Mendelian Genetics

Gregor Mendel ~ 1822-1884 Father of modern genetics Gregor Mendel ~ 1822-1884 Father of modern genetics. Mendel was an Austrian monk and mathematician. One of his assignments in the monastery was to tend the garden. Pea Plants Traits- a distinct variant of a phenotypic character of an organism that may be inherited (eye color) Self-pollination- purebred Cross-pollination- hybrid

Genes and Dominance Gene- a DNA code sequence Allele- different forms of a gene Dominant- always expressed if present Recessive- always masked if dominant is present Phenotype- observable physical characteristics Genotype- actual genetic makeup Homozygous- same Heterozygous- different

Haploid daughter cells Segregation The separation of alleles on different chromosomes during meiosis. Each allele ends up in a different egg or sperm cell. Diploid mother cell Haploid daughter cells

Fertilization Fertilization- the union of an ovum and a sperm cell. Zygote- the first new diploid cell of an individual made by fertilization.

Mendel’s Laws of Heredity Law of Segregation (1st Law) - Alleles for the same gene are separated during meiosis when the chromosomes separate. Law of Independent Assortment (2nd Law) - Genes on different, nonhomologous chromosomes assort independently during meiosis. (They are “shuffled” like cards.) Assortment occurs during meiosis. Principle of Dominance - Some traits are dominant, and some are recessive. Dominant traits will always be expressed when they are present.

Punnett Square ~ A device that is used to predict the Punnett Square ~ A device that is used to predict the possible gene combinations for a trait that two parents can pass to their offspring. Monohybrid cross ~ A cross of two parents to evaluate what happens with one set of alleles. In other words, seeing how one gene will be passed to offspring.

Tall vs. Short Pea Plants Phenotypic Ratios: Show the ratio of the different possible phenotypes of offspring. Genotypic Ratios: Show the ratio of the different possible genotypes of offspring. Probabilities: Show the percentages of chance for each type of phenotype or genotype Purebred Parents: TT x TT P1 Cross TT x tt F1 Cross Tt x Tt

Monohybrid Cross Practice

Actual vs. Hypothetical A couple has a 50% chance of having a girl every time they have a baby. They have four children, and all are girls. What is the hypothetical number of girls and boys? What is the actual number of girls and boys?

Mendel’s Law of Independent Assortment tells us that all possible gene combinations of the traits being considered can be found among the progeny (offspring) This is displayed in dihybrid crosses in that all possible combinations of genes are produced.

Today we know Mendel’s 2nd Law holds true only if two conditions are met: the genes are on separate chromosomes OR 2. the genes are widely separated on the same chromosome

Linked Genes- genes for different traits are close together on the same chromosome, so they are passed on to offspring together.

With Mendel, Not with Mendel gene for one trait exists as 2 alleles 3 possible genotypes & 2 possible phenotypes Consider Yellow vs. green Genotypes? YY, Yy, yy Phenotypes? Yellow, green gene for one trait exists as 2 alleles 3 possible genotypes & 3 possible phenotypes Consider Black and White fur Genotypes? BB, BW, WW Phenotypes? Black, grey, white Black, black and white, white

Incomplete Dominance- describes genes that are neither dominant or recessive. The traits show as a “mixed” phenotype. Ex. Red + White = Pink r ~ red allele y ~ yellow allele w ~ white allele rr ~ red flower yy ~ yellow flower ww ~ white flower ry ~ orange flower rw ~ pink flower

Incomplete Dominance Determine the offspring produced when a rabbit with black fur is crossed with a rabbit with white fur. bb = black fur ww = white fur

Incomplete Dominance and Human Health Brachydactyly ~ Condition in which the patient is missing a bone in each finger or toe. Some people are missing genes for having fingers and toes! Having one normal gene and one no-toe gene results in a condition in which a bone is missing. Genotype nn bb nb Phenotype normal fingers and toes no fingers or toes Short fingers and toes missing a bone

Sickle-Cell Anemia ~ Incomplete dominance condition in which patient has two genes for abnormal hemoglobin, the pigment in red blood cells. This causes the RBC to collapse into a banana shape during stress or exercise. The RBCs “clog up” the blood vessels. Sickle-Cell Trait ~ Condition in which a person has one gene for normal hemoglobin and one gene for sickle-cell anemia. Cells are normal except during heavy exercise. Tionne Watkins (T-Boz) of TLC has sickle-cell anemia.

Co-dominance Co-dominance- traits that have more than one dominant allele. Both colors are displayed. Ex. Red + White = Red and White Spotted RR = Red WW = White RW = Red and White Spotted

Co-dominance Determine the genotypes and phenotypes of the offspring produced when a homozygous black chicken is crossed with a homozygous white chicken. BB = Black WW = White BW = Black and White Speckled

Co-dominance Cattle can be red, white, or roan. Determine the offspring produced when a roan bull is crossed with a homozygous white cow.

Multiple Alleles if there are 4 or more possible phenotypes for a particular trait, then more than 2 alleles for the trait must exist there are more than two possible genes that can be inherited for a trait individuals, however, will still only inherit 2 alleles (1 from mom, 1 from dad) Examples Blood type- (Co-dominance is exhibited here as well!)

Blood type is determined by proteins on the surface of your red blood cells. Type A Dominant Type B Type AB Co-Dominant Type O Recessive

Identify: Mendel’s Laws Tt T t

Identify: Mendel’s Laws

Identify: Mendel’s Laws T masks t

Incomplete Dominance or Codominance?

Incomplete Dominance or Codominance?