Please write AT THE TOP of your dragon picture… Your names Your egg number The name of your baby dragon

Take home message from Dragon Genetics Project... You should understand… Alleles are genes (DNA) Each organism gets 2 alleles per trait 1 from mom; 1 from dad Alleles are on chromosomes Gametes give alleles to “babies”

Introduction to Mendel Honors Genetics Ms. Gaynor Heredity Introduction to Mendel Honors Genetics Ms. Gaynor

Transmission (passing down) of Traits How? One possible explanation of heredity is a “blending” hypothesis genetic material contributed by two parents mixes

Another Hypothesis An alternative to the blending model is the hypothesis of inheritance (genes) Parents pass on discrete heritable units (factors) called genes

Gregor Johann Mendel 1843 Documented a mechanism of inheritance through his experiments with garden peas Figure 14.1

Gregor Johann Mendel Mendel discovered the basic principles of heredity By breeding garden peas in carefully planned experiments

Mendel’s Experimental Method Why use pea plants? available in many varieties easy to get he could strictly control which plants mated with which Grow quickly

Pea Plant Fertilization Self fertilization : mate with self  produce identical offspring TRUE or PURE breeds Cross fertilization : mate with another  can produce different offspring HYBRIDS

SELF Cross B A

Procedure: Crossing pea plants

Mendel’s Procedures Mendel chose to track Only those characteristics (traits) that varied in an “either-or” manner Mendel also made sure that He started his experiments with varieties that were “true-breeding”

True Breeding vs. Hybridization In a typical breeding experiment Mendel mated 2 DIFFERENT, true-breeding varieties called hybridization The true-breeding parents (Pure breeding made through true breeding mated two of the SAME varieties so these plants are “TRUE” for only 1 trait (can only make offspring w/ this trait)

Mendel’s Generations Original Parents Are called the P generation The next generations is called the F1 generation When 2 F1 individuals are mated together it produces the F2 generation

Generations (in general) P = parental generation of a cross F1 = the first generation after the parental (the results of the 1st cross) F2 = a cross between F1 individuals yields F2 (2nd cross)

Mendel’s Results When Mendel crossed contrasting, true-breeding traits All of the offspring showed only ONE of the 2 traits When Mendel crossed two of these F1 plants Many of the plants had the F1 shown trait, but some had the other trait that wasn’t shown in F1

Mendel discovered Where did the white color go? A ratio of about 3:1, purple to white flowers, in the F2 generation P Generation (true-breeding parents) Purple flowers White  F1 Generation (hybrids) All plants had purple flowers F2 Generation Where did the white color go? Figure 14.3

Mendel’s Conclusions Mendel reasoned that In F1 plants, only purple flower factor was affecting flower color in the hybrids Purple flower color was dominant, and white flower color was recessive Some FACTOR was being transferred from parent to offspring

Alleles Alleles = alternative forms of genes (Mendel’s “factors”) Each individual has 2 alleles for the same gene (because there are 2 homologous chromosomes) Each parent passes one allele for each gene to his/her offspring

Useful Genetic Vocabulary Homozygous A pair of IDENTICAL alleles for that gene Exhibits true-breeding aa = homozygous recessive (or just recessive) HH = homozygous dominant Heterozygous A pair of alleles that are different for that gene Aa or Hh

Recessive is… Recessive an allele that does NOT produce a characteristic effect when present with a dominant allele only expressed when the determining allele is present in the homozygous condition aa or hh

Dominant is… Dominant an allele that produces the same phenotypic effect whether inherited with a homozygous or heterozygous allele Aa or AA, Hh or HH The allele that is expressed Not necessarily better, stronger, etc.

Mendel’s Law of Segregation The two alleles for a characteristic separate (segregate) during gamete formation (Anaphase I of meiosis) end up in different gametes Each gamete gets 1 allele ONLY for each gene

Mendel’s Model Mendel developed a model to predict inheritance Mendelian Genetics states There will be a 3:1 inheritance pattern in his F2 offspring if 2 of his F1 offspring were crossed

Allele for purple flowers Allele for white flowers Recall…Alleles Alternative versions of genes account for variations in inherited characters, which are now called alleles Allele for purple flowers Locus for flower-color gene Homologous pair of chromosomes Allele for white flowers

For each characteristic, An organism inherits TWO alleles, one from each parent A genetic locus is actually represented twice (once on each of the homologues)

Mendelian Genetics aka-COMPLETE DOMINANCE If the 2 alleles at a locus differ (heterozygous) Then the dominant allele determines organism’s appearance The recessive allele has no noticeable effect on organism’s appearance (it is hidden) The 1st allele is “completely dominant” over the 2nd allele

Mendelian Genetics COMPLETE DOMINANCE Ex: Tongue rolling = trait Tongue roller = dominant (T) Non-tongue roller = recessive (t) What is the phenotype of an individual with a genotype TT? tt? Tt?

More Genetic Vocabulary An organism’s phenotype Is its physical outcome Ex: Blue eyes, brown hair, etc An organism’s genotype Is its genetic makeup A.k.a.-the allele combination Ex: aa, Aa, AA http://www.hippocampus.org/Biology;jsessionid=C83A30FA6EDF5E6BAEEDC6F71B0363E3

Non-Mendelian Genetics INCOMPLETE DOMINANCE Does not follow Mendel’s pattern… If 2 alleles at a locus differ (heterozygous) Then the dominant allele “mixes with” the recessive allele to determines organism’s appearance The recessive allele is NOT hidden An “inbetween or mixed” phenotype is the result

Non-Mendelian Genetics INCOMPLETE DOMINANCE Ex: Hair texture = trait Curly = dominant (H) Straight = recessive (h) What would a “mix” of curly and straight be??? What is the phenotype of an individual with a genotype HH? hh? Hh?