Mendelian Genetics Mendelian Genetics Heredity the passing of

Mendelian Genetics

Mendelian Genetics • Heredity – the passing of traits from parents to offspring • Genetics: The scientific study of heredity

Mendelian Genetics • Chromosomes- rod-shaped structures in the nucleus that transmits genetic information • Genes- units of hereditary information found on the chromosomes

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) dominant

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

Important Vocabulary Identify each of the pairs below as homozygous dominant, homozygous recessive, or heterozygous. Yy Heterozygous rr Homozygous recessive Tt Heterozygous SS Homozygous dominant TT Homozygous dominant aa Homozygous recessive Bb Heterozygous Ss Heterozygous

Important Vocabulary • Allele- each form of a gene for a certain trait. Ex. B = dominant allele (brown eyes) b = recessive allele (blue eyes)

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

Important Vocabulary • Examples of genotype and phenotype

Important Vocabulary • Examples of genotype of phenotype

Figure 14. 5 Genotype versus phenotype

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

1856 -1865 Gregor Mendel -Austrian Monk – 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

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 • F 1 generation – hybrid offspring of parentals that were allowed to selfpollinate • F 2 generation – offspring of F 1’s

*Flower color : purple (P) vs. white (p) PP x pp All Pp PP, Pp & pp

Figure 11 -3 Mendel’s Seven F 1 Crosses on Pea Plants Section 11 -1 Go to Section: Seed Shape Seed Color Round Yellow Seed Coat Color Gray Pod Shape Pod Color Flower Position Smooth Green Axial Tall Short Wrinkled Green White Constricted Yellow Terminal Round Yellow Gray Smooth Green Axial Plant Height Tall

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. P Parental Round RR Wrinkled rr RR F 1 First Filial All Round Rr F 2 Second Filial

Mendel’s 3 principles • Principle of Segregation- the members of each pair of genes separate, or segregate, when gametes are formed.

Mendel’s 3 Principles Principle of Independent Assortmenttwo 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.

Mendel’s 3 principles • Principle of Independent Assortment Rr. Yy RY Yellow Round Ry Green Round R = round r = wrinkled Y = yellow y = green r. Y ry Yellow Green Wrinkled

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)

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

Punnett Square Practice Violet flowers are dominant to white flowers. Diagram a Punnett Square for 2 heterozygous flowers. What is the parents’ V v VV Vv V v Vv vv genotype(s)? Vv What is the parents’ phenotypes(s)? violet What is the genotypic ratio for the offspring? 1: 2: 1 What is the probability of producing a white flower? (In percent) 25%

Punnett Square Practice Black rabbits are dominant over brown rabbits. A heterozygous male is crossed with a brown female. What is the mother’s flowers. genotype? bb B b Bb bb b b Bb bb What is the father’s genotype? Bb Diagram a Punnett Square for this cross. What is the genotypic ratio? 1: 1 What is the phenotypic ratio? 1: 1

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 F 1 Hybrids for Hair Color and Length: Bb. Ss FOIL – First, Outer, Inner, Last Possible gametes passed on to offspring: BS, Bs, b. S, and bs –place in punnett square

Dihybrid Crosses Bb. Ss x Bb. Ss

Dihybrid Cross • Example: Watermelon color and shape – G- green g- striped – S- short s- long – Cross two Hybrids for Shape and Color: Gg. Ss GS GS GGSS Gs g. S GGSs Gg. SS gs Gg. Ss Gs GGSs GGss Gg. Ss Ggss g. S Gg. Ss gg. SS gg. Ss gs Gg. Ss Ggss gg. Ss ggss

Dihybrid Cross • Now that the Punnett square is complete, determine the Phenotypic ratio 9 _______Green, short GS Gs g. S gs 3 _______Green, long GGSS GGSs Gg. SS Gg. Ss Green, short 3 _______Striped, short GS 1 _______Striped, long GGSs GGss Gg. Ss Ggss Gs Green, short Green, long Therefore, the ratio is: 9: 3: 3: 1 g. S Gg. Ss gg. SS gg. Ss Green, short Striped, short_________ gs Gg. Ss Green, short Ggss gg. Ss ggss Green, long Striped, short Striped, long

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

Codominance • Codominance Both alleles are expressed in the phenotype Ex. Cow Hair Color RR – Red WW – White RW – Roan (Red & White)

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’ R W RR RW R W RW WW genotype? RW 2. What is the parents’ phenotype? Pink 3. What is the genotypic ratio for this cross? 1: 2: 1 4. What is the phenotypic ratio for this cross? 1: 2: 1 5. What is the probability of producing a red flower? 25% 6. What is the probability of producing a pink flower? 50%

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

Blood types • Diagram a cross for a man with blood type AB and a woman with blood type O. A B AO BO O O AO BO What is the children’s genotype(s)? AO, BO What is the children’s phenotypes(s)? Blood type A or B What is probability of producing a child with blood type O? (in percent) 0 What is the probability of producing a child with blood type B? (In percent) 50%

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? 23 (46 total) • What is the difference between male and female chromosomes? Pair # 23 XX Female – and Male – XY

Karyotype – Picture of Chromosomes #1 -22 are Autosomal #23 is a Sex Chromosomes Is this karyotype for a male or female?

Sex-Linked Genes • Ex. Colorblindness is carried on the sexchromosomes • It is a recessive trait

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

Sex-Linked Genes • Ex. Colorblindness is carried on the sexchromosomes • 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 Xc. Y

Side note…. . • If a female is XCXc then she is called a carrier. She carries the recessive allele, but does not express it.

Sex-Linked Punnett Square • C – Normal Vision and c - Colorblind C c c • X Y crossed with X X - colorblind Male x Carrier Female c X Y X Xc 2. What is the male’s genotype? Xc. Y 1. What is the female’s genotype? C C X C c X X C X Y 3. What is the probability of producing a colorblind child? X c c X Y 50% 4. What is the probability of producing a colorblind female? 50% 5. What is the phenotypic ratio for this cross? 1: 1: 1: 1

Pedigrees Pedigree- Diagram showing the inheritance of a trait in a family *Colored boxes and circles show the trait

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 (dominant phenotype, recessive phenotype)

Pedigree Symbols

• affected individuals have at least one affected parent • the phenotype generally appears every generation • two unaffected parents only have unaffected offspring

• unaffected parents can have affected offspring • affected progeny are both male and female

Sex-linked Recessive

Pedigrees • Curly hair is dominant and straight hair is recessive. The colored figures in the pedigree show which individuals have Cc straight hair. curly Determine the genotypes and phenotypes for the pedigree in the diagram cc cc straight Cc curly ? cc cc curly straight ? cc Cc ? Cc straight curly