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  • 1. Genetics:The Science of Heredity
    12th Applied Science

2. Gregor Mendel
The first recorded scientific study of how traits pass from one generation to the next was done by Gregor Mendel, a monk!
In 1856, he began experimenting with garden peas.
I. Introduction to Genetics
3. I.Introduction to Genetics
He believed he could predict the kinds of flowers and fruits a plant would produce.
To do this he believed that something had to be known about the parents of the plants.
Each different form of a characteristic, such as a stem height, is called a TRAIT.
Today, Mendels discoveries form the foundation of Genetics.
Father of Genetics
4. I.Introduction to Genetics
Mendels Experiments
Fertilization occurs when egg and sperm join.
Before this can happen in pea plants, pollen must reach the pistil of the flower.This process is called pollination.
Mendel developed a method by which he cross pollinated, or crossed pea plants.
5. I.Introduction to Genetics
Crossing Pea Plants
An organism that always produces the same traits in its offspring is called a PUREBRED.
Example:PUREBRED short pea plants always come from short parent plants.
Tall plants that always produce tall plants are considered PUREBRED tall plants.
6. I.Introduction to Genetics
Crossing Pea Plants
In one experiment, Mendel crossed purebred tall plants with purebred short plants.
Scientists call the parent plants the parental generation or the P generation
The offspring from this cross are the first fillial generation or the F1 generation.
Fillial comes from the word fillia:the Latin word for daughter
All of the offspring from this cross were TALL.
7. I.Introduction to Genetics
Crossing Pea Plants
When the plants in the F1 generation were full grown, Mendel allowed them to self pollinate.
Some of the plants in the F2 generation were a mix of tall and short plants.
were tall
were short.
8. I.Introduction to Genetics
9. Dominant and Recessive Traits
Genes are factors that control traits.
Genes are made up ofDNA
Genes are found on chromosomes.
I.Introduction to Genetics
10. Dominant and Recessive Traits
The different forms a gene may have for a trait are its alleles.
Each new organism inherits two alleles from its parents.
One from the egg (mother) and the other from the sperm (father).
A pea plant may inherit two alleles for tall stems, two alleles for short stems, or one of each.
I.Introduction to Genetics
11. Dominant and Recessive Traits
An organisms traits are controlled by the alleles it inherits from its parents.
Dominant Allele is one whose trait always shows up in the organism when the allele is present.
Recessive Allele is hidden whenever the dominant allele is present.
A trait controlled by a recessive allele will only show up if the organism does not have the dominant allele.
I.Introduction to Genetics
12. Dominant and Recessive Traits in Pea Plants are shown in the table to the right.
If the dominant allele is present it will mask the recessive allele.
Example:If a pea plant has both purple and white flower alleles the purple allele will be the one that is visible to you.
I.Introduction to Genetics
13. II.Probability and Heredity
Probability is the number that describes how likely it is that an event will occur.
Probability is different then the odds.
Probability = what you want / total chances
Odds= what you want:what you dont want
14. II.Probability and Heredity
Punnett Squares
A handy tool to use to predict results in Mendelian Genetics is the Punnett Square.
A Punnett Square is a chart that shows all the possible combinations of alleles that can result from a genetic cross.
Y= Yellow
y= Green
15. II.Probability and Heredity
Punnett Squares
Dominant alleles are represented by capital letters.
Recessive alleles are represented by lower case letters.
An organism that has two identical alleles is called HOMOZYGOUS.
An organism that has two different alleles is called HETEROZYGOUS.
Y= Yellow
y= Green
Yy= Heterozygous
yy= Homozygous
16. II.Probability and Heredity
Using a Punnett Square
Monohybrid Cross deals with only one trait.
Yellow pea plants being crossed with green pea plants.
Di-hybrid cross deals with two traits.
a.TallYellow Pea Plants crossed with Tall Green Pea Plants
17. TtYy X TtyyTall Yellow Pea Plants X Tall Green Pea Plants
Plant one is Heterozygous Tall; Heterozygous Yellow.
Plant Two is Heterozygous tall green pea plants.
18. 19. II.Probability and Heredity
An organisms phenotype is its physical appearance, or its visible traits.
Phenotypic Ratio
The ratio of phenotypes found in the Punnett Square.
Pea plants can have one of two different phenotypes for stem height-Short or Tall.
An organisms genotype is its genetic makeup, or allele combinations.
Although all of the tall plants have the same phenotype, they can have two different genotypes-TT or Tt
A Genotypic Ratio is the ratio of genotypes found in a Punnett Square.
20. Comparing Phenotype and Genotype
II.Probability and Heredity
21. G.CoDominance
H.Incomplete Dominance
For some alleles, an inheritance pattern called co-dominance exists.
In co-dominance, the alleles are neither dominant nor recessive.
As a result, both alleles are expressed in the offspring.
When two traits are not completely dominant over each other.
This results in a blending of the two traits.
RR = Red Flowers
WW= White Flowers
RW = Pink flowers
II.Probability and Heredity
22. Please Review the following videos on Blended Schools:
Mendelian Genetics- A Quick Tutorial
Incomplete and Codominance Review
End of Genetics Section I Notes!!
Complete the Punnett Square Packet!!
II.Probability and Heredity
23. Punnett Square Packet Answers