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biology final exam (text four)

Terms in this set (59)

Mendel performed a monohybrid cross between purebred parent plants that differ in only one character and found that the F1 plants all had purple flowers.
-Was the factor responsible for inheritance of white flowers now lost as a result of the cross?
-By mating the F1 plants with each other, Mendel found the answer to this question to be no.

Mendel figured out that the gene for white flowers did not disappear in the F1 plants but was somehow hidden or masked when the purple-flower factor was present.

He also deduced that the F1 plants must have carried two factors for the flower-color character,
-one for purple and
-one for white.


From these results and others, Mendel developed four hypotheses:

1. ​There are alternative versions of genes that account for variations in inherited characters.
- The alternative versions of genes are called alleles.

2. ​For each inherited character, an organism inherits two alleles, one from each parent.
-An organism that has two identical alleles for a gene is said to be homozygous for that gene.
-An organism that has two different alleles for a gene is said to be heterozygous for that gene.

3. ​If the two alleles of an inherited pair differ, then one determines the organism's appearance and is called the dominant allele, and the other has no noticeable effect on the organism's appearance and is called the recessive allele.
-Geneticists use uppercase italic letters (such as P) to represent dominant alleles and lowercase italic letters (such as p) to represent recessive alleles.

4. ​***A sperm or egg carries only one allele for each inherited character because the two alleles for a character segregate (separate) from each other during the production of gametes.
-This statement is called the law of segregation.
-When sperm and egg unite at fertilization, each contributes its alleles, restoring the paired condition in the offspring.

A Punnett square highlights
-the four possible combinations of gametes and
-the resulting four possible offspring in the F2 generation.

Each square represents an equally probable product of fertilization.

Geneticists distinguish between an organism's
-physical appearance, its phenotype, and
-genetic makeup, its genotype.

Mendel found that each of the seven characters he studied had the same inheritance pattern: A parental trait disappeared in the F1 generation, only to reappear in one-fourth of the F2 offspring.
-The underlying mechanism is explained by Mendel's law of segregation:
-Pairs of alleles segregate during gamete
formation;
-the fusion of gametes at fertilization creates
allele pairs again.
The polymerase chain reaction (PCR)
-is a technique by which a specific segment of DNA can be amplified: targeted and copied quickly and precisely, and
-permits a scientist to obtain enough DNA from even minute amounts of blood or other tissue to allow a DNA profile to be constructed.

In principle, PCR is simple.
-A DNA sample is mixed with nucleotides, the DNA replication enzyme DNA polymerase, and a few other ingredients.
-The solution is then exposed to cycles of heating (to separate the DNA strands) and cooling (to allow double-stranded DNA to re-form).
-During these cycles, specific regions of each molecule of DNA are replicated, doubling the amount of that DNA.
-The result of this chain reaction is an exponentially growing population of identical DNA molecules.

A DNA molecule within a starting sample is likely to be very long. But, most often, only a very small target region of that large DNA molecule needs to be amplified.

The key to amplifying one particular segment of DNA and no others is the use of primers, short (usually 15-20 nucleotides long), chemically synthesized single-stranded DNA molecules.

The primers bind to sequences that flank the target sequence, marking the start and end points for the segment of DNA to be amplified.

In addition to forensic applications, PCR can be used in the treatment and diagnosis of disease. PCR can be used to
-amplify, and thus detect, HIV in blood or tissue samples and
-diagnose hundreds of human genetic disorders by being used with primers that target the genes associated with these disorders.