Presentation on theme: "Do Now: Using the following words, explain how you inherit different characteristics: Chromosomes Meiosis Fertilization."— Presentation transcript:
Do Now: Using the following words, explain how you inherit different characteristics: Chromosomes Meiosis Fertilization
Each chromosome in a homologous pair contains one “factor” or gene for a particular characteristic. During meiosis when the chromosomes separate, each newly formed sex cell contains just one gene for each trait. When fertilization occurs, the offspring receives one gene for each trait from each parent for a total of two genes per characteristic.
For Example: # 4 from Mom # 4 from Dad Both have hair color information
Genetics The study of the ways in which hereditary material is passed on from parents to offspring.
Before scientists knew about chromosomes and genes… Gregor Mendel studied hereditary by carrying out experiments with pea plants. He used probability to analyze experiments. He is known as the “father of genetics”
Why Pea Plants? Easy to grow Mature quickly (short life span) Traits are sharply contrasted and easy to observe (Ex: tall vs. short, green vs. yellow) Easy to control pollination and reproduction
How do plants make offspring? What is “natural pollination”? –Pollination Pollen grains produced on anther are transferred to the stigma (top of the female reproductive system) Self pollination: –Pollen from a plant pollinates a stigma on the same plant (same flower or different flower) Cross pollination –Pollen from a plant pollinates a stigma on a totally different plant.
Mendel’s method Manual pollination (Selective breeding) –Occurs when anthers are removed from the flowers of a plant (contain the pollen grains at the top). Then you choose which flowers to pollinate.
Mendel’s Experiments Looked at seven characteristics –Characteristics are an inheritable factor, such as color, size, seed texture, etc. Each characteristic occurred in only two contrasting traits –A trait is a genetically determined variant of a characteristic
Characteristics studied Height tall or short Flower position axial or terminal Pod color green or yellow Pod appearance inflated or constricted Seed texture smooth or wrinkled Seed color yellow or green Flower color purple or white
CHARACTERS (characteristics) AND VARIANTS (traits)
Mendel studied 7 traits Each experiment started with a “pure bred” plant. Mendel allowed plants to self-pollinate for several generations to be certain that the offspring were pure for the trait he was studying.
Next experimental steps: Mendel pollinated plants that were pure for one trait with plants that were pure for the contrasting trait (MONOhybrid cross). Pure plants made up the parent or P generation. Mendel carefully recorded the PHENOTYPE of the offspring. –What does phenotype mean? He studied three generations P, F1, F2
P generation: “parents;” First generation in the cross F generations: results of the cross; - F1 – 1 st generation; offspring of P generation - F2 – 2 nd generation; offspring of F1 generation
Examples of True Breeding: You will receive 2 chromosomes (homologous pairs) for a pure plant. We will only look at the height characteristic (Tall is dominant to short). You will breed your plant with a partner that has a plant that is pure for the contrasting plant. –One pure Tall plant with one pure Short plant Remember each new plant can only inherit ONE chromosome from each parent.
What are the possible chromosome combinations for the F1 generation? What are the possible phenotypes of the F1 generation? Write them down! Write a sentence explaining why this happens.
What would happen if you took two plants from the F1 generation and cross them? TRY IT! What are the possible chromosome combinations for the F2 generation? What would the phenotypes of the offspring be? Write a sentence explaining the outcome and explain how it is different from a true breeding cross.
Offspring: F1 generation (See picture!) Hybrids –Have gene for both traits but only show one trait
Example: - Purple was crossed with white and we got ALL purple.
Mendel crossed (pollinated) two F1 hybrid plants to get F2 generation: Three-fourths of the offspring show one trait, and one-fourth show the “hidden” trait that did not appear in the F1 generation.
Dominant traits: Traits that were expressed in the F1 generation
Recessive Traits: “hidden” traits that did not show up until the F2 generation
Law of Dominance When an organism is hybrid for a pair of contrasting traits, only the dominant trait can be seen in the hybrid. –While this was true for Mendel’s data with the pea plants, this is only true for SOME traits!
Law of segregation “Factors” that occur in pairs are separated from each other during gamete formation (homologous chromosomes are separated during meiosis) and recombined at fertilization. –only one trait for each characteristic is passed from a parent to the offspring.
Law of Independent Assortment: “factors” for one characteristic does not affect the inheritance of other characteristics. –This actually only applies to SOME characteristics In meiosis, chromosomes separate independently from one another.
We call these “factors” Genes! Genes – control a characteristic that can be inherited Example of characteristic: Hair color, seed shape, height; Allele – controls the variation of a feature (characteristic) – AKA trait. Example of trait: brown, blonde, black hair
More Vocab! Alleles: different copies of forms of a gene controlling a certain characteristic Homozygous: when alleles for a certain trait in an organisms are the same (pure) Heterozygous: when alleles for a certain gene are different (hybrid) Phenotype: physical trait of an organism Genotype: genetic makeup of an organism
CHARACTERS (characteristics) AND VARIANTS (traits)
Genotype: the alleles that an organism has. - alleles are abbreviated using the first letter of the dominant trait. (with some exceptions that we will get to) - a capital letter represents the dominant ex: P for purple flower allele - a lower case represents the recessive. ex: p for white flower allele What would be the genotype for a purple flower that is heterozygous? Homozygous?
Monohybrid cross: cross that focuses on the alleles of a single characteristic; How do we show the possibilities? - punnett square
PUNNETT SQUARE Allele in Egg 1 Zygote formed if sperm 1 fertilizes egg 1 Allele in Egg 2 Allele in sperm 1 Allele in sperm 2 Zygote formed if sperm 2 fertilizes egg 1 Zygote formed if sperm 1 fertilizes egg 2 Zygote formed if sperm 2 fertilizes egg 2
In pea plants, tallness is dominant to short or dwarf. Cross a pure tall male to a pure dwarf female pea plant. Show both ratios phenotype & genotype for the offspring.
Step 1: what are the parent’s genotypes? –Mom? –Dad? tt TT
Step 2: Set up and complete Punnett Square tt T T Tt Tt Tt Tt
Step 3: ANSWER THE QUESTION tt T T Tt Tt Tt Tt Offspring genotypes: Offspring phenotypes:
What would be the genotypes and phenotypes of the F2 generation if you cross two F1 plants? What are the geneotypes of the two plants you are crossing? Set up your Punnett Square. Don’t forget to answer the question!
Mendel’s Experiments Demonstrated Complete Dominance Other Inheritance Patterns: Incomplete dominance when both alleles are present, the two traits blend together and create an intermediate trait (Red + White = Pink) Codominance: When both alleles are present you see both traits of the characteristic are visible (Red+White=Red and White)
Other inheritance patterns: Sometimes depend on the gender (male/female) Why???? Think about sex chromosomes and the difference between males and females!
Polygenic – Multiple genes each with 2 alleles Creates additive/ quantitative effect SKIN PIGMENTATION
Other Exceptions: Linked Genes: genes that are on the same chromosome. Does the law of independent assortment apply? Can they be separated? Will they always separate?
What does this mean? It means that you can pass on an allele that you got from your mom and an allele you got from your dad ON THE SAME CHROMOSOME However, it is more likely that two alleles that start on the same chromosome will get passed on together.