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Gregor Mendel and Heredity

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Jessica Copeland

on 20 November 2017

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Transcript of Gregor Mendel and Heredity

Gregor Mendel and Heredity
Who is Gregor Mendel?
Gregor Mendel is a priest from the nineteenth century and he tended a garden in a central European monastery. He was very curious about why pea plants had different characteristics. He was able to observe that some pea plants grew tall, while others grew short. He also observed that some produced green seeds, while others produced yellow seeds.
His curiosity in these observations lead him to begin several experiments in his peaceful garden, which later revolutionized the study of heredity.
Mendel's Experiments
He studied seven pea plant traits, each with two possible characteristics.
Then he crossed plants with each of the seven different traits and studied which trait showed up in their offspring.
Looking further into Mendel's experiments
First we need to understand how plant pollination occurs.
What came from his discoveries?
His discoveries led to great discoveries about genetics.
A distant relative is coming to stay with your family for a month. They have never met you or seen a picture of you. You go to the airport to pick them up and need to describe yourself to them so that they are able to find you in the crowd at the airport. In a few words, how would you describe yourself so they would recognize you?
You just described yourself using traits.
Trait
- a characteristic that an organism can pass on to its offspring through its genes
Heredity
The passing of physical characteristics from parent to offspring.
"Father of Genetics"
Why did he chose to use pea plants?
Pea plants are easy and fast to grow. Pea plants also have 7 distinct traits that are easy to track and analyze.
1. Who is Gregor Mendel?


2. Why was he important to the study of genetics?
Check your understanding!
The pistil produces female sex cells (eggs) and the stamens produce the pollen which contains the male sex cells (sperm).
A new organism begins to form when egg and sperm join in a process called

fertilization
.
Fertilization cannot occur until pollen reaches the pistil of the pea plant flower.
How does this pollination process occur?
Pea plants are
self-pollinating
so pollen from the flower lands on the pistil of the same flower.
Mendel developed a method by which he
cross-pollinated
pea plants. To do this, he removed pollen from a flower on one plant and then brushed the pollen onto a flower of a second plant.
Mendel started his experiment with
purebred
plants.
The first step of Mendel's experiment:
To prevent self-pollination, Mendel removed the pollen-producing structure from a pink flower.
Mendel then used a brush to remove pollen from a white flower on another plant. He brushed this pollen onto the pink flower.
A purebred organism is the offspring of many generations that have the same trait.
The egg cells in the pink flower were then fertilized by sperm from the white flower. After some time passed, peas formed in the pods.
1. What kind of plants did Mendel start with at the beginning of his experiment?
Check your understanding!
2. What is the process called when a new organism begins to form when egg and sperm join?
Parental generation
: Purebred tall plants were crossed with purebred short plants.
The Different Generations
The Results!
After performing his experiments, Mendel came to the conclusion that individual factors (genetic information) must control the inheritance of traits in peas.
The female parent contributes one factor, while the male parent contributes the other factor.
He also discovered that one factor in the pair can hide the other factor.
Dominant vs. Recessive Alleles
Mendel's experiment showed that parents' traits do not simply blend in the offspring. Instead, traits are determined by individual, separate alleles inherited from each parent.
Significance of Mendel's Findings
F1 Generation
: All of the offspring are tall. The shortness trait seemed to have disappear!
F2 Generation
: The offspring from the F1 generation were a mix of tall and short plants.
Mendel observed that in all of his crosses between pea plants,
only one form of the trait appeared in the F1 generation
. This made it seem like one trait disappeared.
When Mendel crossed the F1 generation plants with themselves,
the "lost" form of the trait always reappeared in the F2 generation
.
The "lost" trait always seemed to appear in about one fourth of the new plants.
Check your understanding!
1. What was the normal outcome for the F1 generation?
2. In the F2 generation, normally half of the new plants expressed the "lost" trait.
True or False
Genes and Alleles
Gene: factors that control a trait
Allele: different forms of the gene
Looking back at Mendel's experiment
In the F1 generation, only tall stems were present. Since we only saw tall stems, we know the dominant tall allele was present.
Understanding How to Represent Alleles
A dominant allele is represented with a capital letter.
A recessive allele is represented with a lower case letter.
An organism's traits are controlled by the alleles it inherits from its parents. Some alleles are dominant, while other alleles are recessive.
A dominant allele is one trait that always shows up in the organism when the allele is present.
A recessive allele is hidden whenever the dominant allele is present. A recessive trait will only appear when a dominant allele is not present.
If the dominant allele is present, it will always hide the recessive gene.
That being said, the pea plants could have inherited both a dominant tall allele and a recessive short allele. When this happens, the plant will be tall.
In the F2 generation, the pea plants that remained short did not have a dominant tall allele present.
R= tall allele
r= short allele
Alleles in Mendel's Experiment
Only dominant tall alleles are present, so as a result this plant will be tall.
Only recessive short alleles are present, so as a result this plant will be short.
These have both the dominant tall allele and the recessive short allele present. The dominant allele always beats the recessive allele, so these plants will be tall.
When a dominant and recessive allele are present, these organisms are called
hybrids
.
Check your understanding!
1. What is it called when a dominant and a recessive allele are present?

2. If both a dominant and recessive allele are present within an organism, which one will we be able to observe?
Ticket Out the Door
What is the significance of Mendel's findings?
The content in this Prezi came from "Georgia: Life Science Explorer"
the scientific study of heredity
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