Transcript heredity
Bell Work: 2/11/14 Create the chart below and fill out as part of the Mitosis vs. Meiosis notes (2nd page) for BW. Write “Compare & Contrast” on your BW sheet. Mitosis Meiosis Mitosis Meiosis •Both are processes of cell division •Both reproduce new cells •Both go through Interphase, Prophase, Metaphase, Anaphase, Telophase, & Cytokinesis •Asexual cell reproduction (only one parent cell is needed) •Produces an exact copy of itself with 46 chromosomes •Reproduces two new cells •Somatic cells: body cells (skin cells, blood cells, bone cells, muscle cells) •Sexual cell reproduction (two parent cells are needed) •Produces cells with half as many chromosomes (23) •Reproduces four new cells •Sex cells (sperm & egg) Objectives • Describe the relationship among genes, chromosomes, and inherited traits. (SPI 0707.4.3) • Interpret a Punnett square to predict possible genetic combinations passed from parents to offspring during sexual reproduction. (SPI0707.4.4) Heredity • Why don’t you look like a rhinoceros? • The answer to this question seems simple: Neither of your parents is a rhinoceros. • But there is more to this answer than meets the eye. • As it turns out, heredity, or the passing of traits from parents to offspring, is more complicated than you might think. • For example, you may have curly hair, while both of your parents have straight hair. You might have blue eyes while both of your parents have brown eyes. • How does this happen? Who was Gregor Mendel? • Read pg. 100 – “Who Was Gregor Mendel? – “Unraveling the Mystery” • Gregor Mendel discovered the principles of heredity while studying the characteristics and traits of pea plants. • A characteristic is a feature that has different forms in a population. – For example, hair color is a characteristic of humans. • The different forms, such as brown or red hair is called a trait. With your elbow partner, name two characteristics in our class and two different traits of those characteristics. Mendel’s First Experiments • One trait was always present in the first generation, and the other trait seemed to disappear. • Mendel chose to call the trait that appeared the dominant trait. • Because the other trait seemed to fade into the background, Mendel called it the recessive trait. • The recessive trait for the white flower reappeared in the second generation. Review: Talk with your group… 1. What is heredity? • The passing of genetic traits from parent to offspring 2. Who was Gregor Mendel? • Discovered the principles, or ideas, of heredity 3. Which trait is present in the first generation? • Dominant trait 4. Which trait is present in the second generation? • Recessive trait Challenge Question So how is it that both of my parents are short, but I am tall? The Family Connections • You and your partner will help each other determine the variation of each characteristic (trait) that each of you possess. Record your traits in the chart labeled “My Characteristics” on the back of the sheet. Traits and Inheritance • Mendel knew from his experiment with pea plants that there must be two sets of instructions for each characteristic. • These instructions for an inherited trait are called genes. • Each parent gives one set of genes to the offspring. • The offspring then has two forms of the same gene for every characteristic- one from each parent. • The two forms (often dominant and recessive) of a gene are known as alleles. • Dominant alleles are shown with a capital letter (P for dominant purple flowers). • Recessive alleles are shown with a lowercase letter (p for recessive white flowers). Just a side note… Bell Work: 2/12/14 Review Question: • What is the difference between a gene and an allele? Challenge Question: • Mendel calculated that ratio of dominant traits to recessive traits. He found a ratio of 3:1. What did this tell him about how traits are passed from parents to offspring? Objectives • Describe the relationship among genes, chromosomes, and inherited traits. (SPI 0707.4.3) • Interpret a Punnett square to predict possible genetic combinations passed from parents to offspring during sexual reproduction. (SPI0707.4.4) Phenotype & Genotype • Genes affect the traits of an offspring. • An organism’s appearance (the way they look) is known as its phenotype. • In pea plants, possible phenotypes for the characteristic of flower color would be purple flowers or white flowers. • The genotype of an organism is the entire genetic makeup of an organism; the combination of genes for a specific trait. – An organism with two dominant or two recessive alleles is homozygous (same size letters- PP or pp). – An organism with one of each (Pp) is heterozygous. Inherited Disorders • Albinism is an inherited disorder that affects a person’s phenotype in many ways. • The boy in the picture has inherited a condition called albinism. • Albinism prevents hair, skin, and eyes from having normal coloring because that person’s gene for producing melanin is mutated. Punnett Square • A Punnett square is used to organize all possible combinations of offspring from particular parents. • Genotype PP is a purebred. • What is the genotype for the offspring to the right? • The dominant allele P ensures that the offspring will have purple flowers. • The recessive allele p may get passed to the next generation. • Why? Quick Lab pg. 107 R= round seeds r= wrinkled seeds • Work with your group to complete the Punnett square. • What would be the phenotypes for these offspring? – RR= round seeds – Rr= round seeds – rr= wrinkled seeds R r R r RR Rr (genotype- two dominant alleles) (genotype- one dominant allele,one recessive allele) Rr rr (genotype- one dominant allele,one recessive allele) (genotype- two recessive alleles) Probability • The mathematical chance that something will happen is known as probability. • Genotype probability: – Pp x Pp cross has a 50% chance of receiving either allele from either parent. – The probability of inheriting two p alleles is ½x½, which equals ¼, or 25%. Monohybrid vs. Dihybrid Punnett Square • A monohybrid Punnett • A dihybrid Punnett square is one where only square is one where two one trait is crossed. traits are crossed. – Example: A tall pea • Example: a tall, green plant TT is crosses with flowered plant TtGg is a short pea plant tt. crossed with a short, yellow flowered plant ttgg. T t t Tt Tt T Tt Tt TG Tg tG tg tg TtGg Ttgg ttGg Ttgg tg TtGg Ttgg ttGg Ttgg tg TtGg Ttgg ttGg Ttgg tg TtGg Ttgg ttGg Ttgg R= round seeds r= wrinkled seeds Rr x rr R= round seeds r= wrinkled seeds Y= yellow seeds y= green seeds RrYy x rryy SpongeBob Genetics • Scientists at Bikini Bottoms have been investigating the genetic makeup of the organisms in this community. • Use the information provided and your knowledge of genetics to complete the SpongeBob Genetics packet. Exit Ticket Create your own monohybrid Punnett Square cross. Use the examples in your notes for ideas.