Mendelian Genetics Creating Gametes Probability Genetic Terms

Performed cross-pollination experiments on pea plants to calculate ratios in which traits appeared Discovered basic principles of heredity Considered the father of genetics Gregor Mendel Summarize Gregor Mendel’s contributions to the study of genetics

Law of segregation – the law stating that members of each pair of genes separate, or segregate, when gametes are formed – Each gamete formed during meiosis receives one member of each chromosome pair Creating Gametes Differentiate between the laws of segregation and independent assortment

Law of independent assortment – the law that describes genes encoding for different traits separating from one another independently during the formation of gametes Creating Gametes Differentiate between the laws of segregation and independent assortment

Probability – the fraction or percentage that describes the likelihood of an event taking place Probability of a coin flip – 50% chance of landing on heads, 50% chance of landing on tails – Probability is a prediction, not a guarantee – Each flip is an independent event with the same probability Probability Calculate probabilities and relate how probabilities influence the production of gametes

Product rule – the rule that states that the probability of two or more independent events occurring together is the product of the individual probabilities of each event occurring alone Using the product rule Step 1Determine the probability of each event. Step 2Multiply the probabilities together to find the probability of both events occurring. Probability Calculate probabilities and relate how probabilities influence the production of gametes

Probability Example Ex) What is the probability of simultaneously flipping a coin that lands on heads and spinning the color red on a four-colored spinner? Step 1Determine the probability of each event. Step 2Multiply the probabilities together to find the probability of both events occurring. There is a one out of eight (12.5%) chance of flipping heads and spinning red simultaneously. Calculate probabilities and relate how probabilities influence the production of gametes

When applying probability to genetic crosses, geneticists assume – A pair of genes will segregate in a 1:1 ratio during meiosis (Law of segregation) – Gametes combine randomly during fertilization Probability Calculate probabilities and relate how probabilities influence the production of gametes

Character – a feature present in an organism’s appearance – Ex) Fur color in mice Trait – a different version of a character – Ex) White or black fur Gene – the unit of hereditary information consisting of a specific nucleotide sequence within DNA Allele – the alternate form of a gene Genetic Terms - Define major genetic terms

Dominant – an allele that is fully expressed in the phenotype – Represented by a capital letter Recessive – an allele that is masked in the phenotype – Represented by a lowercase letter Genetic Terms

Genotype – the genetic makeup of an organism – Written as two letters Phenotype – the physical and physiological traits of an organism – Descriptive Genetic Terms

Homozygous – the state of having two of the same alleles for a given genetic character – Ex) Homozygous dominant genotype RR results in phenotype red flowers Heterozygous – the state of having two different alleles for a given genetic character – Ex) Heterozygous genotype Rr results in phenotype red flowers Genetic Terms

Mendelian Genetics Pedigrees

Learning about human genetics requires researching previous matings Pedigree – a family tree describing the occurrence of heritable characters in parents and offspring across generations Pedigrees Interpret and analyze genetic pedigrees

Widow’s peak results from a dominant allele Pedigrees can help predict future offspring Pedigrees

Analyzing a pedigree Step 1Determine if the trait in the pedigree is dominant or recessive. Step 2Determine the genotypes of the individuals. Step 3Use the genotypes to create a Punnett square to solve the problem. Pedigrees

Pedigrees Example Part 1 Step 1Determine if the trait in the pedigree is dominant or recessive. Ex) Some people have attached earlobes while others have free earlobes. Analyze the provided pedigree that traces this trait in a family. First, determine if the allele for attached earlobes is dominant or recessive. Then, calculate the probability of the couple in the second generation having a third child with attached earlobes. Attached earlobes is recessive.

Pedigrees Example Part 2 Step 2Determine the genotypes of the individuals. Ex) Some people have attached earlobes while others have free earlobes. Analyze the provided pedigree that traces this trait in a family. First, determine if the allele for attached earlobes is dominant or recessive. Then, calculate the probability of the couple in the second generation having a third child with attached earlobes. Ee x Ee

Pedigrees Example Part 3 Step 3Use the genotypes to create a Punnett square to solve the problem. Do these results make sense? Ex) Some people have attached earlobes while others have free earlobes. Analyze the provided pedigree that traces this trait in a family. First, determine if the allele for attached earlobes is dominant or recessive. Then, calculate the probability of the couple in the second generation having a third child with attached earlobes. Yes. 25% chance of having a child with attached earlobes

Mendelian Genetics Punnett Squares

Punnett square – a chart used to visualize the possibilities of a genetic cross – Organizes possible gamete configurations in order to calculate genotype and phenotype ratios Probability ≠ guarantee Punnett Squares Solve Punnett square problems focusing on Mendelian genetics

Solving genetics problems using Punnett squares Step 1Draw and label Punnett square with parent genotypes. Step 2Use parent genotypes to find each box’s genotype. Step 3Determine genotypic percentages and ratios. Step 4Use dominance to determine phenotype in each box. Step 5Determine phenotypic percentages and ratios. Punnett Squares

A single-trait cross focuses on one character Monohybrid cross – a genetic cross involving individuals both heterozygous for one trait Punnett Squares

Punnett Squares Example Part 1 Step 1Draw and label a Punnett square with parent genotypes. Ex) In mice, the allele for black fur color (B) is dominant over the allele for white fur color (b). A homozygous dominant black mouse mates with a white mouse. Determine the expected genotype and phenotype percentages of the offspring.

Punnett Squares Example Part 2 Step 2Use parent genotypes to find each box’s genotype. Step 3Determine genotypic percentages and ratios. Ex) In mice, the allele for black fur color (B) is dominant over the allele for white fur color (b). A homozygous dominant black mouse mates with a white mouse. Determine the expected genotype and phenotype percentages of the offspring.

Punnett Squares Example Part 3 Yes. Ex) In mice, the allele for black fur color (B) is dominant over the allele for white fur color (b). A homozygous dominant black mouse mates with a white mouse. Determine the expected genotype and phenotype percentages of the offspring. Step 4Use dominance to determine phenotype in each box. Step 5Determine phenotypic percentages and ratios. Does the result make sense?

Step 1Draw and label Punnett square with parent genotypes. Punnett Squares Example Part 1 Ex) In a particular species of flower, red flower color (R) is dominant over white flower color (r). A heterozygous red flower is crossed with another heterozygous red flower. What are the chances of producing offspring with white flowers from this particular cross?

Punnett Squares Example Part 2 Step 2Use parent genotypes to find each box’s genotype. Step 3Determine genotypic percentages and ratios. Ex) In a particular species of flower, red flower color (R) is dominant over white flower color (r). A heterozygous red flower is crossed with another heterozygous red flower. What are the chances of producing offspring with white flowers from this particular cross? or

Punnett Squares Example Part 3 Step 4Use dominance to determine phenotype in each box. Step 5Determine phenotypic percentages and ratios. Does the result make sense? Ex) In a particular species of flower, red flower color (R) is dominant over white flower color (r). A heterozygous red flower is crossed with another heterozygous red flower. What are the chances of producing offspring with white flowers from this particular cross? Yes. or

A double-trait cross focuses on two characters Dihybrid cross – a genetic cross involving individuals both heterozygous for two traits – Requires a larger Punnett square because an individual in a dihybrid cross can produce four possible gametes Punnett Squares

Step 1Draw and label Punnett square with parent genotypes. Punnett Squares Example Part 1 Ex) In pea plants, there are two alleles for seed shape. The dominant allele is for round seeds (R), and the recessive allele is for yellow pods (g). If two pea plants heterozygous for both characters were crossed, what would be the expected phenotypic ratios of the offspring for these two characters?

Punnett Squares Example Part 2 Step 2Use parent genotypes to find each box’s genotype. Step 3Determine genotypic percentages and ratios. Ex) In pea plants, there are two alleles for seed shape. The dominant allele is for round seeds (R), and the recessive allele is for yellow pods (g). If two pea plants heterozygous for both characters were crossed, what would be the expected phenotypic ratios of the offspring for these two characters?

Punnett Squares Example Part 3 Step 4Use dominance to determine phenotype in each box. Ex) In pea plants, there are two alleles for seed shape. The dominant allele is for round seeds (R), and the recessive allele is for yellow pods (g). If two pea plants heterozygous for both characters were crossed, what would be the expected phenotypic ratios of the offspring for these two characters?

Punnett Squares Example Part 5 Step 5Determine phenotypic percentages and ratios. Does the result make sense? Ex) In pea plants, there are two alleles for seed shape. The dominant allele is for round seeds (R), and the recessive allele is for yellow pods (g). If two pea plants heterozygous for both characters were crossed, what would be the expected phenotypic ratios of the offspring for these two characters? Yes.