Mendel The Father of Genetics
Mendel Objectives
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Explain Mendel’s principles of inheritance, including examples of these principles expressed in organisms.
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Use a Punnett Square to predict the genotypes and phenotypes of offspring produced from parental crosses.
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Apply the Punnett Square technique to studying rat characteristics.
Gregor Mendel is often called the father of genetics, the study of inheritance.
Gregor Mendel observed, experimented, and analyzed data. His laws provided an accurate description of some forms of inheritance, laying the groundwork for future advancements. It took almost a century for other researchers to develop an explanation, or theory, for what Mendel was describing.
Law: Description of a natural phenomenon supported by a body of knowledge.
Theory: Explanation of a natural phenomenon supported by a body of knowledge.
This video provides an overview of Mendel and his work.
Key Terminology
Gene: the part of DNA that codes for a protein
Allele (or factor): version of a gene
Dominant: this allele’s protein is produced
Recessive: when the dominant allele is present, the recessive allele’s protein is not produced
Genotype: the combination of alleles (factors) in an organism
Phenotype: the observable traits
Punnett Squares
Once you know the alleles present in sperm and egg, it is possible to predict the genotypes and phenotypes of the offspring.
Punnett squares are a technique for keeping alleles straight as you predict the offspring from generations of crosses.
Here is a step-by-step demonstration of a Punnett Square
We are using domesticated rats to demonstrate Punnett squares, and for genetic and behavioral study in future guides.
If you want to see the adoption process for these rats, watch this video. If not, you can skip to the next video.
This video shows six rats numbered one through six. Take notes on their appearance and behaviors. After the video you will be completing a Punnet square and predicting which of the males are related.
Rat coat (fur) texture and color
Rat coat color, pattern, and texture all have a genetic basis
Smooth Hair
Dominant (AA, Aa) long thin hair that lays flat; photo = rat #2
Rex Hair
Recessive (aa) waved or curled hair; rat = #3
Brown Hair
Dominant (BB, Bb) wild-type agouti hair; rat = #1
Beige Hair
recessive bb) lacks the pigment found in agouti hair; rat = #6
We’re crossing two parent rats. One is true-breeding smooth and the other is true-breeding rex. The genotype of the true-breeding smooth parent is “AA” and the genotype of the rex parent is _____.
Predict the F1 offspring genotypes and phenotypes, using a Punnett Square.
hint: all of the F1 generation should have the same genotype and phenotype, similar to the Punnett Square in the video.
These male rats were from two different litters. Typically siblings have the most structural traits in common. From your video lecture observations, which of the rats do you think are related?
answer: rats 2 and 5 are brothers (smooth hair, dumbo ears); rats 3, 4, and 6 are brothers (rex hair, standard ears). #1 is a bit of a mystery: he has rex hair and dumbo ears, and distinct behaviors from the other rats. We’ll have more on their shared and contrasting behaviors in an upcoming guide.
Rats show many of the structures and behaviors we are studying in this course.
Here the rats are showing different degrees of competitive behavior after being fed.
Next we will explore cleaning behaviors which often have a genetic basis.
Check your knowledge. Can you:
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explain Mendel’s principles of inheritance, including examples of these principles expressed in organisms?
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use a Punnett Square to predict the genotypes and phenotypes of offspring produced from parental crosses?
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apply the Punnett Square technique to studying rat characteristics?
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