Punnett Square Genetics
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Punnett Square Genetics Intro. • Trait: genetically determined feature of an organism • Gene: a section of a chromosome that codes for a trait; you have 2 alleles for every gene • Allele: alternate forms of a gene that are shown with letters; you received one allele from each parent Punnett Square Genetics Intro. • Dominant: the allele that will be expressed even if a recessive one is present • Recessive: these alleles are hidden when dominant ones are present; the only way recessives will be expressed is if there are two of them for the gene Punnett Square Genetics Intro. • Genotype: the allele combination possessed; it is written out in letters • Phenotype: the features determined by the genes; it is written out in words Part 1 – Simple Crosses #1 R r R RR Rr R RR Rr Genotype ratio 2/4 RR : 2/4 Rr Phenotype ratio 4/4 Round Part 1 – Simple Crosses #2 G g G GG Gg G GG Gg Genotype ratio 2/4 GG : 2/4 Gg Phenotype ratio 4/4 Green Part 1 – Simple Crosses #3 T t T TT Tt t Tt tt Genotype ratio 1/4 TT : 2/4 Tt : 1/4 tt Phenotype ratio 3/4 tall : 1/4 short Part 1 – Simple Crosses #4 r r R Rr Rr r rr rr Genotype ratio 2/4 Rr : 2/4 rr Phenotype ratio 2/4 Round : 2/4 wrinkled Part 1 – Simple Crosses #5 G g G GG Gg g Gg gg Genotype ratio 1/4 GG : 2/4 Gg : 1/4 gg Phenotype ratio 3/4 green : 1/4 yellow Part 1 – Simple Crosses #6 G G g Gg Gg g Gg Gg Genotype ratio 4/4 Gg Phenotype ratio 4/4 Green Part 1 – Simple Crosses #7 T T t Tt Tt t Tt Tt Genotype ratio 4/4 Tt Phenotype ratio 4/4 tall Part 1 – Simple Crosses #8 b b B Bb Bb b bb bb Genotype ratio 2/4 Bb : 2/4 bb Phenotype ratio 2/4 brown : 2/4 white Part 2 - Pedigree Charts #1 • Does the trait show up more often in males or females or does it affect males and females [somewhat] equally? Males • Are there carriers? Yes • Therefore it is: Sex-linked recessive Part 2 - Pedigree Charts #2 • Does the trait show up more often in males or females or does it affect males and females [somewhat] equally? Equal • Are there carriers? No • Therefore it is: Autosomal dominant Part 2 - Pedigree Charts #3 • Does the trait show up more often in males or females or does it affect males and females [somewhat] equally? Females • Are there carriers? No • Therefore it is: Sex-linked dominant Part 2 - Pedigree Charts #4 • Does the trait show up more often in males or females or does it affect males and females [somewhat] equally? Equal • Are there carriers? Yes • Therefore it is: Autosomal recessive Part 3 – Special Punnett Squares #1 i IA IB IA IAIA IAIB IAi IB IAIB I BI B IBi i IAi IBi ii IAIA IBIB ii IAi IBi IAIB = 1/9 = 1/9 = 1/9 = 2/9 = 2/9 = 2/9 Type A Type B Type AB = 3/9 = 3/9 = 2/9 “Universal Recipient” = 1/9 “Universal Donor” Type O Part 3 – Special Punnett Squares #2 R R r Rr Rr r Rr Rr Genotype ratio 4/4 Rr Phenotype ratio 4/4 pink Part 3 – Special Punnett Squares #3 R r R RR Rr r Rr rr Genotype ratio 1/4 RR : 2/4 Rr : 1/4 rr Phenotype ratio 1/4 red : 2/4 pink : 1/4 white Part 3 – Special Punnett Squares #4 r r R Rr Rr r rr rr Genotype ratio 2/4 Rr : 2/4 rr Phenotype ratio 2/4 pink : 2/4 white Part 3 – Special Punnett Squares #5 XH Xh Y XHXh XHY H = normal; h = hemophilia 1/4 XHXh = carrier female 1/4 XhXh = hemophiliac female Xh XhXh XhY 1/4 XHY = normal male 1/4 XhY = hemophiliac male Part 3 – Special Punnett Squares #6 XC Xc Y XCXc XCY C = normal; c = color-blind 2/4 XCXc = carrier female 2/4 XCY = normal male XC XCXc XCY Enrichment Sample Problem #1 Step 1 Determine the genotypes of the parents. Step 2 Determine the gamete genotypes produced by each parent. Step 3 Set up a Punnett square using the gamete genotypes. Step 4 Combine the gamete genotypes from one parent with those from the other parent to show all possible offspring genotypes. Step 5 State the genotype ratio and the phenotype ratio. RT RT RT RT RT RRTT RRTT RRTT RRTT RT RRTT RRTT RRTT RRTT RT RRTT RRTT RRTT RRTT RT RRTT RRTT RRTT RRTT Enrichment Sample Problem #2 Step 1 Determine the genotypes of the parents. Step 2 Determine the gamete genotypes produced by each parent. Step 3 Set up a Punnett square using the gamete genotypes. Step 4 Combine the gamete genotypes from one parent with those from the other parent to show all possible offspring genotypes. Step 5 State the genotype ratio and the phenotype ratio. RT RT rT Rt RRTt RRTt RrTt RrTt Rt RRTt RRTt RrTt RrTt Rt RRTt RRTt RrTt RrTt Rt RRTt RrTt RrTt RRTt rT Enrichment Sample Problem #3 Step 1 Determine the genotypes of the parents. Step 2 Determine the gamete genotypes produced by each parent. Step 3 Set up a Punnett square using the gamete genotypes. Step 4 Combine the gamete genotypes from one parent with those from the other parent to show all possible offspring genotypes. Step 5 State the genotype ratio and the phenotype ratio. GT Gt gT gt GT GGTT GGTt GgTT GgTt Gt GGTt GGtt GgTt Ggtt gT GgTT GgTt ggTT ggTt gt GgTt ggTt ggtt Ggtt Enrichment Practice #1 RB A. RrBb x RRBB C. 16/16 running, black mice Rb rB rb RB RRBB RRBb RrBB RrBb RB RRBB RRBb RrBB RrBb RB RRBB RRBb RrBB RrBb RB RRBB RRBb RrBB RrBb Enrichment Practice #2 A. RRBB x Rrbb C. 16/16 running, black mice RB RB RB RB Rb RRBb RRBb RRBb RRBb Rb RRBb RRBb RRBb RRBb rb RrBb RrBb RrBb RrBb rb RrBb RrBb RrBb RrBb Enrichment Practice #3 A. rrbb x rrbb C. 16/16 waltzing, brown mice rb rb rb rb rb rrbb rrbb rrbb rrbb rb rrbb rrbb rrbb rrbb rb rrbb rrbb rrbb rrbb rb rrbb rrbb rrbb rrbb Enrichment Practice #4 A. RRBb x rrbb C. 8/16 running, black mice : 8/16 running, brown mice RB Rb RB rb RrBb Rrbb RrBb Rrbb rb RrBb Rrbb RrBb Rrbb rb RrBb Rrbb RrBb Rrbb rb RrBb RrBb Rrbb Rrbb Rb Heterozygous blue, homozygous tail B = blue b = yellow X Yellow, heterozygous tail T = tail t = no tail What are the parent genotypes? BbTT X bbTt What are the possible gamete genotypes? BT, BT, bT, bT, bT, bt, bT, bt BT BT bT bT bT BbTT BbTT bbTT bbTT bt BbTt BbTt bbTt bbTt bT BbTT BbTT bbTT bbTT bt BbTt BbTt bbTt bbTt
