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AP Biology 2006-2007 Beyond Mendel’s Laws of Inheritance.

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Presentation on theme: "AP Biology 2006-2007 Beyond Mendel’s Laws of Inheritance."— Presentation transcript:


2 AP Biology 2006-2007 Beyond Mendel’s Laws of Inheritance

3 AP Biology Rules of Probability  Addition Rule- probability that any one of two or more mutually exclusive events will occur is calculated by adding the individual probabilities. Example- the chance of getting heads or tails on a coin toss heads- ½ tails – ½ ½ +1/2 = 1

4 AP Biology Rules of Probability Multiplication- probability that two or more independent events will occur together Ex- What is the chance that two coins tossed together will both land heads up? probability of 1 head- ½ probability of 2 heads ½ x ½ = 1/4

5 AP Biology Probability Problems  Chance of rolling a three on a die? 1/6  Chance of getting any other number other than three? 5/6  Chance of rolling a 1 and then a 2 and then 4? 1/6 x 1/6 x 1/6 = 1/216  Parents are PP and pp- chance that offspring will be Pp? 1 x 1 = 1  Parents are PpYy x Ppyy chance that offspring will be ppYy? Pp= ½ x ½ Yy= ½ x 1 total=1/8

6 AP Biology Incomplete dominance  Heterozygote shows an intermediate, blended phenotype  example:  RR = red flowers  rr = white flowers  Rr = pink flowers  make 50% less color RR  RR  WW  RW WWRW

7 AP Biology Incomplete dominance true-breeding red flowers true-breeding white flowers X P 100% 100% pink flowers F 1 generation (hybrids) self-pollinate 25% white F 2 generation 25% red 1:2:1 50% pink

8 AP Biology Codominance  There are two or more alleles that are dominant in a phenotype.  Both alleles are expressed in heterozygous condition.  Ex: Red – RR, white – WW, red and white - RW

9 AP Biology Multiple Alleles  2 alleles affect the phenotype equally & separately  not blended phenotype  human ABO blood groups  3 alleles  I A, I B, i  I A & I B alleles are co-dominant  glycoprotein antigens on RBC  I A I B = both antigens are produced  i allele recessive to both

10 AP Biology Polygenic inheritance  Some phenotypes determined by additive effects of 2 or more genes on a single characteristic  phenotypes on a continuum  human traits  skin color  height  weight  intelligence  behaviors

11 AP Biology Sex linked traits  Genes are on sex chromosomes  as opposed to autosomal chromosomes  first discovered by T.H. Morgan at Columbia U.  Drosophila breeding  good genetic subject  prolific  2 week generations  4 pairs of chromosomes  XX=female, XY=male 1910 | 1933

12 AP Biology Hemophilia Hh x HH XHYXHY XHXhXHXh XHXhXHXh XHXH XhXh XHYXHY Y XHXH sex-linked recessive XHXH Y male / sperm XHXH XhXh female / eggs XHXHXHXH XHXhXHXh XHYXHYXhYXhY XHXHXHXH XHYXHY XHXhXHXh XhYXhY carrierdisease

13 AP Biology Pedigree Analysis  Used to predict inheritance based on past phenotypes

14 AP Biology Generation skipped Autosomal Recessive Inheritance- cystic fibrosis

15 AP Biology Generations are not skipped Autosomal Dominant Inheritance- Huntington Disease

16 AP Biology Human disorders  The family pedigree  Recessive disorders: Cystic fibrosisTay- Sachs Sickle-cell  Dominant disorders: -Huntington’s

17 AP Biology Practice Question Sickle cell anemia is caused by the mutation of a single base pair in the gene for hemoglobin. This mutation results in hemoglobin molecules that form long chains in low-oxygen settings and stretch the blood cells into their characteristic sickled shape. What would the result be if a different base pair in the sickle cell hemoglobin gene were to become mutated? A. The effects of sickle cell would be increased B. The effects of sickle cell would be reduced C. The new mutation would increase resistance to malaria D. It is impossible to predict what the effect would be without knowing more about the mutation

18 AP Biology Practice Problem In the cross AaBBcc x aaBbCc, what is the probability of an offspring that is aaBbcc? A 1/2 B 1/4 C 1/8 D 1/16

19 AP Biology Practice Problem What type of inheritance pattern is illustrated above?

20 AP Biology  In humans & other mammals, there are 2 sex chromosomes: X & Y  2 X chromosomes  develop as a female: XX  gene redundancy, like autosomal chromosomes  an X & Y chromosome  develop as a male: XY  no redundancy Genetics of Sex XY X X XX XY 50% female : 50% male XX

21 AP Biology Huh! Sex matters?! F 2 generation 100% red-eye female 50% red-eye male 50% white eye male Discovery of sex linkage P X F 1 generation (hybrids) 100% red eye offspring true-breeding white-eye male true-breeding red-eye female

22 AP Biology Genes on sex chromosomes  Y chromosome  few genes other than SRY  sex-determining region  master regulator for maleness  turns on genes for production of male hormones  X chromosome  traits other than sex determination  mutations: (all are recessive)  hemophilia  Duchenne muscular dystrophy  color-blindness

23 AP Biology X-inactivation  Female mammals inherit 2 X chromosomes  one X becomes inactivated during embryonic development  condenses into compact object = Barr body  which X becomes Barr body is random  patchwork trait = “mosaic” XHXH XhXh XHXhXHXh patches of black patches of orange tricolor cats can only be female

24 AP Biology Sex Linked Traits  Usually found on the X chromosome  Only if she is homozygous recessive, will she exhibit the trait  Expressed more with males since they have only one X

25 AP Biology Sex Linked diseases in humans  Duchenne muscular dystrophy  Hemophilia  Colorblindness

26 AP Biology Hemophilia in the Russian Family

27 AP Biology Linked Genes  Are physically close to each other and get inherited together even with crossing over  The greater the distance between the genes, the greater the chance of separation during crossing over

28 AP Biology Map Units  Morgan and Sturtevant developed the genetic map that shows a list of ordered loci on a chromosome  The distance between the genes is called a map unit  A recombinant frequency of 1% = 1 map unit

29 AP Biology  If the black body gene (b) is 17% or 17 map units from the vestigal wing gene (vg) and the cinnabar eye gene (cn) is 9.75% or 9.75 map units from the b gene, what are the order of the genes on the chromosome? Example

30 AP Biology Locates genes with respect to chromosomal features as stained bands Cytogenic Maps

31 AP Biology Alternative Systems

32 AP Biology Nondisjunction

33 AP Biology Down Syndrome Remember this

34 AP Biology  Plants- are actually less serious  Animals (one too many or too few chromosomes), are very serious or fatal due to gene imbalances Aneuploidy- too many or too few

35 AP Biology XO Turner Syndrome- Monosomy

36 AP Biology XXY- Klinefelter Syndrome

37 AP Biology  Tall, thin, larger build  More prone to acne  Increased testosterone levels XYY- Jacob’s Syndrome

38 AP Biology  Some traits vary depending on which parent passes it on  The section of DNA has a methyl group (-CH3) added on  Certain cancers can be stimulated this way  Fragile X syndrome can come from father Genomic Imprinting

39 AP Biology  These defects originate in the mitochondrial DNA. Some examples are:  Some forms of Diabetes  Some forms of Deafness  Multiple sclerosis  Some forms of epilepsy Mitochondrial Defects

40 AP Biology Environmental effects  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 Coat color in arctic fox influenced by heat sensitive alleles

41 AP Biology Human Genetic Diseases to Know  Huntington’s (AD)  Colorblindness (SR)  Hemophilia (SR) Cystic Fibrosis (AR) Sickle cell anemia (AR) PKU (AR) Tay Sachs (AR)

42 AP Biology

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