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Sections 3-1 and 3-2 Review for Quiz
Terms in this set (34)
The different forms of a gene.
A condition in which neither of the alleles of a gene is dominant or recessive.
An allele whose trait always shows up in the organism when the allele is present. In Mendel's experiments, a capital "T" represented this trait.
A segment of DNA on a chromosome that codes for a specific trait.
The scientific study of heredity.
An organism's genetic makeup, or allele combinations.
The passing of traits from parent to offspring. Gregor Mendel experimented with hundreds of pea plants to understand this process.
Having two different alleles for a trait.
Having two identical alleles for a trait.
An organism that has two different alleles for a trait; an organism that is heterozygous for a particular trait.
An organism's physical appearance, or visible traits.
The likelihood that a particular event will occur.
A chart that shows all the possible combinations of alleles that can result from a genetic cross. Objective: Students will use the Punnett Square to predict the outcomes of a genetic cross.
*Start with four-square Punnett Square
*Punnett squares are used to predict the results of a genetic cross.
*Place alleles of the parents on the outside of the square.
An organism that always produces offspring with the same form of a trait as the parent.
An allele that is masked when a dominant allele is present. In Mendel's experiments, they were represented by a lowercase "t".
A characteristic that an organism can pass on to its offspring through its genes.
Why did Mendel choose pea plants for his experiments?
Gregor Mendel chose pea plants for his experiments because of three reasons:
1. This plant exhibits a number of contrasting traits that Mendel could easily study.
2. A relatively large number of seeds are produced.
3. Pea plants can self-pollinate and be easily cross-pollinated.
In a flower, the female reproductive cells are produced by this plant part.
Pollen, which contains the male reproductive cells, are produced by this plant part.
Purebred tall plants were crossed with other purebred tall plants to produce purebred tall. Purebred short plants were crossed with other purebred short plants to produce purebred short plants. The tall plants have the tall factor only. The short plants have the short factor only. Both are purebred.
Purebred tall plants were crossed with purebred short plants. The result was all tall offspring. All of the F1 generation has both the tall factor and short factor but the tall (dominant) one hides the short (recessive) one.
F1 offspring are allowed to self-pollinate. The result was three quarters (75%) of the offspring were tall with one quarter (25%) short. The three tall plants received the tall factor from at least one parent. The one short plant received the short factor from both parents. Both could receive the tall or short factor from each parent.
The seed shape, seed color, seed coat color, pod shape, pod color, flower position, and stem height.
Mendel was an Austrian monk. His experiments are the basis for genetics. In his experiments he used thousands of garden pea plants. He was called the "Father of Genetics" after he lived, due to his secretive talent during his time.
Crossing pea plants
A. Mendel would remove the pollen producing parts of a flower to prevent self-pollination.
B. He would then use a brush to remove the pollen from the flower of another plant and apply it to the first flower.
Steps of Mendel's Experiments
Mendel studied the inheritance of one trait at a time (for example: the plant's height or color of flowers).
Mendel first self-pollinated tall pea plants: Mendel noticed that only tall plants were produced. He concluded, that the tall pea plants must contain a factor for tallness.
Mendel then self-pollinated short pea plants: This resulted in only short pea plants. Once again he concluded that pea plants must contain some factor for height (in this case shortness).
The next step of Mendel's experiment was to cross tall pea plants with short pea plants:
P Generation: Mendel called these plants his P generation (for parent).
F1 Generation: Mendel called these plants his F1 generation. The resulting plants were all tall.
Mendel then self-pollinated these tall plants: The resulting generation was approximately three quarters tall and one quarter short. Mendel called these his F2 generation.
1. Some factors determine the inheritance of height. These factors must occur in pairs, with one factor coming from each parent.
2. Mendel reasoned that there were two types of factors. The first factor he called dominant (in this case tall), the second factor recessive (short).
3. When an organism has a dominant and recessive factor (as in the F1 generation), the dominant factor hides the recessive.
Scientists now referred to Mendel's factors as genes; Genes control traits. Different forms of a gene are called alleles. The gene in Mendel's pea plants that control height has one allele for tall and one allele for short.
Using Symbols in Genetics
Alleles in organisms are represented using a standard shorthand. Capital letter represent dominant alleles such as "T" for tallness in Mendel's pea plants. Recessive alleles are represented by the lower case form of the same letter. Therefore, the shortness allele is represented by "t".
Since an organism has two alleles for each trait, a combination of two of these letters represent the alleles an organism has for a trait. Mendel's pea plant could have two tall alleles (TT), two short alleles (tt), or one of each (Tt). A purebred organism has two of the same allele such as TT or tt. A hybrid organism has two different alleles for a trait such as Tt.
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