Mendelian Genetics

1. Mendelian Genetics

2. Genetics the branch of Biology that deals with INHERITANCE (the passing of traits from parents to offspring) Gregor Mendel ~Austrian monk who studied pea plants in the 1850’s ~theorized that characteristics are inherited as a result of the transmission of “factors” from parents to offspring (he didn’t know about genes & chromosomes!)

4. Mendel used pea plants b/c he noticed contrasting traits: Tall plants vs. short plants Green pods vs. yellow pods Wrinkled seeds vs. smooth seeds

5. “Brother Mendel, we grow tired of peas”

6. ~his work wasn’t valued until the early 1900’s when scientists began observing contrasting traits in Drosophila (fruit flies) and when better microscopes led to the discovery of chromosomes

7. Drosophila have short life cycles and few chromosomes and therefore are easy to study in genetics

8. Mendel is considered to be the “Father of Genetics”

9. The garden at Mendel’s Monastery

10. II. The Gene-ChromosomeTheory- gene- allele- another word for gene ex) 2 alleles/genes for flower color: one white, one purple loci- chromosomes contain genes which have all the instructions for the traits of an organism -the unit of hereditary material found on chromosomes - genes are made of DNA Latin for “place”; the place/position on a chromosome where you find a gene/allele

11. Loci on fruit fly chromosome Add drosophila loci picture

12. Homologous chromosomes: pairs of chromosomes that have genes for the same traits. You have 2 genes for every trait and they’re located on homologous chromosomes. XX (double stranded homologs) II (single stranded homologs)

13. Major Genetic Concepts • Dominant Allele • represented by a _________letter • example: tallness=______ • Recessive Allele- • represented by a _________letter • example: lack of tallness (shortness)=_____ • the allele (gene) that is • expressed if present • the “stronger” allele capital T the gene that isn’t expressed if dominant is present. - the “weaker”, rarer allele lower case t

14. Genotype- Homozygous- the genes (letters) of a trait described as homozygous or heterozygous ex) Dd; heterozygous DD; homozygous dominant dd; homozygous recessive also called pure when both genes are the same, either dominant or recessive. ex) TT, tt, DD, dd

15. Heterozygous- also called ________ Phenotype- hybrid -when both genes are different; one dominant, one recessive ex) Dd, Tt the physical appearance of a trait ex) tall, short, curly, straight (the genotype is the musical score and the phenotype is the music we hear) Ataxia video link

16. ~Mendel wondered how he could cross 2 tall pea plants and end up w/some tall & some short ~he theorized that the recessive trait can disappear in 1 generation and show up in the next generation as follows:

17. Genes T,t are SEGREGATED or separated during MEIOSIS Tt Parents: Tt x meiosis T t T t fertilization TT Tt Tt tt F1 possibilities All of the genes are RECOMBINED RANDOMLY during fertilization (this diagram is a graphical representation of a Punnet Square)

18. Law of Segregation and Recombination: Mendel explained that “factors” which occur in pairs are separated from each other during gamete formation and recombined at fertilization. Law of Independent Assortment: Mendel concluded that different traits are inherited independently of one another (genes for different traits are separated & distributed to gametes independently of one another when they are on different chromosomes).

19. He learned this after doing dihybrid crosses which examine 2 traits (like pea color & pea plant height); yellow peas aren’t always on tall plants… More on dihybrids to come…..

20. PUNNETT SQUARE- Predicts possible outcomes of a genetic cross T OR t T T T T T t t Segregation- Only 1 gene from each parent is passed along due to meiosis Filling in the squares represents fertilization Which recombines genes OR t t t Results: 75% dominant 25% recessive

21. Problems: If a heterozygous freckled person marries a non-freckled person, what is the chance that they will have a non-freckled baby? Freckles (F) no freckles (f) F f Ff Ff f f 50% chance of Non-freckled (ff) baby ff ff

22. 2. The gene for brown eyes (B) is dominant over the gene for blue eyes (b). Show the results of a cross between a hybrid brown-eyed woman and a hybrid brown-eyed man. B=brown b=blue B b phenotypegenotype 75% brown 50% Bb 25% blue 25% BB 25%bb BB Bb B b Bb bb

23. Normal skin pigmentation (A) is dominant • over albino (a). Show the cross of an albino • man with a woman who is homozygous normal. A= normal a=albino A A phenotypegenotype 100% 100% normal heterozygous Aa Aa a a Aa Aa

26. Ff freckled tt non taster Bb brown hh no disease +,+ has blood factor mm light skin CC color vision

27. Ff freckeld TT Taster bb blond hh no disease +,- has blood factor mm light skin Cc color vision

28. ff no freckles tt non taster BB brown hair Hh has disease -,- doesn’t have blood factor MM dark skin cc color blind Can’t tell if he was Ff or ff yes FF Can’t tell if parents were Tt or tt Can’t tell if parents were Bb or bb yes brown dark Can’t tell if parents were Cc or cc

29. Intro to dihybrid crosses (not in note pkt) As Mendel continued his study of peas, he noticed that different traits (pea color, pea shape) were inherited independently of one another. When he crossed yellow x yellow, the F2 smooth smooth generation had : yellow, yellow, green, green smooth wrinkled smooth wrinkled

30. We know now, that during meiosis, genes for different traits are separated and distributed to gametes independently of one another. (when they’re on different chromosomes). Genes located on the same chromosome do NOT sort independently (aka gene linkage). Breeding experiments that examine 2 different traits are called dihybrid crosses

31. Dihybrid Crosses In guinea pigs, black coat color (B) is dominant to albino (b); coarse coat (R) is is dominant to smooth (r) . Two animals are selected for breeding. Their genotypes are BBRR and bbrr. Give the results of the following including expected genotypes and phenotypes of: a) the F1 generation b) the F2 generation c) offspring produced from a cross of an F1pig with one having genotype BBRr

32. a) BBRR x bbrr pure parents BR br gametes BbRr F1 generation 100% black course

33. F2: BbRr x BbRr BR BR Br Br possible bR bR gametes br br Key B=black b=albino R=Coarse r=smooth BR Br bR br BR Br bR br Phenotype results 9 black coarse 3 black smooth 3 albino coarse 1albino smooth 9:3:3:1

34. BbRr x BBRr BR BR Br Br possible bR gametes br BR Br BR Br bR br Phenotype results 6 black coarse 2 black smooth

35. Statistically: If x = the number of traits in the cross 2x= # phenotypes 3x= # genotypes 4x= # individuals Monohybrid Results: 2 phenotypes Tt x Tt 3 genotypes 4 individuals

36. DihybridTtBb x TtBb Results: (2)2= 4 phenotypes 9:3:3:1 (3)2= 9 genotypes (4)2= 16 individuals Trihybrid TtBbRr x TtBbRr Results: (2)3= 8 phenotypes (3)3= 27 genotypes (4)3= 64 individuals

37. Dihybrid Problems….answers • L= long G = gray • l = vestigal g = ebony F1 llgg x LLGG LG LlGg lg 100% LlGg; long, gray

38. F2 LlGg x LlGg LG Lg lG lg LG Lg lG lg LLGG LLGg LlGG LlGg LLGg LLgg LlGg Llgg 9 long gray 3 long ebony 3 vest. gray 1 vest ebony LlGG LlGg llGG llGg LlGg Llgg llGg llgg

39. 2. R= red T = tall r = yellow t = dwarf F1 RRtt x rrTT Rt RrTt rT 100% RrTt; tall, red

40. F2 RrTt x RrTt RT Rt rT rt RT Rt rT rt RRTT RRTt RrTT RrTt RRTt RRtt RrTt Rrtt 9 red tall 3 red short 3 yellow tall 1 yellow short RrTT RrTt rrTT rrTt RrTt Rrtt rrTt rrtt

41. 3. T = taste N = normal pigment t = non taste n = albino from his mother from her father Mom: ttNn x Dad: Ttnn tN tn TtNn Ttnn ttNn ttnn Tn tn 25% taster, normal 25% taster, albino 25% non-taster, normal 25% non-taster, albino

42. 4. B= bark E = erect ears b = silent e = droopy ears EeBb x eebb EB Eb eB eb eb EeBb Eebb eeBb eebb 25% each: erect barking erect silent drooping barking drooping silent

43. Intermediate Inheritance Many genes do not follow the patterns of dominance: may produce a trait between the 2 parents- INCOMPLETE DOMINANCE (blending) red flowers +white flowers=pink flowers “R”+“W”= “RW”

44. OR May produce a trait that expresses 2 dominant alleles at the same time : CODOMINANCE red fur + white fur= red &white fur CR+ CW = CRCW Ex) blood type AB: IAIB

45. Test Cross: Consider a phenotypically tall organism. What is it’s genotype? Is it TT or Tt? To answer this question, you would do a test cross: definition: *By observing the phenotypes of the offspring, we can trace back to the genotype of the parent: If the genotype If the genotype of the parent was of the parent was homozygous (TT), heterozygous (Tt), all the offspring are tall: 50% of the offspring are tall and 50% are short: when an organism showing the dominant trait is crossed with a pure recessive to determine if that dominant organism is homozygous or heterozygous T T T t t t t t

46. Problem: 1. A cattle rancher buys a black bull which is supposed to be a purebred. Black coat is dominant to red. The new owner decides to be sure he has gotten a good deal by mating the bull with several red cows. Such crosses are called test crosses. If the farmer really got a good deal, what color calves should be born? B B B= black b= red b b They should all be black

47. Multiple Alleles: ~when there are more than 2 (“multiple”) alleles for a trait ~example: Human blood groups have 3 alleles: IA where I is dominant IB and i is recessive i ~the possible combinations of these 3 blood alleles are as follows: Blood type genotype Phenotype A B AB O IAIA or IAi IBIB or IBi IAIB ii

48. Problems: • A couple preparing for marriage have their blood typed along with the other required blood tests. Both are type AB. They ask what types of blood their children may have. What will you tell them? IA IB Phenotype Genotype 50% AB IAIB 25% A IAIA 25% B IBIB IA IB IAIAIAIB IAIBIBIB

49. A type A person marries a type A person. Their firstborn has type O blood. What are the genotypes of the parents and the child? • parent ___ ___ parent ___ ___ child ___ ___ IA i IA i i i IA i Each parent must have a recessive gene to give to the child IA IA IAi IAi ii IA i

50. 3. A wealthy, elderly couple die together in an accident. Soon a man shows up to claim their fortune claiming that he is their long lost son. Other relatives dispute the claim. Hospital records show that the deceased couple were blood types AB and O. The person claiming to be their son was type O. Do you think the man is an imposter? IA IB 50% A 50% B He was an imposter! i i IA i IBi IA i IBi