Mendels Laws of Genetics How traits are passed from parents to offspring.
Genetics A gene is a segment of DNA that codes for a protein which determines one particular trait Genetics is the study of how genes are passed on from parents to offspring
Differentiation Genes signal different cells to create proteins that give them unique shapes & functions These cells grow & divide to make tissues that form the organs of the developing baby
Fertilization: new life is formed Life begins when two gametes (sperm + egg) join A complete set of chromosomes results (23 + 23) The zygote starts as a single cell, but soon begins to divide (via mitosis = identical cells) Genes are "turned" on and off, causing cells to differentiate (change to have different forms/jobs)
Heredity & Inherited Traits The chromosomes from your mom and dad have given your cells instructions to make YOU! Each characteristic you inherited from your parents is called a trait (eye color, earlobe shape, height, personality traits, etc.) For each trait, you have a pair of alleles (onefrom your mother andone from your father)
Alleles: variations of a gene Gene AllelesEye Color Blue, brown, green, hazelPea height Tall, shortPea color Yellow, greenFlower position Axial, terminal
Gregor Mendel An Austrian scientist-turned-monk noticed patterns in the monasterys garden Studied the inherited traits of pea plants and found predictable, numerical ratios in the offspring Observed some traits were dominant over others (i.e. yellow peas overpowered or occurred1822-1884 more often than green pea seeds)
Mendels Experiments He wondered if traits seen in different generations of pea plants were • determined by environmental factors (soil composition, temperature, sunlight) OR • "handed down" by parents (chromosomes werent even discovered yet, so he had no idea how) In his highly controlled experiments, he tested the hypothesis that each trait was determined by a set (not one, but TWO) inherited factors from each parent Do you see the Scientific Method at work here?
Dominant and Recessive Traits
Mendel’s Crosses Observed phenotype, the outward expression of the genes the F1 generation are tall, showing that trait is dominant The dwarf plant has the recessive trait (it is overpowered by the tall allele)
Genotypes: Genes and Alleles The genetic make-up of an organism is its genotype Every organism is diploid (has 2 copies of each chromosome) Each trait is designated by a different letter DOMINANT ALLELES ARE CAPITAL LETTERS recessive alleles are lowercase letters
Genotype determines Phenotype Homozygous means the two alleles are the same Heterozygous means the two alleles are different Genotype Genotype Phenotype Homozygous TT Dominant dominant Homozygous tt Recessive recessive Heterozygous Tt Dominant
Punnet Square: Monohybrid Cross Used to predict the outcome of a genetic cross
Dihybrid Cross What happens to two genes on different chromosomes? Homologous pairs of meiotic chromosomes line up randomly at the equatorial plane in Metaphase I The two traits separate during meiosis, resulting in offspring with different combinations of traits This results in four different possible combinations of chromosomes and genes in the gametes
The Law of Segregation Diploid chromosomes of parents undergo meiosis Alleles separate as they become haploid egg or sperm They are combined again during fertilization to produce a diploid offspring