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ISU BSC 101 - Inheritance of Traits

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BSC 101 1st Edition Lecture 7Outline of Last Lecture I. Section 3.3: Selection Pressuresa. Sexual Selectionb. CoevolutionII. Section 3.4: Speciationa. Reproductive Isolationb. Reproductive BarriersIII. Section 3.5a: Species Unique Evolutionary HistoryIV. Section 3.5.b: Adaptive RadiationV. Section 3.5c: ExtinctionOutline of Current Lecture I. Section 18.1: HumansII. Section 18.2a: How Traits are Inheriteda. Gregor Mendelb. Law of Segregationc. Independent Assortmentd. Punnett SquaresIII. Section 18.3: Complex Patterns of InheritanceIV. Section 18.4: Determining GenderV. Section 18.5: DomesticationVI. Section 18.6: Genes and ProteinsCurrent LectureSection 18.1:Humanso You are a mixture of half your mother’s DNA and half your father’s.o You carry 25% of the same DNA as your grandparents, 12.5% of the same DNA as your great grandparents and so on…o Thousands of traits make up humans.o Each human has 46 chromosomes (23 from mom, 23 from dad) which each carry up to 25,000 genes.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Occupies only 5% of our genome.o Origin of the human species… Hominids (humans and great apes) originate in Africa 6 million years ago. Branched off the evolutionary tree from chimpanzees. Humans adapt to their environments (example; in cold regions, humans have larger bones and carry more fat). Homo sapiens species emerges 150,000 years ago, creating the human species.o Sexual Reproduction: the creation of genetically different offspring from the fusion of male and female gametes.  Half of the genetic material of the offspring comes from one parental gamete andthe other half comes from the other parental gamete.o Gametes: sex cells (either sperm or egg).Section 18.2a: How Traits are InheritedGregor Mendelo 1822-1884o The founder of our modern understanding of genetic traitso Before Mendel, scientists believes the offspring were a blending of its two parents. Example; the offspring of a black fox and white fox was a grey fox.o Studied a pea plant to make his discoveries.o Discovered that parents have discreet particles (genes) that are independent of each other and their offspring would contain one of their two genes, not be a mixing of them both.o Discovered the difference between dominant and recessive genes. Dominant genes: the allele that is preferentially expressed; only one copy of the allele is needed for expression of the phenotype. If present, it overshadows the recessive gene and is the present phenotype. Represented with a capital letter. Recessive genes: the allele that is not preferentially expressed; both genes need to carry a recessive allele for the expression of the phenotype. Represented with a lower case letter.o Homozygous trait: individual with two similar alleles for a single trait. Homozygous dominant: two dominant alleles. (PP) Homozygous recessive: two recessive alleles. (pp)o Heterozygous trait: individual with two different alleles for a single trait. One dominant and one recessive allele. (Pp) The phenotype displays the dominant allele.o Locus: the location of the gene on a chromosome.Mendel’s Model for Dominant and Recessive Genes in a Pea PlantLaw of Segregation: Each parent contributes one of the two alleles that are passed down to the offspring. The members of each pair of alleles that code for a specific trait separate during meiosis.o Each gamete receives half of the genetic compliment of the parent.o If one parent is homozygous dominant (PP) and one parent is homozygous recessive (pp) for that trait, the offspring will receive one dominant allele (P) and one recessiveallele (p) from its parents making it heterozygous (Pp).Independent Assortment: The allele pairs of different traits separate during meiosis and pass on independently of each other to the offspring.o If both parents are heterozygous (Pp) and display the dominant phenotype, the offspring has a 25% chance of being homozygous recessive (pp) after receiving the recessive allele from both parents. It will then take on the recessive phenotype, explaining why some offspring look nothing like their parents.Punnett Squares: a graphic tool used to show potential allelic combinations found in gametes and to predict the odds of each of the offspring genotypes occurring.o A graphical representation of all the potential combinations of genotypes that can occur in offspring, given the genotypes to their parents.o This is an example of a Punnett square from two parents that are heterozygous.o The offspring has a 25% chance of being homozygous dominant, a 25% chance of being homozygous recessive, and a 50% chance of being heterozygous.o The offspring also has a 75% chance of demonstrating the dominant phenotype, and a 25% chance of independent assortment demonstrating the recessive phenotype despite both parents demonstrating the dominant one.Section 18.3:Complex Patterns of InheritanceIncomplete Dominance: Occurs when two alleles are needed to express a trait, but the dominant trait does not completely mask the recessive trait.o Example: when a red snapdragon (RR) is crossed with a white one (rr), the heterozygous (Rr) offspring are then pink.Codominance: the expression of both the dominant and recessive traits in thephenotype of the organism.o Phenotype is determined by multiple alleles (three or more). o Example; in blood types there are three alleles (A, B, O) which codefor four phenotypes (A, B, AB, and O). O is the recessive allele. A and B are codominant. If you get a combination of A andO, you get an A blood type. If you get a combination of Band O, you get a B blood type. And if you get a combination of A and B, you get a codominant AB blood type.Pleiotropy: genetic condition in which one gene controls two or more distinct and seeminglyunrelated phenotypic traits.o Example: a large percentage of white cats with blue eyes are deaf because of the pleotropic effect where the fur and eye color are associated with hearing loss.Polygenic Inheritance: Polygenic traits are influenced by more than one gene.o Example; in parakeets, feather color is polygenic. One gene codes for blue feathers, one gene codes for yellow feathers.  If both genes of the parakeet code for dominant blue and dominant yellow feathers (BBYY, BbYy, BbYY, BBYy), then the parakeet will be green.  If only the blue


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