6.1 mendel’s investigations
TRANSCRIPT
6.1 Mendel’s Investigations
What is Genetics?● The science of heredity
○ How characteristics are passed from parents to offspring (parent to child)
Key Ideas of Genetics:
● Genetics is the science of heredity○ Heredity- How characteristics are passed from parents to
offspring (parent to child)○ Understanding genetics and heredity is key to understanding what
makes each organism unique.
● Every living thing—plant or animal, microbe or human being—has a set of characteristics inherited from its parent or parents.
What is an inheritance?
● It is something we each receive from our parents—a contribution that determines our blood type, the color of our hair, and so much more.
● What kind of inheritance makes a person’s face round or hair curly?
Gregor Mendel’s Question and Finding:Where does an organism get its unique characteristics?● Before this time, people believed that offspring have a “blend” (or mix) of
characteristics from their parents. This was known as the “blending theory of inheritance”)
An individual’s characteristics are determined by factors that are passed from one parental generation to the next.
● Mendel determined that there are dominant and recessive traits
The Experiments of Gregor Mendel
The modern science of genetics was founded by an Austrian monk named Gregor Mendel.
Mendel was in charge of the monastery garden, where he was able to do the work that changed biology forever.
The Experiments of Gregor Mendel
Mendel carried out his work with ordinary garden peas, partly because peas are small and easy to grow. A single pea plant can produce hundreds of offspring.
Today we call peas a “model system” because they are small, quick and easy to grow, and have many characteristics/traits.
The Experiments of Gregor Mendel
Scientists use model systems because they are convenient to study and may tell us how other organisms, including humans, actually function.
Pea plants are fast-growing and they have characteristics that are easy to see and study.
The Role of Fertilization● Mendel decided to “cross” his plants—he caused one plant to reproduce with
another plant.
● This allowed Mendel to cross pea plants of different height or color to determine what that offspring would look like.○ The offspring of crosses between parents with different traits are called hybrids.
Mendel’s ExperimentsWhen doing genetic crosses, we call the original pair of plants the P, or
parental, generation.
Mendel’s ExperimentsTheir offspring are called the F1, or “first filial,” generation.(F1 are the kids)
Mendel’s ExperimentsFor each trait studied in Mendel’s experiments, all the offspring had the
characteristics of only one of their parents, as shown in the table.
Parent
Offspring
Mendel’s ExperimentsIn each cross, the other parent’s trait seemed to have disappeared.
Gregor Mendel
Mendel’s ExperimentsMendel also experimented with flower petal colors:
● When Mendel crossed purple flowers with white flowers, what did he see?○ Why aren’t there any white flowers?
When the F1 generation is crossed, their offspring are called the F2 generation (the F2 generation is the grandkids to the parents)
● What did Mendel see in the F2 generation?
Mendel’s Laws of Inheritance:From these results, Mendel determined the law of segregation:
● There are two factors that determine different characteristics and one dominates over the other.
Mendel’s Dominant and Recessive Traits:● The dominant trait will always show itself● A recessive trait will only be present when the dominant allele for the trait is
not present
Do you think this is always true?
Mendel’s Laws of Inheritance:From these results, Mendel also determined the law of independent assortment:
● Heredity factors for different characteristics are inherited independently of each other.
● During gamete formation, the alleles for each gene segregate from each other, so that each gamete carries only one allele for each gene.
● In other words, each offspring has the same likelihood of inheriting certain characteristics during gamete formation.
Genes and Alleles● Each of the traits Mendel studied was controlled by one gene that occurred in
two forms.○ Ex: Green or yellow color; tall or short height, etc.
● These gene variations produced different expressions, or forms, of each trait.
● The different forms of a gene are called alleles.
● The location of these genes on a chromosome is called the locus.
Genes - a trait (height, eye color, etc.)
Allele - a form of that trait (brown, blonde, black, red hair)
Genotype and PhenotypeGenotype: The alleles that an individual inherits
● Homozygous: the two alleles are the same○ Can be dominant or recessive
● Heterozygous: the two alleles are different
Phenotype: The organism’s characteristic (what it physically looks like)
Genotype and Phenotype PracticeMendel worked with purple and white flowers. He took a purple flower (homozygous dominant), and crossed it with a white flower (homozygous recessive). Using this information we can write the genotype and phenotype:
Purple Flower:
Genotype: PP
Phenotype: purple
White Flower:
Genotype: pp
Phenotype: white
When choosing a letter to use for the genotype, you want to use the first letter of the dominant trait. A capital letter means the trait is dominant, lower case means it is recessive
Genotype and Phenotype Practice● What if Mendel had used a heterozygous purple flower? What would the
genotype be?○ Pp
● What effect would this have on the F1 generation (the offspring) when crossed with white flowers?
