Science – Genetics: The Study of Heredity – Flashcards
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Heredity
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The passing on of physical characteristics from parents to offspring (traits from one generation to the next)
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Gregor Mendel
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Considered the father of genetics because of his work with cross-pollinating pea plants
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Trait
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A specific characteristic that an organism can pass on to its offspring through its genes
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Genetics
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The scientific study of heredity (what is passed down from generation to generation by DNA)
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Fertilization
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Occurs when the sperm from the male connects with the egg of the female and a new organism begins to form
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Purebred
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An organism that is the offspring of many generations that have the same traits.
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F1 Offspring
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The "First Filial Generation" - The sons and daughters of two purebred plants that have been cross-pollinated. Mendel crossed purebred tall plants with purebred short plant, but the results was ONLY SHORT plants.
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Filial
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Son or daughter of the F1 generation
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F2 offspring
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The "Second Filial Generation" - Sons and daughters of cross-pollinated plants that showed traits from the original parents. Mendel allowed the fully-grown F1 plants to self-pollinate - surprisingly, the Second Filial generation were a mix of BOTH tall (3/4 th's, or 75%) and short (1/4 th, or 25%) plants. The SHORT trait had reappeared.
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Genes (definition 1)
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Factors that control a trait (that are passed on from one generation to the next)
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Alleles
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Different forms of a gene. Dominant traits will ALWAYS show up in offspring, and recessive traits will ONLY show up WHEN PAIRED WITH ANOTHER RECESSIVE TRAIT.
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Dominant Allele
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The trait that ALWAYS shows-up in the (new/offspring) organism when the dominant allele is present (like the TALL trait in Mendel's experiments)
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Recessive Allele
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A trait that is hidden whenever the dominant allele is present. This trait will ONLY show-up IF the organism does NOT have the dominant allele.
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Hybrid
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An organism that has 2 different alleles for a trait - it is HETEROZYGOUS for a particular trait.
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Probability
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- A number that describes how likely it is that an event will occur. - The laws of probability predict what is LIKELY to occur, NOT necessarily what WILL occur. - Mendel realized that the mathematical principles of probability could be used to predict the results of genetic crosses.
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Punnett Square
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- A chart that shows all the possible combinations of alleles that can result from a genetic cross. - A visual representation of the events that occur at MEIOSIS.
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Using a Punnett Square, you can...
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see the different combinations of genetic crosses that will result in the offspring as a result of traits that are passed on from the parents. Each parent contributes one allele to each offspring.
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Phenotypes
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Physical appearance and visible traits in an organism
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Genotypes
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An organism's genetic make-up, or allele combinations
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Homozygous traits
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An organism with that has 2 IDENTICAL alleles for a trait.
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Heterozygous traits
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- An organism with that has 2 DIFFERENT alleles for a trait. - Also known as "HYBRID"
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Codominance
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Occurs when the alleles are NEITHER recessive or dominant, but both traits (alleles) show up in the offspring
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Walter Sutton and his "hypothesis"
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- American geneticist who wanted to understand how sex cells form. - He studied grasshoppers and "hypothesized" (thought) that chromosomes were the key to understanding how offspring have the traits of their parents.
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Sutton's Observations and Discovery
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- That a grasshopper had 24 chromosomes, and its offspring ALSO had exactly 24 chromosomes. - The chromosomes existed in 12 pairs, with ONE chromosome in each pair from the MALE parent and ONE chromosome from the FEMALE parent.
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Body/Sex cells in grasshoppers
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Body cells of a grasshopper have 24 chromosomes, while sex cells only have 12. Also, the 24 chromosomes existed in 12 pairs.
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Chromosome theory of inheritance
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- Genes are carried from parents to their offspring ON chromosomes - Alleles are literally carried ON the chromosomes of the parents and passed to the offspring.
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Meiosis
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The process by which the number of chromosomes is reduced by half to form sex cells (sperm and eggs)
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Sex cells
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Sperm and Eggs
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During Meiosis...
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- The chromosome pairs separate and are distributed to TWO different cells. - The resulting sex cells have only HALF as many chromosomes as the other cells in the organism
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Chromosome Pairs
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- Each sex cell has ONE chromosome from each original pair. - However, the offspring still ends-up with the normal number of chromosomes because it receives half from each parent. - HUMANS HAVE 23 PAIRS OF CHROMOSOMES (vs. grasshoppers who have 24 pairs)
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Genes on Chromosomes
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- Chromosomes are made up of many genes joined together like beads on a string. - The chromosomes in a pair may have DIFFERENT alleles for some genes, and the SAME alleles for others.
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20,000-25,000
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The number of chromosomes you have in your body, even though you only have 23 pairs
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The Main Function of Genes
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- To control the production of proteins in an organism's cells - To contain the code that determines the structure of a protein.
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Chromosomes and DNA
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- Chromosomes are composed mostly of DNA. - A gene is a section of a DNA molecule that contains the information to code for ONE specific protein.
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Proteins
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Help to determine the size, shape, color, and many other traits of the organism
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DNA and Nitrogen Bases
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DNA of made up of FOUR Nitrogen Bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). These bases form the "rungs" on the DNA ladder
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Nitrogen pairs
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AT and CG
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Gene (Definition 2)
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A section os a DNA molecule that contains information to code for a specific protein
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How Many Bases a Gene May Contain
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A single gene on a chromosome may contain several hundred to a million or more nitrogen bases
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The Order of Nitrogen Bases
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Forms a genetic code that specifies what type of proteins will be produced
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Chain Molecules
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Proteins made of individual amino acids
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Protein Synthesis
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- During this process, the cell uses information from a gene on a chromosome to produce a specific protein. - Takes place on the ribosomes in the cytoplasm of the cell
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During Protein Synthesis...
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The cells use information from a gene on a chromosome to produce specific proteins
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Before Protein Synthesis can take place...
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- A 'messenger' must first carry the genetic code from the DNA (located inside the nucleus) to the cytoplasm (located outside the nucleus). ****- This genetic "messenger" is called "RNA" (Ribonucleic acid) - ****
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Messenger RNA
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Copies the coded message from the DNA in the nucleus, and carries the message to the ribosomes in the cytoplasm.
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Transfer RNA
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Carries amino acids to the ribosomse and adds them to the growing proteins.
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How many "strands" does DNA, and RNA, have?
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DNA has 2 strands RNA only has one strand
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How is RNA formed?
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- RNA bases pair-up with DNA bases: - Guanine always pairs with Cytosine; and Adenine always pairs with Uracil. - So, RNA contains: Guanine, Cytosine, Adenine, and Uracil.
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What id the difference between the DNA and RNA combination of "bases?"
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Uracil takes the place of Thymine in RNA (DNA contains: RNA contains: Guanine, Cytosine, Adenine, and Thymine. RNA contains: RNA contains: Guanine, Cytosine, Adenine, and Uracil.)
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Protein Synthesis, Step One
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DNA provides code to form messenger RNA
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Protein Synthesis, Step Two
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Messenger RNA attaches to Ribosome
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Protein Synthesis, Step Three
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Transfer RNA attaches to Messenger RNA
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Protein Synthesis, Step Four
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Protein Production Continues
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Mutations
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Can cause a cell to produce an incorrect protein during protein synthesis. The organism's trait, or phenotype, may be different from what it normally would have been.
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Mutation in Body Cell
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The mutation will not be passed on to the offspring
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Mutation in a Sex Cell
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The mutation can be passed on the offspring
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Where Mutations occur
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DNA replication process
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Chromosomes incorrectly separating during Meiosis
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When this mutation occurs, a cell can end up with too many or too few chromosomes
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A Mutation is harmful if...
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It reduces the organism's chances of survival; depends on environment
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Gene Mutations
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Have enabled some kinds of bacteria to become resistant to certain antibiotics; antibiotics do not kill the bacteria that have the mutation
