chapter 12

Mendel's experimental method

1. Produce true-breeding strains for each trait he was studying 2. Cross-fertilize true-breeding strains having alternate forms of a trait (reciprocal crosses) 3. Allow the hybrid offspring to self-fertilize for several generations and count the number of offspring showing each form of the trait

Homozygous

2 of the same allele

The F1 generation of the monohybrid cross purple (PP) x white (pp) flower pea plants should? a. All the F1 plants had white flowers. b. The F1 plants had a light purple or blended appearance. c. All the F1 plants had purple flowers. d. The most of the F1 (3/4) had purple flowers, but 1/4 of the plants had white.

All had purple flowers

F2 generation

Although hidden in the F1 generation, the recessive trait had reappeared among some F2 individuals Counted proportions of traits Always found about 3:1 ratio

Gregor Mendel

Chose to study pea plants why? Other research showed that pea hybrids could be produced Many pea varieties were available Peas are small plants and easy to grow Peas can self-fertilize or be cross-fertilized

Traits

Expression of a characteristic or heritable feature passed from parent to offspring

F1 generation

F1 plants resembled only 1 parent Referred to this trait as dominant Alternative trait was recessive

Which of the following is NOT a part of Mendel's five element model? a. Traits have alternative forms (what we now call alleles). b. Parents transmit discrete traits to their offspring. c. If an allele is present it will be expressed. d. Traits do not blend.

If an allele is present it will be expressed.

Phenotype

Observable expression of a trait

Alleles

One or two alternative forms of a gene

Phenotypes like height in humans, which show a continuous distribution, are usually the result of? a. an alteration of dominance of multiple allels of a single gene b. the presence of multiple allels for a single gene c. The action of ONE gene on MULTIPLE phenotypes d. the action of MULTIPLE genes on a SINGLE phenotype

The action of multiple genes on a single phenotype

Genotype

Total of all genes present in the cells of an organism, also used to describe a set of alleles at a single gene locus

Heredity

Transmission of characteristics from parent to offspring

Allele

alternative form of a gene

What is the probability of obtaining an individual with the genotype bb from a cross between two individuals with the genotype Bb? a. 1/2 b. 1/4 c. 1/8 d. 0

b. 1/4

Japanese four o'clocks that are red and tall are crossed to white short ones, producing an F1 that is pink and tall. If these genes assort independently, and the F1 is self-crossed, what would you predict for the ratio of F2 phenotypes? a. 3 red tall : 1 white short b. 1 red tall : 2 pink short : 1 white short c. 3 pink tall : 6 red tall : 3 white tall : 1 pink short : 2 red short : 1 white short d. 3 red tall: 6 pink tall : 3 white tall : 1 red short : 2 pink short : 1 white short

c. 3 red tall:6 pink tall:3 white tall:1 red short:2 pink short:1 white short

When you cross true-breeding tall and short tobacco plants you get an F1 that is intermediate in height. When this F1 is self-crossed, it yields an F2 with a continuous distribution of heights. What is the best explanation for these data? a. Height is determined by a single gene with incomplete dominance b. Height is determined by a single gene with many alleles c. Height is determined by the additive effects of many genes d. Height is determined by epistatic genes

c. Height is determined by the additive effects of many genes.

Traits are transmitted?

directly from parent to offspring

Dominant trait appears in

every generation

True-breeding purple

flowered plant is PP (Homozygous dominant)

True-breeding white

flowered plant is pp (Homozygous recessive)

Parents transmit discrete factors that are called?

genes

Pp is

heterozygote purple-flowered plant

Polygenic inheritance is?

multiple genes are involved in controlling the phenotype of a trait ex: human height

An organisms __ is/are determined by it's __? a. genotype; phenotype b. phenotype; genotype c. alleles; phenotype d. F1 generation; alleles

phenotype; genotype

Rule of addition: When crossing Pp x Pp, the probability of producing Pp offspring is?

probability of obtaining Pp (1/4), PLUS probability of obtaining pP (1/4) ¼ + ¼ = ½

P is dominant allele

purple flowers

What property distinguished Mendel's investigation from previous studies?

quantified his results

Physical basis for allele segregation is?

the behavior of chromosomes during meiosis

Rule of multiplication: When crossing Pp x Pp, the probability of obtaining pp offspring is?

Probability of obtaining p from father = ½ Probability of obtaining p from mother = ½ Probability of pp= ½ x ½ = ¼

Mendel discovered the ratio is actually 1:2:1

1 true-breeding dominant plant (purple) 2 not-true-breeding dominant plants (purple and white) 1 true-breeding recessive plant (white)

The F1 plants from the previous question are allowed to self-fertilize. The phenotypic ratio for the F2 should be? a. All purple b. 1 purple:1 white c. 3 purple:1 white d. 3 white:1 purple

3 purple:1 white

Mendel's model assumes that each trait is determined by a single factor with alternate forms. We now know that this is too simplistic and that a. a single GENE may affect more than ONE trait b. a single TRAIT may be affected by more than ONE gene c. a single GENE can affect more than ONE trait, and TRAITS may be affected by more than ONE GENE. d. a single gene can affect more than one, and traits may be affected by more than ONE gene

a single gene can affect more than one trait, and traits may be affected by more than one gene.

In a cross of Aa Bb cc X Aa Bb Cc, what is the probability of obtaining an individual with a genotype AA Bb Cc? a. 1/16 b. 3/16 c. 1/64 d. 3/64

a. 1/16

T.A. Knight - 1823

crossed 2 varieties of garden pea, Pisum sativa Crossed 2 true-breeding strains 1st generation resembled only 1 parent strain 2nd generation resembled both

Josef Kolreuter-1760

crossed tobacco strains to produce hybrids that differed from both parents

If the two genes in the previous question showed complete linkage, what would you predict for an F2 phenotypic ratio? a. 1 red tall: 2 pink short: 1 white short b. 1 red tall: 2 red short: 1 white short c. 1 pink tall: 2 red tall: 1 white short d. 1 red tall: 2 pink tall: 1 white short

d. 1 red tall: 2 pink tall: 1 white short

Heterozygous

different alleles

p is recessive allele

white flowers

Heredity occurs?

within species