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Genetics A study of inheritance Gregor Mendel • Father of modern genetics Gregor Mendel • Father of modern genetics • Researched with pea plants Gregor Mendel • Father of modern genetics • Researched with pea plants • Developed ideas of dominance and trait segregation Phenotype • Phenotype – Physical characteristics Genotype • Phenotype – Physical characteristics • Genotype – Genes we inherit from our parents Phenotype Notice the similarities: – Facial structure Phenotype Notice the similarities: – Facial structure – Eyes Phenotype Notice the similarities: – Facial structure – Eyes – Smile Phenotype Notice the similarities: – – – – Facial structure Eyes Smile Ears Phenotype Notice the similarities: – – – – – Facial structure Eyes Smile Ears Nose Phenotype Notice the similarities: – – – – – – Facial structure Eyes Smile Ears Nose Neck Mendelian Genetics Mendel studied a number of characteristics in pea plants including: •Height - short or TALL Mendelian Genetics Mendel studied a number of characteristics in pea plants including: •Height - short or TALL •Seed color - green or YELLOW Mendelian Genetics Mendel studied a number of characteristics in pea plants including: •Height - short or TALL •Seed color - green or YELLOW •Seed shape - wrinkled or ROUND Mendelian Genetics Mendel studied a number of characteristics in pea plants including: •Height - short or TALL •Seed color - green or YELLOW •Seed shape - wrinkled or ROUND •Seed coat color - white or GRAY Mendelian Genetics Mendel studied a number of characteristics in pea plants including: •Height - short or TALL •Seed color - green or YELLOW •Seed shape - wrinkled or ROUND •Seed coat color - white or GRAY •Pod shape - constricted or SMOOTH Mendelian Genetics Mendel studied a number of characteristics in pea plants including: •Height - short or TALL •Seed color - green or YELLOW •Seed shape - wrinkled or ROUND •Seed coat color - white or GRAY •Pod shape - constricted or SMOOTH •Pod color - yellow or GREEN Mendelian Genetics Mendel studied a number of characteristics in pea plants including: •Height - short or TALL •Seed color - green or YELLOW •Seed shape - wrinkled or ROUND •Seed coat color - white or GRAY •Pod shape - constricted or SMOOTH •Pod color - yellow or GREEN Mendelian Genetics We will work with the following three: •Height - short or TALL •Seed color - green or YELLOW •Seed shape - wrinkled or ROUND •Seed coat color - white or GRAY •Pod shape - constricted or SMOOTH •Pod color - yellow or GREEN •Flower position - terminal or AXIAL Mendel's Four Hypotheses • 1) There are alternative forms of “heritable factors” (what we now call genes). – Alternative forms are called alleles. In our flowers we have two alleles for color, purple and white. • 2) Each individual inherits two copies of these alleles. These may be two of the same (e.g., two alleles for purple), or two different ones (one for white, one for purple). – - if an individual has two of the same alleles, it is termed “homozygous” – - if an individual has two different alleles, it is “heterozygous”. Mendel's Four Hypotheses • 3) If the two alleles are different (the individual is a heterozygote), then one of – the alleles will determine the individual's appearance. This is the "dominant“ allele. – - the other allele essentially has no effect on the individual, and is called “recessive”. • 4) a gamete carries only 1 allele for each trait (because alleles separate from each other during production of gametes. Homozygous • Homozygous – Homo means "same or common". – Homozygous means that both alleles are the same. Genotypes such as BB, bb, B1B1 are homozygous. Heterozygous • Heterozygous – Hetero means "different". Heterozygous means that the two alleles are not the same. Thus, genotypes such as Bb, are heterozygous Predicting Inheritance To determine the chances of inheriting a given trait, scientists use Punnett squares and symbols to represent the genes. UPPERCASE letters dominant genes. are used to represent lowercase letters are used to represent recessive genes. Predicting Inheritance For example: T = represents the gene for TALL in pea plants t = represents the gene for short in pea plants So: TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant. Remember there are two genes for every trait! Predicting Inheritance For example: Mendels’ Principle of Dominance T = represents the gene for TALL in pea plants tSome = represents the gene short inand pea others plants are genes (alleles) arefor dominant recessive. The phenotype (trait) of a dominant gene will be seen when it is paired with a recessive gene. So: TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant. Remember there are two genes for every trait! Predicting Inheritance Let’s cross a totally dominant tall plant (TT) with a short plant (tt). Each plant will give only one of its’ two genes to the offspring or F1 generation. TT x tt T T t t Predicting Inheritance Let’s cross a totally dominant tall plant (TT) with a short plant (tt). “Law” of Segregation Mendels’ Each plant will give only one of its’ two genes to Eachoffspring gene (allele) from the other so that the or F1separates generation. the offspring get only one gene from each parent for a given trait. TT x tt T T t t Punnett Squares Tt Tt The genes from one parent go here. The genes from the other parent go here. Tt Tt Punnett Squares T T t Tt Tt t Tt Tt Punnett Squares T T t Tt Tt t Tt Tt Punnett Squares T T t Tt Tt t Tt Tt Punnett Squares T T t Tt Tt t Tt Tt Punnett Squares T T t Tt Tt t Tt Tt Punnett Squares t t T T Tt Tt Tt Tt F1 generation Interpreting the Results The genotype for all the offspring is Tt. The genotype ratio is: Tt - 4/4 The phenotype for all the offspring is tall. The phenotype ratio is: tall - 4/4 Punnett Squares T t ?? ?? Your Turn!! T ?? ?? t Punnett Squares T t T t TT Tt Tt tt F2 generation Punnett Squares Next, give the genotype and phenotype T (F2 generation). t ratios of the offspring T TT Tt t Tt tt Punnett Squares Genotype ratio: TT - 1 T t T TT Tt t Tt tt Punnett Squares Genotype ratio: TT - 1, Tt - 2 T t T TT Tt t Tt tt Punnett Squares Genotype ratio: TT - 1, Tt - 2, tt - 1 T t T TT Tt t Tt tt Punnett Squares Genotype ratio: TT - 1, Tt - 2, tt - 1 T t T TT Tt t Tt tt Phenotype ratio: Tall - 3 Punnett Squares Genotype ratio: TT - 1, Tt - 2, tt - 1 T t T TT Tt t Tt tt Phenotype ratio: Tall - 3, short - 1 Punnett Squares This is a monohybrid T cross. We worked with t only one trait. The height of the plant. T TT Tt t Tt tt Punnett Squares This is a monohybrid T cross. We worked with t only one trait. The height of the plant. T TT Tt t Tt tt Nondisjunction • Nondisjunction is the failure of chromosome pairs to separate properly during meiosis or mitosis. • Examples of Nondisjunction: • A. Down's Syndrome: 47 chromosomes with 3 #21 chromosomes. • B. Triple-X Syndrome: 47 chromosomes caused by 3 X chromosomes. – Can cause women to be taller • C. Klinefelter's Syndrome: 47 chromosomes caused by 2 X chromosomes and 1 Y chromosomes. – Men are unable to have children • D. Turner's Syndrome: 45 chromosomes with 1 X chromosome (caused by the absence of one of the X chromosomes or a Y chromosome). – Women can not have children and may be shorter.