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Download Lesson 12: Single Trait Inheritance lecture unit3Lesson12
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Content Review: • Nucleotides, DNA, genes, chromosomes, and codons are all terms used to describe our genetic information. Take each pair of terms and describe their relationship. • Nucleotides and genes • Genes and Chromosomes • DNA and codons • Chromosomes and DNA Lesson 12: Single Gene Inheritance • relate your understanding of genes and DNA to chromosomes; • relate your understanding of alleles to Mendelian concepts of segregation and dominance; • understand how meiosis leads to the production of haploid gametes; • relate the outcome of meiosis to the establishment of Punnett squares; • extend your understanding of genetics to include incomplete dominance (leaving pedigree analysis to Lesson 14) What did we inherit from our parents? http://www.aiesec.org.nz/waikato/nzms/father.jpg In organisms like humans, chromosomes come in matched pairs. How do we refer to the GENES we inherited from our parents? A B Genes come in different forms, called alleles U U W w Example: A, B vs. O alleles for blood type HOMOZYGOUS for U gene HETEROZYGOUS for W gene How are chromosomes randomly passed on to offspring? Matched chromosomes pair up Sex cells = gametes. 5.9 Matched chromosomes separate Ours are HAPLOID http://fig.cox.miami.edu/~cmallery/150/life/meiosis.pics.jpg Meiosis G g g G g G g G What happens after chromosomes are divided in meiosis? Haploid + Haploid = Diploid Meiosis followed by fertilization g G You try it first G g GG Gg Gg gg Take a minute to talk about probability g G g G What is the probability of getting Gg? GG? gg? 1/4 1/4 1/4 1/4 What did Mendel tell us about the inheritance of traits? •Crossed peas for seven contrasting characteristics •Looked at offspring and “grand” offspring •Carefully, mathematically, analyzed the data CONCLUSION Traits are controlled by factors (alleles) that come in pairs What else did Mendel tell us about the inheritance of traits? How are phenotype and genotype related? Flower color is the phenotype P P p p (appearance) PP pp Pp is the genotype (makeup of alleles) P p Pp Punnett squares predict offspring from parents genotypes Parent’s haploid gametes PP Pp P p P PP Pp p Pp pp Pp Diploid progeny pp If I cross Pp purple by the white parent, what kinds of “kids” will I see? Pp x pp Try it! p p P Pp Pp p pp pp p Do you know any human single gene traits? Check your partner’s phenotype for these traits. Can you determine their genotype? First Thing Mendel Didn’t Know RR Rr rr Two doses of “R” allele – very red One dose of “R” allele – pink No doses of “R” allele white Mendel would have been surprised! “R” vs. “r” now refers to whether or not allele makes a protein, and “contributes” to phenotype RR Rr “R” is contributing “r” is non-contributing rr You mate two pink snapdragons. ____ is the proportion of red offspring from this trait that shows ________________. Try it! Try another one! A gene called “Insulin-like growth factor” (I) controls size in dogs. A Great Dane is homozygous for the I allele, whereas a toy poodle is homozygous for the “i” allele. A mating between the two gives a middle sized dog. Assume there is only this one gene that influences size and determine what sizes (and in what proportion) would be seen if the Great Dane mated with the middle-sized GreatOodle. Can you think of any traits in humans controlled by incomplete dominance? Try it! Cross two heterozygous parents. C1 = Curly hair C2 = straight hair Another example: not just ONE ethanolresponse gene: GOOD ADH function = contributing allele GOOD ADH function = Increased dosage desired GOOD ALDH function = contributing allele GOOD ALDH function = Few side effects ADH ALDH With SOME Alcohol response genes Therefore, if ALDH works poorly, aldehyde builds up. Drinker Feels more sick. ADH ALDH Alcohol dehydrogenase Aldehyde dehydrogenase How to designate alleles for incompletely dominant traits? http://english.gov.cn/images http://www.travelinnermongolia.com Rapid metabolism of aldehyde ALDH2*1 allele Slow metabolism of aldehyde ALDH2*2 allele Why not “A” vs. “a”? “Brain Storm” by alexiuus.deviantart.com SNPs and alcoholism http://www.travelinnermongolia.com http://english.gov.cn/images PMID: 9347089 Mongolian Chinese Very low frequency of ALDH2*2 allele Han Chinese Somewhat higher frequency of ALDH2*2 allele PROTECTS from ethanol Rapid metabolism of aldehyde Slow metabolism of aldehyde abuse