INTRO TO GENETICS

GREGOR MENDEL

• Known as the Father of Genetics• Studied pea plants and discovered the basics of

heredity and genetics

GREGOR MENDEL

• The study of heredity is genetics• The passing on of traits from one generation to

the next is heredity.• Mendel started with true-breeding plants (plants

that always produced identical offspring)We will call these plants P for parental.• He then crossed these plants. The offspring of

these plants (we will call F1)were identical to each and to one of the parents.

TRUE BREEDING PLANTS

CHROMOSOME DNA GENE RELATIONSHIP

• Genes determine specific traits• Different forms of genes are called alleles

GREGOR MENDEL

• Mendel noticed that one trait appeared more often than the other trait. The trait that appeared more often is called the dominant gene.• The gene that was not dominant was called

recessive. The dominant gene hid the recessive.• This is known as the Law of Dominance.• The gene for brown eyes is dominant over the

gene for blue eyes. Therefore, if you get both alleles, you will have brown eyes.

GREGOR MENDEL

• Therefore, if Mendel crossed a purple flower (which is dominant) with a white flower (recessive) all offspring will be purple

OTHER DOMINANT TRAITS IN PEA PLANTS

DOMINANT AND RECESSIVE TRAITS

• How do you get a recessive trait to show?• Recessive traits show only if NO dominant trait

exists• We use capital letter for dominant traits and

lowercase letters for recessive traits. For example, we use W to represent the dominant allele for purple flowers. w represents the recessive allele for white flowers.

GENOTYPE VS PHENOTYPE

• The genotype of an organism is the combination of alleles it has for a particular trait.• For example: Bb, dd, EE• One letter represents the gene from the mother

and the other letter is from the father so the baby has 2 letters.• For most traits there are 3 possible genotypes:

BB, Bb, bb

GENOTYPE VS PHENOTYPE

• If there are 2 capital letters or two lowercase letters in the genotype (BB or bb), then the trait is called homozygous. • If there is one capital letter and one lower case

letter (like Bb), then the genotype is heterozygous or a hybrid.• The phenotype is the physical characteristics of

an organism. (what they look like) The phenotype is an expression of the genotype

GUINEA PIGS

• Guinea pigs fur: brown fur is dominant over white fur. Brown fur will be B and white fur will be b.

Genotype Definition Phenotype

RECAP

• If an individual receives a dominant gene for a trait from its mother and a recessive gene for that trait from its father, it will display the dominant trait• Traits such as flower color come from the different

forms of the same gene. These different gene forms are called alleles.• These genes can be the same alleles or different.• The recessive gene will only be expressed if the

individual has two recessive alleles.

LAW OF SEGREGATION

• Each allele for a trait segregates (separates) during gamete production so that each gamete carries only one of the genes. These two alleles do not mix with each other.• This observation is known as the Law of

Segregation. In other words, when an individual forms sex cells, the different forms of the gene will separate. • The individual will not pass on a combination of

both for that one trait.

MONOHYBRID CROSSES

• Inheritance patterns of only one trait studied. One allele from a female egg is joined with one allele from a male sperm.• What if a heterozygous pea plant for flower color

is crossed with another heterozygous plant? What will be the phenotypes and genotypes of the offspring?

PROBABILITY: THREE THINGS YOU SHOULD KNOW

• 1. Probability predicts what is most likely to occur, but what actually occurs may be different• 2. Each outcome is not influenced by the

outcomes before it. • 3. The actual results will be closer to the

predicted results for a large number of outcomes.

USING A PUNNETT SQUARE

• Punnett squares are a way scientists make genetic predictions. Punnett squares show all possible combinations from a genetic cross.• Remember, dominant alleles are represented by

capital letters, and lowercase letters stand for recessive alleles.