Download Unit 6 Student Notes - Flushing Community Schools

Name: _________________________
Unit 6 Notes
 In 1851, Gregor Mendel (a priest from Europe) taught
 In the garden, Mendel grew hundreds of pea plants and began noticing that they
 Some pea plants were
 Some pea plants produced
 Mendel observed that the pea plant’s traits were
 Heredity = the passing of physical characteristics from parents to offspring.
 Genetics = the scientific study of heredity
 Mendel is known as the
 Mendel’s Peas
 A new organism begins to form when egg and sperm are
 When plants fertilize themselves,
 Mendel developed a method by which he could cross-pollinate his
 Mendel’s Experiments
 Mendel started his experiments with
 Purebred = offspring of many generations that have the same trait.
 Mendel’s First Experiment
 Mendel crossed ____________________ with _____________________
(P1 generation)
 The offspring of the P1 cross were called the ______________________
(F1 generation)
 The offspring of the F1 cross were called the ______________________
(F2 generation)
 See results in Figure 2, p. 78
 Note: the F2 offspring are
 Dominant and Recessive Alleles
 Mendel’s experiments taught him that individual genes must
 Alleles = the different forms of a gene
 Example: stem height gene has a
 The female parent gives one allele, the
 Mendel also learned that one allele can
Name: _________________________
 Example: the _______________ masked the _______________ in the F1
generation (Figure 2, p. 78)
 Individual alleles control the
 Dominant allele = one whose trait always shows up in the organism when
the allele is present
 Recessive allele = one whose trait is hidden whenever the dominant allele
is present.
 Examples:
 If we cross two tall P1 plants, can we have a short F1 plant? _____
 If we cross one tall P1 plant and one short P1 plant, can we have a
short F1 plant? _____
 Offspring are hybrids (they have two different alleles for the
same trait)
 If we cross two short P1 plants, can we have a short F1 plant? _____
 Using Symbols in Genetics
 Scientists use letters to
 A dominant allele is represented by a
 Example: dominant tall stem height = _____
 A recessive allele is represented by the lowercase version of
 Example: recessive short stem height = _____
 When two dominant parents produce offspring _____
 When one dominant and one recessive parent produce offspring  __________
 When two recessive parents produce offspring  _____
 Probability = the likelihood that a particular event will occur
 Principles of Probability
 If you tossed a coin…
 What is the probability that the coin would land heads up? _____
 What is the probability that the coin would land tails up? _____
 In twenty tosses, how many would you predict would land heads up? _____
 The laws of probability predict what is likely to occur – not
 Probability and Genetics
 Mendel was the first scientist to recognize that the principles of probability can
Name: _________________________
 Mendel counted the offspring of every
 Example: Mendel crossed two plants hybrid for stem height (Tt x Tt) –
_____ of the F1 offspring had tall stems, _____ had short stems
 Therefore, the probability of producing long-stemmed offspring is
_______, and the probability of producing short-stemmed offspring is
_______
 Punnett Squares
 Punnett square = = chart that shows all the possible combinations of alleles that
can result from genetic crosses
 Punnett squares can also predict the probability of a particular outcome.
 Phenotype = physical appearance (what it looks like)
 Examples:
 Genotype = genetic makeup (what allele combination is present)
 Examples:
 Homozygous = an organism that has identical alleles for a trait
 Examples:
 Heterozygous = an organism that has two different alleles for a trait
(hybrid)
 Examples:
 For the following examples, use these abbreviations:
 Homozygous dominant tall = ______
 Heterozygous (hybrid) tall = ______
 Homozygous recessive short = _____
 Example:
 P1: dominant tall x dominant tall
 F1 result  __________
 _____ chance of being _____
 Example:
 P1: dominant tall x hybrid tall
 F1 result  __________
 _____ chance of being _____
Name: _________________________
 Example:
 P1: dominant tall x recessive short
 F1 result  __________
 _____ chance of being _____
 Example:
 P1: hybrid tall x hybrid tall
 F1 result  __________
 _____ chance of being _____
 _____ chance of being _____
 Example:
 P1: hybrid tall x recessive short
 F1 result  __________
 _____ chance of being _____
 _____ chance of being _____
 Example:
 P1: recessive short x recessive short
 F1 result  __________
 _____ chance of being _____
 Codominance
 Sometimes, a dominant allele and a recessive
 Codominance =
 Examples:
 Chickens in Figure 10, p. 89
 Labrador
 Chromosomes and Inheritance
 In 1903, Walter Sutton studied
 Chromosome theory of inheritance = genes are carried from parents to their
offspring on chromosomes
Name: _________________________
 Sex cells (eggs and sperm) contain half the number of
 Meiosis = the process by which the number of chromosomes is reduced by half to
form sex cells (eggs and sperm)
 See “Meiosis” on p. 94-95
 Meiosis and Punnett Squares
 See Figure 14, p. 95
 Also, a Punnett square can be used to determine the
 Example:
 P1: _____ (male) x _____ (female)
 F1 results  2 females, 2 males
 _____ chance of being _______
 _____ chance of being _______
 Chromosomes
 Organisms can vary greatly in the number of chromosomes in their body cells
 Humans have ___________________ (23 pairs) per body cell
 Dogs have ___________________ per body cell
 Goldfish have ___________________ per body cell
 Note: larger organisms do not
 Although your body may only have 23 pairs of chromosomes, your body cells
contain between ________________________________ – each controlling a
particular trait
 That is why no two
 See Figure 15, p. 96
 The Genetic Code
 The main function of genes is to control the
 Proteins help determine the size, shape, and
 Chromosomes are
 DNA is composed of four different nitrogen bases (____________, ___________,
____________, ____________)
 A single “rung” on the DNA “ladder” contains hundreds of
 The nitrogen bases are
 Example: ATGACGTAC
 The order of the nitrogen bases along a gene forms a genetic code that
Name: _________________________
 Groups of three nitrogen bases result in the
 Amino acids combine to
 Think of the following analogy:
 Nitrogen bases =
 Amino acids =
 Protein =
 How Cells Make Proteins
 Protein synthesis = the production of proteins
 The cell uses information from a gene on a chromosome to
 Takes place on the ribosomes in the
 The Role of RNA
 RNA and DNA are similar, but
 RNA looks like only one
 RNA contains a
 RNA has the nitrogen bases adenine, guanine, and cytosine, but has
____________ (U) instead of thymine
 Types of RNA
 Messenger RNA (mRNA) = copies the coded message from the DNA in
the nucleus and carries the message to the cytoplasm
 Transfer RNA (tRNA) = carries amino acids and adds them to the growing
protein
 Translating the Code
 See “Protein Synthesis” p. 100-101
 Know steps one through four!
 Mutations
 Types of Mutations
 Single-base substitution (Example:
 Chromosomes do not separate evenly during meiosis (resulting in
 The Effects of Mutations
 Helpful mutations – Example:
 Harmful mutations – Example:
 Neither helpful nor harmful mutations – Example:
Name: _________________________
 Chapter 4-1
 Traits Controlled by Single Genes
 Many traits are controlled by a
 Often one allele is dominant, and
 Example: Figure 2, p. 111
 P1 genotype: _____ x _____
 P1 phenotype: _____________ x _____________
 F1 genotype: 1 _____, 2 _____, 1 _____
 F1 phenotype: _____ widow’s peak, _____ straight hair line
 Multiple Alleles
 Some human traits are controlled by a single
 Multiple alleles =
 Example: Human blood types (Figure 3, p. 112)
 There are four main blood types – _____, _____, _____, _____
 Three alleles control the
 The allele for type A and the
 The allele for type
 Note:
 People with type O blood are “______________________”
 People with type AB blood are “______________________”
 Traits Controlled by Many Genes
 Some human traits show a large number of phenotypes because the
 Examples:
 Height –
 Skin color –
 The genes act together as a
 Male or Female?
 The sex of a baby is determined by
 Each human body cell has
 One pair is made of two sex chromosomes
 The sex chromosomes determine
 The sex chromosomes are the only pair of
Name: _________________________
 Remember from Chapter 3: _____ (Female), _____ (Male)
 See Figure 5, p. 113
 Sex-Linked Genes
 Sex-linked genes =
 Because males have only one X chromosome, males are more likely than
 Example: _________________________________
 See Figure 6, p. 114
 See Figure 7, p. 115
 It takes two recessive alleles to have a

Carrier =
 But, it takes only one recessive allele to have a
 The Effect of the Environment
 The effects of genes are often
 Examples:
 Diet
 Due to better eating habits, the average height of adults in the U.S.
 Medical care
 Living conditions
 Chapter 4-2
 Genetic Disorders
 Genetic disorder =
 Genetic disorders are caused by mutations (changes in a
 Examples:




 Cystic Fibrosis
 Cystic fibrosis = genetic disorder in which the
 Bacteria grow in the
 The mutation that causes cystic fibrosis is
 Currently, there is no
Name: _________________________
 Sickle-Cell Disease
 Sickle-cell disease = genetic disorder that
 Hemoglobin =
 When oxygen concentrations are low, red blood cells
 Figure 9, p. 118
 The sickle-shaped cells cannot carry as much oxygen and
 The mutation that causes sickle-cell disease is
 Currently, there is no
 Hemophilia
 Hemophilia = genetic disorder in which a
 A person with hemophilia can
 The mutation that causes hemophilia is caused by a recessive allele on the
 Currently, there is no
 People with hemophilia can live normal lives –
 Down Syndrome
 Down syndrome = results when a person’s cells have an
 People with Down syndrome have a distinctive physical appearance and
 p. 117
 Heart defects are
 Despite limitations, people with Down syndrome can
 Pedigrees
 Pedigree =
 Geneticists use pedigrees to trace the
 See Figure 10, p. 119
 Circle =
 Square =
 Colored shape =
 Half-colored shape =
 No color in shape =
 Horizontal line =
 Vertical line & bracket =
 Diagnosing Genetic Disorders
Name: _________________________
 Scientists began diagnosing genetic disorders with
 Today, scientists use tools such as amniocentesis and
 Amniocentesis = procedure done before a baby is born which
 Cells are taken from the
 Karyotype =
 Made from the
 Genetic counseling =
 Chapter 4-3
 People have developed several ways to
 Selective breeding
 Selective breeding = the process of selecting a few organisms with
 Techniques
 Inbreeding = involves crossing
 Hybridization = involves crossing
 Cloning
 Clone = an organism that is
 In plants, scientists grow new plants from cuttings (small parts of
 In animals, scientists remove an egg, replace the
 This process takes three different
 This is controversial, since removing the nucleus can be
 Genetic Engineering
 Genetic engineering = genes from one organism are
 Also called “gene splicing” because DNA is
 Genetic engineering was first
 See “Genetic Engineering” on p. 126
 We use genetically engineered bacteria to create insulin (a drug to
 We also use bacteria to create human growth hormone (a protein
 Genetic Engineering in Other Organisms
 Bacteria have been implanted into tomatoes, wheat, and rice to enable
them to:
 Survive in
 Grow in
Name: _________________________
 Resist
 Genes have been inserted into animals, which then create
 Example: cows can produce a protein that clots blood – helping
 Gene therapy = process of using genetic
 Working copies of a gene are
 Example: “engineered” viruses can be inserted into the
 DNA Fingerprinting
 DNA fingerprinting =
 Scientists have found ways gather DNA samples from
 These techniques have
 The Human Genome Project
 Genome =
 Researchers estimate that there are __________-__________ genes in
one cell’s DNA
 The main goal of the Human Genome Project is to identify the
 This would help us understand the following:
 How
 What
 What causes
 Potential treatments/cures for