BSC 2011 Lecture 10 Medelian Genetics
BSC 2011 Lecture 10 Medelian Genetics 2011
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This 3 page Class Notes was uploaded by rcg16b Notetaker on Friday September 30, 2016. The Class Notes belongs to 2011 at Florida State University taught by Dr. Kevin Dixon in Fall 2016. Since its upload, it has received 12 views. For similar materials see Biological Sciences II in BSC at Florida State University.
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Date Created: 09/30/16
Lecture 10 Mendelian Genetics Reading: Chapter 14.1 Concepts • Spade foot toads-‐‑ environmental factors can influence gene expression o Thyroxin levels can vary in individual tadpoles of the same species § Size of the pond § Carnivores are larger than omnivores § What they eat • Carnivores have bigger and shorter digestive tubes than omnivores o Traits are not dependent on the genotype, the trigger is the environment • Be able to explain the impor tance of inheritance to biology (and evolution in particular) o Helped discover chromosomes, DNA and genes o We learned that § we share about half of genes from mother and half from father § What trait is expressed in the child depends on the trait and th genes • Be able to explain how Mendel did his experiments? o Cross pollinated two contrasting, true breeding pea varieties § True breeding-‐‑ over many generations of self pollination produced the same variety (makes them homozygous) § Only self fertilized (used a paint brush to pollinate flowers) o Terms to know about his experiments: § Hybridization-‐‑ mating of two true breeding varieties § P generation-‐‑ true breeding parents (homozygous) § F1 generation-‐‑ hybrid offspring (heterozygous) § F2-‐‑ when the F1 hybrids self pollinate (pundit square) o Discovered § ¾ were purple and ¼ were white in the F1 generation § the white allele is still lives! § environmental factors can cause deviations in the 3:1 ratio § law of segregation-‐‑ alleles separate during gamete formation and randomly reunite during fertilization § the law of independent assortment-‐‑ each pair of alleles segregates independently of each other pair of alleles during g amete formation o All of his F1 progeny were monohybrids which means they were heterozygous for one particular character being followed in the cross o Mendel’s Model § Alternative versions of genes account for variations in inherited characters • Alleles-‐‑ alternative version of a gene § For each character, an organism inherits two copies (two alleles) of a gene, one from each parent § If the two alleles at a locus differ, then one, the dominant allele, determines the organism’s appearance § Law of segregation • Be able to distinguish between Mendelian inheritance and blending inheritance? o Blending-‐‑ offspring “blend” the traits of both par ents WRONG § Would cause variation to go away completely o Mendelian-‐‑ Mendel’s model, particulate inheritance § Each individual has two copies of genes and they each pass one on to offspring • Be able to explain the significance of the Law of Segregation o Look at this image to see differences between the law of independent assortment and the law of segregation: § http://www.bio.miami.edu/~cmallery/150/mendel/c8.15x2.mendel.laws.jpg o The two alleles for a heritable character segregate (separate) during gamete formation and end up in different gametes randomly o An egg or a sperm gets only one of the two alleles that are present o In chromosomes, the segregation corresponds to the distribution of the two members of a pair of homologous chromosomes to different gametes in meiosis P p P PP Pp p Pp pp § 3:1 Phenotypic ratio p p P Pp Pp p pp pp § 1:1 Phenotypic ratio o Note: a parent passes on either their fathers allele or their mothers allele and environmental factors can affect gene expression and mess Mendel ’s model up • Dihybrid cross o Previously we only considered monohybrid crosses o Example: pea color and pea shape YR Yr yR yr YR DD DD DD DD Yr DD DP DD DP yR DD DD PD PD yr DD DP PD PP § Y= yellow, y=green § R= round, r=wrinkled § P= recessive § 9 where both traits are dominant § 3 where Y is dominant and r is recessive § 3 where y is recessive and R is dominant § 1 where they are both recessive § 9:3:3:1 ratio o Displays the law of independent assortment -‐‑ segregation in one gene is independent of segregation in another gene § Segregation of one locus is independent of segregation at another locus § Mostly true, but not universal • Terms: Gene, allele, locus, heterozygote, homozygote, genotype, phenotype, dominant, Recessive, F1, F2, monohybrid • Another example AB Ab aB ab Ab AABb AAbb AaBb Aabb Ab AABb AAbb AaBb Aabb Ab AABb AAbb AaBb Aabb Ab AABb AAbb AaBb Aabb You’re only going to get the A phenotype. 1:1:0:0
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