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Regents Biology 2007-2008 Genetics & The Work of Mendel.

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Presentation on theme: "Regents Biology 2007-2008 Genetics & The Work of Mendel."— Presentation transcript:


2 Regents Biology Genetics & The Work of Mendel

3 Regents Biology Modern genetics began in the mid- 1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas used good experimental design used mathematical analysis collected data & counted them excellent example of scientific method Gregor Mendel

4 Regents Biology Pollen transferred from white flower to stigma of purple flower all purple flowers result Mendels work ? self-pollinate Bred pea plants cross-pollinate true breeding parents raised seed & then observed traits allowed offspring to self-pollinate & observed next generation

5 Regents Biology Mendel collected data for 7 pea traits

6 Regents Biology 2 nd generation 3:1 75% purple-flower peas 25% white-flower peas Looking closer at Mendels work Parents 100% 1 st generation (hybrids) 100% purple-flower peas X true-breeding purple-flower peas true-breeding white-flower peas self-pollinate

7 Regents Biology What did Mendels findings mean? Some traits mask others purple & white flower colors are separate traits that do not blend purple x white light purple purple masked white dominant allele functional protein affects characteristic masks other alleles recessive allele no noticeable effect allele makes a non-functioning protein homologous chromosomes Ill speak for both of us! allele producing functional protein mutant allele malfunctioning protein

8 Regents Biology Genotype vs. phenotype Difference between how an organism looks & its genetics phenotype description of an organisms trait genotype description of an organisms genetic makeup Explain Mendels results using …dominant & recessive …phenotype & genotype F1F1 P X purplewhite all purple

9 Regents Biology Making crosses Can represent alleles as letters flower color alleles P or p true-breeding purple-flower peas PP true-breeding white-flower peas pp PP x pp PpPp F1F1 P X purplewhite all purple

10 Regents Biology Punnett squares Pp x Pp Pp male / sperm P p female / eggs PP 75% 25% 3:1 25% 50% 25% 1:2:1 % genotype % phenotype PPPpPp PpPppp PpPp PpPp 1 st generation (hybrids) Aaaaah, phenotype & genotype can have different ratios

11 Regents Biology Any Questions??

12 Regents Biology Beyond Mendels Laws of Inheritance

13 Regents Biology Extending Mendelian genetics Mendel worked with a simple system peas are genetically simple most traits are controlled by single gene each gene has only 2 version 1 completely dominant (A) 1 recessive (a) But its usually not that simple!

14 Regents Biology Incomplete dominance Hybrids have in-between appearance RR = red flowers rr = white flowers Rr = pink flowers make 50% less color RRRrrr RR WW RW

15 Regents Biology Incomplete dominance true-breeding red flowers true-breeding white flowers X P 100% 100% pink flowers 1 st generation (hybrids) self-pollinate 25% white 2 nd generation 25% red 1:2:1 50% pink

16 Regents Biology Incomplete dominance RW male / sperm R W female / eggs RR RWWW RW 25% 1:2:1 25% 50% 25% 1:2:1 % genotype % phenotype RR RW WW 25% 50% RW x RW

17 Regents Biology Codominance Equal dominance human ABO blood groups 3 version A, B, i A & B alleles are codominant both A & B alleles are dominant over i allele the genes code for different sugars on the surface of red blood cells name tag of red blood cell

18 Regents Biology Genetics of Blood type pheno- type genotype antigen on RBC antibodies in blood donation status AA A or A i type A antigens on surface of RBC anti-B antibodies __ BBB or B i type B antigens on surface of RBC anti-A antibodies __ AB both type A & type B antigens on surface of RBC no antibodies universal recipient Oi ii i no antigens on surface of RBC anti-A & anti-B antibodies universal donor

19 Regents Biology Blood donation clotting

20 Regents Biology One gene: many effects The genes that we have covered so far affect only one trait But most genes are affect many traits 1 gene affects more than 1 trait dwarfism (achondroplasia) gigantism (acromegaly)

21 Regents Biology Acromegaly: André the Giant

22 Regents Biology Aa x aa Inheritance pattern of Achondroplasia aa A a Aa A a Aa x Aa Aa aa Aa 50% dwarf:50% normal or 1:1 AA aa Aa 67% dwarf:33% normal or 2:1 Aa

23 Regents Biology Many genes: one trait Polygenic inheritance additive effects of many genes humans skin color height weight eye color intelligence behaviors

24 Regents Biology Human skin color AaBbCc x AaBbCc can produce a wide range of shades most children = intermediate skin color some can be very light & very dark

25 Regents Biology Albinism Johnny & Edgar Winter albino Africans melanin = universal brown color

26 Regents Biology OCA1 albinoBianca Knowlton

27 Regents Biology Coat color in other animals 2 genes: E,e and B,b color (E) or no color (e) how dark color will be: black (B) or brown (b) E–B–E–bbeeB–eebb

28 Regents Biology Phenotype is controlled by both environment & genes Color of Hydrangea flowers is influenced by soil pH Human skin color is influenced by both genetics & environmental conditions Environment effect on genes Coat color in arctic fox influenced by heat sensitive alleles

29 Regents Biology Genetics of sex Women & men are very different, but just a few genes create that difference In mammals = 2 sex chromosomes X & Y 2 X chromosomes = female: XX X & Y chromosome = male: XY XY XX

30 Regents Biology Sex chromosomes

31 Regents Biology Sex-linked traits Sex chromosomes have other genes on them, too especially the X chromosome hemophilia in humans blood doesnt clot Duchenne muscular dystrophy in humans loss of muscle control red-green color blindness see green & red as shades of grey XY XX

32 Regents Biology Sex-linked traits XHXH Y male / sperm XHXH XhXh female / eggs XHXHXHXH XHXhXHXh XHYXHYXhYXhY XHXhXHXh XHXH XhXh XHYXHY Y XHXH XHXHXHXH XHYXHY XHXhXHXh XhYXhY sex-linked recessive 2 normal parents, but mother is carrier HH Hh x XHYXHY XHXhXHXh

33 Regents Biology


35 Dominant most common allele Polydactyly dominant allele Because an allele is dominant does not mean… it is better, or it is more common

36 Regents Biology Polydactyly recessive allele far more common than dominant only 1 individual out of 500 has more than 5 fingers/toes so 499 out of 500 people are homozygous recessive (aa) the allele for >5 fingers/toes is DOMINANT & the allele for 5 digits is recessive individuals are born with extra fingers or toes

37 Regents Biology Hound Dog Taylor

38 Regents Biology Any Questions?

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