Connect!

•Think of 3 traits you inherited.•Why do you think you inherited these traits? •Why aren’t we identical to our parents?•Why is each person a unique individual?•What is DNA and why is it important?•Explain why ducks produce ducklings and not piglets when they reproduce.

The Gene-Chromosome Theory

GENES – Characteristics of organisms are inherited as a result of transmission of hereditary factors called genes

• Genes exist at definite locations in a row on chromosomes.

The Gene-Chromosome Theory

• Chromosomes are found in the nucleus of cells.

Chunk Time!

• What are the hereditary factors that transmit traits called?

• Explain the Gene-Chromosome Theory.

• Where are chromosomes found?

• Organisms inherit 2 alleles for each trait: one from Mom and one from Dad.

A human cell nucleus contains 23 pairs of chromosomes.They are all well known and numbered. We all have two ch. 19s, two ch. 12s, two ch. 11s, etc…

Chunk Time!

• What is an allele?

• How many alleles do you receive for one trait?

• How many pairs of chromosomes are there in a human body cell nucleus?

• Think…how many total chromosomes in a human body cell nucleus?

Homologous Chromosomes• are the two matching chromosomes –

one from Mom, one from Dad

• the same genes in the same order are on each chromosome of the pair

• however, the alleles might be different… one might be for blue eyes, the other might be for brown eyes

When a cell is getting ready to divide, each single homologous chromosome is replicated.

Chunk time!

• What are homologous chromosomes?• Describe the genes on homologous

chromosomes.• Are the genetic messages identical on

homologous chromosomes?• What happens to each chromosome when

a cell is getting ready to divide?

One arm of the duplicated

chromosome is called a chromatid.

The centromere holds the two sister chromatids together, and is where spindle fibers will attach during cell division to pull the sister chromatids apart.

DNA molecule

The spiral staircase shape is called a double helix.

The DNA is coiled very tightly to form the arms of the chromosome.

Chunk Time!

• What is a chromatid?• Why are they called “sister chromatids”?• What is a centromere?• What is the function of the centromere?• What are the arms of the chromosome

made of?• What is the shape of the DNA molecule?

Can you

believe this?!!!