AP Biology Mendelian Genetics Genetics Unit

AP Biology History of Genetics : Gregor Mendel (Austrian monk) presented results of 10 years of experimentation on pea plants. 2. Late 1800’s: increased research in microscopy and cytology (study of cells) recognized each chromosome transferred (contribution from parent) : chromosomes in gametes (sex cells) found to be involved in reproductive cycle. Gregor Mendel studied genetics using pea plants.

AP Biology : fruit fly began to be used for genetic research because of very short generation span ’s: chemical techniques developed to reveal association between genes in chromosomes and proteins made in the cell : DNA’s responsibility is to code for production of proteins (acts like a recipe book) one gene codes for production of only one protein : Watson and Crick proposed model of DNA structure to be coiled spiral ladder (double helix). Drosophila used as experimental model in genetics. In 1962 Watson and Crick win the Nobel Prize for discovering the structure of DNA. DNA codes for protein.

AP Biology ’s: genetic code deciphered ’s: description of how a gene produces a protein (how nucleotide bases can create recipe for specific order of amino acids to build specific proteins : scientists in United States organized Human Genome Project (HGP), an international effort to completely map and sequence the human genome 11. Feb HGP published working draft of 3 billion base pairs of DNA. DNA codes for protein.

AP Biology Gregor Mendel Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas.  Used experimental method.  Collected data and counted traits in peas.

AP Biology Pollen transferred from white flower to stigma of purple flower anthers removed all purple flowers result Mendel’s Work: Bred Pea Plants F1F1 P F2F2 self-pollinate  Cross-pollinated true breeding parents (P).  Raised seed and then observed traits (F 1 ).  F = filial (kids)  Allowed offspring to self-pollinate and observed next generation (F 2- grandkids ).

AP Biology F 2 generation 3:1 75% purple-flower peas 25% white-flower peas Looking Closer at Mendel’s Work P 100% F 1 generation (hybrids) 100% purple-flower peas X true-breeding purple-flower peas true-breeding white-flower peas self-pollinate Where did the white flowers go? White flowers came back!

AP Biology What did Mendel’s findings mean?  Traits come in alternative forms = alleles  Purple vs. white flower color  Different alleles vary in the sequence of nucleotides at the specific locus of a gene.  Locus = gene location.  Some difference in sequence of A, T, C, G purple-flower allele & white-flower allele are two DNA variations at flower-color locus different versions of gene at same location on homologous chromosomes

AP Biology What did Mendel’s findings mean?  Some traits mask others.  Purple and white flower colors are separate traits that do not blend  Purple x white ≠ light purple  Purple masked white  Dominant Allele  Functional protein.  Masks other alleles.  Represent with a capital letter (T).  Recessive Allele  Allele makes a malfunctioning protein.  Represent with a lower case letter (t). homologous chromosomes I’ll speak for both of us! wild type allele producing functional protein mutant allele producing malfunctioning protein

AP Biology Genotypes  Homozygous = same alleles = PP, pp  Heterozygous = different alleles = Pp homozygous dominant homozygous recessive heterozygous

AP Biology Genotype vs. phenotype Difference between how an organism “looks” & its genetics.  Phenotype  Description of an organism’s trait.  The “physical.”  Genotype  Description of an organism’s genetic makeup. Explain Mendel’s results using …dominant & recessive …phenotype & genotype F1F1 P X purplewhite all purple

AP Biology Phenotype vs. Genotype 2 organisms can have the same phenotype but have different genotypes. homozygous dominant PPpurplePpPp heterozygous purple Can’t tell by lookin’ at ya!

AP Biology Mendel’s 1 st Law of Heredity Law of segregation.  During meiosis, alleles segregate.  Homologous chromosomes separate.  Each allele for a trait is packaged into a separate gamete. PP P P pp p p PpPp P p

AP Biology Law of Segregation  Which stage of meiosis creates the law of segregation? Whoa! And Mendel didn ’ t even know DNA or genes existed! Anaphase 1

AP Biology Monohybrid cross Some of Mendel’s experiments followed the inheritance of single characters.  Flower color.  Seed color.  Monohybrid crosses.

AP Biology Punnett squares Pp x Pp Pp male / sperm P p female / eggs PP 75% 25% 3:1 25% 50% 25% 1:2:1 % genotype % phenotype PPPpPp PpPppp PpPp PpPp F 1 generation (hybrids) Aaaaah, phenotype & genotype can have different ratios

AP Biology Monohybrid Cross Practice In corn, normal kernels are dominant to waxy kernels. If you crossed a waxy kernel plant to a heterozygous normal plant what type of seeds would be produced?