BIOLOGY 151 1st Edition Lecture 21 Outline of Last Lecture 1. Origins of genetic variation among offspring2. Independent assortment of chromosomes3. Crossing over4. Random fertilization5. Inheritance characteristics6. Cross plants with different traitsOutline of Current Lecture 1. Diploid parent can have 2 different alleles of a gene2. Genotype of diploid (zygote) can be...3. Segregation of alleles during meiosis4. What genotype is a flower plant with a purple phenotype?5. What happens if you follow 2 genes at the same time?6. Independent assortment of non-homologous chromosomes7. Independent assortment of chromosomes and probabilities8. Complications with Mendelian inheritance9. Example (of 2) - biochemical synthesis of arginineCurrent Lecture - 3/9Diploid parent can have 2 different alleles of a gene:- normal allele (functional)- abnormal allele (less functional)- homologous pair of chromosomesGenotype of diploid (zygote) can be:- homozygous - alleles of a gene on both homologous are identical (or close enough)- heterozygous - one of the 2 alleles of that gene is different - may have identical phenotype: they look the same- dominant alleles control phenotype even if only 1 homologous chromosome has that allele- recessive alleles control phenotype only if both homologous have that alleleSegregation of alleles during meiosis:- 2 alleles- chromosomes replicate (meiosis 1) - separate homologues- meiosis 2 - games, separate sistersWhat genotype is a flower plant with a purple phenotype?:- PP (homozygotic) or Pp (heterozygotic)- could mate the plant to itself for several generations, see if the purple phenotype breeds "true" - no white flowers- could do a "test cross"- cross the purple plant to homozygous recessive- use pedigrees to figure out dominance, etc. What happens if you follow 2 genes at the same time?:- a dihybrid crossThese 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.- assume the 2 genes are on different (non-homologous) chromosomesIndependent assortment of non-homologous chromosomes:- 4 different combinations in gametes- match homozygotes to test which trait is dominant- now mate heterozygotes- independent assortment of non-homologous chromosomes- RrYy parent makes 4 different combinations in gametesIndependent assortment of chromosomes and probabilities:- gametes get 1 of each possible 2 chromosomes: 2 x 2 = 4 possible combinations in gametes- 3: 2 x 2 x 2 = 8- 2^n possible combinations if N = # of homologue pairs heterozygotic for any geneComplications with Mendelian inheritance:1. What if an allele is not really dominant or recessive, more than 2 alleles, cause multiple phenotypes?2. What if 1 phenotype is caused by more than 1 gene?3. What if 2 genes are on the same chromosome?4. What if a gene is on a sex chromosome (sex-linked)?- incomplete dominance = heterozygote has phenotype that is intermediate between that of homozygotes- codominance = different alleles give different dominant traits- ex. blood groups- different carbohydrates on blood cells- different alleles of 1 gene code for different forms of enzyme that can make either A, B, or no carbohydrates Example (of 2 biochemical synthesis of arginine:- 3 genes coding for 3 different enzymes in different steps of synthesis pathway- bread mold is haploid- if 'r' alleles produce enzymes with have slightly reduced catalytic activity- inheritable quantitative variation in trait often due to effects of more than 1 gene in pathway = polygenic trait (more complex with diploid
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