1. Genetics and Heredity (Mendelian)

2. History Genetics is the study of genes. Genetics is the study of genes. Inheritance is how traits, or characteristics, are passed on from generation to generation. Inheritance is how traits, or characteristics, are passed on from generation to generation. Chromosomes are made up of genes, which are made up of DNA. Chromosomes are made up of genes, which are made up of DNA. Genetic material (genes,chromosomes, DNA) is found inside the nucleus of a cell. Genetic material (genes,chromosomes, DNA) is found inside the nucleus of a cell. Gregor Mendel is considered “The Father of Genetics" Gregor Mendel is considered “The Father of Genetics"

3. Genetics Notes Who is Gregor Mendel? Principle of Independent Assortment – Inheritance of one trait has no effect on the inheritance of another trait “Father of Genetics”

4. 4 Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

5. 5 Applying the Law of Segregation

6. Gregor Mendel Austrian Monk. Austrian Monk. Experimented with “pea plants”. Experimented with “pea plants”. Used pea plants because: Used pea plants because: – They were available – They reproduced quickly – They showed obvious differences in the traits Understood that there was something that carried traits from one generation to the next- “FACTOR”.

7. Mendel's Plant Breeding Experiments Gregor Mendel was one of the first to apply an experimental approach to the question of inheritance. For seven years, Mendel bred pea plants and recorded inheritance patterns in the offspring. Particulate Hypothesis of Inheritance Parents pass on to their offspring separate and distinct factors (today called genes) that are responsible for inherited traits.

8. What genetic principles account for the transmission of such traits from parents to offspring? The Blending Hypothesis of Inheritance In the early 1800’s the blending hypothesis was proposed. Genetic material contributed by the two parents mixes in a manner analogous to the way blue and yellow paints blend to make green. What would happen if this was the case?

9. Mendelian Genetics Dominant traits- traits that are expressed. Dominant traits- traits that are expressed. Recessive traits- traits that are covered up. Recessive traits- traits that are covered up. Alleles- the different forms of a characteristic. Alleles- the different forms of a characteristic. Punnett Squares- show how crosses are made. Punnett Squares- show how crosses are made. Probability- the chances/ percentages that something will occur. Probability- the chances/ percentages that something will occur. Genotype- the types of genes (Alleles) present. Genotype- the types of genes (Alleles) present. Phenotype- what it looks like. Phenotype- what it looks like. Homozygous- two of the same alleles. Homozygous- two of the same alleles. Heterozygous- two different alleles. Heterozygous- two different alleles.

10. Traits Genetics – study of how traits are passed from parent to offspring

11. Traits are determined by the genes on the chromosomes. A gene is a segment of DNA that determines a trait.

12. Chromosomes come in homologous pairs, thus genes come in pairs. Homologous pairs – matching genes – one from female parent and one from male parent Example: Humans have 46 chromosomes or 23 pairs. One set from dad – 23 in sperm One set from mom – 23 in egg

13. Alleles: alternative versions of a gene. The gene for a particular inherited character resides at a specific locus (position) on homologous chromosome. For each character, an organism inherits two alleles, one from each parent

14. How do alleles differ? Dominant - a term applied to the trait (allele) that is expressed regardless of the second allele. Recessive - a term applied to a trait that is only expressed when the second allele is the same (e.g. short plants are homozygous for the recessive allele). Dominant allele Recessive allele

15. Dominant and Recessive Genes Gene that prevents the other gene from “showing” – dominant Gene that may NOT “show” even though it is present – recessive Symbol – Dominant gene – upper case letter – T Recessive gene – lower case letter – t Dominant color Recessive color

16. Example: Straight thumb is dominant to hitchhiker thumb T = straight thumb t = hitchhikers thumb (Always use the same letter for the same alleles— No S = straight, h = hitchhiker’s) Straight thumb = TT Straight thumb = Tt Hitchhikers thumb = tt * Must have 2 recessive alleles for a recessive trait to “show”

17. Both genes of a pair are the same – homozygous or purebred TT – homozygous dominant tt – homozygous recessive One dominant and one recessive gene – heterozygous or hybrid (carrier) Tt – heterozygous BB – Black Bb – Black w/ white gene bb – White

18. Genotype and Phenotype Combination of genes an organism has (actual gene makeup) – genotype Ex: TT, Tt, tt Physical appearance resulting from gene make-up – phenotype Ex: hitchhiker’s thumb or straight thumb

19. White fur (b) Punnett Square and Probability Used to predict the possible gene makeup of offspring – Punnett Square Example: Black fur (B) is dominant to white fur (b) in mice 1.Cross a heterozygous male with a homozygous recessive female. Black fur (B) White fur (b) Heterozygous male White fur (b) Homozygous recessive female

20. To test the particulate hypothesis, Mendel crossed true- breeding plants that had two distinct and contrasting traits—for example, purple or white flowers. What is meant by “true breeding?” Mendel cross-fertilized his plants by hand. Why is it important to control which plants would serve as the parents?

21. For each monohybrid cross, Mendel cross-fertilized true-breeding plants that were different in just one character—in this case, flower color. He then allowed the hybrids (the F1 generation) to self-fertilize.

22. Typical breeding experiment P generation (parental generation) F1 generation (first filial generation, the word filial from the Latin word for "son") are the hybrid offspring. Allowing these F1 hybrids to self-pollinate produces: F2 generation (second filial generation). It is the analysis of this that lead to an understanding of genetic crosses.

23. Mendel studies seven characteristics in the garden pea

24. Law of Dominance In the monohybrid cross (mating of two organisms that differ in only one character), one version disappeared. What happens when the F1’s are crossed?

25. Probability and Punnett Squares Punnett square: diagram showing the probabilities of the possible outcomes of a genetic cross

26. Genotype versus phenotype. How does a genotype ratio differ from the phenotype ratio?

27. Punnett squares - probability diagram illustrating the possible offspring of a mating. Ss X Ss gametes

28. Testcross A testcross is designed to reveal whether an organism that displays the dominant phenotype is homozygous or heterozygous.

29. Sex Determination Humans – 46 chromosomes or 23 pairs 22 pairs are homologous (look alike) – called autosomes – determine body traits 1 pair is the sex chromosomes – determines sex (male or female) Females – sex chromosomes are homologous (look alike) – label XX Males – sex chromosomes are different – label XY

30. XX XY X Y What is the probability of a couple having a boy? Or a girl? Chance of having female baby? 50% male baby? 50% Who determines the sex of the child? father X X

31. 31 Dihybrid Cross A breeding experiment that tracks the inheritance of two traits. A breeding experiment that tracks the inheritance of two traits. Mendel’s “Law of Independent Assortment” Mendel’s “Law of Independent Assortment” a. Each pair of alleles segregates independently during gamete formation a. Each pair of alleles segregates independently during gamete formation b. Formula: 2 n (n = # of heterozygotes) b. Formula: 2 n (n = # of heterozygotes)

32. 32 Summary of Mendel’s laws LAW PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods