January 26, 2016
Bell Work:
 What is one thing you know about genetics?
Objective:
The student will be able to…
1. Describe the importance of genetics.
Today in History
 1802 Congress passed an act calling for a library
to be established within the U.S. Capitol.
 1837 Michigan became the 26th state.
Genetics
Origins of Genetics
 Heredity is the passing of characteristics from
parents to offspring
 From the beginning of time humans have altered
crops and animals based on specific traits, but
heredity remained a mystery before the
discovery of DNA and chromosomes
Terms to Know
 DNA: the material that contains the information
that determines inherited characteristics
 Chromosome: one of the structures in the
nucleus that are made up of DNA and protein
 Heredity: the passing of characteristics from
parents to offspring
Mendel’s Breeding Experiments
 An Austrian monk, Gregor Johann Mendel began
the scientific study of heredity over a century ago
 He used the garden pea for his experiments
 He was the first to develop rules that accurately
predicted patterns of heredity
Mendel’s Breeding Experiments
 The patterns that Mendel discovered form the
basis of genetics
 Genetics is the science of heredity and of the
mechanisms by which traits are passed from
parents to offspring
Mendel’s Breeding Experiments
 Mendel repeated the experiments of T.A. Knight
 Knight crossed garden peas with purple and white
flowers. He discovered that all of the offspring had
purple flowers. When he bred the offspring he
discovered that they produced purple and white
flowers
Mendel’s Breeding Experiments
 Mendel’s experiments differed from Knight’s
because Mendel counted the number of each
kind of offspring and analyzed the data
Terms to Know
 Genetics: the science of heredity and of the
mechanisms by which traits are passed from
parents to offspring
 Traits: a distinct variant of a phenotypic
characteristic of an organism
 A distinct version of a characteristic of an organism
Useful Features in Peas
 Several characteristics exist in two clearly
different forms
 The male and female reproductive parts of
garden peas are enclosed within the same flower
 This allows you to control mating
 The garden pea is small, grows easily, matures
quickly, and produces many offspring
Why are large, slow growing
organisms poor subjects for genetic
experiments?
Traits Expressed as Ratios
 A monohybrid cross is a cross that involves one
pair of contrasting traits
Traits Expressed as Ratios
 Mendel performed his experiments in three steps:
1.
Mendel allowed each variety to self-pollinate for
several generations to ensure true breeding
 True breeding is when all offspring would display one
form of the character
 These true breeding plants were the parental generation
or the P generation (the first two individuals that are
crossed in a breeding experiment)
Traits Expressed as Ratios
2. Mendel cross-pollinated two P generation plants
that had contrasting traits
 The offspring are the first filial generation or the F1
generation
 Mendel recorded the number of F1 plants exhibiting
each trait
Traits Expressed as Ratios
3. Mendel allowed the F1 generation to self
pollinate
 The offspring are the second filial or F2 generation
 Each F2 plant was characterized and counted
What do we know?
Mendel’s Results
 Each of Mendel’s F1 plants showed only one form
of the character
 This is the dominant trait
 The missing trait reappeared in some of the
plants from the F2 generation
 This is the recessive trait
Mendel’s Results
 For each of the seven characters Mendel studied,
there was a 3:1 ratio of plants expressing the
contrasting traits in the F2 generation
Terms to Know
 Monohybrid Cross: a cross between individuals that
involves one pair of contrasting traits
 True Breeding: describes organisms or genotypes that
are homozygous for a specific a trait and thus always
produce offspring that have the same phenotype for that
trait
 P generation: parental generation, the first two
individuals that mate in a genetic cross
Terms to Know
 Cross pollination: Pollinating a flower from a different
plant
 F1 generation: first filial the first generation of
offspring obtained from an experimental cross of two
organisms
 F2 generation: second filial the second generation of
offspring, obtained from an experimental cross of two
organisms; the offspring of the F1 generation
Terms to Know
 Dominate Trait: the trait that is expressed
 Recessive Trait: the trait that is not expressed
when the dominant trait is present
Mendel’s Theory of Heredity
 Before Mendel’s experiments many people thought
offspring were a blend of traits
 Mendel’s results did not support this hypothesis.
 Mendel correctly concluded that each trait has two
“heritable factors”
 Offspring receive one “heritable factor” from each
parent
Mendel’s Hypotheses
 Mendel developed four hypotheses based directly
on the results of his experiments
 These four hypotheses make up the Mendelian
theory of heredity
 This is the basis of the science of genetics
Mendel’s Hypotheses
 For each inherited character, an individual has
two copies of the gene– one from each parent.
Mendel’s Hypotheses
 There are alternative versions of genes.
 Examples include:
 Purple and white flowers
 Yellow and green peas
 Tall and dwarf plants
 The different versions of genes are called alleles
Mendel’s Hypotheses
 When two different alleles occur together, one of
them may be completely expressed, while the other
may have no observable effect on the organism’s
appearance.
 The form that is always expressed is dominant
 The form that is not expressed (unless an organism is
homozygous recessive) is recessive
Mendel’s Hypotheses
 When gametes are formed, the alleles for each
gene in an individual separate independently of
one another. Thus, gametes carry only one allele
for each inherited character. When gamete unite
during fertilization, each gamete contributes one
allele.
Terms to Know
 Allele: one of the alternative forms of a gene that
governs a characteristic, such as hair color.
What do we know?
Ticket Out
 What is Mendel’s first hypothesis?