Presentation on theme: "1.Why do organisms need haploid cells? 2.What would happen if “crossing over” didn’t occur during Meiosis? 3.What are gametes?"— Presentation transcript:
1.Why do organisms need haploid cells? 2.What would happen if “crossing over” didn’t occur during Meiosis? 3.What are gametes?
Heredity Heredity is the passing on of characteristics from parents to offspring. These characteristics are called traits
Section 10.1 Summary – pages 253-262 It was not until the mid-nineteenth century that Gregor Mendel, an Austrian monk, carried out important studies of heredity. Gregor Mendel
Section 10.1 Summary – pages 253-262 Mendel argued that parents pass on to their offspring factors (now called genes) that are responsible for inherited traits. Mendel was the first person to succeed in predicting how traits are transferred from one generation to the next.
Section 10.1 Summary – pages 253-262 Mendel chose to use the garden pea in his experiments. Garden pea plants reproduce sexually, which means that they produce male and female sex cells, called gametes. Mendel chose his subject carefully
Section 10.1 Summary – pages 253-262 When Mendel wanted to breed, or cross, one plant with another, he opened the petals of a flower and removed the male organs. Remove male parts Mendel wanted to pick his own parent plants
Section 10.1 Summary – pages 253-262 He then dusted the female organ with pollen from the plant he wished to cross it with. Pollen grains
Section 10.1 Summary – pages 253-262 He only wanted to study one trait at a time at first. So he picked two plants that were the same in every way, except height. SHORTTALL
Section 10.1 Summary – pages 253-262 The tall pea plants he worked with were from populations of plants that had been tall for many generations and had always produced tall offspring. They were said to be pure-bred tall- “pure-bred” means that it comes from two parents with the same form of a trait.
Section 10.1 Summary – pages 253-262 Likewise, the short plants he worked with were pure-bred for shortness.
Section 10.1 Summary – pages 253-262 A hybrid is the offspring of parents that have different forms of a trait, such as tall and short height. Parents Hybrid Offspring
Monohybrid crosses Mendel’s first experiments are called mono-hybrid crosses Mono means “one” Hybrid means “parents with different forms of a trait” So we are crossing two parent plants that differ from each other by a one trait— which in this case is height.
Section 10.1 Summary – pages 253-262 He cross-pollinated the tall pea plant with pollen from a short pea plant. All of the offspring grew to be as tall as the taller parent. The First Generation
Section 10.1 Summary – pages 253-262 Mendel allowed the tall plants in this first generation of offspring to pollinate. What happened? The Second Generation P1- Parents F1- first generation of offspring F2- second generation of offspring
Section 10.1 Summary – pages 253-262 Mendel concluded that each organism has two genes that control each of its traits. We now know that these genes are located on chromosomes. Gene
Section 10.1 Summary – pages 253-262 Genes exist in alternative forms. We call these different gene forms alleles. Chromosome # 1 Inherited from mom Gene for Hair Texture Chromosome # 1 Inherited from dad Gene for Hair Texture Mom’s allele codes for Straight hair Dad’s allele codes for Curly hair
Section 10.1 Summary – pages 253-262 An organism’s two alleles are located on their homologous chromosomes—one inherited from the female parent and one from the male parent. B b Bb
Section 10.1 Summary – pages 253-262 Mendel called the over-powering allele “dominant” and the trait that sometimes disappeared “recessive”. Mendel concluded that the allele for tall plants is dominant to the allele for short plants. Rule of Dominance Bb
Section 10.1 Summary – pages 253-262 It is customary to use the same letter for different alleles of the same gene. TT T T tt t t Tall plant Short plant All tall plants F1F1 T for Tall t for Short The letter “T” equals height. Big T is Tall Little T is Short
Section 10.1 Summary – pages 253-262 An uppercase letter is used for the dominant allele and a lowercase letter for the recessive allele. The dominant allele is always written first for each trait. TT T T tt t t All tall plants F1F1 Tall plant Short plant Tt
Section 10.1 Summary – pages 253-262 The law of segregation states: every individual has two alleles of each gene. (one inherited from mom, one inherited from dad) But, when gametes (or sex cells) are produced, each gamete only receives one of these alleles to pass on. The Law of Segregation Bb B b bb bb
Section 10.1 Summary – pages 253-262 Phenotypes and Genotypes The way an organism looks and behaves is called its phenotype. (brown eyes) The allele combination an organism contains is known as its genotype. (Bb) An organism’s genotype can’t always be known by its phenotype. Bb BB
Section 10.1 Summary – pages 253-262 An organism is homozygous for a trait if its two alleles for the trait are the same. The pure-bred tall plant that had two alleles for tallness (TT) would be homozygous for the trait of height. TT
Section 10.1 Summary – pages 253-262 An organism is heterozygous for a trait if its two alleles for the trait differ from each other. Therefore, the tall plant that had one allele for tallness and one allele for shortness (Tt) is heterozygous for the trait of height. Tt
What is the phenotype of the pea plant below? What is the genotype of the pea plant ? tt So therefore, what would you call this trait? Homozygous short
Section 10.1 Summary – pages 253-262 A Punnett square is a quick way to find the possible allele combinations in offspring. Lets say: one parent has a genotype of Tt the other parent also has Tt Punnett Squares Remind me of what the Law of Segregation states. TTTt tt Tt T t
Section 10.1 Summary – pages 253-262 Remember, Mendel performed experiments on pea plants that only differed in one trait: HEIGHT Di-hybrid crosses Mendel then decided to perform another set of crosses in which he used peas that differed from each other only in TWO traits rather than one.
Di-hybrid crosses These experiments were called Di-hybrid crosses: Di means “two” - because there were only two differences Hybrid because the parents were different from each other (in two ways) Cross because he chose the parents to breed with each other The pea plants were the same in every way, EXCEPT PEA SHAPE (round, wrinkled) and PEA COLOR (yellow, green)
Section 10.1 Summary – pages 253-262 Mendel took pure-bred plants with round yellow peas and crossed them with pure-bred plants with wrinkled green seeds. In pea plants: Yellow is Dominant “Y” and Green is Recessive “y” Round is Dominant “R” and Wrinkled is Recessive “r” THE TWO DIFFERENCES RR YYrr yy
Section 10.1 Summary – pages 253-262 What happened with the first generation of offspring? What happened with the second generation of offspring? P1- Parents F1- first generation of offspring F2- 2 nd generation of offspring
Section 10.1 Summary – pages 253-262 The Law of Independent Assortment states: genes for different traits—for example, eye shape and eye color— are inherited independently of each other. The Law of Independent Assortment Bb bb rrRR Bb Rr
Section 10.1 Summary – pages 253-262 A Punnett square for a dihybrid cross will need to be four boxes on each side for a total of 16 boxes. Dihybrid crosses Punnett Square of Dihybrid Cross Gametes from RrYy parent RYRyrYry Gametes from RrYy parent RY Ry rY ry RRYY RRYy RrYYRrYy RRYy RrYy Rryy RrYYRrYyrrYY rrYy RrYy Rryy rrYy rryy