chromosome
DNA wraps up very tightly into a form called chromosomes. Chromosomes are in a cell’s nucleus.
What are chromosomes?
A chromosome is a small structure in the nucleus of a cell that is made of tightly-wrapped DNA.
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gene
Genes are passed from parents to their child and decide traits like hair texture and color.
What other traits do you think genes could determine?
A gene is a section of DNA that decides an organism's traits (characteristics).
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inherit
Puppies inherit traits like fur length and color from their parents.
Name some traits that the puppies in the picture inherited from their mom. The mom is the big dog in the picture.
Inherit means receive through genetics from a parent.
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trait
Examples of traits in humans include eye color and hair color.
Name some of your traits. If you have a pet, name some of the traits of your pet.
A trait is a feature or characteristic of an organism.
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allele
Different alleles cause horses to have different fur colors.
Name another trait in horses that might change because of a different allele.
Alleles are different versions of a certain gene.
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dominant
Face freckles are dominant. If a person has ONE copy of the face freckles gene, that person will show the trait.
In the picture, which person has at least ONE copy of the face freckle gene? How do you know?
Dominant means a version of a gene that will be expressed (shown) if it is present.
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recessive
Not having face freckles is a recessive trait. A person needs to have two copies of the recessive allele to NOT have face freckles.
In the picture, which person has TWO copies of the recessive allele? How do you know?
Recessive means a version of a gene that will be hidden by a dominant allele; these traits are only expressed (shown) when there is no dominant allele present.
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heterozygous
The chromosome on the right has two different versions of the gene (one yellow, one blue). This is heterozygous.
The prefix “hetero” means “other” or “different”. Why are some chromosomes called “heterozygous”?
Heterozygous means having two different alleles for a certain gene.
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homozygous
The chromosomes in the left box each have two identical (same) copies of the gene. These are homozygous.
The prefix “homo” means “the same”. Why are some chromosomes called “homozygous”?
Homozygous means having two identical (same) alleles for a certain gene.
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genotype
The tall plant’s genotype for height is TT, and the short plant’s genotype for height is tt.
Do you think it is possible for two organisms to have a different genotype, but have the same trait?
A genotype is the combination of alleles for a certain trait; for example AA or Aa.
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phenotype
This picture of corn shows that there are many different phenotypes for color.
What are examples of phenotypes you can see in people, plants or animals?
A phenotype is an expressed trait (shown characteristic).
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Punnett square
This Punnett square is used to predict (try to tell) how tall the offspring of one tall plant and one short plant could be.
Do you think the offspring of these two plants would be tall or short?
A Punnett square is a diagram that can predict the genotypes and phenotypes of offspring (children).
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codominant
Red and white fur color are codominant in cows. The cow offspring inherited a red allele and white allele, and is both red and white.
“Co-” is a prefix that means “with” or “together.” Do you think “codominant” is a good name? Why?
Codominant means neither allele is dominant over the other and the heterozygous phenotype show both traits at the same time.
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incomplete dominance
Homozygous four o’clock flowers can be either red (RR) or white (WW). Heterozygous four o’clock flowers (RW) are pink—a mix of red and white.
If the colors yellow and red were incompletely dominant, what do you think the heterozygous color would be?
Incomplete dominance means neither allele is dominant over the other and the heterozygous phenotype shows a blend (mix) of both traits.
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sex-linked trait
Color blindness is a sex-linked trait because the gene that decides this trait is on the X chromosome. Can you see the numbers in this image?
What might be other sex-linked traits? Hint: Think of traits that you are more likely to see in males.
Sex-linked trait means a trait is decided by a gene on a sex chromosome (X or Y).
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carrier
This female fly is a carrier for white eyes (Xr) because she could pass the recessive allele to her offspring.
What other “carriers” do you know of?
A carrier is an organism that has a recessive allele for a trait and may pass the recessive allele to their children.
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generation
The first generation is the parent plants. The second generation is the offspring (children).
Name some people in your family that are in your generation.
Generation is a way to describe where an organism belongs among its relatives (family members).
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1st generation
2nd generation
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pedigree
Shaded (colored in) shapes in the pedigree chart mean the person has the trait that is being tracked (followed).
Which individuals in this pedigree do you think have the trait being tracked?
A pedigree is a chart that tracks (follows) a certain trait over many generations in a family.
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