Patterns of Inheritance

1. Patterns of Inheritance Chapters 14 and 15

2. Objectives • Describe Mendel’s experimental framework and approach • Explain the distinction between the terms in the following pairs: gene and allele, dominant and recessive, homozygous and heterozygous, phenotype and genotype, and monohydrid cross and dihybrid cross

3. Explain the experimental background of Mendel’s principal of independent assortment; define this principle and explain its chromosomal basis • Describe the four patterns of inheritance that do not follow Mendel’s principles • Explain how chromosomes (including sex chromosomes) determine gender differently in a variety of organisms • Describe the pattern of inheritance of sex-linked characteristics

4. Introduction • Observation of organisms and offspring show patterns of inheritance • Can be explained by behavior of chromosomes during meiosis and fertilization

5. Historical ideas • Greeks-believed in pangenesis; inheritance “particles” for each characteristic collect in eggs an sperm, passed to next generation • 19th century-“blending” hypothesis; characteristics of parents blend in offspring

6. Gregor Mendel and Modern Genetics • university trained in experimental technique • had background in mathematics and understood probabilities • worked with peas • short life span • numerous and distinctive characteristics • mating can be controlled

7. intentionally self-fertilized flower by covering with bag or cross-fertilized flowers by dusting carpels of one with pollen from other • continuous self-fertilization for many generations resulted in true breeding plants

8. Monohybrid vs Dihybrid • Monohybrid means dealing with a single trait • Like eye color or hair color • Dihybrid means dealing with two traits at the same time • Like eye color and hair color

9. Mendel used monohybrid and dihybrid crosses • developed two principles on the basis of two types of experiments • monhybrid cross-hybridized two true-breeding plants for one form of a single characteristic • dihybrid cross-hybridized plants that combined two of the seven characteristics he studied

10. In the Mendel experiments: • true-breeding plants are P (parental) generation • offspring is F1 (first filial) generation • offspring of two F1’s is F2 (second filial) generation • Mendel published in obscure journal in 1866 • argued that there are discrete, heritable factors (now called genes) that retain individuality from generation to generation

11. Important Terminology Alleles = Alternative forms of a gene occupying the same locus One form of allele is dominant (R), the other is recessive (r). Genotype= Actual combination of alleles. Ex. RR or rr. Phenotype: What you see when you look at the individual R or r Meant for visualization…in reality genes are MUCH smaller than bands seen on stained chromosomes

12. Homologous chromosomes each carry one allele for a trait • reside at same locus ( location) on homologous chromosomes • one inherited from male, one inherited from female parent • So recall… Humans have 1-23 from each parent X 2 • Haploid is one set (23) • Diploid is both sets (46)

13. Ways of expressing genetic information • Conventions for alleles: • F-the dominant (purple) allele, f-the recessive (white) allele • P generation means Parental • F1 Offspring Produced By the Parents “ Like the Children” • F2 More Or Less Like “the Grandchildren” • Phenotype-physical characteristics of organism • Purple flower color • Genotype- genetic make up of organism • FF or Ff or ff • Punnett Square used to track gametes and offspring

14. Law of Segregation of Alleles • The allele for a given trait located on each homologous chromosome separates during meiosis. • Why???????

15. The Principal of Segregation • Pairs of genes segregate (separate) during gamete formation; fertilization pairs genes again • Mendel’s observations • monohybrid cross with flower-color trait • all F1 offspring purple • 929 F2 offspring, 705 purple, 224 white  3:1 = Characteristic ratio from monohybrid cross • observed same pattern for all seven characteristics

16. Independent Assortment • This concept involves segregation (separation) of multiple pairs of alleles • This actually happens during meiosis • In this class, we will deal only with the situation in which the different pairs of alleles are located on different homologous chromosome pairs.

18. Mendel developed four hypotheses • there are alternative forms of genes-alleles • for each inherited characteristic, each organism has two genes • one from each parent • may be same or different alleles • sperm or egg carries only one allele for each characteristic (Haploid) • allele pairs segregate during gamete formation (meiosis)

19. Can use these principles to determine unknown genotypes • Use TEST CROSS • involves crossing unknown genotype (shows dominant phenotype) with recessive phenotype (homozygous) • Two possible genotypes for unknown give different phenotypic ratios in F1 • Unknown homozygous-all offspring dominant phenotype • Unknown heterozygous-1/2 offspring dominant, 1/2 offspring recessive

20. Independent events: outcome of one event does not influence outcome of subsequent event • RULE OF MULTIPLICATION-PROBABILITY OF TWO EVENTS OCCURRING TOGETHER IS PRODUCT OF TWO EVENTS OCCURRING APART • can predict probability of particular genotype • Allows you to answer the probability of getting two children with WW genotype • Probability of the 1st child being WW x probability of the second child being WW

21. Determining genotype a parent can produce

22. Genotype • Homozygous: means that an individual has two of the same alleles • Homozygous dominant: two dominant alleles • Homozygous recessive: two recessive alleles • Example: PP or pp • If there is a dominant allele, then the individual will only show to dominant allele

23. Genotype • Heterozygous: means that an individual has one dominant allele and one recessive allele for a given trait • Example: Pp is heterozygous for the purple color • Also known as a carrier • The individual carries the recessive allele but does not show it

24. And More definitions Hemizygous: indicates a gene is present and active with only one copy; Normally reserved for X-linked genes in males that have XY sex determination for the purpose of this class

25. Guinea Pig Genetics Two basic hair types: Long hair and short hair What is the phenotype of this guinea pig? What is the phenotype of this guinea pig?

26. Guinea Pig Genetics Two basic hair types: Long hair and short hair Short hair is dominant (H) Long hair is recessive (h) What is the genotype for this guinea pig? What is the genotype for this guinea pig?

27. How do we determine what type of offspring the parents can produce? • Punnet Squares

28. MONOHYBRID CROSSES • involves 1 trait • need to know genotype of both parents: If homozygous (RR or rr) If heterozygous (Rr) or r r R R R r Meiosis Meiosis Gametes will all be the same (R or r) Half the gametes will be R and half will be r

29. The Punnett Square • Shows the gametes from both parents: ♀ Mother (Rr) ♂ Father (Rr)

30. The Punnett Square • Shows the genotypes of all possible offspring ♀ Mother (Rr) R r R ♂ Father (Rr) r

31. The Punnett Square • Can be used to calculate frequency ♀ So, if two heterozygous individuals mate (Rr x Rr): Offspring: _____ are heterozygous _____ are homozygous recessive _____ are homozygous dominant So, if two heterozygous individuals mate (Rr x Rr): Offspring: _____ are heterozygous _____ are homozygous recessive _____ are homozygous dominant (Rr) R r R ♂ Rr RR (Rr) r rr Rr Rr

32. Example 1: In Guinea Pigs, short hair (H) is dominant to long hair (h). Cross a heterozygote short haired guinea pig with a long haired guinea pig. • What gametes will each pig produce? • What percentage of the offspring will be: • HH • Hh • hh • What percentage of offspring will have: • Short hair • Long hair

33. DIHYBRID CROSSES… • two traits • assume they assort independently: • Mendel’s Law of Independent Assortment: During metaphase, each pair of alleles segregates independently of other pairs of alleles If parent is RrDd: R Each gamete will have R or r Each gamete will also have D or d r D Meiosis d

34. R R r S phase of Meiosis D r D d d DIHYBRID CROSSES… Now imagine that we want to look two different genes An organism with genotype RrDdhas 2n = ___chromosomes R r D d

35. During Prophase I 2 sets of homologous chromosomes with their sister chromatids R R r D r D d d

36. D D d d During Prophase I – Metaphase I & Independent Assortment 50% 50% D r R or r R D r d R r d R 2n 2n Cell goes through Meiosis I and II

37. r R D D R r D D R r d d R r d d These are gametes; sperm or eggs R D D r R D r D or R d r d R d r d n n

38. Consequence:The Punnett Square will have 4 entries per parent RD rD Rd rd

39. Da Da da da The FOIL Method:Determines the gametes an organism can produce D d a a = First Outer Inner Last What gametes will genotype ddAA produce? What gametes will genotype DdAa produce?

40. Notice how these three rows repeat. If we took out those 3 rows, does it change the %?

41. The 2n Rule:Helps determine the number of different gametes an organism can produce D d a a The 2n rule with heterozygotes: - n = number of heterozygote pairs - one heterozygote (Dd) = 1 - 21 = 2, two possible types of gametes - Da & da -How many for ddAA? _______

42. Example 2: In Guinea Pigs, short hair (H) is dominant to long hair (h). Additionally, black eyes (B) are dominant to pink eyes (b). Cross a guinea pig that is heterozygous for both short hair and black eyes with a guinea pig that has long haired and is heterozygous for black eyes.

43. HB Hb hB hb Example 2: Cross a HhBb guinea pig with a hhBb guinea pig. Let’s determine what type of gametes the HhBb pig will produce. F O I L H h B b = • The 2nrule: • n = 2 (two heterozygote traits Hh and Bb) • 22 = 4, four possible types of gametes • -verified by FOIL • -What type of gametes will the hhBb pig produce?

44. Genotypes: HhBB= ____ HhBb= ____ Hhbb = ____ hhBB = ____ hhBb = ____ hhbb = ____ Phenotypes: Short hair, black eyes = ___ Short hair, pink eyes = ____ Long hair, black eyes = ____ Long hair, pink eyes = ____ Short hair, black eyes (HhBb) X long hair, black eyes (hhBb) pig:

45. Genotypes: HhBB= 1/8 HhBb= 1/4 Hhbb = 1/8 hhBB = 1/8 hhBb = 1/4 hhbb = 1/8 Phenotypes: Short hair, black eyes = 3/8 Short hair, pink eyes = 1/8 Long hair, black eyes = 3/8 Long hair, pink eyes = 1/8 Short hair, black eyes (HhBb) X long hair, black eyes (hhBb) pig: HB hb Hb hB hB HhBB HhBb hhBB hhBb hb HhBb Hhbb hhBb hhbb

46. Non-Mendelian Inheritance • A type of inheritance that does not follow strict patterns of dominant vs. recessive • There are several different types we will explore

47. Non-Mendelian Inheritance • Relationship between genotype and phenotype not simple • Incomplete dominance: one allele not completely dominant in heterozygote • example-color in snapdragons • Note that in incomplete dominance the F1 offspring may attain a phenotype that was not present in either parent

48. Multiple Alleles • Many genes have more than one allele or even two alleles • ABO blood groups in humans controlled by three alleles • A and B dominant over O and co-dominant with each other; results in 6 genotypes and four phenotypes (A, B, AB, and O) • Not the same as codominance only- ex. MN system co-dom. In past used to disprove or suggest parentage in paternity suits, now DNA fingerprinting used

49. The ABO Genotypes and Phenotypes Genotype Phenotype AA = Type A AO = Type A BB = Type B BO = Type B OO = Type O AB = Type AB

50. Pleiotropy • Single genes can affect multiple characteristics • Calledpleiotropy • examples sickle cell anemia, Marfan’s syndrome