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Incomplete Dominance & Codominance Regents Biology 2007-2008 Incomplete Dominance In incomplete dominance, neither allele is dominant so there is a blending of __________ traits when two different alleles for the ______ same trait occur together. Colors blend together heterozygous (______________ individuals = 3rd phenotype) Regents Biology red pink white Incomplete Dominance In Four O’ Clocks, if you cross a red RR _____ WW (which is always pure) with a white _____ (that is also always pure) , you get a RW (which pink _____ is always hybrid / heterozygous RW RW RW Regents Biology RW Incomplete dominance P X true-breeding red flowers true-breeding white flowers 100% pink flowers 1st 100% generation (hybrids) self-pollinate 25% red 2nd generation Regents Biology 50% pink 25% white 1:2:1 Incomplete dominance RW x RW % genotype male / sperm female / eggs R R W RR W RR RW RW 25% 25% 50% 50% RW RW WW WW 25% 25% 1:2:1 Regents Biology % phenotype 1:2:1 Incomplete Dominance RR and blue In another flower, if red ____ BB flowers are crossed, they produce ____ RB flower a 3rd purple ____ What would be the genotype ratio and phenotype ratio if you crossed two purple flowers…? Regents Biology Incomplete Dominance Cross of two purple flowers RB X ____ RB ____ What are gamete possibilities? R genotype ratio RR 1RR : 2RB : 1BB R red phenotype ratio 1red : 2 purple : 1 blue RB B purple Can you have a heterozygous red or Regents Biology no hybrid blue flower? ___ B RB purple BB blue Codominance alleles contribute to the phenotype Both _______ of the organism by showing up simultaneously (at the same time) in heterozygous individuals. In cattle and horses, if you cross a pure ____ red (RR) with a pure ______ white (WW), you get (RW) which produces the color roan _____. Regents Biology Codominance These cattle or horses actually have both red and white hairs intermixed, or are spotted. Roan is a third ___________. phenotype If you cross a roan with a white… R W W RW roan WW white W RW roan WW white Regents Biology Codominance Andalusian chickens also show this pattern of inheritance. If you cross a black (BB) chicken with a white (WW) chicken, you get black+white speckled (BW) chicken Regents Biology Multiple Alleles Blood type in humans is an example of this inheritance pattern. four different The ______ blood groups: A, B, O, and AB Are produced three different by ______ alleles: A, B, and O Regents Biology Phenotype Genotype A AA or AO B BB or BO AB AB only O OO only Genetics of Blood type phenogenotype type A B antigen on RBC antibodies in blood donation status A A or A i type A antigens on surface of RBC anti-B antibodies __ BB 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 ii no antigens on surface of RBC anti-A & anti-B antibodies universal donor AB O Regents Biology Blood donation clotting clotting clotting clotting Regents Biology clotting clotting clotting Multiple Alleles Examples of Blood type crosses Regents Biology Environment effect on genes Phenotype is controlled by both environment & genes Human skin color is influenced by both genetics & environmental conditions Color of Hydrangea flowers Regents Biologyby soil pH is influenced Coat color in arctic fox influenced by heat sensitive alleles Sex-Linked Traits Sex Determination Females – XX Males – XY X X X Y Almost all sex-linked traits are found on the X chromosome Y chromosome contains very few genes and is mainly involved in sex determination Regents Biology Sex-Linked Traits It is possible for a female to be a carrier of an Xlinked trait, but not express it Men will express all X-linked traits they inherit Regents Biology X-linked recessive, carrier mother Unaffected father Carrier mother Unaffected Affected Carrier Unaffected son Unaffected daughter Carrier daughter Affected son Sex-linked traits Sex chromosomes have other genes on them, too especially the X chromosome hemophilia in humans blood doesn’t clot Duchenne muscular dystrophy in X humans X loss of muscle control red-green color blindness see green & red as shades of grey Regents Biology X Y sex-linked recessive Sex-linked traits 2 normal parents, but mother is carrier HY x XHh H Xh XHH male / sperm XH XH Y XH XH XH XH Y Xh XH Xh XhY Y XH XH Xh Xh Regents Biology female / eggs XH Y