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 rr Tt SS TT aa Bb Ss Homozygous dominant Homozygous recessive Homozygous dominant 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 GenotypePhenotype YY yellow seeds Yyyellow seeds yygreen 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

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 F1 generation – hybrid offspring of parentals that were allowed to self- pollinate F2 generation – offspring of F1’s

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

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

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 RR

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 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.

Mendel’s 3 principles Principle of Independent Assortment RrYy R = round r = wrinkled Y = yellow y = green RY Ry rY ry Yellow Green Round Round Wrinkled 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’ 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 V v VV Vv Vv vv Vv violet 25% 1:2:1

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 b Bb bb bb Bb 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 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

Dihybrid Crosses BbSs x BbSs

Dihybrid Cross Example: Watermelon color and shape –G- green g- striped –S- short s- long –Cross two Hybrids for Shape and Color: GgSs GS gs gS Gs GS GsgS gs GGSS GGSsGgSSGgSs GGSsGGssGgSsGgss GgSSGgSsggSSggSs GgSs Ggss ggSsggss

Now that the Punnett square is complete, determine the Phenotypic ratio Dihybrid Cross GGSSGGSsGgSSGgSs GGSsGGssGgSsGgss GgSSGgSsggSSggSs GgSsGgssggSsggss _______Green, short _______Green, long _______Striped, short _______Striped, long Therefore, the ratio is: _________________ GS Gs gS gs GS Gs gS gs Green, short Green, long Striped, short Striped, long :3:3:1

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 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’ 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 R W RR RW RW WW RW 1:2:1 Pink 1:2:1 25% 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. 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 O AO BO AO, BO Blood type A or B 50% 0

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

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 sex- chromosomes 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: X C X C or X C Y

Sex-Linked Genes Ex. Colorblindness is carried on the sex- chromosomes It is a recessive trait – X c How many genes do females need to express the trait (colorblindness)? 2 X c X c How many genes do males need to express the trait (colorblindness)? 1 X c Y

Side note….. If a female is X C X c 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 X Y crossed with X X - colorblind Male x Carrier Female X Y X c C c c C c X X X Y C c C ccc 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? XCXcXCXc XcYXcY 50% 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  dominant phenotype, recessive  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 straight hair. Determine the genotypes and phenotypes for the pedigree in the diagram cc straight cc straight cc straight cc straight cc straight Cc curly Cc curly Cc curly ? curly ? curly Cc curly ? curly Cc curly