Genetics. the branch of Biology that deals with INHERITANCE (the passing of traits from parents to offspring)

Transcription

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!)

3

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 Heredity clip

9 The garden at Mendel s Monastery

10 II. The Gene-ChromosomeTheorychromosomes contain genes which have all the instructions for the traits of an organism -the unit of hereditary material found on chromosomes - made of DNA gene- allele- another word for gene ex) 2 alleles/genes for flower color: one white, one purple loci- 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 III.Major Genetic Concepts III.Dominant Allele-the allele (gene) that is expressed if present -the stronger allele represented by a letter capital example: tallness= T the gene that isn t expressed if dominant is present. - the weaker, rarer allele Recessive Allelerepresented by a letter lower case example: lack of tallness (shortness)= t

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

15 Heterozygous- also called Phenotypehybrid -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 Parents: Tt x Tt meiosis T t T t fertilization F TT 1 possibilities Tt All of the genes are RECOMBINED RANDOMLY during fertilization (this diagram is a graphical representation of a Punnet Square) Tt tt

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 TT T t Segregation- Only 1 gene from each parent is passed along due to meiosis OR t Tt t t Filling in the squares represents fertilization Which recombines genes Results: 75% dominant 25% recessive

21 Problems: 1.If a heterozygous freckled person marries a non-freckled person, what is the chance that they will have a non-freckled baby? F f Freckles (F) no freckles (f) f Ff ff 50% chance of Non-freckled (ff) baby f 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 B BB Bb phenotype genotype 75% brown 50% Bb 25% blue 25% BB 25%bb b Bb bb

23 3.Normal skin pigmentation (A) is dominant over albino (a). Show the cross of an albino man with a woman who is homozygous normal. A A A= normal a=albino Albino people Albino animals a Aa Aa phenotype genotype 100% 100% normal heterozygous a Aa Aa

24

25

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

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

28 ff tt BB Hh no freckles non taster brown hair has disease -,- MM doesn t have blood factor 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 F 2 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); rough 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 F 1 generation b) the F 2 generation c) offspring produced from a cross of an F 1 pig with one having genotype BBRr

32 a) BBRR x bbrr pure parents BR br gametes BbRr F 1 generation 100% black rough

33 b)f 2 : BbRr x BbRr BR BR BR Br Br possible br br gametes br br BR Br br br BBRR BBRr BbRR BbRr Key B=black b=albino R=rough r=smooth Br br br BBRr BBrr BbRr Bbrr BbRR BbRr bbrr bbrr BbRr Bbrr bbrr bbrr Phenotype results 9 black rough 3 black smooth 3 albino rough 1albino smooth 9:3:3:1

34 c)bbrr x BBRr BR BR Br Br possible br br gametes BR Br br BR BBRR BBRr BbRR Br BBRr BBrr BbRr Phenotype results 6 black rough 2 black smooth br BbRr Bbrr

35 Bill Nye episode Genes (youtube link)

36 Statistically: If x = the number of traits in the cross 2 x = # phenotypes 3 x = # genotypes 4 x = # individuals Monohybrid (already on note pkt) Results: 2 phenotypes Tt x Tt 3 genotypes 4 individuals

37 Dihybrid TtBb 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

38 Dihybrid Problems.answers 1. L= long G = gray l = vestigal g = ebony llgg x LLGG LG lg LlGg F 1 100% LlGg; long, gray

39 F 2 LlGg x LlGg LG Lg lg lg LG LLGG LLGg LlGG LlGg Lg lg lg LLGg LLgg LlGg Llgg LlGG LlGg llgg llgg LlGg Llgg llgg llgg 9 long gray 3 long ebony 3 vest. gray 1 vest ebony

40 2. R= red T = tall r = yellow t = dwarf RRtt x rrtt Rt rt RrTt F 1 100% RrTt; tall, red

41 F 2 RrTt x RrTt RT Rt rt rt RT RRTT RRTt RrTT RrTt Rt rt rt RRTt RRtt RrTt Rrtt RrTT RrTt rrtt rrtt RrTt Rrtt rrtt rrtt 9 red tall 3 red short 3 yellow tall 1 yellow short

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

43 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

44 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

45 OR May produce a trait that expresses 2 dominant alleles at the same time : CODOMINANCE red fur + white fur = red & white fur C R + C W = C R C W Ex) blood type AB: IAI B

46 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: when an organism showing the dominant trait is crossed with a pure recessive to determine if that dominant organism is homozygous or heterozygous *By observing the phenotypes of the offspring, we can trace back to the genotype of the parent: If the genotype of the parent was homozygous (TT), all the offspring are tall: t t T Tt Tt T Tt Tt If the genotype of the parent was heterozygous (Tt), 50% of the offspring are tall and 50% are short: t t T Tt Tt tt tt t

47 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 Bb B Bb B= black b= red b Bb Bb They should all be black

48 Selective Breeding Humans use selective breeding to take advantage of naturally occurring in genetic variation plants, animals, and other organisms, to pass desired traits on to the next generation of organisms. Most and domestic animals have crop plants been produced through selective breeding. Ex:, various breeds of dogs thoroughbred racehorses, disease-resistant, potatoes drought resistant corn

49 Multiple Alleles: ~when there are more than 2 ( multiple ) alleles for a trait ~example: Human blood groups have 3 alleles: I A where I is dominant I B and i is recessive i ~the possible combinations of these 3 blood alleles are as follows: Blood type Phenotype A B AB O genotype I A I A or I A i I B I B or I B i I A I B ii

50 Problems: 1. 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? I A I B I A I B I A I A I A I B Phenotype Genotype 50% AB I A I B 25% A I A I A 25% B I B I B I A I B I B I B

51 2. 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 I A i parent i child i i I A I A i I A I A I A I A i Each parent must have a recessive gene to give to the child i I A i ii

52 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? I A I B 50% A i I A i I B i 50% B He was an imposter! i I A i I B i

53 Sex Determination: ~there are 2 types of chromosomes: sex chromosomes (1 pair) autosomes (all other pairs) ~in each diploid human cell this looks like: sex chromosomes 1 pair autosomes 22 pairs 23 homologous pairs or chromosomes 46 ~The genotype XX represents a female ~The genotype XY represents a ~The sex of an individual is determined by the at the time of. fertilization ~The human egg contains only chromosomes while the human sperm can contian either X or Y chromosomes. X Y X XX XY X XX XY X male sperm Every time a man and woman have a child there is a 50 / 50 chance it will be a boy or girl.

54 Sex Linkage: ~sex-linked traits are caused by genes found on the X chromosome ~sex-linked traits are recessive ~since they are recessive, fewer females are afflicted with these traits because they have another X chromosome which is dominantly normal. Males have only one X chromosome so when they have a sex-linked gene, they ll display the trait. ~the genotype of a sex-linked trait is represented as X or X ~females with one gene for the trait ( X X ) are called carriers ~examples of sex-linked traits: hemophilia, colorblindness

55 1. A man normal for blood clotting marries a woman who is a carrier for hemophilia. What are the chances they will have a child with hemophilia? X Y X XX XY 25% chance of a child with hemophilia: X XX XY 25% normal female (XX) 25% carrier female (XX) 25% normal male (XY) 25% hemophila male (XY)

56 2.What is the probability that a woman with normal vision who marries a colorblind man will have a colorblind child? X X XX X XX 0% chance: 50% carrier females 50% normal males Y XY XY

57 3. A man with a normal vision and a woman with normal vision have 3 sons. Two of the sons have normal color vision and one of them is color-blind. What are the probable genotypes of the parents? X Y X X XX XX XY XY XY and XX ; The gene for color blindness must be hidden/carried by mother to be passed on

58 The Y chromosome QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture.

59 The Wolfman and the Chromosomal basis of heredity Link in above ppt doesn t work, use this one

60 Pedigree charts: used to show he presence or absence of a certain trait in families through several generations. **they re kind of like a genetic family tree Bb bb bb Bb Bb bb Bb

61 1 X X X Y XX XY XX XY 3

62 Human Pedigree A diagram showing the transmission of a trait through several generations of a family is called a pedigree. In Figure 1, generation 1 is made up of grandparents, generation II is their children, and generation III is their grandchildren. 1. Study the pedigree diagram and the key in Figure 1 to learn the symbols.

63 1. How many generations are shown? 3 2. How many men are shown? 5 women? 9 3. How many women have cystic fibrosis? 2 4. How many men have cystic fibrosis? 1 5. How many marriages are shown? 4 6. How many single women are in the family? 5 7. How many children are there? 4 8. How many grandchildren are there? 5 One Republic music video I lived 9. Do you think the gene for cystic fibrosis is dominant or recessive? Recessive b/c it remains hidden in several people

64 Use A to represent the allele for the ability to taste PTC, a dominant allele. Use aa for the PTC nontaster, who exhibits the recessive trait. Aa aa Aa aa aa aa aa aa Aa aa aa aa aa aa Aa Aa