Gene- Section of the DNA responsible for a trait.

Chromosome- A rod Shape structure, located in the nucleus that carries DNA.

The DNA Connection• Chromosomes are composed of DNA• DNA molecules are composed of four nitrogen

bases:Adenine (A)Thymine (T)Guanine (G)Cytosine (C)• A binds to T• C binds to G

• The order of the nitrogen bases along a gene forms a genetic code that specifies what type of protein will be produced.

• During protein synthesis, the cell uses information from a gene on a chromosome to produce a specific protein.

• Mutation- A change in a gene

• Mutations can cause a cell to produce an incorrect protein. As a result, the organism trait may be different from what it normally would have been.

Mendel’s Experiment

Experiment 1

Procedure

Crossed purebred tall plants with purebred short plants.

Result

All the offspring were tall. (He called these plants the f1 generation.

Experiment 2

Crossed f1 generation offspring

Result

3 were tall, 1 was short.

The ‘hidden’ trait reappeared.

• Heredity- Passing of physical characteristics from parent to offspring.

• Trait- Form of a characteristic. Example- Stem height, Seed color

• Genetics- Scientific study of heredity.

• Purebred/Homozygous- Offspring (baby, new organism) of many generations with the same trait. (Example purebred short plants always come from short parent plants)

• Hybrid/ Heterozygous- Organism with two different alleles for a trait.

What Mendel learned

• Allele- Different forms of a gene. (For example tall or short)

• Dominant Allele- Trait that always shows up. ( For example the tall trait)

• Recessive Allele- Hidden whenever the dominant allele is present. (For Example the Short Trait)

Symbols for alleles

• A dominant allele is represented with a capital letter. (Allele for tall is T)

• A recessive allele is represented by the lowercase version of the letter. (Allele for short is t)

• A purebred tall plant has two dominant alleles (TT)- The plant will always be tall.

• A purebred short plant has two recessive alleles (tt)- The plant will always be short.

• A hybrid plant has one of each, and would have one of each (Tt)- Since tall is the dominant trait, this hybrid plant will be tall.

Genotype- Genetic makeup. It is represented by a pair of letters (TT, Tt, tt)

Phenotype- Physical Appearance (tall, short)

Genotype Phenotype

TT Tall

Tt Tall

tt Short

Punnett Square- Used to determine the probability of a genetic outcome

Sample Problem

• 1. A Punnett square is shown below. The dominant• trait is represented by R. The recessive trait is• represented by r.

What percentage of the offspring will mostlikely show the dominant trait?(1) 25% (3) 75%(2) 50% (4) 100%