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Alien Genetics
A Science and Math Overlap
Genetics
The field of biology that studies heredity (the passing of traits from one generation to the next)
Genes• The section of DNA that codes for a
certain trait.
• Every characteristic is controlled by a pair of genes – one from the organism’s mother, and one from its father.
• Alleles are the different forms of a gene.
The Law of Dominance• If one or both alleles in an organism are
for the dominant characteristic, then the organism will exhibit that dominant characteristic.
• The recessive characteristic will only be shown if both alleles are for that recessive characteristic.
Guessing game!!!
For each allele pair, guess which one is dominant and which is recessive in humans:– Eye color: Brown or
blue/grey/green/hazel?
Guessing game!!!
For each allele pair, guess which one is dominant and which is recessive in humans:– Earlobes: Unattached
(A) or attached(B)?
Guessing game!!!
For each allele pair, guess which one is dominant and which is recessive in humans:– Number of digits: five
fingers/toes on each hand/foot, or having extra fingers/toes?
The Law of Segregation• Gametes are the sex cells (sperm and
ovum) that combine to form a new offspring.
• Each gamete randomly gets one of each pair of alleles for each trait, so that when the two gametes combine, the offspring has a complete set of pairs.
Genotype
• The combination of alleles in an organism
• Homozygous: The two alleles for the trait are the same.
• Heterozygous: The two alleles for the trait are different.
Phenotype• The trait that is displayed by the organism
• What genotypes – combinations of dominant and recessive alleles – would make an organism display the dominant trait?
• What genotypes would make the organism display the recessive trait?
Punnett Square• A chart used to predict the possible
genotypes (and phenotypes) of the offspring of a cross between two parent organisms
• From this, you can figure out the probability of each genotype (and phenotype) occurring in the offspring.
Haha!
Allele Representation
The same letter is used to represent both alleles for a trait, but the capital is used for the dominant allele, and the lowercase is used for the recessive allele.
Our First Cross• The alien species that we’re going to
study follows the same genetics laws that we humans, here on Earth, do.
• In this alien species, having blue skin is a dominant trait and having green skin is a recessive trait. Let’s use B’s for blue skin and b’s for green skin.
Our First Cross
• The mom alien is homozygous with blue skin. What is her genotype?
• The dad alien is homozygous with green skin. What is his genotype?
A Punnett Square Looks Like…
Setting up the Punnett Square
The two alleles from one parent go above the two columns, and the two alleles from the other parent go to the left of the two rows.
B B
b
b
Filling in the Punnett Square
Put the letter pair (one from the top, one from the side) in each box.
B B
b
b
Bb Bb
BbBb
Probability• The likelihood of something happening
• In fraction form, the numerator is the number of desired outcomes (what you are looking for) and the denominator is the number of total outcomes (all of the possibilities).
• To change to a percent, divide numerator by denominator and multiply by 100.
GenotypesWhat are the possible genotypes in the offspring of a cross between a homozygous blue-skinned alien mom and a homozygous green-skinned alien dad?
B B
b
b
Bb Bb
Bb Bb
What is the probability of each genotype in the offspring of a cross between a homozygous blue-skinned alien mom and a homozygous green-skinned alien dad?
B B
b
b
Bb Bb
Bb Bb
Genotypes
PhenotypesWhat are the possible phenotypes in the offspring of a cross between a homozygous blue-skinned alien mom and a homozygous green-skinned alien dad?
B B
b
b
Bb Bb
Bb Bb
PhenotypesWhat is the probability of each phenotype in the offspring of a cross between a homozygous blue-skinned alien mom and a homozygous green-skinned alien dad?
B B
b
b
Bb Bb
Bb Bb
Another Cross
• Let’s look at a different pair of aliens. In this pair, both parents are heterozygous with blue skin.
• What are the parents’ genotypes for skin color?
Complete the Punnett Square
Try it on your own!
Check your Punnett Square
Does yours match mine?
B b
B
b
BB Bb
Bb bb
GenotypesWhat are the possible genotypes in the offspring of a cross between a heterozygous blue-skinned alien mom and a heterozygous blue-skinned alien dad?
B b
B
b
BB Bb
Bb bb
GenotypesWhat is the probability of each genotype in the offspring of a cross between a heterozygous blue-skinned alien mom and a heterozygous blue-skinned alien dad?
B b
B
b
BB Bb
Bb bb
PhenotypesWhat are the possible phenotypes in the offspring of a cross between a heterozygous blue-skinned alien mom and a heterozygous blue-skinned alien dad?
B b
B
b
BB Bb
Bb bb
Phenotypes
What is the probability of each phenotype in the offspring of a cross between a heterozygous blue-skinned alien mom and a heterozygous blue-skinned alien dad?
B b
B
b
BB Bb
Bb bb
