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Genetics & The Work of Mendel
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____________________
Pairs of matching chromosomes, with one being inherited from each parent.
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Chromosome from DAD: P Chromosome from MOM: p
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ALLELES- _______________________________________________________.
Alleles for a trait are located at corresponding positions on homologous chromosomes called _______________. ALLELES Chromosome from MOM A b C d e Chromosome from DAD A B c d E
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When 1 allele masks (hides) the effect of another, that allele is called ________________ and the hidden allele is called _____________. Dominant alleles are represented by a _________ letter Recessive alleles are represented by a _________ letter
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What are Dominant Genes?
Hereford: ___________________________ Dominant: WW or Ww Recessive: ww ONLY
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What are Recessive Genes?
___________________________. Dominant: PP or Pp Recessive: pp ONLY
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PHENOTYPE (___________________________________________)
how the trait physically shows up in the organism; it is the observable Examples of phenotypes: blue eyes, brown fur, striped fruit, yellow flowers
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__________________________________________
GENOTYPE ______________________________________________. As a result of sexual reproduction, there are 2 letters in the genotype __________________________________________ 3 possible GENOTYPES: 2 capital letters (like "TT") – ______________________ 1 of each ("Tt") - _____________________ 2 lowercase letters ("tt") – ________________________
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homozygous DOMINANT or purebred tall
Genotype Symbol Genotype Vocabulary Phenotype homozygous DOMINANT or purebred tall heterozygous or hybrid homozygous RECESSIVE or purebred short
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Gregor Mendel ( ) Austrian monk Called the “______________ ___________________" for his study of the inheritance of _______ in pea plants.
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Mendel collected data for 7 pea traits
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Gregor Mendel ( ) Mendel's work was not recognized until the turn of the 20th century
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? P = parents F = filial generation Mendel’s work Bred pea plants
Pollen transferred from white flower to stigma of purple flower Bred pea plants cross-pollinate _____________________ raised seed & then observed traits allowed offspring to __________________ & observed next generation all purple flowers result P = parents F = filial generation self-pollinate ?
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Looking closer at Mendel’s work
true-breeding purple-flower peas true-breeding white-flower peas X Parents 100% 1st generation (hybrids) purple-flower peas In a typical breeding experiment, Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties. The true-breeding parents are the P generation and their hybrid offspring are the F1 generation. Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 generation. self-pollinate 2nd generation 3:1 75% purple-flower peas 25% white-flower peas
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Homozygous-recessive
Homozygous-dominant PP x pp P P p p Homozygous-recessive
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all the F1 (1st filial generation) offspring are ______________________________
100% purple offspring
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Heterozygous - hybrid Pp x Pp P p P p Heterozygous - hybrid
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the F2 (2nd filial generation) shows a 3:1 ratio, with ________________________________________
P p Phenotypic ratio: ______________________ Genotypic ratio P p
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What did Mendel’s findings mean?
Some traits mask others purple & white flower colors are separate traits that do not blend purple x white ≠ light purple _______________________ __________________ affects characteristic masks other alleles allele makes a non-functioning protein I’ll speak for both of us! allele producing functional protein mutant allele malfunctioning protein homologous chromosomes
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PP pp x X Making crosses Can represent alleles as letters
flower color alleles true-breeding purple-flower peas true-breeding white-flower peas F1 P X purple white all purple PP x pp
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phenotype & genotype can have different ratios
Punnett squares Aaaaah, phenotype & genotype can have different ratios Pp x Pp 1st generation (hybrids) % genotype % phenotype P p male / sperm PP Pp P p female / eggs Pp pp
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B Bb x Bb b Monohybrid Cross
Example:Cross between two ___________________________________ BB = brown eyes Bb = brown eyes bb = blue eyes B b Bb x Bb
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B b Bb x Bb 1/4 = BB - brown eyed 1/2 = Bb - brown eyed
Monohybrid Cross B b Bb x Bb 1/4 = BB - brown eyed 1/2 = Bb - brown eyed 1/4 = bb - blue eyed
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Mendel was working out many of the genetic rules!
Dihybrid cross Other of Mendel’s experiments followed the inheritance of 2 different characters ________________________ Mendel was working out many of the genetic rules!
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P YYRR yyrr F1 YyRr F2 x true-breeding yellow, round peas
Dihybrid cross P true-breeding yellow, round peas true-breeding green, wrinkled peas x YYRR yyrr Y = yellow R = round y = green r = wrinkled F1 generation (hybrids) yellow, round peas YyRr Wrinkled seeds in pea plants with two copies of the recessive allele are due to the accumulation of monosaccharides and excess water in seeds because of the lack of a key enzyme. The seeds wrinkle when they dry. Both homozygous dominants and heterozygotes produce enough enzyme to convert all the monosaccharides into starch and form smooth seeds when they dry. self-pollinate F2 generation 9/16 yellow round peas 3/16 green round peas 3/16 yellow wrinkled peas 1/16 green wrinkled peas
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RrYy x RrYy RY Ry rY ry x RY Ry rY ry possible gametes produced
Dihybrid Cross Example:cross between round and yellow heterozygous pea seeds. R = round r = wrinkled Y = yellow y = green RrYy x RrYy RY Ry rY ry x RY Ry rY ry possible gametes produced
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Dihybrid Cross RY Ry rY ry RY Ry rY ry
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YyRr x YyRr YR Yr yR yr YR Yr yR yr YYRR YYRr YyRR YyRr YYRr YYrr
Dihybrid cross YyRr YR yr YyRr Yr yR YR yr or YyRr x YyRr 9/16 yellow round YR Yr yR yr YR Yr yR yr 3/16 green round YYRR YYRr YyRR YyRr BINGO! YYRr YYrr YyRr Yyrr 3/16 yellow wrinkled YyRR YyRr yyRR yyRr 1/16 green wrinkled YyRr Yyrr yyRr yyrr
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RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy
Dihybrid Cross RY Ry rY ry RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy
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Extending Mendelian genetics
Mendel worked with a simple system peas are genetically simple most traits are controlled by single gene each gene has only 2 version 1 completely dominant (A) 1 recessive (a) But its usually not that simple!
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Incomplete Dominance Incomplete dominance is when both alleles are expressed and results in an __________________ ________________. The hybrid is _______________ ________________. When expressing incomplete dominant alleles, _____________________________________________ _____________________________________________.
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RR Rr rr Incomplete dominance Hybrids have “in-between” appearance
RR = red flowers rr = white flowers Rr = pink flowers make 50% less color RR WW RW RR Rr rr
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P 1st 2nd X true-breeding red flowers true-breeding white flowers
Incomplete dominance true-breeding red flowers X P true-breeding white flowers 100% pink flowers 1st generation (hybrids) self-pollinate 25% white 2nd generation 25% red 50% pink
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Incomplete Dominance P (parental) generation
Homozygous Incomplete Dominance P (parental) generation R R W W Homozygous
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Incomplete Dominance F1 (First Filial) generation
W W 100% pink offspring
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Incomplete Dominance F1 x F1
Heterozygous Incomplete Dominance F1 x F1 R W R W Heterozygous
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Incomplete Dominance F2 (Second Filial) generation
W R W
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RR R W RW RR RW R W RW WW RW WW
Incomplete dominance RW x RW % genotype % phenotype RR R W male / sperm RW RR RW R W female / eggs RW WW RW WW
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Co-dominance Some alleles are equally strong and neither are masked by the other. Alleles which are ________________________ are said to be “______________________". The hybrid is ________________________________.
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Co-dominance
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Co-dominance
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