Mendelian Genetics (bio test 6)

Heredity

transmission of traits from one generation to the next

Genetics

study of heredity

Gregor Mendel

• Austrian monk

• Deduced fundamental principles of genetics by breeding pea plants

Character

flower color of pea plants

Trait

being white of purple

P generation

“parent generation, true breeding, homozygous (2 of same alleles)

F1 generation

offspring from 2 alleles

F2 generation

offspring of offspring, from 2 alleles

Allele

a version of a gene found at a specific spot on a chromosome; dominant

or recessive

Monohybrid cross

Tt x Tt → 3:1

Dihybrid cross

BbEe x BbEe → 9:3:3:1

Law of dominance

when an organism inherits two different alleles for a gene, the dominant allele is expressed and the recessive allele is masked

• Example: AA × aa → all Aa offspring

• Result: all offspring show the dominant phenotype even though they carry one recessive allele

Law of segregation

the two alleles for a gene separate during meiosis so each gamete receives only one allele

• Occurs during: meiosis when homologous chromosomes (and ultimately the alleles they carry) separate into different gametes

• Result: offspring receive one allele from each parent

Law of independent assortment

the way one pair of alleles separates during meiosis does not affect how another pair of alleles separates

• Occurs because: homologous chromosome pairs line up randomly during meiosis

• Result: genes on different chromosomes are inherited independently, creating many different combinations of traits

What is true-bred

• A plant that always produces offspring with the same trait when self-pollinated or crossed with another true-breeding plant of the same trait

• Genotype: homozygous for the trait (AA or aa)

• Example: a true-breeding purple pea plant (PP) always produces purple-flowered offspring, while a true-breeding white pea plant (pp) always produces white-flowered offspring