Lecture 5

Question 1

Blending Theory

Answer 1

viewed traits as a mixture of parental characteristics, where offspring displayed intermediate characteristics
eg. black cat w/ white cat–> gray cat

Question 2

What are the 5 experimental innovations Mendel used?

Answer 2

1) controlled crosses between plants (artificial cross-fertilization, restricted nature’s cross-pollination)
2) use of pure/true-breeding strains to begin (consistently produced phenotype w/o variation)
3) selection of dichotomous traits (single traits with two phenotypes–> no ambiguity)
4) quantification of results (counted results–> ratios of heritability)
5) use of replicate, reciprocal (same phenotype, switch sex) and test crosses (identify alleles of uncertain genetic makeup)

Question 3

In crossing the pea plants, what did Mendel call each generation?

Answer 3

P (pure-bred parents)–> F1 (1st gen, artificially fertilized)–> F2 (2nd gen, self-fertilized or artificially)

Question 4

Define reciprocal cross.

Answer 4

When plants with the same phenotype but sexes of parents are swapped. Always performed in pairs.

Question 5

Define test cross.

Answer 5

Crosses designed to identify alleles carried by an organism whose genetic makeup is uncertain, uses homozygous recessive genotype to determine if organism is hetero/homo/dom or recessive

Question 6

Define dominant.

Answer 6

a gene that is expressed when only one copy of the gene is present, even when there is another allele present, present in the F1

Question 7

Define recessive.

Answer 7

a version of a gene that is not expressed when present with a dominant allele

Question 8

At what generation could Mendel tell that the blending theory was incorrect?

Answer 8

As early as F1, because the daughter flowers, were not a mixture between the colors, but the dominant allele (one color)

Question 9

Are the pure breeding plants Mendel used in the P generation homozygous or heterozygous?

Answer 9

Homozygous, because they could only produce their phenotype.

Question 10

Genotypic ratio

monohybrid cross

Answer 10

1:2:1
AA: Aa:aa

Question 11

Phenotypic ratio

monohybrid cross

Answer 11

1:3
1 a: for every 3 As

Question 12

Law of Segregation

Answer 12

The two alleles for each trait (one from each parent) will separate during gamete formation, and each have an equal (50/50) change of inclusion in a gamete

-Meiosis I

Question 13

Was the F1 progeny hetero or homozygous?

Answer 13

Hetero

Question 14

Define dihybrid cross.

Answer 14

Crosses between organisms that differ in two traits (color and shape)
P= RRGG x rrgg
F1= RrGg

Question 15

Law of Independent Assortment

Answer 15

During gamete formation, the segregation of alleles of one gene is independent of the segregation of another gene.
eg. color and shape are inherited separatley

-Meiosis II (after crossing over)