GENETICS Ch. 12*Definition: the study of heredity

~heredity: the passing of traits from parent to offspring.

Gregor Mendel

the “Father of Modern Genetics” • Austrian monk• 1860’s• used garden pea plants why?

3 reasons:

1. the structure of the pea flowers (usually

self-pollinates).

2. the presence of contrasting traits.

3. rapid reproductive cycle (~90 days).

http://www.flinnsci.com/introgenetics

• *Mendel studied 7 distinct characters (physical features that are inherited; ex. flower color)…pg. 268 – *YOU ARE RESPONSIBLE FOR KNOWING THESE!

• Trait: one of several possible forms of a character; ex. purple or white

• Mendel’s experiments used monohybrid crosses (a 4 box Punnett square) in order to study one pair of contrasting traits (ex. purple vs. white for flower color).

• P generation F1 F2(true-breeding parents) (1st filial) (2nd filial)

-VOCAB-

• ~purebred: an organism that receives the same genetic traits from both of its parents (*self-pollination in plants).

• ~hybrid: an organism that receives different forms of a genetic trait from each parent (purple X white).

• gene: sections of a chromosome that code for a trait.

*most organisms have 2 copies (homologous chromosomes) of every gene and chromosome…1 from each parent.

• allele: versions of a gene (ex. tall vs. short for plant height)…T and t

• dominant allele: the expressed form of a gene when 2 different alleles are present.

*ex. Tt (T is dominant; the plant is tall)• recessive allele: a form of a gene that is not

expressed when the dominant allele is present (masked).

*ex. Tt…short is only expressed when in the form of tt

Mendel and Modern Genetics 12.2

• genotype: the set of alleles an individual has for a character.

*genetic makeup -includes both genes in a

homologous pair of chromosomes. -ex. Rr, rr, RR• phenotype: the trait that results from a

set of alleles.– *-ex. tall, short, purple, white.

• Genotype determines phenotype!

• homozygous: 2 alleles in a gene pair are identical.

• heterozygous: 2 alleles in a gene pair are different.

• Punnett square: shows the expected outcomes of a genetic cross.

*shows all possible combinations of gametes. (ch.12.3)

• Probability: the likelihood that a specific event will occur. – can be written as a %, fraction, ratio, or in words

• EXAMPLES

• Test Cross: used to determine an organism’s genotype.

-done by breeding the organism whose genotype is unknown with a homozygous recessive organism (known genotype).

-ex. G = green (dominant)

g = yellow (recessive)

-Question: what is the genotype of a plant with green peas?...to find the answer, we can perform a test cross.

Mono vs. Dihybrid Crosses

• Monohybrid Cross: predicts the offspring of a cross for one trait (ex. plant height).

• Dihybrid Cross: predicts the offspring of a cross for two traits (ex. plant height and seed shape).

EXAMPLES (dihybrid)

• coin toss with 2 pennies the outcome of 1 flip doesn’t influence the outcome of the other b/c the coins are not attached in any way (independent of one another).