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Introduction to Genetics Chapter 11
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The Work of Gregor Mendel
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Genetics The scientific study of heredity.
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Vocabulary to Know Trait: a specific characteristic varying among individuals ex: eye color Gene: a portion of DNA determining a trait; found on the chromosomes ex: the gene for eye color Trait: a specific characteristic varying among individuals ex: eye color Gene: a portion of DNA determining a trait; found on the chromosomes ex: the gene for eye color
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Vocabulary (continued) Hybrid: the offspring of two parents with different traits Gametes: reproductive cells (aka: sex cells; sperm & egg) Hybrid: the offspring of two parents with different traits Gametes: reproductive cells (aka: sex cells; sperm & egg)
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Allele: the form of a gene Allele: the different forms of a gene * Represented by a letter. ex: Widow’s Peak = W * Organisms have two alleles for each trait, one inherited from the mother and one from the father. ex: WW Allele: the different forms of a gene * Represented by a letter. ex: Widow’s Peak = W * Organisms have two alleles for each trait, one inherited from the mother and one from the father. ex: WW
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Forms of Alleles Dominant Allele: trait will be expressed with only one copy present * Represented with capital letters. ex: W (Widow’s peak) Recessive Allele: trait will only be expressed when no dominant alleles are present * Represented with lower case letters. ex: w (No widow’s peak) Dominant Allele: trait will be expressed with only one copy present * Represented with capital letters. ex: W (Widow’s peak) Recessive Allele: trait will only be expressed when no dominant alleles are present * Represented with lower case letters. ex: w (No widow’s peak)
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Gregor Mendel Considered the father of genetics. Mid-1800s Monk who experimented with pea plants in the monastery garden. Considered the father of genetics. Mid-1800s Monk who experimented with pea plants in the monastery garden.
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Mendel’s Conclusions 1.Inheritance is determined by factors passed from one generation to the next. 2. Principle of dominance: Some alleles are dominant and others are recessive. 1.Inheritance is determined by factors passed from one generation to the next. 2. Principle of dominance: Some alleles are dominant and others are recessive.
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Mendel’s Conclusions 3. Segregation: A gamete carries only one copy of each gene. 4. Principle of independent assortment: Genes for different traits segregate independently from one another. 3. Segregation: A gamete carries only one copy of each gene. 4. Principle of independent assortment: Genes for different traits segregate independently from one another.
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Applying Mendel’s Principles
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Allele Combinations Homozygous: both alleles are the same ex: WW or ww Heterozygous: alleles are different ex: Ww (capital letter is always 1st!) Homozygous: both alleles are the same ex: WW or ww Heterozygous: alleles are different ex: Ww (capital letter is always 1st!)
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Genotype: the actual allele combination; what the genes say ex: WW, Ww, ww Phenotype: the trait observed ex: Widow’s Peak Genotype: the actual allele combination; what the genes say ex: WW, Ww, ww Phenotype: the trait observed ex: Widow’s Peak
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Punnett Squares Used to predict the genotypes of offspring when the genotypes of both parents is known.
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Other Patterns of Inheritance
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Incomplete Dominance The heterozygous phenotype (Ww) is somewhere between both homozygous phenotypes (WW & ww). Ex: pink flowers
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Codominance Both alleles contribute to the phenotype; neither allele is dominant. Ex: roan cattle Both alleles contribute to the phenotype; neither allele is dominant. Ex: roan cattle
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Multiple Alleles More than two allele possibilities. Ex: blood type More than two allele possibilities. Ex: blood type
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Polygenic Traits Traits controlled by more than one gene. Ex: skin color Traits controlled by more than one gene. Ex: skin color
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Meiosis
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Words to Know Haploid: “one set”; cells that contain one set of each chromosome (gametes); 1n Example: in humans n=23, so human haploid cells (gametes) have 1(23) or 23 total chromosomes Diploid: “two sets”; cells that contain two sets of each chromosome ; 2n Example: in humans n=23, so human diploid cells have 2(23) or 46 total chromosomes Haploid: “one set”; cells that contain one set of each chromosome (gametes); 1n Example: in humans n=23, so human haploid cells (gametes) have 1(23) or 23 total chromosomes Diploid: “two sets”; cells that contain two sets of each chromosome ; 2n Example: in humans n=23, so human diploid cells have 2(23) or 46 total chromosomes
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Homologous Chromosomes The pair of chromosomes that have the genes for the same traits. A copy is inherited from each parent. The pair of chromosomes that have the genes for the same traits. A copy is inherited from each parent.
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Meiosis A type of cell division that produces gametes containing half the number of chromosomes as a body cell. Contains two separate rounds of division, called Meiosis I & Meiosis II. For example, during meiosis in humans, diploid cells with 46 chromosomes are divided into 4 haploid sex cells (gametes) with 23 chromosomes each. Animation/ Animation/ A type of cell division that produces gametes containing half the number of chromosomes as a body cell. Contains two separate rounds of division, called Meiosis I & Meiosis II. For example, during meiosis in humans, diploid cells with 46 chromosomes are divided into 4 haploid sex cells (gametes) with 23 chromosomes each. Animation/ Animation/
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Phases of Meiosis Interphase: cell grows, replicates its chromosomes and prepares to divide. Prophase I: chromosomes take shape; homologous chromosomes pair up, forming a tetrad Crossing over can occur! Chromosomes touch & exchange genes. This can mix up linked genes. (ones found on the same chromosome that occur together). Interphase: cell grows, replicates its chromosomes and prepares to divide. Prophase I: chromosomes take shape; homologous chromosomes pair up, forming a tetrad Crossing over can occur! Chromosomes touch & exchange genes. This can mix up linked genes. (ones found on the same chromosome that occur together).
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Metaphase I, Anaphase I, Telophase I Chromosomes line up across the cell’s center. Homologous chromosome pairs separate. Nuclear membrane reforms & cytokinesis occurs.
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Similar to Mitosis, except 4 haploid daughter cells are created. Meiosis II Metaphase II: Chromosomes line up across the cell’s center. Prophase II: No Replication occurs!
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Meiosis II (continued) Anaphase II: Chromosomes separate. Telophase II: Nuclear membrane reforms & cytokinesis occurs.
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The end result: In males, all 4 of the daughter cells become sperm. In females, the division of the cytoplasm is uneven, so only 1 egg is produced. The other three cells, called polar bodies are not used for reproduction. In males, all 4 of the daughter cells become sperm. In females, the division of the cytoplasm is uneven, so only 1 egg is produced. The other three cells, called polar bodies are not used for reproduction.
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Genetic Recombination The reassortment of chromosomes and the genetic information that they carry by segregation and crossing over. For example: In humans, n = 23, so the number of different gametes that can be produced is 2 23 (more than 8 million). When fertilization occurs, 2 23 x 2 23, or 70 trillion different zygotes are possible and this is without accounting for crossing over! Zygote: the fertilized egg The reassortment of chromosomes and the genetic information that they carry by segregation and crossing over. For example: In humans, n = 23, so the number of different gametes that can be produced is 2 23 (more than 8 million). When fertilization occurs, 2 23 x 2 23, or 70 trillion different zygotes are possible and this is without accounting for crossing over! Zygote: the fertilized egg
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Mitosis vs. Meiosis MitosisMeiosis Two identical daughter cells are formed. Each daughter cell has one complete set of chromosomes. (diploid) Four different gamete cells are created (although in females, only 1 is viable). Each gamete cell has half of the total number of chromosomes. (haploid) http://www.pbs.org/wgbh/nova/miracle/divi_flash.html
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Linked genes Genes that are located on the same chromosome & thus, tend to be inherited together.
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Human Heredity
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Genome: the full set of genetic information carried in an organism’s DNA Humans have 46 chromosomes in their genome. Karyotype: a picture of all diploid pairs of chromosomes, arranged in order of decreasing size
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Chromosome Types Autosomes: the remaining 44 human chromosomes other than the sex chromosomes Sex chromosomes: the pair of chromosomes determining gender Males have XY. Females have XX. In female cells, most of the genes in 1 X are randomly switched off (called Barr bodies). Ex: female calico cats Autosomes: the remaining 44 human chromosomes other than the sex chromosomes Sex chromosomes: the pair of chromosomes determining gender Males have XY. Females have XX. In female cells, most of the genes in 1 X are randomly switched off (called Barr bodies). Ex: female calico cats
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Sex-linked genes A gene located on a sex chromosome. Genes on the Y chromosome are only found in males. Genes on the X chromosome are found in both genders. For recessive traits on the X, they are more common in males than females. Ex: color-blindedness, hemophilia A gene located on a sex chromosome. Genes on the Y chromosome are only found in males. Genes on the X chromosome are found in both genders. For recessive traits on the X, they are more common in males than females. Ex: color-blindedness, hemophilia
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Pedigree A chart used to show the presence or absence of a trait within a family.
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Human Genetic Disorders
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Nondisjunction When homologous chromosomes fail to separate during meiosis. Creates monosomy and trisomy. When homologous chromosomes fail to separate during meiosis. Creates monosomy and trisomy.
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http://learn.genetics.utah.edu/content/chro mosomes/diagnose/ http://learn.genetics.utah.edu/content/chro mosomes/diagnose/ WHEN A MISTAKE IS MADE…
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