AP Biology Beyond Mendel’s Laws of Inheritance (14 continued) and 15

AP Biology Extending Mendelian genetics  Mendel worked with a simple system  peas are genetically simple  most traits are controlled by a single gene  each gene has only 2 alleles, 1 of which is completely dominant to the other  The relationship between genotype & phenotype is rarely that simple

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

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

AP Biology Co-dominance  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

AP Biology Figure 8.11 ABO Blood Reactions Are Important in Transfusions

AP Biology Pleiotropy  Most genes are pleiotropic  one gene affects more than one phenotypic character  1 gene affects more than 1 trait  dwarfism (achondroplasia)  gigantism (acromegaly)

AP 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  lethal dominant inheritance dwarf

AP Biology Extending Mendelian Genetics for Two or More Genes  Some traits may be determined by two or more genes

AP Biology Epistasis B_C_ bbC_ _ _cc  One gene completely masks another gene  coat color in mice = 2 separate genes  C,c: pigment (C) or no pigment (c)  B,b: more pigment (black=B) or less (brown=b)  cc = albino, no matter B allele  9:3:3:1 becomes 9:3:4

AP Biology Epistasis in Labrador retrievers  2 genes: (E,e) & (B,b)  pigment (E) or no pigment (e)  pigment concentration: black (B) to brown (b) E–B–E–bbeeB–eebb

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

AP Biology Figure Eggs Sperm Phenotypes: Number of dark-skin alleles: /81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1 / 64 6 / / / / 64 6 / 64 1 / 64 AaBbCc

AP Biology Figure 14.UN03 Complete dominance of one allele Relationship among alleles of a single gene Description Example Incomplete dominance of either allele Codominance Multiple alleles Pleiotropy Heterozygous phenotype same as that of homo- zygous dominant Heterozygous phenotype intermediate between the two homozygous phenotypes Both phenotypes expressed in heterozygotes In the whole population, some genes have more than two alleles One gene is able to affect multiple phenotypic characters ABO blood group alleles Sickle-cell disease PP Pp CRCRCRCR CRCWCRCW CWCWCWCW IAIBIAIB I A, I B, i

AP Biology Figure 14.UN04 Epistasis Polygenic inheritance Relationship among two or more genes Description Example The phenotypic expression of one gene affects that of another A single phenotypic character is affected by two or more genes 9 : 3 : 4 BbEe BE bE Be be AaBbCc

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

AP Biology autosomal chromosomes sex chromosomes Classes of chromosomes

AP Biology 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

AP Biology RRrr What’s up with Morgan’s flies? x rr R R Rr 100% red eyes Rr x Rr R r RR Rrrr Rr 3 red : 1 white 

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

AP Biology XRXRXRXR XrYXrY Let’s reconsider 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

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  many effects = pleiotropy!  X chromosome  other genes/traits beyond sex determination  mutations:  Hemophilia  color-blindness

AP Biology  Sex-linked  usually means “X-linked”  more than 60 diseases traced to genes on X chromosome  153 million bp Human X chromosome

AP Biology Map of Human Y chromosome? < 70 genes on Y chromosome

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

AP Biology  Each chromosome has hundreds or thousands of genes (except the Y chromosome)  Genes located on the same chromosome that tend to be inherited together are called linked genes Concept 15.3: Linked genes tend to be inherited together because they are located near each other on the same chromosome © 2011 Pearson Education, Inc.

AP Biology Figure P Generation (homozygous) Wild type (gray body, normal wings) F 1 dihybrid (wild type) Testcross offspring TESTCROSS b  b  vg  vg  b  b vg  vg b b vg vg Double mutant (black body, vestigial wings) Double mutant Eggs Sperm EXPERIMENT RESULTS PREDICTED RATIOS Wild type (gray-normal) Black- vestigial Gray- vestigial Black- normal b  vg  b vg b  vgb vg  b  b vg  vg b b vg vgb  b vg vgb b vg  vg If genes are located on different chromosomes: If genes are located on the same chromosome and parental alleles are always inherited together: : : : : : : : : : b vg

AP Biology Figure Testcross parents Replication of chromosomes Gray body, normal wings (F 1 dihybrid) Black body, vestigial wings (double mutant) Replication of chromosomes Meiosis I Meiosis II Meiosis I and II Recombinant chromosomes Eggs b  vg  b vg b  vg  b  vg b vg  b vg b  vg  b  vg b vg b vg  Testcross offspring 965 Wild type (gray-normal) 944 Black- vestigial 206 Gray- vestigial 185 Black- normal Sperm Parental-type offspring Recombinant offspring Recombination frequency 391 recombinants 2,300 total offspring  100  17%  b  vg  b vg  b  vg b vg

AP Biology Figure Chromosome Recombination frequencies 9% 9.5% 17% b cn vg RESULTS Mapping the Distance Between Genes Using Recombination Data:

AP Biology Alterations of Chromosome Structure Breakage of a chromosome can lead to four types of changes in chromosome structure (a) Deletion (b) Duplication (c) Inversion (d) Translocation A deletion removes a chromosomal segment. A duplication repeats a segment. An inversion reverses a segment within a chromosome. A translocation moves a segment from one chromosome to a nonhomologous chromosome. ABCDEFGH ABCEFGH ABCDEFGH ABCDEFGHBC ABCDEFGH ADCBEFGH ABCDEFGH MNOPQR G MNOC HFED ABPQ R Normal chromosome 9 Normal chromosome 22 Reciprocal translocation Translocated chromosome 9 Translocated chromosome 22 (Philadelphia chromosome)

AP Biology Figure 1 : Chromosome translocations. a)An idiogram of a reciprocal translocation between chromosomes 12 and 17. b) An ideogram of a Robertsonian translocation between chromosomes 14 and 21. Braude, P. et al. Preimplantation genetic diagnosis. Nature Reviews Genetics 3:(12) , doi: /nrg953 (2002). All rights reserved.

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 Acidic pH Basic pH

AP Biology MELANOCYTES

AP Biology How melanin is produced

AP Biology Bacterial Conjugation and Recombination

AP Biology Gene Transfer by Plasmids

AP Biology GHOSTS

AP Biology Male pattern baldness  Sex influenced trait  autosomal trait influenced by sex hormones  age effect as well = onset after 30 years old  dominant in males & recessive in females  B_ = bald in males; bb = bald in females

AP Biology Genetics of Blood type pheno- type genotype antigen on RBC antibodies in blood donation status AI A I A or I A i type A antigens on surface of RBC anti-B antibodies __ BI B I B or I B i type B antigens on surface of RBC anti-A antibodies __ ABI A I B 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

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