Heredity Genes HEREDITY GENETICS Biological Traits and Heredity
Heredity & Genes HEREDITY & GENETICS
Biological Traits and Heredity (don’t copy) Standard: Students will recognize how biological traits are passed on to successive generations. a) explain the roles of genes and chromosomes in the process of inheriting a specific trait. b) Compare and contrast that organisms reproduce asexually and sexually c) Recognize that selective breeding can produce plants or animals with desired traits.
Heredity Vocabulary Genetics • __________: the scientific study of heredity Heredity • __________: the passing of physical characteristics from parents to offspring. DNA • __________: contains your genes; found in the nucleus
Heredity Vocabulary Genes • __________: the factor that controls a trait; found on chromosomes Traits • __________: the different forms of a characteristic (ex. dimples: present or absent)
Heredity Vocabulary Alleles • __________: the letters that represent the different forms of a gene (dimples: D = present; d = absent) Dominant • __________: the traits that overshadows and is expressed (capital letter) Recessive • __________: the trait that hides in the background (lowercase letter).
Heredity Vocabulary Genotype • __________: combination of alleles (such as DD, Dd, dd) Phenotype • __________: the physical appearance of a trait (ex. dimples or no dimples)
Heredity Vocabulary Homozygous / purebred • __________________: two alleles/letters for one trait that are the same (ex: DD or dd) Heterozygous / hybrid • __________________: two alleles/letters for one trait that are different (ex. Dd)
Heredity Vocabulary Mitosis • ___________: cell reproduction – when one body cell becomes two Meiosis • ___________: produces 4 sex cells – sperm or egg that are used to pass a parent’s traits to offspring.
PLEASE COPY IN NOTEBOOK Asexual Reproduction: • One Parent • Offspring’s DNA is identical to parent • Population of clones • Examples: bacteria, some plants, Watch brainpop: Asexual Rep. Sexual Reproduction: • Two Parents • Offspring’s DNA is a blend of both parents • Population is diverse • Examples: flowers (pollen), cats, fish (lay eggs)
BASIC VOCABULARY Heredity: the passing of traits from parents to offspring Traits: physical characteristics Genetics: study of heredity Purebred: an offspring that always produces other offspring with the same traits
Gregor Mendel – Austrian monk and math & science teacher – He discovered the principles of heredity while studying garden pea plants – Mendel’s experiments with peas led him to being named the “Father of Genetics”
Mendel’s Peas Mendel chose to study peas because they can self-pollinate or cross pollinate. This means a pea plant can produce offspring by itself to create a purebred (or true-breeding plant) with identical traits or a pea can cross with another pea plant to produce offspring with mixed traits from both parent plants.
Mendel’s Peas • Mendel studied 7 traits of pea plants, but only studied ONE trait at a time. • For example, to see how height was passed from parent to offspring, Mendel took pollen from a true-breeding tall pea plant and crosspollinated it with a true-breeding short pea plant. • This formed a hybrid: offspring of parents that have different forms of a trait. Watch Brainpop: Heredity
Some Pea Traits that Mendel Studied
Genes and Alleles • The set of instructions for You inherit a combination inherited traits are called of two alleles from your genes. parents. • You inherit your genes from your parents. • The different forms of a gene are called alleles. • For example: genes for height can produce genes for tall plants (TT, Tt) or genes for short plants (tt).
Dominant and Recessive Traits in Peas Mendel crossed plants with different traits and found that some traits showed up more often – dominant trait, while other traits didn’t show up again until later generations – recessive trait
Dominant and Recessive Traits in Peas • For each of the 7 traits that Mendel studied in peas, there is a dominant allele and a recessive allele. • If a plant inherits both a dominant allele and a recessive allele (hybrid), the dominant allele masks the recessive allele.
Mendel’s Laws of Heredity • 1 st Law: Law of Segregation – every organism has two alleles of each gene and when gametes (sex cells) are produced, the alleles separate. Ex. Tt T in one sex cell, t in another sex cell • 2 nd Law: Law of Independent Assortment – genes for different traits are inherited separately from each other. – Example: Hair color does not affect eye color.
Heredity Vocabulary Phenotype • Genotype: the allele combination of a particular trait of an organism. (BB, bb, Bb) • Phenotype: the way an organism looks or behaves. (brown) Genotype
• Homozygous: An organism with two identical alleles for a trait. purebred (BB, bb) • Heterozygous: An organism that has two different alleles for a trait. hybrid (Bb)
Dominant vs. Recessive Alleles Dominant Allele • the trait always shows up if an organism carries it • represented by a capital letter (T=tall) Recessive Allele • the trait is covered up (masked) by dominant trait • represented by a lowercase letter (t=short) • Hybrid: an organism has 2 • will show up if organism different alleles for 1 trait has 2 recessive alleles (tt) (Tt)
Stop Copying Notes for next slides. Open Hard Book to pg. 118
Back to the Peas… This Mendel guy sure loved his peas. • Easy to study • A lot of offspring • Looked at 7 traits
Part 1: Practice Problems Have your book open to page 118 Table 1 Are the following alleles DOMINANT or recessive? 1. Round seed DOMINANT! 2. Wrinkled seed recessive 3. Green seed recessive 4. Tall plant DOMINANT! 5. Short plant recessive
Part 2: What will it look like? DOMINANT + DOMINANT = DOMINANT + recessive = DOMINANT recessive + DOMINANT = DOMINANT recessive + recessive = recessive
Part 3: Labeling alleles Scientists LOVE to use abbreviations!!! They will represent the allele with a letter. Uppercase for DOMINANT and lowercase for recessive. Example: Round seed = R and wrinkled seed = r ** always create a key and make sure to use letters that look different as lowercase
Key to alleles: Trait Round seed Wrinkled seed Yellow seed Green seed Allele R r Y Tall Short T t y
Try it now! Mendels Pea Plants Alleles What will it look like? 1. RR 2. Rr 3. rr 4. Yy 5. YY 6. yy 7. Tt 8. tt Trait Allele Round seed R Wrinkled seed r Yellow seed Y Green seed y Tall T Short t
Part 4: Super Challenge! 9. Rr Tt 10. rr YY Tt Trait Allele Round seed R Wrinkled seed r Yellow seed Y Green seed y Tall T Short t
Punnett Squares • Punnett Squares were created by Reginald Punnett to predict the probability and possible genotypes in offspring. • Probability is the likelihood that a particular event will occur. Probability determines what is likely to occur, not what does occur.
Example Problem • In pea plants, tall plants are dominant to short plants. Show the genotypes and phenotypes that are produced when two heterozygous, tall plants are crossed with each other.
Instructions for Punnett Squares • Write the genotype of one parent across the top. • Write the genotype of the other parent down the side. • Fill in each box with the letter above and to the left of it. T T t t
Looking at Results • What is the chance that the offspring will be tall? • 75% (3 out of 4) • What is the chance that the offspring will be short? • 25% (1 out of 4) T t T TT Tt tt
Example Problem 2 • Black hair is dominate to brown hair. B is representative of black hair and b is representative of brown hair. Complete the punnett square if the mother is HOMOZYGOUS RECESSIVE and the father is HETEROZYGOUS. B b b Bb bb There is a 50% the offspring will have black hair and a 50% chance that the offspring will have brown hair.
Try it: • Cross Blue flowered plant (BB) with white flowered plant (bb) B b b B
Be sure to answer all the questions: • List the possible genotypes: Bb • List the possible phenotypes: Blue • What is the chance of blue flowers? 100% • What is the chance of white flowers? 0%
Try it #2: • Cross blue flowered plant (Bb) with white flowered plant (bb) B b b b
Be sure to answer all the questions: • List the possible genotypes: Bb, bb • List the possible phenotypes: Blue, white • What is the chance of blue flowers? 50% • What is the chance of white flowers? 50%
1)Alleles – E or e 2)Traits – Eye color 3)Recessive – e 4)Genotype – EE, Ee, or ee 5)Homozygous – EE or ee 6)Dominant – E 7)Heterozygous – Ee 8)Phenotype - Green
Incomplete Dominance Alleles are neither dominant nor recessive. Both traits are expressed by blending together. Example: snapdragons (red flowers + white flowers = pink flowers) + =
Selective Breeding • Humans breed organisms with desired traits to create more with the same trait. • Example: different dog breeds are the result of many generations of breeding.
Two kinds of Reproduction Asexual Reproduction Sexual Reproduction • Only one parent is needed • Offspring are copies of the parent • Example: bacteria cells multiplying by splitting. • Two parents are needed • Offspring have combined traits of parents with many variations possible • Example: 2 cats mate to produce a litter of kittens
Meiosis is a type of cell division which produces sex cells used for sexual reproduction. Each cell has half the number of chromosomes as the parent cell. In animals, meiosis occurs in the sex organs - ovaries and testes. A gamete, or sex cell, is a haploid cell – meaning this cell contains only one of each kind of chromosome versus a diploid cell found in body cells, which have 2 of each kind of chromosome.
Meiosis in Humans • Human body cells have 23 PAIRS of chromosomes. • Human sex cells have 23 SINGLE chromosomes • Sperm + Egg = fertilized new life (23 single) (23 pairs)
MITOSIS VS. MEIOSIS • Mitosis results in the production of TWO genetically identical diploid cells, whereas Meiosis produces four genetically different haploid cells in 2 stages known as Meiosis I & Meiosis II.
MITOSIS VS. MEIOSIS
TRY IT
Brain. Pop: Genetics
All Life has it!
DNA Structure & Replication • DNA (Deoxyribonucleic acid) – genetic material that carries information about an organism from one generation to the next. • DNA is found in the chromatin in the nucleus of a cell. • A DNA molecule looks like a twisted ladder, called a double helix.
• DNA is made up of units called nucleotides, each made up of three components: – a 5 -carbon sugar called deoxyribose – a phosphate group that makes up the “sides” of the ladder. – a nitrogen base that makes up the “rung” of the ladder.
Four Nitrogen bases: adenine, thymine, guanine, and cytosine Chargraff’s Rule: Adenine and Thymine always join together. A ↔ T Cytosine and Guanine always join together. C ↔ G
• During DNA Replication, a DNA molecule “unzips” between its paired bases. New bases pair up with bases on old strand forming two identical DNA strands.
Genetic Mutations • Mutations: any change that occurs in a gene or chromosome that causes the wrong protein to form that causes the organism’s traits to be different than it normally would have been. • Types of Mutations: a) Wrong base copied during DNA replication. ‘A’ instead of ‘C’ (Can cause white fur instead of brown).
Mutations Continued b) Chromosomes don’t separate correctly (can cause a cell to have too few or too many chromosomes) c) Mutation in a body cell affects only the cell that carries it. Mutation in a sex cell can be passed on to offspring and affect the offspring’s phenotype
Examples of Genetic Mutations
(Don’t believe everything you see on the Internet)
- Slides: 60