Chapter 11: Introduction to

Genetics

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Before I continue!

Section 11.1 The Experiments of Gregor Mendel

Benchmark: SC.912.N.1.1, SC.912.L.16.1

• Genetics is the scientific study of heredity.

• Gregor Mendel did an experimented in which he crossbred pea plants and discovered that the traits could be passed onto another.

• Mendel’s discovery with the peas is now used as a “model system.”

• A model system is convenient because it may tell us how other organisms (including humans) actually function.

The Role of Fertilization

• Fertilization: During this process it is when the male and female reproductive join.

• Trait: a specific characteristic. For example: flower color!

• Hybrid: The offspring of parents with different traits.

• When Mendel began his experiment, he used the pollen to cross breed them. He knew a male reproductive cell was sperm and a female reproductive cell was an egg.

Genes and Alleles• An individual’s characteristics are

determined by factors that are passed from one parental generation to the next.

• When doing genetic crosses, we call each parental figure P and each offspring F for first filial.

• The factors that are passed on to the offspring are called genes.

• The different forms of genes are called alleles.

Dominant and Recessive Alleles

• Mendel’s second conclusion is called the principle of dominance.

• The principle of dominance states that some alleles are dominant and others are recessive.

• An organism with a recessive allele will express that trait when a dominant form isn’t present.

• In Mendel’s experiment, the trait for tall plants was dominant and short plants was recessive.

Segregation• Mendel didn’t stop crossing after the

parents. • Mendel asked himself if the traits the

parents had simply disappeared or would they show up again.

• So Mendel crossed the first filial and got new results.

• The new results were the second filial group.

The F1 Cross

• When Mendal crossed the first filial he was shocked to discover that in the F2 generation, the recessive traits were present.

• Only ¼ of the F2 plants showed the recessive traits.

Explaining the F1 Cross

• Segregation: separation of alleles during gamete formation.

• Gametes: Sex cells.• Mendel concluded that

the alleles for tallness and shortness segregated during the formation of the gametes.

The Formation of Gametes

• During Gamete formation, the alleles for each gene segregate from each other, so that each gamete carries only on allele for each gene.

• The F1 plants produces only two kinds of gametes; tall allele and short allele.

• A capital letter represents a dominant allele.

• A lower case letter represents a recessive allele.

11. 2 Applying Mendel’s Principals

Benchmark: SC.912.L.16.1• Probability: the likelihood a

particular event will occur.• Probability in genetics is what the

phenotype of the said organism or thing will come out to be.

• This could be compared to flipping a coin.

• When Mendel crossbred his pea plants, he had a lot of different outcomes and data in store.

Using Segregation to Predict Outcomes

• Homozygous: Organisms that have to identical alleles.

• Heterozygous: Organisms that have two different alleles for the same gene.

• The way that alleles segregate during gamete formation is as random as a coin flip.

• The principles of probability can be used to predict the outcomes of a genetic cross.

Probabilities Predict Averages

• Probabilities predict the average outcome of a large number of events.

• The larger number of offspring, the closer the results will be to the predicted values.

Genotype and Phenotype

• Genotype: genetic make-up. • Phenotype: physical traits. • Just because something has

the same phenotype DOES NOT mean it can have the same genotype.

• The genotype of an organism is inherited, while the phenotype just solely relies on the genotype.

Using Punnett Squares

• Punnett squares use mathematical probability to help predict the genotype and phenotype combinations in genetic crosses.

• Constructing a punnett square is easy, just draw a square with four sections.

• The possible genotypes are written in the boxes.

• The outcomes are your possible outcomes.

Independent Assortment

• How do alleles segregate when more than one gene is involved?

• Mendel wanted to know if the factor of one trait affected another.

• Example: Would the shape of the seed effect seed color?

The Two Factor Cross: F1

• Mendel crossed only true breeding plants in this one.

• They came up with only round, yellow seeds.

• However, these seeds were all hybrids having a heterozygous genetic make-up.

The Two Factor Cross: F2

• The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.

• In the second part of Mendel’s experiment, he crossed the F1 plants to produce the F2 offspring.

• Each F1 offspring was heterozygous. • The F12 plants, in Mendel’s experiment,

produced 556 seeds.

Chapter 11.3 Other Patterns of Inheritance

Benchmark: SC.912.L.16.2• What are some exceptions

to Mendel’s principles? • There are many exceptions

to Mendel’s principles. • For example, not all genes

show simple patterns of inheritance.

Incomplete Dominance

• Incomplete Dominance: One allele is not completely dominant over the other.

• Incomplete dominance states that some alleles are neither dominant nor recessive.

• For example, in flower colors, sometimes a flower may have a mix between the two and make a new color.

• The heterozygous phenotype lies somewhere between the two homozygous phenotypes.

Codominance

• Codominance: the phenotypes produced by both alleles are clearly expressed.

• For example, chickens will have the black and white colors that their parents had.

• In humans, a gene for protein that controls cholesterol levels in the blood, show codominance.

Multiple Alleles

• Many genes exist in several different forms and are therefore said to have multiple alleles.

• Multiple Alleles: A gene with two or more alleles.

• Rabbit’s coat color is an example. • The color of a rabbit’s coat is determined

by one gene with at least FOUR different alleles.

Polygenic Traits

• Many traits are produced by the interaction of several genes.

• Polygenic traits: traits controlled by two or more genes.

• In humans, the variety of skin color is an example of polygenic traits.

• Also,

Genes and the Environment

• Environment conditions can effect gene expression and influence genetically determined traits.

• For example, the western white butterfly changes color from the Summer to the Autumn.

• It is effected by temperature and it is also the color change in their wings.

11.4 Meiosis Benchmark: SC.912.L.16.16• How many sets of genes are found in most

adult organisms?• In this, you will learn how meiosis is

important in genetics. • The phases of meiosis.

Diploid Cells

• Homologous: each of the four corresponding cells from the male parent has a corresponding chromosome from the female parent.

• Diploid: two sets. • The diploid cells of most adult organisms

contain two complete sets of inherited chromosomes and two complete sets of genes.

Haploid Cells

• Haploid: means one set. • Sex cells are usually haploid. • For example: sperm.

Phases of Meiosis

• Meiosis: is a process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.

• Meiosis is NOT the same as Mitosis.

Meiosis I

• Prophase I: This is where the cell is separating after Interphase I. Interphase happens ONLY ONCE.

• In between, Crossing over occurs!• Metaphase I and Anaphase I: During metaphase I of meiosis, paired

homologous chromosomes line up across the center of the cell. In anaphase I, spindle fibers pull each homologous chromosome pair toward opposite ends of the cell.

• Telophase I and Cytokinesis: In telophase I, the nuclear membrane forms around each cluster of chromosomes. Cytokinesis follows telophase I, producing two diploid daughter cells.

Meiosis II• Prophase II: The cell’s chromosomes, each consisting of two chromatids,

become visible. • Metaphase II, Anaphase II, Telophase II, and Cytokinesis: These four things

are similar to Meiosis I, but it results in four daughter HAPLOID cells.

Gametes and Zygotes

• A gamete is a sex cell. • Zygote: a fertilized egg. • The gametes in males are sperm.• In woman they are eggs.

Gene Linkage and Mapping

• Gene linkage is grouping different genes into different groups. This was discovered by Thomas Hunt.

• Gene mapping is trying to figure where each gene and mapping where each gene is located.