 3A hybrid (heterozygous) brown eyed father and a hybrid (heterozygous) brown eyed mother want to see the probability for their children’s eye color.

1. What would be the genotype of the children?

2. What would be the phenotype of the children?

Punnett Squares 3

B

b

B b

BB

Genotype(s): Heterozygous & Homozygous

Phenotype: 75% Brown Eyes : 25% Blue Eyes

B b

B b

b b

Punnett Squares (Monohybrid Cross)

Genotype(s): ___________________________

Phenotype: ___________________________

Punnett Squares (Dihybrid Cross)

Genotypes:

Phenotypes:

Credits

http://www.accessexcellence.org/RC/AB/BC/Gregor_Mendel.htmlhttp://www.accessexcellence.org/RC/VL/GG/mendel.htmlhttp://www.mendel-museum.org/eng/8garden/http://www.dushkin.com/connectext/psy/ch02/eyes.mhtmlhttp://www.anistonavenue.com/new_pics_13.htmhttp://biology.about.com/library/glossary/bldefalleles.htmhttp://www.windows.ucar.edu/tour/link=/earth/Life/genetics_inheritance.htmlhttp://student.biology.arizona.edu/sciconn/heredity/worksheet_heredity.htmlhttp://anthro.palomar.edu/mendel/mendel_2.htmwww.scienceatclifton.co.uk/clifton/punnett.htm