GENETICS NISHITA AND EVA

WHAT IS GENETICS? Genetics is the study of genes, heredity, and genetic variation in living organisms. It is generally considered a field of biology, but it intersects frequently with many of the life sciences and is strongly linked with the study of information systems.

Gregor Mendel Brought experimental and quantitative approach to genetics Bred pea plants to study inheritance Why peas? Control mating (self- vs. cross- pollination) —Many varieties available Short generation time

Elementary Terms ¢homozygous = 2 same alleles (PP or pp) ¢heterozygous = 2 different alleles (Pp) ¢Phenotype: expressed physical traits ¢Genotype: genetic make-up

MENDELIAN GENETICS The breeding experiments of the monk Gregor Mendel in the mid‐1800s laid the groundwork for the science of genetics. Alleles of a given locus segregate into separate gametes. The Law of Segregation: “The alleles of a given locus segregate into separate gametes”. When two organisms, each homozygous for two opposing traits are crossed, the offspring will be hybrid but will only exhibit only the dominant trait. The trait that remains hidden is known as the recessive trait. The Law of Independent Assortment: It states that the alleles of one gene sort into the gametes independently of the alleles of another gene. 

MENDELIAN GENETICS Inherited traits are encoded in the DNA in segments called genes, which are located at particular sites in the chromosomes (genes are Mendel's “factors.”) Genes occur in pairs called alleles, which occupy the same physical positions on homologous chromosomes; both homologous chromosomes and alleles segregate during meiosis, which results in haploid gametes. The chromosomes and their alleles for each trait segregate independently, so all possible combinations are present in the gametes.

MENDELIAN GENETICS The expression of the trait that results in the physical appearance of an organism is called the phenotype in contrast to the genotype. The alleles do not necessarily express themselves equally; one trait can mask the expression of the other. The masking factor is the dominant trait, the masked the recessive. If both alleles for a trait are the same in an individual, the individual is homozygous for the trait, and can be either homozygous dominant or homozygous recessive. If the alleles are different—that is, one is dominant, the other recessive—the individual is heterozygous for the trait.

Chromosome Theory of Inheritance •Genes have specific locations (loci) on chromosomes •Chromosomes segregate and assort independently

Testcross and Punnett Squares To reveal the genotype of a plant with a dominant phenotype, Mendel developed the idea of a testcross. In a testcross, a plant of unknown genotype is crossed with a homozygous recessive plant.

Non-mendelian genetics •Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations: –When alleles are not completely dominant or recessive –When a gene has more than two alleles –When a gene produces multiple phenotypes

DEGREES OF DOMINANCE Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways A trait controlled by two or more sets of alleles is called polygenic inheritance and can involve alleles on multiple chromosomes.

Drosophila Traits for wings, leg length, and eye color are carried on the same chromosome. These genes are linked together on the same chromosome and will sort into the same gamete.

CALCULATING GENETICS ½ x ½ = ¼ Rule of addition: Chance that an event can occur 2 or more different ways Sum of separate probabilities Ex.) 1/4 Pp +1/4 Pp →1/2 Pp Rule of Multiplication: Probability that two or more independent events will occur together is the product of their individual probabilities. Ex.) Probability of H x H → HH ½ x ½ = ¼

Carbohydrate Allele (a) The three alleles for the ABO blood groups and their carbohydrates (b) Blood group genotypes and phenotypes Genotype Red blood cell appearance Phenotype (blood group) A B AB O IA IB i ii IAIB IAIA or IAi IBIB or IBi

POLYGENIC INHERITANCE an additive effect of two or more genes on a single phenotype Ex.) skin color

GENETIC DISORDERS

SICKLE CELL ANEMIA A mutated form of hemoglobin distorts the red blood cells into a crescent shape at low oxygen levels Most common among those of African descent

CYSTIC FIBROSIS Autosomal recessive Characterized by the buildup of thick, sticky mucus that can damage the body’s organs Symptoms: damage to respiratory system and chronic digestive problems

TAY SACHS Autosomal recessive Harmful quantities of a fatty substance buildup in tissues and nerve cells in the brain Caused by insufficient activity of an enzyme called beta- hexosaminidase A that catalyzes the biodegradation of acidic fatty materials

HUNTINGTON’S DISEASE Degenerative disease of nervous system No phenotypic effects until later in life (35-40 yrs) Irreversible and fatal

KLINEFELTER’S SYNDROME Only in males Occurs when a boy is born with one or more extra X chromosomes Common Symptoms: body hair. enlarged breasts, and wide hips

TRISONOMY 21 Commonly referred to as down syndrome Caused by chromosomal disjunction Common Symptoms: Flattened nose and face, slanting eyes, single fold in the palm of the hand and wide spread first and second toe.

Kahoot https://create.kahoot.it/#user/8db8128e-dbdf-419c-8739-034b938c3197/kahoots/created