genetics intro. 8th

GENETICS

What is Genetics?

• Genetics is the science that studies the process of heredity.

What is heredity?

• The passing on of traits from parent to offspring.

What is a trait?

• A unique characteristic.• For example: hair color, eye color, height, tongue rolling, widows peak, etc

How are traits passed on?

• Traits are passed on from parent to offspring through DNA.

BrainPop DNA

What is DNA

• DNA is the chemical building block of life.

• Every human cell contains a nucleus with DNA.

• DNA is made up of 4 base pairs:– Adenine, Thymine, Cytosine, and Guanine

Watson and Crick• Are the two scientists who discovered the shape of DNA.

• They called the shape a double helix.

• Each chromosome is a long strand of DNA.

• Every cell has 23 homologous pairs of chromosomes

How does DNA make a human?

• The genetic code is spelled out with just four chemical letters, or bases: adenine (A), thymine (T), cytosine (C), guanine (G).

• These pair up, A with T and C with G.• The human genome has between 2.8 and 3.5 billion base pairs!

DNA double helix• The base pairs form the rungs of the ladder-like DNA double helix. Running up and down the ladder are the long sequences of bases which are the code for life.

• Each cell in the human body contains 2 meters (6 feet) of DNA!

DNA video

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Genes

• As little as 3% of the total genome is made of genes - the rest is meaningless “junk”.

• Genes are special sequences of hundreds or thousands of base pairs that provide the templates for all the proteins which the body needs to produce.

Chromosomes

• The total number of genes is not known. The estimate ranges from 30,000 - 120,000!

• All genes are wrapped up into bundles called chromosomes.

• Every human has 23 pairs of chromosomes, one half of each pair from each parent!

Nucleus and the cell

• The 46 chromosomes are held in the nucleus found in most cells in the human body. Nearly every cell in the body contains the full DNA code for producing a human.

Heredity

• Heredity is the passing on of traits from parent to offspring.

BrainPop ON Heredity

Dominant Trait

• The stronger of two traits.

• Represented with a capital letter.

• R

Recessive Trait

• The weaker of two traits.

• Represented with a lower case letter.

• r

Genotype

• Every one has two genes for a trait. One gene from mom and one gene from dad.

• If mom gives you a dominant gene and dad gives you a recessive gene your genotype would be:

• Rr

What is a genotype?

• The genotype is the genetic make-up of a trait.

• The letters that represent the genes are the genotype.

• Rr

Phenotype

• The phenotype is the physical characteristic that you can see.

• For example: brown hair, brown eyes, widows peak, etc..

Homozygous genotype

• If both parents give you a dominant gene, your genotype would be homozygous dominant.

• RR• Homozygous - means both genes are the same!

• If both parents give you a recessive gene, your genotype would be homozygous recessive.

• rr

Heterozygous genotype

• If one parent gives you a dominant gene, and the other parent gives you a recessive gene, you will have a heterozygous genotype

• Rr• Heterozygous - means the two letters are different

Punnett squares

• Are tools used in genetics to predict the genotype and phenotype of offspring.

How to use a Punnett square