Mendelian Inheritance I Flashcards
What is the blending hypothesis?
In the 1800s, the most widely favored explanation for heredity was “blending”–the hypothesis that genetic material from the two parents blends together. (Such as having a red flower mate with a white flower and yielding pink offspring)
According to the blending hypothesis, if you crossed a smooth pea with a wrinkly pea, what would the result be?
A semi-wrinkly pea.
According to Mendel’s results, when a smooth pea and wrinkly pea are crossed, what were the results?
A smooth pea. (The point here is that Mendel’s hypothesis did not align with the blending hypothesis).
What two pieces of evidence contradict the blending hypothesis?
- Examination of populations (we do not see uniformity)
- Reappearance of traits after skipping a generation.
Why were peas ideal for Mendel’s experiments?
They grew quickly, the mating of plants can be controlled, have ideal characteristics such as color, shape, flower color, and height, and each characteristic was on a different allele.
What are true-breeding plants?
Plants that produce offspring of the same variety when they self-pollinate.
What is hybridization?
Mating two contrasting, “true-breeding” varietes.
What is the P (F0) generation?
The generation of the true-breeding parents.
What is the F1 generation?
The generation of hybrid offspring that stems from matings in the P generation.
What is the F2 generation?
The generation that is produced when F1 individuals self-pollinate.
What did Mendel do in the P generation?
He crossed parents that differed in an obvious characteristic, such as purple vs white flowers.
What happened in the F1 generation of Mendel’s experiments?
One parent’s character disappeared. ( in example, all had purple flowers)
What happened in the F2 generation of Mendel’s experiments?
The trait that had disappeared in the last generation reappeared in a 1:3 ratio.
What did Mendel say was affecting flower color in the F1 hybrids?
He said that only the “purple flower factor” was affecting flower color in the F1 hybrids.
What was Mendel’s “heritable factor”?
What we now call a gene.
What is the particulate hypothesis?
The idea that parents pass on discrete heritable units (genes). Mendel, through his experiments with garden peas, documented a particulate mechanism of heredity.
What are alleles?
Alternative versions of genes account for variation in inherited characters. These alternative versions of a gene are called alleles.
In the P generation, how do the two alleles at a locus on a chromosome compare?
They are identical.
In the F1 hybrids generation, how do the two alleles at a locus on a chromosome compare?
They may differ.
What is a heterozygous organism?
An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that character.
What is a homozygous organism?
An organism with two identical alleles for a character is said to be homozygous for the gene controlling that character (these organisms are true-breeding).
What happens if the two alleles at a locus differ?
One (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance.
What does the law of segregation say?
It states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes.
How are alleles distributed to eggs and sperm?
An egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism.
