Overview
In this lesson, we will study how the DNA and chromosomes in our cells code for the same traits, but those traits can be expressed differently. We will also have a little fun seeing how genetic coding works internally and externally.
Imagine that you are in your favorite ice cream shop. The shop has many flavors of ice cream. So you can order vanilla, chocolate, strawberry, lemon, pineapple, etc. You get the picture.
Using this analogy, genes are the ice cream, and alleles are the different flavors. For example, the gene that codes for eye color is the same, but people can have alleles for brown eyes, blue eyes, green eyes, or gray eyes. The genes are the same; the alleles are different.
The DNA of any two human beings is 99% to 99.9% identical. The other small percentage of variation is due to the alleles of genes on chromosomes. Alleles are responsible for the differences between individuals.
Genes
Genes are clusters of DNA located on specific sections of chromosomes. Genes are the basic units of heredity and contain the codes for every part of an organism.
The same genes code for the same characteristics in all human beings. For example, the genes that code for eye color and the brain, heart, teeth, and skin are the same and are located on the same areas of chromosomes.
Alleles
Alleles are versions of a gene. They are located at the same place on a chromosome pair. An individual inherits two alleles for each gene, one from each parent.
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What do these two women have in common?
Click on the photo for the answer.
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Even with twins, alleles can be the same or different, resulting in identical or fraternal twins. Because children receive one set of genes with their alleles from each parent, genetic expressions are unpredictable and can result in differences between people in the same gene pool.
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DOMINANT ALLELES VS. RECESSIVE ALLELES
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Alleles can be dominant or recessive. If the alleles of a gene are different, only the dominant allele is expressed. The dominant allele masks the expression of the recessive allele.
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Genotype
Phenotype
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Genotype (think internal genetic information) refers to the alleles that code for different expressions of the same gene. For example, you have alleles that code for brown and blue eye color, but no one can see your genes or alleles.
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Phenotype (think outward physical visibility) refers to the expression of the paired alleles. Your phenotype is what everyone sees. You and other people can see that you have brown eyes.
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Let's look at dominant and recessive genotypes that result in different phenotypes. Remember, the same genes (genotype) code for the same traits in people, but the alleles determine the physical appearance (phenotype) that differs from person to person.
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Cheek dimples (D) Dominant
No cheek dimples (d) Recessive
If you have dimples, circle the uppercase "D" on your sheet. If you do not have dimples, circle the lowercase "d" on your sheet.
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Widow's peak (H) Dominant
Straight hairline (h) Recessive
If you have a widow's peak circle the uppercase "H" on your sheet. If you have a straight hairline, circle the lowercase "h" on your sheet.
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Attached earlobes (e) Recessive
Detached earlobes (E) Dominant
If you have detached earlobes, circle the uppercase "E" on your sheet. If you have attached earlobes, circle the lowercase "e" on your sheet.
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Non-tongue roller (r) Recessive
Tongue roller (R) Dominant
If you can roll your tongue, circle the uppercase "R" on your sheet. If you cannot roll your tongue, circle the lowercase "r" on your sheet.
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Non-tongue folder (f) Recessive
Tongue folder (F) Dominant
If you can fold your tongue, circle the uppercase "F" on your sheet. If you cannot fold your tongue, circle the lowercase "f" on your sheet.
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Cleft chin (L) Dominant
Smooth chin (l) Recessive
If you have a cleft chin, circle the uppercase "L" on your sheet. If you have a smooth chin, circle the lowercase "l" on your sheet.
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Left thumb on top (T) Dominant
Right thumb on top (t) Recessive
If your left thumb is on top, circle the uppercase "T" on your sheet. If your right thumb is on top, circle lowercase "t" on your sheet.
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Right-handedness (M) Dominant
Left-handedness (m)
If you are right-hand dominant, circle the uppercase "M" on your sheet. If you are left-hand dominant, circle the lowercase "m" on your sheet.
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Hitchhiker's thumb (b) Recessive
Straight thumb (B) Dominant
If you have a straight thumb, circle the uppercase "B" on your sheet. If you have a hitchhiker's thumb, circle the lowercase "b" on your sheet.
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Straight pinkies (g) Recessive
Bent pinkies (G) Dominant
If you have bent pinkies, circle the uppercase "G" on your sheet. If you have straight pinkies, circle the lowercase "g" on your sheet.
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Click here to learn about eye color
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WOO-HOO!!! WE DID IT!
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Join a Game
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Join a Game
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