mendelian inheritance

Question 1

how did mendel discover the basic principles of heredity?

Answer 1

By breeding garden peas in a series of expriments. Mendel chose to track flower color (which appeared in two distinct forms).

Question 2

why did he use peas

Answer 2

1. They were available in many varieties (e.g. purple vs. white)
2. short generation time and large number of offspring in a short period.
3. he could control mating between plans through cross-pollination.

Question 3

what is cross-pollination?

Answer 3

fertilization between two different plants

Question 4

how did mendel control cross-pollination during his experiments

Answer 4

He removed immature stamens of a plant before they produced pollen and dusted pollen from another plant onto the carpel of the altered flower.

Question 5

why didn’t mendel choose to track a character that varied on a continuum (e.g. seed weight) when tracking the peas?

Question 6

Describe Mendel’s experiments in depth.

Answer 6

He used purple and white true-breeding flowers as P generations (homozygous dominant or recessive) and cross-pollinated the contrasting true-breeding pea varieties.

This true-breeding crossing, hybridization, resulted in F1 generations that were ALL purple flowers.

When he let the F1 generations self-pollinate (cross-pollinate with other F1 hybrids), he produced the F2 generation that showed a ratio of purple to white colors, 3:1

Question 7

What did he conclude from this experiment?

Answer 7

The heritable factor for the rececssive trait, white flowers, had not been destroyed or blended in F1, but was simply masked by the trait of the dominant trait, which was purple.

From this he concluded the law of segregation and the law of independent assortment.

Question 8

What was the initial hypothesis of inheritance and why is it incorrect?

Answer 8

The original hypothesis was called the “blending hypothesis” which predicted that the genetic material of both parents “mixed” in the offspring, just like blue + yellow = green. This was proven false because if the purple and white flowers mixed, the offspring would be pale purple. However, the results did not reflect this.

Question 9

Describe Mendel’s Model

Answer 9

Mendel’s model describes the 3: 1 inheritance patterns consistently observed in the F2 offspring. The concepts of the model are as follows:

1. Alternative versions of genes account for variations in inherited characters. e.g. the gene for flower color appears in 2 variations (alleles), contributing to the inheritance patterns.
2. For each character, an organism inherits two copies (alleles) of a gene, one from each parent.
3. If the two alleles at a locus differ, then the
   dominant allele determines the organism’s appearance; the recessive allele, has no noticeable effect on the organism’s appearance.
4. law of segregation: the two alleles for a character
   segregate during gamete formation and
   end up in different gametes. This explains that 50% of the gametes have one allele, and 50% have the other.

Question 10

what is the law of segregation?

Answer 10

The two alleles for one character segregate during meiosis and end up in different gametes. So one sperm or egg will only receive one allele out of the two that are present in somatic cells. This corresponds with the behavior of homologous chromosome pairs as they segregate into gametes.

Question 11

Does Mendel’s Model account for the 3:1 ratio observed in the F2 generation of his experiments? Explain.

Answer 11

Yes. The model predicts that half the offspring would be purple and half would be white (specifically law of segregation). Half of the plants received the white allele, half received purple.

It is a 3:1 ratio because 1/4 of the generation had (pp), 1/4 had (ww), and 1/2 had (pw). It shows that the alleles are segregated 50/50 in the four types of phenotypes available.

Question 12

What is the difference between phenotype and genotype?

Answer 12

The phenotype is the observable traits or appearance, and the genotype is the genetic makeup.

The phenotype of the flowers are: purple or white.

The genotype of the flowers are: PP, pp, Pp, pP

Question 13

What is a testcross and its purpose?

Answer 13

Breeding an unknown organism with an unknown genotype with a recessive heterozygous organism. This can help reveal the genotype of the uknown organism.

Question 14

what is the law of independent assortment?

Answer 14

The hypothesis that alleles for two genes in a dihybrid cross are assorted independently into gametes, and not as packages from the parents.

Question 15

what is a monohybrid?

Answer 15

A monohybrid is heterozygous for one character being tracked in a cross (monohybrid cross between heterozygotes).

Question 16

What is a dihybrid?

Answer 16

A dihybrid is heterozygous for two characters (e.g. YyRr)

Question 17

how did mendel discover the law of independent assortment?

Answer 17

rather than tracking one trait, like he did to find the law of segregation, he tracked two traits simultaneously (e.g. seed color and shape). By crossing two true-breeding varieties (YYRR and yyrr), he produced F1 offspring that were dihybrids. When they self-pollinated to create F2 offspring, the two pairs of alleles segregated randomly and not as a package, which meant there were all allelic combinations in the ratio of 9:3:3:1.