GENETICS AND HEREDITY genes found on chromosomes in

the nucleus of a cell, code for the inherited characteristics we call traits

the passing of traits from parents to offspring is known as heredity

the scientific study of heredity is called genetics

lacking today’s technology the first studies of genetics were based on physical appearance and mathematics

GREGOR MENDEL

Mendel was an Austrian monk who loved gardening and mathematics

he designed simple experiments with pea plants to determine how heritable traits were transferred from one generation to the next

MENDEL’S PEA TRAITS

MENDEL’S CONCLUSIONS1. each trait is controlled by two genes that

they receive from their parents

2. Some genes are dominant over others (shown in capital letters)

3. Genes that are masked by dominant genes are called recessive genes (shown in lower case letters)

4. the combination of these two genes determines the traits offspring will exhibit

5. how often these traits will appear is predictable

TERMINOLOGY

GENOTYPE actual genetic code (Bb)

PHENOTYPE the way genes are expressed; what is seen on the outside

PUREBRED (homozygous) having two identical genes for a trait (BB or bb)

HYBRID (heterozygous) having two different genes for a trait (Bb)

REGINALD PUNNETT

based on the work of Mendel, he developed the “Punnett Square” as a method of predicting the results of a genetic cross (breeding)

dominant genes are symbolized by capital letters

recessive genes are symbolized by lower case letters

CROSS #1Tall purebred pea plant (TT)

x

Short purebred pea plant (tt)

Tall (T) dominant

Short (t) recessive

RESULT:

4/4 tall hybrid offspring

GENOTYPE BOX

PHENOTYPE BOX

t t

T

T

Tt Tt

Tt Tt

CROSS #2Tall hybrid pea plant (Tt)

x

Tall hybrid pea plant (Tt)

Tall (T) dominant

Short (t) recessive

RESULT:

1/4 tall purebred offspring

2/4 tall hybrid offspring

1/4 short purebred offspring

GENOTYPE BOX

PHENOTYPE BOX

T t

T

t

TT Tt

Tt tt

Principles of Genetics1. Inherited traits are passed on from parents to

offspring.

2. The traits of an organism are controlled by genes.

3. Organisms inherit genes in pairs. One gene comes from each parent.

4. Genes can be dominant or recessive. Dominant genes can mask recessive genes.

5. A Punnett square can be used to predict the results of a cross.