Chapter 10 Vocabulary Gregor Mendel Fertilization Heredity Garden Pea Plants Trait Gametes Genetics Zygote XMEN Pollination
I) Why Mendel Succeeded • Gregor Mendel-Austrian Monk who worked on heredity in mid 19th century • Heredity-def-pg253- the passing on of characteristics from parents to offspring • Trait-def-pg253-characteristics which are inherited • 1st person to succeed in predicting how trails are transferred from 1 generation the next generation • Genetics-def-pg253-branch of biology that studies heredity
I) Why Mendel Succeeded A) Mendel Chose his subjects carefully • When Mendel did his genetics experiments he used the same type of garden pea plant • Mendel selected the garden pea plant for the following reasons; • Reproduces sexually-gametes (both male or female sex cells can be produced • Pea plant allows for self-pollination of plants • Garden pea plants have short growing cycle • Garden pea plants have distinct traits • Garden pea plants structure lends it self experimentation
I) Why Mendel Succeeded B) How garden pea plants reproduce? i) Vocabulary • Gametes-def-pg253-male/female sex cells • Fertilization-def-pg253-when male gametes unite with female gametes • Zygote-def-pg253-the resulting fertilized egg that comes from the process of fertilization • Pollination-def-pg253-transfer of pollen grains from male reproductive organs to female reproductive organs in a plant.
I) Why Mendel Succeeded ii)Steps to sexual reproduction 1) Gametes produced: (a) male gametes form in pollen grains-produced in male reproductive organs (b)female gametes-formed in female reproductive organs • Fertilization of gametes occurs by transfer for pollen grains from a male reproductive organs to a female reproductive organ, this process is called pollination • Zygote then forms and develops into a seed • because pea plants normally self-pollinate only when Mendel wanted to cross (2) different pea plants he would do this by cross-pollination(by hand), this allowed him to ensure the parentage of each plant
I) Why Mendel Succeeded C) Mendel-the Careful researcher • Mendel carefully controlled his experiments & the peas he used • How? • He studied (1) trait at a time • He analyzed his data mathematically • The plants he used had the same trait for multiple generations before being used (i.e. tall plants/short plants) • Purebred-def-offspring of parents with same forms (alleles) of a trait • Hybrid-def-pg255-the offspring of parents that have different forms of a trait.
II)Mendel’s Monohybrid Crosses • Vocabulary • Monohybrid cross-def-when organisms are crossed & only one trait is observed • Dihybrid cross-def-when organisms are crossed & two traits are observed • Genotype-def-the genetic make-up of an organism • Phenotype-def-the way an organism or behaves/ a physical characteristic • Alleles-def-different/alternate gene forms • Dominant-def-the observed/dominant trait of an organism that masks the recessive form of a trait • Recessive-def-trait of an organism that can be masked by dominant form of trait requires (2) alleles to be expressed • Homozygous-def-an organism which has (2) identical/same alleles for trait • Heterozyogous-def-an organism which has (2) different alleles for a trait
II)Mendel’s Monohybrid Crosses B) Mendel’s Monohybrird Experiments i) Parental Generation (P1) • Mendel took Tall Pea Plants x Short Pea Plant (over 6 ft) (less than 2 ft) Cross pollinated plants & observed ii)1st Generation (F1) • Mendel’s Results From: Tall Pea Plants x Short Pea Plant (over 6 ft) (less than 2 ft) • Results- All pea plants were tall
II)Mendel’s Monohybrid Crosses iii) 2nd Generation (F2) • Mendel allowed all tall plants from 1st generation self-pollinate & observed results: Tall Pea Plants x Tall Pea Plant (1st generation) (1st generation) Results-3 tall plants & 1 short plant
II)Mendel’s Monohybrid Crosses iv) Mendel’s other monohybrid crosses • Mendel did similar monohybrid cross experiments with a total of seven different traits (refer to Figure 10.3) • Mendel studied each of these traits one at a time & independent of each other • In even case he found: • F1 generation-1 trait seemed to disappear • F2 generation-the disappearing trait came back in ¼ of the plants
II)Mendel’s Monohybrid Crosses C) The rule of unit factors • 2 factors (alleles) always control each of the pea traits • NOTE-2 or more factors/alleles may control traits in other organisms. • Factors = genes (alternate forms are called alleles) • Each factor can be located on chromosomes • Allele Examples from Mendel’s experiment: (see Figure 10.3)
II)Mendel’s Monohybrid Crosses • The pea plant can have 2 alleles that are could be for seed shape: • Possibility 1- they are both round (homozygous dominant) • Possibility 2-one is round and the other is wrinkled (heterozygous dominant) • This means that an organism’s 2 alleles are located on different copies of the chromosome & each chromosome comes from each parent.
II)Mendel’s Monohybrid Crosses D) The rule of dominance (aka Law of Dominance) • Law of Dominance states whenever the dominant allele is present it will always be expressed. • Mendel observed this in the F1 generation when all the pea plants were tall (that the dominant allele was present & therefore expressed. • Note- whenever this is written as a genotype we use the same letter for the different alleles, but the dominant allele is always the uppercase letter & the recessive allele is always the lower case letter. • Ex/ R = round seed shape (dominant) r = wrinkled seed shape (recessive)
II)Mendel’s Monohybrid Crosses E)Law of Segregation • Law of segregation states that every individual has two alleles of each gene & when gametes are produced, each gamete receives one of these alleles • In other words a trait may have 2 alleles that determine the trait and when they are passed on to the gametes (sex cells) the move independent of each other. • The gametes will then randomly pair to produce 4 combinations of alleles
II)Mendel’s Monohybrid Crosses F) Law of Independent Assortment • Law of independent assortment states that genes for different traits are inherited independent of each other • Ex/ Pea Plant genes for round and wrinkled & yellow and green won’t necessarily be sort together this is why you can have 4 different combinations of alleles versus 2 types of combinations.
III) Punnett Square i) History of Punnett Squares • 1905 Reginald Punnett-English biologist created a shorthand for determining expected proportions of possible genotypes in the offspring of a cross • REMEMBER THAT PUNNETT SQUARES WILL ONLY GIVE YOU A PREDICTION NOT THE ACTUAL RESULTS OF A CROSS. ii) How to use a Punnett Square? • If you know the genotypes of the parents you can determine the possible offspring’s traits • Ex/ Pea Plant-green vs yellow seeds • Parent 1-Homozygous green • Parent 2-Homozygous yellow • Remember Green = Recessive & Yellow = Dominant • G= yellow (dominant) • g=green (recessive)
III) Punnett Square Parent 1-Homozygous Recessive g g G Parent 2-Homozgyous Dominant G
IV) Dihybrid Cross • What happens to Punnett Square when you are looking at 2 traits? • Dihybrid cross-def-when organisms are crossed & two traits are observed • How to do a dihybrid cross in a Punnett Square? • Remember that because of Mendel’s laws of assortment & segregation will be applied in a dihybrid cross: • Fill in Dihbyrid Cross of: Pod Color and Seed Shape • Parent 1: Homozygous Dominant Green Pod & Heterzygous dominant round seed • Genotype:_________________________________ • Phenotype:_________________________________ • Parent 2: Heterozygous Dominant Green Pod & homozygous recessive wrinkled seed • Genotype:_____________________________________ • Phenotype:____________________________________
Dihybrid Cross Parent 1: Possible Allele Combinations Parent 2: Possible Allele Combinations