Chapter 11: Introduction to Genetics Biology- Kirby.
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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.
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.
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.
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:
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.
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.
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.
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.
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.
11-2: 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.
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.
11-2: Probability & Punnett Squares
• 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.
11-3: Exploring Mendelian Genetics
• To test independent assortment, Mendel crossed true-breeding round yellow peas (RRYY) with wrinkled green peas (rryy).
• F1 Cross:
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.
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.
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)
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.
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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