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Mendelian Genetics
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Mendelian Genetics Heredity – the passing of traits from parents to offspring Genetics: The scientific study of heredity
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Mendelian Genetics Chromosomes- rod-shaped structures in the nucleus that transmits genetic information Genes- units of hereditary information found on the chromosomes
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Important Vocabulary dominant- a gene that masks the expression of another gene in a pair (Symbol- capital letter) recessive- a gene in a pair that is hidden by the dominant gene (Symbol- lower case letter) Parent 1 R = red dominant Parent 2 r = yellow recessive Offspring Red (Rr)
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Important Vocabulary Homozygous- two genes in a pair that are identical. Ex. Homozygous dominant- RR GG Homozygous recessive- rr gg Heterozygous- individual with one dominant and one recessive gene in a pair. Ex. Rr or Gg
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Important Vocabulary Identify each of the pairs below as homozygous dominant, homozygous recessive, or heterozygous. Yy rr Tt SS TT aa Bb Ss Heterozygous Homozygous recessive Heterozygous Homozygous dominant Homozygous recessive Homozygous dominant Heterozygous Heterozygous
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Important Vocabulary Allele- each form of a gene for a certain trait . Ex. B = dominant allele (brown eyes) b = recessive allele (blue eyes)
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Important Vocabulary Genotype- the pair of alleles represented by the capital and lower case letters. Phenotype- the trait that is actually expressed in an organism Examples Genotype Phenotype YY yellow seeds Yy yellow seeds yy green seeds
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Important Vocabulary Examples of genotype and phenotype
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Important Vocabulary Examples of genotype of phenotype
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Figure 14.5 Genotype versus phenotype
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Inheritance You get your genes from your parents
In meiosis, half of the chromosomes in a pair come from the Dad, half come from the Mom What we know today is based on the work of Gregor Mendel
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1856-1865 Gregor Mendel -Austrian Monk Paper was published in 1866,
– pea plants in monastery garden – COUNTED the plants and compiled data (QUANTITATIVE APPROACH to science) Paper was published in 1866, but not enough was understood to truly value this work. Today known as father of modern genetics
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Mendel chose to use plants that were true-breeding…
P generation – parentals; true-breeding (On their own create identical offsprings) parents that were cross-pollinated F1 generation – hybrid offspring of parentals that were allowed to self-pollinate F2 generation – offspring of F1’s
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*Flower color : purple (P) vs. white (p)
PP x pp All Pp PP, Pp & pp
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Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants
Section 11-1 Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall Go to Section:
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Mendel’s 3 principles Principle of Dominance- one factor (gene) in a pair may prevent the other factor (gene) in a pair from being expressed. Round RR All Round Rr F1 First Filial F2 Second Filial P Parental Wrinkled rr
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Mendel’s 3 principles Principle of Segregation- the members of each pair of genes separate, or segregate, when gametes are formed.
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Mendel’s 3 Principles Principle of Independent Assortment- two or more pairs of genes segregate independently of one another during the formation of gametes In other words….. Just because a seed is round does not mean that it has to be yellow.
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Mendel’s 3 principles Principle of Independent Assortment RrYy
R = round r = wrinkled Y = yellow y = green RY Ry rY ry Yellow Green Yellow Green Round Round Wrinkled Wrinkled
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Punnett Square Device for predicting the results of a genetic cross between individuals of a known phenotype. Example Character – flower color Alleles – Purple (P) and white (p) Note: Purple is dominant with a capital letter and white is recessive shown with a lowercase of dominant trait Genotypic combos possible – two dominants: PP (homozygous dominant) two recessives: pp (homozygous recessive) One of each: Pp (heterozygous)
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Monohybrid crosses – only one character considered
Steps to do: Write out genotypes of parents Write out possible gametes produced Draw 4 box Punnett square Put one parent on the left side and one parent across the top Fill in boxes Determine genotypes by reading Punnett starting from top left Determine phenotypes by reading from genotype list
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Punnett Square Practice
Violet flowers are dominant to white flowers. Diagram a Punnett Square for 2 heterozygous flowers. What is the parents’ genotype(s)? What is the parents’ phenotypes(s)? What is the genotypic ratio for the offspring? What is the probability of producing a white flower? (In percent) V v Vv violet VV Vv V v 1:2:1 Vv vv 25%
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Punnett Square Practice
Black rabbits are dominant over brown rabbits. A heterozygous male is crossed with a brown female. flowers. What is the mother’s genotype? What is the father’s genotype? Diagram a Punnett Square for this cross. What is the genotypic ratio? What is the phenotypic ratio? B b bb Bb Bb bb b 1:1 Bb bb 1:1
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Dihybrid (Two-Factor)Cross
Because genes separate independently we can determine the possible outcomes of a two-factor cross. Example: Guinea pig hair color and length B- black b- brown S- short s- long F1 Hybrids for Hair Color and Length: BbSs FOIL – First, Outer, Inner, Last Possible gametes passed on to offspring: BS, Bs, bS, and bs –place in punnett square
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Dihybrid Crosses BbSs x BbSs
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Dihybrid Cross Example: Watermelon color and shape Gs gS GS gs GS GGSS
G- green g- striped S- short s- long Cross two Hybrids for Shape and Color: GgSs Gs gS GS gs GS GGSS GGSs GgSS GgSs Gs GGSs GGss GgSs Ggss gS GgSS GgSs ggSS ggSs GgSs ggSs ggss gs Ggss
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Dihybrid Cross Now that the Punnett square is complete, determine the Phenotypic ratio 9 GS Gs gS gs _______Green, short _______Green, long _______Striped, short _______Striped, long Therefore, the ratio is: _________________ 3 GGSS GGSs GgSS GgSs GGss Ggss ggSS ggSs ggss Green, short Green, short Green, short Green, short 3 GS Gs gS gs 1 Green, short Green, long Green, short Green, long 9:3:3:1 Green, short Green, short Striped, short Striped, short Green, short Green, long Striped, short Striped, long
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Beyond Dominant and Recessive
Incomplete Dominance One allele is not completely dominant over the other – something in the middle is expressed Ex. Red and White Snapdragons – Make Pink (Like mixing paints) p. 272 in your book Red – RR White – WW Pink – RW Only one phenotype for each one genotype
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Codominance Codominance Both alleles are expressed in the phenotype
Ex. Cow Hair Color RR – Red WW – White RW – Roan (Red & White)
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R W RR RW R W RW WW Incomplete Dominance
Example: Flower color is an incomplete dominant trait. One red gene and one white gene produces a pink flower. Cross two pink flowers. 1. What is the parents’ genotype? 2.What is the parents’ phenotype? 3. What is the genotypic ratio for this cross? 4. What is the phenotypic ratio for this cross? 5. What is the probability of producing a red flower? 6. What is the probability of producing a pink flower? R W RW Pink RR RW R W 1:2:1 1:2:1 RW WW 25% 50%
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Beyond Dominant and Recessive
Multiple Alleles Genes have more then two alleles Ex. Blood Type Color Coats in Rabbits A and B are also codominant
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A B AO BO O AO BO Blood types
Diagram a cross for a man with blood type AB and a woman with blood type O. What is the children’s genotype(s)? What is the children’s phenotypes(s)? What is probability of producing a child with blood type O? (in percent) What is the probability of producing a child with blood type B? (In percent) A B AO, BO Blood type A or B AO BO O AO BO 50%
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Sex-linked traits Sex-linked traits- traits that are controlled by genes found on the sex chromosomes. The X chromosome contains the gene and the Y chromosome does not. How many pairs of chromosomes do humans have? What is the difference between male and female chromosomes? Female – and Male – 23 (46 total) Pair # 23 XX XY
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Karyotype – Picture of Chromosomes
#1-22 are Autosomal #23 is a Sex Chromosomes Is this karyotype for a male or female?
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Sex-Linked Genes Ex. Colorblindness is carried on the sex-chromosomes
It is a recessive trait
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What about genes located on the sex chromosomes?
Very few genes are located on the Y chromosome……Most are located on the X So females carry two genes and males only carry one. Draw a punnett square with the sex chromosomes……XX x XY Link the gene to the X only. EX: XCXC or XCY
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Sex-Linked Genes Ex. Colorblindness is carried on the sex-chromosomes
It is a recessive trait – Xc How many genes do females need to express the trait (colorblindness)? 2 Xc Xc How many genes do males need to express the trait (colorblindness)? 1 XcY
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Side note….. If a female is XCXc then she is called a carrier. She carries the recessive allele, but does not express it.
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Sex-Linked Punnett Square
C – Normal Vision and c - Colorblind X Y crossed with X X - colorblind Male x Carrier Female X Y X C c c c 1. What is the female’s genotype? 2. What is the male’s genotype? 3. What is the probability of producing a colorblind child? 4. What is the probability of producing a colorblind female? 5. What is the phenotypic ratio for this cross? XCXc X X X Y XcY C C C c 50% c c c c 50% 1:1:1:1
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Pedigrees Pedigree- Diagram showing the inheritance of a trait in a family *Colored boxes and circles show the trait
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Pedigrees Family history that shows how a trait is inherited over several generations. Carriers: those heterozygous for a trait. Can determine if autosomal (occurs equally both sexes) sex-linked (usually seen in males) heterozygous (dominant phenotype) homozygous (dominantdominant phenotype, recessive recessive phenotype)
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Pedigree Symbols
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affected individuals have at least one affected parent
the phenotype generally appears every generation two unaffected parents only have unaffected offspring
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unaffected parents can have affected offspring
affected progeny are both male and female
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Sex-linked Recessive
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Pedigrees Curly hair is dominant and straight hair is recessive. The colored figures in the pedigree show which individuals have straight hair. Determine the genotypes and phenotypes for the pedigree in the diagram cc straight Cc curly ? curly cc straight cc straight Cc curly Cc curly cc straight ? curly cc straight Cc curly ? curly Cc curly
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