Gregor Mendel and the Fundamentals of Genetics

1. Chapter 9 Fundamentals of Genetics Table of Contents Section 1 Mendel’s Legacy Section 2 Genetic Crosses

2. Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel • The study of how characteristics are transmitted from parents to offspring is calledgenetics. • Known as the “father of genetics” but not the first person to study genetics. • A fair number of practical breeding experiments were done in ancient times. • People knew there was a connection between sex and reproduction.

3. Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel, continued • Mendel’s Garden Peas • Mendel observed characteristics of pea plants. • Traits are genetically determined variants of a characteristic. • Every day we observe heritable variations (eyes of brown, green, blue, or gray) among individuals in a population. • These traits are transmitted from parents to offspring. • Each characteristic occurred in two contrasting traits. • Traits create breeds. • Another example: dogs were domesticated by 12,000 years ago; selective crossing has given us all the many breeds we have today

4. Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel, continued • Mendel’s Methods • Mendel used cross-pollination techniques in which pollen is transferred between flowers of two different plants. • Studied the traits that came about.

6. Section 1 Mendel’s Legacy Chapter 9 Mendel’s Experiments • Mendel bred plants for several generations that were true-breeding for specific traits and called these the P generation. • Offspring of the P generation were called the F1 generation. • Offspring of the F1 generation were called the F2 generation.

7. Section 1 Mendel’s Legacy Chapter 9 Three Steps of Mendel’s Experiments

8. Section 1 Mendel’s Legacy Chapter 9 Mendel’s Experiments Click below to watch the Visual Concept. Visual Concept

9. Section 1 Mendel’s Legacy Chapter 9 Mendel’s Results and Conclusions • Recessive and Dominant Traits • Mendel concluded that inherited characteristics are controlled by factors that occur in pairs. • In his experiments on pea plants, one factor in a pair masked the other. The trait that masked the other was called the dominant trait. The trait that was masked was called the recessive trait.

10. Mendel developed a hypothesis to explain these results that consisted of four related ideas. 1. Alternative versions of genes (different alleles) account for variations in inherited characters. • The purple-flower allele and white-flower allele are two DNA variations at the flower-color locus. • 2. For each character, an organism inherits two alleles, one from each parent. • In the flower-color example, the F1 plants inherited a purple-flower allele from one parent and a white-flower allele from the other

11. 3.If two alleles differ, then one, the dominantallele, is fully expressed in the the organism’s appearance. • The other, the recessive allele, has no noticeable effect on the organism’s appearance. • Mendel’s F1 plants had purple flowers because the purple-flower allele is dominant and the white-flower allele is recessive. 4. The two alleles for each character segregate (separate) during gamete production. • The separation of alleles into separate gametes is known as Mendel’s law of segregation. • If an organism has 2 identical alleles for a particular character, then that allele exists as a single copy in all gametes. • If 2 different alleles are present, then 50% (1) of the gametes will receive one allele and 50% (1) will receive the other.

12. Section 1 Mendel’s Legacy Chapter 9 Mendel’s Results and Conclusions, continued • The Law of Segregation • The law of segregation states that a pair of factors is segregated, or separated, during the formation of gametes.

13. Section 1 Mendel’s Legacy Chapter 9 Mendel’s Results and Conclusions, continued • The Law of Independent Assortment • Thelaw of independent assortment states that factors for individual characteristics are distributed to gametes independent of one another. • The law of independent assortment is observed only for genes that are located on separate chromosomes or are far apart on the same chromosome.

14. Section 1 Mendel’s Legacy Chapter 9 Support for Mendel’s Conclusions • We now know that the factors that Mendel studied are alleles, or alternative forms of a gene. • One allele for each trait is passed from each parent to the offspring.

15. Section 1 Mendel’s Legacy Chapter 9 Mendel’s Conclusions Click below to watch the Visual Concept. Visual Concept

16. Section 2 Genetic Crosses Chapter 9 Genotype and Phenotype • The genotype is the genetic makeup of an organism. • The phenotype is the appearance of an organism.

17. Section 2 Genetic Crosses Chapter 9 Probability • Probabilityis the likelihood that a specific event will occur. • A probability may be expressed as a decimal, a percentage, or a fraction.

18. Section 2 Genetic Crosses Chapter 9 Calculating Probability Click below to watch the Visual Concept. Visual Concept

19. Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses • A Punnett square can be used to predict the outcome of genetic crosses. • A cross in which one characteristic is tracked is a monohybrid cross.

20. Section 2 Genetic Crosses Chapter 9 Punnett Square with Homozygous Cross Click below to watch the Visual Concept. Visual Concept

21. Section 2 Genetic Crosses Chapter 9 Monohybrid Cross of Heterozygous Plants

22. Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued • A testcross, in which an individual of unknown genotype is crossed with a homozygous recessive individual, can be used to determine the genotype of an individual whose phenotype expresses the dominant trait.

23. Section 2 Genetic Crosses Chapter 9 Testcross Click below to watch the Visual Concept. Visual Concept

24. Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued • Complete dominanceoccurs when heterozygous individuals and dominant homozygous individuals are indistinguishable in phenotype. • This is what we have been crossing the last couple days, traits that had complete dominance.

25. Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued • Incomplete dominanceoccurs when two or more alleles influence the phenotype and results in a phenotype intermediate between the dominant trait and the recessive trait. • This occurs in some flowers. If you cross a red rose with a white rose, the offspring will all come out PINK!

26. Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued • Codominanceoccurs when both alleles for a gene are expressed in a heterozygous offspring. • This occurs in bulls. When a Roan bull (red colored fur is crossed with a White bull, all the offspring have red and white fur.

27. Section 2 Genetic Crosses Chapter 9 Predicting Results of Dihybrid Crosses • A cross in which two characteristics are tracked is adihybrid cross.

28. Chapter 12 • Chromosome • Genes reside on Chromosomes • Sex chromosomes contain genes that determine an organism’s sex (gender). • In mammals, an individual carrying two X chromosomes is female. • An individual carrying an X and a Y chromosome is male. • The remaining chromosomes that are not directly involved in determining the sex of an individual are called autosomes.

29. Karyotypes: Male and Female

30. Effects of Gene Location • Sex-Linked Genes and Traits • Genes found on the X chromosome are X-linked genes. • A sex-linked trait is a trait whose allele is located on a sex chromosome. • Because males have only one X chromosome, a male who carries a recessive allele on the X chromosome will exhibit the sex-linked trait. • Linked Genes • Pairs of genes that tend to be inherited together are calledlinked genes. • Chromosome Mapping • The farther apart two genes are located on a chromosome, the more likely a cross-over will occur

31. Mutations • Germ-cell mutationsoccur in gametes and can be passed on to offspring. • Somatic-cell mutationsoccur in body cells and affect only the individual organism. • Chromosome mutationsare changes in the structure of a chromosome or the loss or gain of an entire chromosome. • Gene mutationsare changes in one or more of the nucleotides in a gene.

32. Chromosome Mutation Gene Mutation

33. Ch 12-2 Inheritance of Traits • Pedigrees • Geneticists use pedigrees to trace diseases or traits through families. • Pedigrees are diagrams that reveal inheritance patterns of genes.

34. Pedigree for Cystic Fibrosis

36. Genetic Traits and Disorders • Polygenic Inheritance • Polygenic characters, such as skin color, are controlled by two or more genes. • Complex Characters • Complex characters, such as polygenic traits, are influenced by both genes and environment. • Multiple Alleles • Multiple-allele characters, such as ABO blood groups, are controlled by three or more alleles of a gene. • (2 visual concepts)

37. Genetic Traits and Disorders • X-Linked Traits • The gene forcolorblindness, an X-linked recessive gene, is found on the X chromosome. • Sex-influenced Trait • A sex-influenced trait, such as pattern baldness, is expressed differently in men than in women even if it is on an autosome and both sexes have the same genotype. • (Visual concepts)

38. Treating Genetic Disorders • Among the treatments are symptom-relieving treatments and symptom-prevention measures, such as insulin injections for diabetes. • Gene Therapy • In gene therapy, a defective gene is replaced with a copy of a healthy gene. • Somatic cell gene therapy alters only body cells. • Germ cell gene therapy attempts to alter eggs or sperm.