Genes and Inheritance

What is DNA? Chromosomes are made up of DNA coiled tightly around proteins called histones. Chromosomes are made up of DNA coiled tightly around proteins called histones. Deoxyribonucleic Acid (DNA) carries the code that tells cells what to do. Deoxyribonucleic Acid (DNA) carries the code that tells cells what to do.

DNA Structure DNA is made up of nucleotides. DNA is made up of nucleotides.

Each Nucleotide is made up of 3 parts; Each Nucleotide is made up of 3 parts; Phosphate group Phosphate group Nitrogenous base Nitrogenous base Pentose sugar Pentose sugar

These nucleotides are arranged in long strands that pair up to form a ladder. These nucleotides are arranged in long strands that pair up to form a ladder. This ladder then twists to form what is called a double helix. This ladder then twists to form what is called a double helix.

Base Pairing There are 4 nitrogenous bases. There are 4 nitrogenous bases. Adenine Adenine Thymine Thymine Cytosine Cytosine Guanine Guanine

Each of these bases can only pair with one other base. Each of these bases can only pair with one other base. Adenine always pairs with thymine Adenine always pairs with thymine Cytosine always pairs with guanine Cytosine always pairs with guanine

So, what? The order in which these base pairs are found on different sections of DNA determine everything about you! The order in which these base pairs are found on different sections of DNA determine everything about you! Our information is organized into genes (like documents), which are organized into chromosomes (files in a filing cabinet) Our information is organized into genes (like documents), which are organized into chromosomes (files in a filing cabinet) The combination of our genes makes all of us unique The combination of our genes makes all of us unique

Gregor Mendel and Genetics

Who’s this guy? Gregor Mendel was an Austrian monk who worked with pea plants. Gregor Mendel was an Austrian monk who worked with pea plants. Mendel worked with pea plants to study heredity. Mendel worked with pea plants to study heredity.

Why pea plants? The four main reasons Mendel worked with pea plants were: The four main reasons Mendel worked with pea plants were: The common pea plant was available throughout Europe The common pea plant was available throughout Europe It is easy to grow and matures quickly It is easy to grow and matures quickly Pea plants self – pollinate, allowing Mendel to control which plants reproduced Pea plants self – pollinate, allowing Mendel to control which plants reproduced Different varieties of pea plants have different traits that can be easily observed from one generation to the next. Different varieties of pea plants have different traits that can be easily observed from one generation to the next.

Mendel’s Experiment The first thing Mendel needed to do was obtain purebred plants for the traits he wanted to study. The first thing Mendel needed to do was obtain purebred plants for the traits he wanted to study. A purebred organism results from many generations of selective breeding. A purebred organism results from many generations of selective breeding.

Plant height was one of the traits Mendel used in his studies of the pea plant. Plant height was one of the traits Mendel used in his studies of the pea plant. Once he had a purebred short and a purebred tall plant he would cross – pollinate them and observe the results. Once he had a purebred short and a purebred tall plant he would cross – pollinate them and observe the results. Mendel called this purebred cross the parent or P generation. Mendel called this purebred cross the parent or P generation.

The Results The offspring of the P generation were called the F 1 generation. The offspring of the P generation were called the F 1 generation. What do you think they looked like? What do you think they looked like? These pea plants were all tall. These pea plants were all tall. Mendel then cross – pollinated these plants with each other and created the F 2 generation. Mendel then cross – pollinated these plants with each other and created the F 2 generation. What do you think they looked like? What do you think they looked like?

These plants were 75% tall and 25% short. These plants were 75% tall and 25% short.

The Principle of Dominance These results led Mendel to conclude that the tall trait was dominant and the short trait was recessive. These results led Mendel to conclude that the tall trait was dominant and the short trait was recessive. A dominant trait is a characteristic that is always expressed. A dominant trait is a characteristic that is always expressed. A recessive trait is a characteristic not usually expressed. A recessive trait is a characteristic not usually expressed.

The presence of the recessive trait in the F 2 generation led Mendel to conclude that inherited traits are controlled by two “factors”. The presence of the recessive trait in the F 2 generation led Mendel to conclude that inherited traits are controlled by two “factors”. These “factors” segregate in gametes, only one in each gamete. These “factors” segregate in gametes, only one in each gamete. Today we know that these factors are genes. The two forms of a gene are called alleles. Today we know that these factors are genes. The two forms of a gene are called alleles.

Law of Segregation The law of segregation states that every individual possess a pair of genes and that each parent passes a randomly selected copy of only one of these to its offspring The law of segregation states that every individual possess a pair of genes and that each parent passes a randomly selected copy of only one of these to its offspring Since there is no decision in choosing which gene gets chosen, the Law of Independent Assortment was also established Since there is no decision in choosing which gene gets chosen, the Law of Independent Assortment was also established

Independent Assortment States that separate traits are passed independently of one another from parent to offspring States that separate traits are passed independently of one another from parent to offspring That is, the biological selection of a particular gene pair for one trait to be passed to the offspring has nothing to do with the selection of the gene for any other trait That is, the biological selection of a particular gene pair for one trait to be passed to the offspring has nothing to do with the selection of the gene for any other trait Alleles of different genes assort independently of one another during gamete formation Alleles of different genes assort independently of one another during gamete formation