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Chapter 11: Introduction to Genetics

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1 Chapter 11: Introduction to Genetics
Biology- Kirby

2 11-1: The Work of Gregor Mendel
Genetics- the scientific study of heredity. Gregor Mendel- monk who used peas to understand principles of genetics. Fertilization- process in sexual reproduction in which male and female cells join to form a new cell.

3 11-1: The Work of Gregor Mendel
True-breeding- describes self-pollinating organisms identical to themselves. Mendel’s pea plants were true-breeding (example-tall plants produced tall plants). Mendel wanted to establish cross-pollination in his plants instead. Cross-pollination- 2 different plants as parents.

4 11-1: The Work of Gregor Mendel
Trait- a specific characteristic that varies from one individual to another. Mendel studied 7 traits in peas: seed shape, seed color, seed coat color, pod shape, pod color, flower position, and plant height. Mendel crossed plants to study these traits in offspring.

5 11-1: The Work of Gregor Mendel
The original plants were called the Parental (P) generation. The offspring were called first filial (F1) generation. Hybrid- the offspring of crosses between parents with different traits. All the offspring had traits of one parent:

6 11-1: The Work of Gregor Mendel
Mendel’s conclusions: 1. biological inheritance is determined by factors that are passed from one generation to the next. Genes- chemical factors that determine traits. Allele- different forms of a gene.

7 11-1: The Work of Gregor Mendel
2. Principle of Dominance- states that some alleles are dominant and others are recessive. Dominant-trait will be expressed. Recessive- trait will not be expressed.

8 11-1: The Work of Gregor Mendel
Mendel crossed all the F1 generation to make a F2 generation. Some of the recessive traits appeared in the F2 generation. Segregation- separation of alleles during gamete formation. Gametes- sex cells. Each F1 plant has 2 gametes; one allele for dominant trait and one for recessive trait.

9 11-2: Probability & Punnett Squares
Probability- the likelihood that a particular event will occur. The principles of probability can be used to predict the outcomes of genetic crosses.

10 11-2: Probability & Punnett Squares
Punnett Square- diagram that shows the gene combinations that might result from a genetic cross. The letters of a punnett square represent alleles; uppercase=dominant, lowercase=recessive. Used to predict and compare genetic variations resulting from a cross.

11 11-2: Probability & Punnett Squares
Homozygous- the alleles are the same; true-breeding organism-example: TT or tt. Heterozygous- the alleles are different; hybrid organism- example: Tt.

12 11-2: Probability & Punnett Squares
Phenotype- physical characteristic- example: tall. Genotype- genetic makeup- example: TT. Organisms can have the same phenotype, but different genotypes; example: TT and Tt.

13 11-2: Probability & Punnett Squares
Punnett Square Examples:

14 11-3: Exploring Mendelian Genetics
Mendel wanted to know if segregation of one allele affected another pair of alleles. Example: Seed shape affect seed color? Independent Assortment- independent segregation of genes during gamete formation.

15 11-3: Exploring Mendelian Genetics
To test independent assortment, Mendel crossed true-breeding round yellow peas (RRYY) with wrinkled green peas (rryy). F1 Cross:

16 11-3: Exploring Mendelian Genetics
F1 genotype: RrYy Mendel crossed F1 plants to get F2 plants: The results had a 9:3:3:1 ratio.

17 11-3: Exploring Mendelian Genetics
The principle of independent assortment states that genes for different traits can segregate independently during gamete formation. Independent assortment also helps give genetic variations in organisms.

18 11-3: Exploring Mendelian Genetics
Some alleles are neither dominant or recessive, and many traits are controlled by multiple alleles and genes. Incomplete dominance- the heterozygous phenotype is in between the 2 homozygous phenotypes. Example- Flowers- Red (RR) & White (WW)=Pink (RW)

19 11-3: Exploring Mendelian Genetics
Codominance- both alleles contribute to the phenotype. Example: Chicken feathers- Black (BB) & White (WW)=Speckled (BW) Multiple Alleles- 3 or more alleles of the same gene. Example: Rabbits fur- Page 273- full color, chinchilla, himalayan, and albino coat colors.

20 11-4: Meiosis Homologous- the chromosomes that have a corresponding chromosome from the opposite sex parent. Diploid- a cell that has both sets of homologous chromosomes (2N). Haploid- a cell that has one set of chromosomes (N).

21 11-4: Meiosis Meiosis- process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. Involves 2 divisions: Meiosis I and Meiosis II

22 11-4: Meiosis Interphase I- Chromosomes replicate before meiosis I.
Prophase I- each chromosome pairs with its corresponding homologous chromosome to from a tetrad. 4 chromatids=tetrad Metaphase I- spindle fibers attach to chromosomes.

23 11-4: Meiosis Anaphase I- the fibers pull the homologous chromosomes toward opposite ends of the cell. Telophase I & Cytokinesis- nuclear envelopes form and the cell separates. Crossing over- the homologous chromosomes exchange alleles from their chromatids during meiosis. This produces new combinations of alleles.

24 11-4: Meiosis Meiosis II: Prophase II- meiosis I results in 2 haploid (N) daughter cells, each with half the number of chromosomes as the original. Metaphase II- chromosomes line up in the middle. Anaphase II- The sister chromatids separate and move toward opposite ends of the cell.

25 11-4: Meiosis Telophase II & Cytokinesis- meiosis II results in 4 haploid (4N) daughter cells. Gamete Formation- In males, sperm are the haploid gametes produced in meiosis. (4) In females, an egg is the haploid gamete produced in meiosis. (1)

26 11-4: Meiosis Mitosis vs. Meiosis
Mitosis results in the production of 2 genetically identical diploid cells. Meiosis produces 4 genetically different haploid cells.

27 11-5: Linkage & Gene Maps Although alleles segregate by independent assortment, some genes are linked together. Gene Map- diagram showing the locations of genes on a chromosome.

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