Heredity
genetics
A scientist and monk, Gregor Mendel, in the 1800s was the first to
actually count numbers of offspring in crosses.
father of genetics.
Mendel's
Experimental Design (image) The garden
pea Fig
11.2
true-breeding varieties Fig 11.3
P or parental generation
F1 generation or first filial generation.
F2 generation.
Used seven pairs of contrasting traits. Table 11.1
dominant
trait
recessive. trait
3:1 dominant
to recessive phenotype in the F2
generation. Fig
11.5
When F2 plants were allowed to self-fertilize, Mendel found a 1:2:1 ratio of
true-breeding dominant to not true-breeding dominant
to true-breeding recessive.
Today we use these
terms:
Each
individual has two factors (we now call these genes) for each character. These are located on homologous
chromosomes. Fig
11.6
character - a heritable feature.
trait - a variant for a
character.
homozygous
heterozygous.
alleles. image
genotype.
phenotype
Analyzing Mendel's
Results
Punnett Squares Fig. 11.7
How Mendel analyzed
flower color Fig
11.8
The Testcross - When
Mendel did not know the genotype of an individual expressing a dominant trait, he did a
test cross by crossing the individual with a homozygous recessive for the character.
Fig 11.9
Mendel's
Laws
Mendel's First Law: Law of
Segregation
Mendel's
Second Law: Law of Independent Assortment was determined when he worked
with two traits at a time in dihybrid crosses. Fig 11.10
Crossing two individuals that are heterozygous for both characters yields a
phenotypic ratio of 9:3:3:1. If the genes are located
on the same chromosome, they would be linked. image
Exceptions
to Mendel's Laws
Continuous Variation
- (polygenic) Fig. 11.12. Human skin color image
and eye color. Eye color.
Pleiotropic Effects
- Ex: cystic fibrosis. Fig 11.13
Incomplete
Dominance - Fig 11.14.
Environmental Effects - Fig 11.15
Epistasis. Fig 11.16 Fig 11.17
and image
Codominance - Fig 11.18
Multiple
Alleles with codominance
Human ABO blood group. Fig. 11.19 and image and image