Chapter 11: Introduction to Genetics. Quick Video… Before I continue!
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Transcript of Chapter 11: Introduction to Genetics. Quick Video… Before I continue!
Chapter 11: Introduction to
Genetics
Quick Video…
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.