Anchor BIO.B.2.1 Compare Mendelian & non-Mendelian patterns of inheritance.
Mendelian Genetics Blue People of Kentucky Methemoglobinemia.
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Transcript of Mendelian Genetics Blue People of Kentucky Methemoglobinemia.
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Mendelian Genetics
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Blue People of Kentucky
Methemoglobinemia
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Genetics
• Genetics is the study of heredity.
• Heredity is the transmission of traits from parent to offspring; an organisms genetic makeup.
• Genes are sections of a chromosome that code for a specific trait. Ex: hair color, height, etc.
• A trait is any characteristic that can be passed from parent to offspring.
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Genetics
• Alleles are the form of the gene that is passed from parent to offspring. • Flower color = gene;
• Purple and white = alleles of the flower color gene
• Multiple alleles are genes with more than 2 alleles• Eye color
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Gregor Mendel• An Austrian monk who is credited as the first person to
study the science of genetics.
• So he is referred to as “the Father of Genetics.”
• Mendel worked with garden pea plants in his experiments• Easy to grow
• Had many traits to study; height, seed shape, pod shape, flower color, etc.
• Reproduced rapidly
• Cross pollination
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Gregor Mendel
• Mendel’s Experiment• Crossed a Tall plant with a short plant
• This is the parent generation, P1
• All offspring were tall
• Crossed two plants from the P1 offspring
• This is the first filial or first generation of offspring, F1
• Crossed Tall plants from the next generation
• This is the second filial generation of offspring after the parents, F2
• Resulted in ¾ Tall plants and ¼ short plants
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Mendel’s Findings
• Concept of Unit Characters: traits are determined by “factors” that occur in pairs. We now know that these unknown “factors” are genes.
• Dominance: One factor of a pair may cover up or prevent the expression of a trait
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Example: Your Mom gives you the gene for having a Unibrow (recessive) and your father gives you the gene for having two eye brows (dominant)
Mom Dad
What will you have?
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Mendel’s Findings
• Law of Segregation: two alleles for a gene will separate during meiosis
• Law of Independent Assortment: alleles separate randomly or independently of each other. This means that seed shape does not affect plant height.
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Because of independent assortment and crossing over during meiosis, there is an infinite number of possible combinations of chromosomes in the gametes, this is called genetic recombination.
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Important Genetics Terms
• Dominant: the “stronger” gene; represented by an uppercase letter
• Recessive: the “weaker” gene; represented by a lowercase letter
B R
b r
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Important Genetics Terms
• Genotype: combination of genes represented by a combination of letters. We generally use the first letter of the dominant gene.
• RR, Rr, rr
• Phenotype: the expression of the gene/trait; what is actually seen or expressed (phenotype = physical trait)
• Tall, short, green, round, wrinkled
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Genotype & Phenotype
Genotype of alleles:R = red flowerr = yellow flower
All genes occur in pairs, so 2 alleles affect a characteristic
Possible combinations are:Genotypes: RR Rr rr
Phenotypes: RED RED YELLOW
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Important Genetics Terms
• Homozygous: gene pairs that are identical• Homozygous dominant: TT, AA, RR
• Homozygous recessive: tt, aa, rr
• Heterozygous: gene pairs that are different. The dominant gene will be expressed in most heterozygous organisms.
• Tt, Aa, Rr
• Hybrid: offspring of parents with gene pairs that are different; another term for heterozygous
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Probability
• The traits you received from your parents were all randomly combined due to chance.
• We use the mathematical study of probability in genetics to help us determine the likelihood of passing on certain traits to future offspring.
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Mendelian Inheritance and Probability
• How do we know what the probability of a cross will be?
• We use a device called a Punnett square to see possible gene combinations.
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Mendelian Inheritance and Probability
• Monohybrid Cross: a cross between organisms that involves one trait.
• Dihybrid Cross: a cross between organisms that involves two traits
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Mendelian Inheritance and Probability
• The probability of a gene combination can be represented by: • A fraction: # of one kind of combination
# of all possible combinations
• A ratio: 1:4, 1:2, 3:4, 4:0, 1:2:1, etc.
• Or a percentage: 25%, 50%, ect.
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Let’s practice… Punnett squares
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WHEN HEREDITY ISN’T SIMPLE
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INCOMPLETE DOMINANCE• The phenotype of the heterozygous organism is “in
between” the dominant and recessive phenotype.
• Example: Snapdragon flowers• Homozygous Dominant = Red (CRCR)
• Homozygous Recessive = White (CWCW)
• Heterozygous = Pink (CRCW)
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CODOMINANCE• Both alleles express themselves independently in the
phenotype. This means that both alleles are expressed equally; both are dominant in a heterozygous organism.
• Cows, horses, people (sickle cell anemia)• Homozygous dominant = Black (BB)
• Homozygous dominant = White (WW)
• Heterozygous = Checkered (BW)
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Multiple Alleles
• Traits controlled by more than two alleles.
• Blood Type
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Sex-Linked Traits
• Traits carried on the sex chromosome
• Sex-linked traits can only be carried on an X chromosome.
• Color Blindness
• Male Pattern Baldness
• Can a father pass a sex-linked trait to his son?
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Autosomal Disorders
• Nondisjunction
• Monosomy• Turner Syndrome
• Trisomy• Trisomy 21 = Down’s Syndrome
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Sex Chromosome Disorders
• Turner’s Syndrome
• Kleinfelter’s Syndrome
• Superfemale
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Dominant Disorders
• Achondroplasia (dwarfism)
• Glaucoma
• Polydactyly
• Brown Teeth
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Recessive Disorders
• Cystic Fibrosis
• Sickle Cell Anemia
• Albinism
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Pedigrees
• Shows the pattern of inheritance within a family