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What makes a family? Cells, Genes, Chromosomes and Traits Cells Genes All living things – people, plants, and animals – are made of cells (say: sels). Our bodies are made of cells. All people or humans have 100 trillion (100,000,000,000,000) cells. All humans have about 200 types of cells.

Each cell has twenty-five thousand (25,000) to thirty-five thousand (35,000) genes (say: jeenz). NO YES

Genes are on chromosomes (say: KRO-moh-somes). Chromosomes are inside cells. Chromosomes are in pairs (2).

 

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Chromosome DNA Each human cell has one nucleus (say: NOO_clee-us). The

nucleus is the brain of the cell.   In humans, the nucleus has forty-six (46) chromosomes or 23 pairs of chromosomes. (23 x 2 = 46)

Half (1/2) of the chromosomes are from your mother. Half (1/2) of the chromosomes are from your father.

23

Chromosomes have DNA. DNA gives cells directions. DNA tells cells what to do.

Fraction Decimal Percent Same 99/1000 .999 99.9% Difference 1/1000 .001 .1%

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X and Y Chromosomes Traits The last pair (2) of chromosomes are the “sex chromosomes” – X and Y. A girl has two XX chromosomes. A boy has one X and one Y chromosome.

girl XX boy XY

Genes have information. The information makes our traits (say: trates). Some traits are inherited. The traits are from our ancestors. Parents, grandparents, great grandparents, great-great grandparents and more are ancestors. We are the offspring or children of our parents.

Ancestors

Great - Grandparents Grandparents Parents Offspring Children (kids)

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Inherited Traits Acquired Traits

Eye color is an inherited trait. What is your eye color?

Hair color Red Brown Black Eyesight Glasses No glasses

Hair color is an inherited trait. What is your hair color? Eyesight is an inherited trait. Do you wear glasses? Skin color, height, foot size, and birthmarks are inherited traits.

Not all traits are inherited. Other traits are acquired. You learn acquired traits. You practice. You learn how to ride a bike. You learn how to read. You learn how to play sports. You learn how to play music.    

           

Acquired traits are also events that happen to you. You break your arm. You cut your hair. You hit your head.

     

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Dominant Gene Recessive Gene Domianant Gene Recessive Gene A dominant gene has one (1) strand of DNA that is stronger than the other strand of DNA.

A recessive gene is one (1) strand of DNA that is weaker than the other strand of DNA.

Eye color: We have BOTH a dominant and recessive gene for eye color. Why does a mother and father with brown eyes have a child with blue eyes? (B = dominant / brown eyes; b = recessive / blue eyes)

Dominant? Recessive?

Dominant? Recessive?

Dominant Recessive

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