is the transmission of traits from one generation to the next.

Who was Gregor Mendel?Gregor Mendel was born in 1822 in Heinzendorf, Austria. Mendel grew up

on a farm and learned a lot about flowers and fruit trees. When he was 21

years old, he entered a monastery. The monks taught science and

performed many scientific experiments. Mendel was sent to Vienna where

he could receive training in teaching. However, Mendel had trouble taking

tests. Although he did well in school, he was unable to pass the final exam.

He returned to the monastery and put most of his energy

into research. Mendel discovered the principles of heredity

in the monastery garden by studying pea plants.

From his previous work with plants, Mendel knew

that the patterns of inheritance were not always clear.

For example, sometimes a trait that appeared in one

generation was not present in the next generation. In

the third generation, though, the trait showed up again.

Mendel noticed these kinds of patterns in several

other living things too. Mendel wanted to learn more

about what was causing these patterns.

To keep his investigation simple, Mendel decided to study only

one kind of organism. Because he had studied garden pea plants before,

they seemed like a good choice.

Like many good ideas, Gregor Mendel’s ideas were not

understood at first. In 1865, Mendel wrote about his studies, but it wasn’t

until after his death, more than 30 years later, that he finally got the

recognition he deserved. Once Mendel’s ideas were found and understood,

the door was open to modern genetics.

are characteristics or features of an organism that are inherited

(passed from parent to offspring).

Examples

eye colornose shape

hair type and color

• Some traits are passed on and others are not

• Dominant traits are traits that hide other traits when passed on to offspring

• Recessive traits are the traits that get hidden by dominant traits

blue eyes

Recessive trait Brown Eyes

Brown Eyes

Dominant trait

• Which traits do you have that are dominant?• Which are recessive?• Let’s take a look at a few examples.

Thumb Shape

Earlobes

Straight

Dominant

Hitchhiker’s

Recessive

Dominant or Recessive?

Hanging free

Dominant

Attached

Recessive

Why are some traits passed on and others are not? The answer lies in our Cells.

Scientist began to experiment with plants and animals to learn how traits are

passed on from parents to offspring.

Vocabulary Review

• The cell is a membrane covered structure that has all the materials necessary for life.

• Nucleus - contains all the genetic information for all life processes.

• Chromosomes are long molecules of DNA; found in the nucleus of eukaryotic cells.

• DNA - “deoxyribonucleic acid”; heredity material that controls all the activities of a cell.

Not all organisms have a nucleus, but all organisms have genes.

Genes are contained in DNA.

• basic unit of heredity• determines a persons traits

(characteristics)• passed on from parent to

offspring through asexual or sexual reproduction

Genes

– nucleus- chromosomes

– DNA- genes

- traitsChromosomes

Cells

Alleles• are the different forms of a gene.• Alleles come in pairs, one set from your father the

other set from your mother.• Geneticists use letters to represent alleles.• Example: Alleles come in pairs, and the allele

for having a Widow's Peak is thought to be dominant, so you only need one copy present

to have the trait.

Straight hairline

Widow’s peak

Genotype vs Phenotype• Genotype is the combination of

alleles an organism inherits from its parents (genes).

• Phenotype is the organisms appearance (physical).

ww

Straight hairline

WW, Ww

Widow’s peak

Genotype vs Phenotype

Other Examples:

Punnett SquareThe Punnett square is a diagram that is used to predict the outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, and is used by biologists to determine the probability of an offspring having a particular genotype. The Punnett square is a summary of every possible combination of one maternal allele with one paternal allele for each gene being studied in the cross.