Chapter 11: Introduction to Genetics Biology- Kirby

Chapter 11:Introduction to

Genetics

Biology- Kirby

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.


• 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.


• 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.


• 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:


• 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.


• 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.


• 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.

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.


• 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.


• Homozygous- the alleles are the same; true-breeding organism-example: TT or tt.

• Heterozygous- the alleles are different; hybrid organism- example: Tt.


• Phenotype- physical characteristic- example: tall.

• Genotype- genetic makeup- example: TT.

• Organisms can have the same phenotype, but different genotypes; example: TT and Tt.


• Punnett Square Examples:

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.


• To test independent assortment, Mendel crossed true-breeding round yellow peas (RRYY) with wrinkled green peas (rryy).

• F1 Cross:


• F1 genotype: RrYy• Mendel crossed F1 plants to get

F2 plants:

• The results had a 9:3:3:1 ratio.


• 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.


• 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)


• 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.

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).

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

11-4: Meiosis

• Interphase I- Chromosomes replicate before meiosis I.

• 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.

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.

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.

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)

11-4: Meiosis

• Mitosis vs. Meiosis–Mitosis results in the

production of 2 genetically identical diploid cells.

–Meiosis produces 4 genetically different haploid cells.

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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Chapter 11: Introduction to Genetics Biology- Kirby