Mendelian Inheritance I

Question 1

What is the blending hypothesis?

Answer 1

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)

Question 2

According to the blending hypothesis, if you crossed a smooth pea with a wrinkly pea, what would the result be?

Answer 2

A semi-wrinkly pea.

Question 3

According to Mendel’s results, when a smooth pea and wrinkly pea are crossed, what were the results?

Answer 3

A smooth pea. (The point here is that Mendel’s hypothesis did not align with the blending hypothesis).

Question 4

What two pieces of evidence contradict the blending hypothesis?

Answer 4

1. Examination of populations (we do not see uniformity)
2. Reappearance of traits after skipping a generation.

Question 5

Why were peas ideal for Mendel’s experiments?

Answer 5

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.

Question 6

What are true-breeding plants?

Answer 6

Plants that produce offspring of the same variety when they self-pollinate.

Question 7

What is hybridization?

Answer 7

Mating two contrasting, “true-breeding” varietes.

Question 8

What is the P (F0) generation?

Answer 8

The generation of the true-breeding parents.

Question 9

What is the F1 generation?

Answer 9

The generation of hybrid offspring that stems from matings in the P generation.

Question 10

What is the F2 generation?

Answer 10

The generation that is produced when F1 individuals self-pollinate.

Question 11

What did Mendel do in the P generation?

Answer 11

He crossed parents that differed in an obvious characteristic, such as purple vs white flowers.

Question 12

What happened in the F1 generation of Mendel’s experiments?

Answer 12

One parent’s character disappeared. ( in example, all had purple flowers)

Question 13

What happened in the F2 generation of Mendel’s experiments?

Answer 13

The trait that had disappeared in the last generation reappeared in a 1:3 ratio.

Question 14

What did Mendel say was affecting flower color in the F1 hybrids?

Answer 14

He said that only the “purple flower factor” was affecting flower color in the F1 hybrids.

Question 15

What was Mendel’s “heritable factor”?

Answer 15

What we now call a gene.

Question 16

What is the particulate hypothesis?

Answer 16

The idea that parents pass on discrete heritable units (genes). Mendel, through his experiments with garden peas, documented a particulate mechanism of heredity.

Question 17

What are alleles?

Answer 17

Alternative versions of genes account for variation in inherited characters. These alternative versions of a gene are called alleles.

Question 18

In the P generation, how do the two alleles at a locus on a chromosome compare?

Answer 18

They are identical.

Question 19

In the F1 hybrids generation, how do the two alleles at a locus on a chromosome compare?

Answer 19

They may differ.

Question 20

What is a heterozygous organism?

Answer 20

An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that character.

Question 21

What is a homozygous organism?

Answer 21

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).

Question 22

What happens if the two alleles at a locus differ?

Answer 22

One (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance.

Question 23

What does the law of segregation say?

Answer 23

It states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes.

Question 24

How are alleles distributed to eggs and sperm?

Answer 24

An egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism.

Question 25

Which concept in meiosis is the segregation of alleles related to?

Answer 25

The segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis.

Question 26

Why don’t an organism’s traits always reveal its genetic composition?

Answer 26

Because of the different effects of dominant and recessive alleles.

Question 27

What are monohybrids?

Answer 27

Individuals that are heterozygous for one character.

Question 28

What is a monohybrid cross?

Answer 28

A cross between monohybrids.

Question 29

How did Mendel identify the law of independent assortment?

Answer 29

He performed a dihybrid cross in which he followed two characters at the same time.

Question 30

What happens when two true-breeding parents differing in two characters are crossed?

Answer 30

They produce dihybrids in the F1 generation which are heterozygous for both characters.

Question 31

What is a dihybrid cross?

Answer 31

A cross between F1 dihybrids.

Question 32

What can a dihybrid cross determine?

Answer 32

It can determine whether two characters are transmitted to offspring as a package or independently.

Question 33

In Mendel’s experiments with dihybrid crosses, what did he find?

Answer 33

The traits he studied–yellow or green and smooth or wrinkled–were independent of each other. The phenotypic ratio was 9:3:3:1.

Question 34

What does the law of independent assortment state?

Answer 34

Each pair of alleles segregates independently of other pairs of alleles during gamete formation.

Question 35

Why does the law of independent assortment only apply to genes on different chromosomes?

Answer 35

Genes located near each other on the same chromosome tend to be inherited together.