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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. AP Biology XRXRXRXR XrYXrY Morgan’s flies… x XrXr Y XRXR 100% red eyes XRXR XRXrXRXr XRYXRY XRYXRYXRXrXRXr x XRXrXRXr XRYXRY XRXR Y XRXR XrXr XRXrXRXr XRYXRYXRXRXRXR XrYXrY 100% red females 50% red males; 50% white males

12. 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

13. 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

14. 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

15. 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

16. AP Biology Pedigree Analysis  A pedigree is a family tree that describes the interrelationships of parents and children across generations  Inheritance patterns of particular traits can be traced and described using pedigrees

17. AP Biology Fig. 14-15b 1st generation (grandparents) 2nd generation (parents, aunts, and uncles) 3rd generation (two sisters) Widow’s peakNo widow’s peak (a) Is a widow’s peak a dominant or recessive trait? Wwww Ww ww Ww wwWW Ww or

18. AP Biology Fig. 14-15c Attached earlobe 1st generation (grandparents) 2nd generation (parents, aunts, and uncles) 3rd generation (two sisters) Free earlobe (b) Is an attached earlobe a dominant or recessive trait? Ff ffFf ff FFor FF Ff