bb2007 120 06 Principles of inheritance 2

bb2007 120 06 Principles of inheritance 2 - Goals for today...

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Unformatted text preview: Goals for today understand the consequences of autosomal recessive or dominant traits familiarize ourselves with the exception from the principle of dominance continue with Mendel's more complex experiments and conclusions Principles of Inheritance, II. ANP 120 Lecture #06 Dominant versus recessive Autosomal recessive traits homozygous recessive affected homozygous dominant tall (both dominant "tall" alleles expressed) heterozygous homozygous recessive tall (only dominant short (both recessive "tall" allele expressed) "short" alleles expressed) homozygous dominant unaffected (no recessive allele) homozygous recessive heterozygous unaffected (dominant affected (both recessive allele expressed) alleles expressed) carries recessive allele Autosomal recessive traits homozygous recessive affected tend to skip generations Autosomal dominant traits heterozygous affected; homozygous dominant rare partial pedigree for albinisim homozygous dominant very strongly affected (both dominant alleles expressed; often lethal) heterozygous affected (dominant allele expressed) homozygous recessive unaffected (both recessive alleles expressed) 1 Autosomal dominant traits heterozygous affected; homozygous dominant rare "every" generation Phenotypic influence of recessive traits example: Tay-Sachs disease partial pedigree for brachydactyly homozygous dominant heterozygous unaffected "unaffected" enzymes: 40-60% lower homozygous recessive affected (death in early childhood) recessive allele "expressed" Sex-influenced traits example: baldness Co-dominance example: ABO genotypes and phenotypes Genotype AA, AO BB, BO Antigen of red blood cells A B A and B None Phenotype (ABO "type") A B AB O b+ b+ b+ b bb influenced by (sex) hormones AB OO Sex-linked traits example: red-green color blindness Sex female Genotype XX XX' X'X' XY X'Y Consequence unaffected unaffected, carrier colorblind unaffected colorblind pure-breeding tall, yellow seeds pure-breeding short, green seeds Parent Generation YYTT F1 Generation X yytt male all tall, yellow seeds YyTt 2 F2 Generation Punnett Square - F2 Generation YyTt x YyTt YT YT Yt Yt yT yt YYTT YYTt YyTT YyTt YYTT YYTt YyTT YyTt YYTt YYtt YYTt YYtt YyTT YyTt YyTT YyTt YyTt YyTt Yytt Yytt YyTt YyTt yyTT yyTT Yytt Yytt 9 / 16 tall, yellow seeds 3 / 16 tall, green seeds 3 / 16 short, yellow seeds 1 / 16 short, green seeds yT yt yyTt yyTt yytt yytt yyTt yyTt Genotype: YyTt No Linkage Chr 1 Chr 2 T Y y t Crossing over Linkage Chr 1 T Y t y Chr 1 Initial pair of chromosomes with 2 linked loci Crossing-over during meiosis Result: OR T y t Y 4 Gametes T Y Y t y T y t 2 Gametes T Y t y 2 Gametes T y t Y Because of linkage A and B (or a and b) are expected to be passed on together. A gene can cross over and exchange with a gene. Gametes have a with B (or A with b) YT Yt yT yt yt YT (not Yt, yT) Yt yT (not YT, yt) Mendel's Principles of Inheritance Mendel's 1st law law of segregation sex cells contain one of each pair of alleles What you should know: what are possible consequences of autosomal recessive and autosomal dominant traits? what are exceptions to the principle of dominance? what is Mendel's 2nd law? what is linkage and what can break linkage? Principle of dominance in a heterozygous only the dominant allele is expressed PLUS (i) phenotypic influence of recessive traits, (ii) sex influenced traits, (iii) co-dominance, (iv) sex-linked traits Mendel's 2nd law law of independent assortment distribution of one pair of chromosomes into gametes does not influence the distribution of another pair 3 ...
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