Name_______________________________________________
Unit 2 Lesson 4 Notes
•
Traits, such as hair color, result from the information stored in genetic material.
•
_____________________ is the passing of genetic material from parents to offspring.
•
_______________________________________ was an Austrian monk. In the 1800s, Mendel
performed the first major experiments in heredity.
•
Mendel studied seven characteristics of pea plants.
•
A ________________________________c is a feature that has different forms in a population.
•
The seven different characteristics Mendel studied were plant height, flower and pod position,
seed shape, seed color, pod shape, pod color, and flower color.
•
Each characteristic had two different forms. These different forms are called _______________.
•
Mendel studied each characteristic separately, always starting with plants that were truebreeding.
•
True-breeding plants always produce offspring with the same trait if allowed to self-pollinate
naturally.
•
Mendel crossed plants that were true-breeding for producing yellow seed pods with plants that
were true-breeding for green seed pods.
•
All of the plants from the first generation produced green seed pods.
•
Mendel called the green seed pod the ________________________t trait, and the yellow seed
pod the _________________________ trait.
•
Next, Mendel let the first generation plants self-pollinate.
•
Out of the generation that resulted, called the second generation, about three-fourths had
green seed pods and one-fourth had yellow pods.
•
The recessive trait had seemed to disappear in the first generation, but it reappeared in the
second generation.
•
Mendel hypothesized that each plant must have two heritable “_________________________”
for each trait, one from each parent.
•
Some traits, such as yellow color, could only be observed if a plant had two of the same factors.
•
A plant with two different factors would show the dominant factor but be able to pass on both
factors to its offspring.
•
Mendel’s ideas can be further explained by our modern understanding of DNA.
•
What Mendel called “factors” are actually segments of DNA known as
______________________.
•
______________________ are segments of DNA. They give instructions for producing a certain
characteristic
•
The offspring has two versions of the same gene for every characteristic—one from each parent.
•
Different versions of a gene are known as ___________________________.
•
_______________________ alleles are shown with a capital letter, and
_______________________ alleles are shown with a lowercase version of the same letter.
•
An organism with one dominant and one recessive allele for a gene is
___________________________for that gene.
•
An organism with two of the same alleles for a gene is ______________________________ for
that gene.
•
The combination of alleles that you inherited from your parents is your
_____________________________.
•
Your observable traits make up your _________________________________.
•
The phenotypes of some traits follow patterns similar to the ones Mendel discovered
•
The __________________________ allele contributes to the phenotype if one or two copies are
present in the genotype.
•
The __________________________ allele contributes to the phenotype only when two copies
of it are present.
•
If one chromosome in the pair contains a dominant allele and the other contains a recessive
allele, the _____________________________ allele determines the phenotype.
•
This is called _______________________________________________.
•
Some characteristics are a result of several genes acting together.
•
Sometimes, one gene influences more than one trait.
•
For example, many genetic disorders, such as sickle cell anemia, are linked to a single gene but
affect many traits.
•
Some traits do not follow the pattern of complete dominance.
•
For traits that show ______________________________________ and
____________________________, one trait is not completely dominant over another.
•
In _______________________________________, each allele in a heterozygous individual
influences the phenotype.
•
The result of incomplete dominance is a phenotype that is a blend of the phenotypes of the
parents.
•
An example of this in humans is hair. A person with one allele for straight hair and one allele for
curly hair will have wavy hair.
•
For a trait that shows _____________________________________, both of the alleles in a
heterozygous individual contribute to the phenotype.
•
Heterozygous individuals have both of the traits associated with their two alleles.
•
Human blood type is an example of codominance.
•
Three alleles, called A, B, and O, play a role in determining blood type.
•
A person with an A allele and a B allele has type AB blood.