genetics intro. 8th
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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
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
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