Patterns of Inheritance

1. Patterns of Inheritance

2. Inheritance Hypotheses • Blending Hypothesis – parental contributions combined • Particulate Hypothesis – parents pass along discrete heritable units

3. Some Important Vocab • Allele= an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome. • Homozygous = two identical alleles (same) • Heterozygous = two different alleles Genotype • The two genes that an organism inherits for a certain trait (Example Tt, TT, or tt) • Phenotype • Physical characteristics (example: tall and short)

4. Analyzing Patterns • Genetic Cross – controlled experiment to determine the inheritance of a trait • P – parental generation • F1 – first generation • F2 – second generation

5. General Patterns of Inheritance • Alternative versions of genes cause variation • Offspring inherit one copy from each parent • Dominant alleles are expressed in phenotype • Alleles for genes separate during meiosis • Gametes fuse randomly

6. Mendel’s Laws • Father of modern genetics • Researched with pea plants • Developed ideas of dominance and trait segregation • Allelic Interactions • Pleiotropy • Epistasis • Environment • Polygenics

7. Law of Segregation Each gene (allele) separates from the other so that the offspring get only one gene from each parent for a given trait. Let’s cross a 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

8. Law of Independent Assortment • Hypothesis: Inheritance of seed shape is independent of inheritance seed color. • Medal crossed two genetic traits: • Yellow vs. Green • Round vs. Wrinkled • Results: Yes, inheritance of seed shape is independent of seed color. • Conclusion: Chromosomes assort independentlyduring meiosis

9. Developed ideas of dominance and trait segregation • Allelic Interactions • Complete dominance • Incomplete dominance • Codominance • Pleiotropy • Epistasis • Environment • Polygenics

10. Punnett Squares A square which can be used to show the random combinations of genes which are possible when a sperm fertilizes an egg. The genes from one parent go here. The genes from the other parent go here.

11. Allelic Interactions • Complete dominance – dominant allele fully expressed • Incomplete dominance – neither allele fully expressed • Codominance – both alleles fully expressed

12. Allelic Interactions: Complete Dominance • Dominant vs. Recessive Gene • Dominant Gene: A gene that always expresses itself. It is symbolized by a CAPITAL letter • Recessive Gene: a gene that expresses itself only when a dominant form of the gene is NOT present. It is symbolized by a lower case letter

13. Allelic Interactions: Complete Dominance • Practice Problem: • Let's say that in seals, the gene for the length of the whiskers has two alleles.  The dominant allele (W) codes long whiskers & the recessive allele (w) codes for short whiskers. a)  What percentage of offspring would be expected to have short whiskers from the cross of two long-whiskered seals, one that is homozygous dominant and one that is heterozygous? b) If one parent seal is pure long-whiskered and the other is short-whiskered, what percent of offspring would have short whiskers?

14. Allelic Interactions: Incomplete Dominance • Neither allele fully expressed • the phenotype of the heterozygote will be intermediate between the phenotypes of the two homozygotes • Example: RR = Red snapdragon flower Rr = pink snapdragon flower rr = white snapdragon flower Practice Problem: Cross a red snapdragon with a pink snapdragon flower. What will the genotype and phenotype % be for the offspring.

15. Co-Dominance • If two alleles have a co dominant relationship, in the heterozygote both alleles will be completely expressed. • Example: blood type

16. Example: Blood Types

17. Co-Dominance What would happen if you crossed a plant with red flowers with a plant with blue flowers? (a) Give the genotypes and phenotypes for the offspring. (b) How many of the plants would have red flowers? _____% (c) How many of the plants would have purple flowers? _____ % (d) How many of the plants would have blue flowers? _____ %

18. Sex Linked (X-Linked) Traits • The genes that are located on the chromosomes are called sex-linked traits • Many traits that are carried on the X chromosome do not have a corresponding spot on the Y chromosome. This causes for some unique possibilities for the offspring. • Ex. Colorblindness in humans, fruit fly eye color, hemophilia.

19. Pleiotropy • Condition where a single gene influences multiple traits • Example: Marfan’s Syndrome

20. Environment • Phenotype = Genotype + Environment • Epigenetics – study of changes in phenotype due to mechanisms other than changes in DNA sequence Epigenetics

21. Polygenics • Traits that are determined by many genes • Examples – eye color, skin color, height, etc.

22. Analyzing Patterns • Pedigree – illustration of relationships among family members over multiple generations

23. Inheritance and Genetic Disorders • Hereditary disorders • Autosomal or sex-linked • Recessive or dominant • Genetic disorders are often polygenic and influenced by environment

24. Autosomal Recessive Disorders • Carriers – heterozygotes that have one allele but not the disorder • Examples – Cystic Fibrosis, Tay Sachs

25. Autosomal Dominant Disorders • Disorders that are expressed with only one copy of the allele • Example – polydactyly • Example – Huntington’s

26. Sex-linked Recessive Disorders • Disorders that are on the sex chromosome • Example – Hemophilia

27. Sex-linked Dominant Disorders