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Chapter 11: Introduction to Genetics

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1 Chapter 11: Introduction to Genetics

2 Quick Video… Before I continue!


4 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.

5 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.

6 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.

7 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.

8 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.

9 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.

10 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.

11 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.

12 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.

13 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.

14 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.

15 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.

16 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.

17 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?

18 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.

19 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.

20 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.

21 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.

22 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.

23 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.

24 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,

25 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.

26 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.

27 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.

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

29 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.

30 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.

31 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.

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

33 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.


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