GENETICS GENETICS & THE WORK OF MENDEL

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  used quantitative analysis collected data & counted them  excellent example of scientific method

Mendel’s work  Mendel bred pea plants to study genetics  Generations  Parent generation = P  Offspring of P generation = F 1 generation (F = filial)  Offspring of F 1 generation = F 2 generation F1F1 P F2F2

F 2 generation 75% purple-flower peas 25% white-flower peas Looking closer at Mendel’s work P F 1 generation (hybrids) 100% purple-flower peas X true-breeding purple-flower peas true-breeding white-flower peas Where did the white flowers go? White flowers came back!

What did Mendel’s findings mean?  Allele – alternate form of a gene  Example: purple vs. white flower color purple-flower allele & white-flower allele are two DNA variations at flower-color locus different versions of gene at same location on homologous chromosomes

Traits are inherited as units  For each trait expressed, an organism inherits 2 alleles, 1 from each parent  diploid organism inherits 2 sets of chromosomes, 1 from each parent homologous chromosomes like having 2 different types of social media Instagram Snapchat What are the advantages of being diploid?

Dominant vs. Recessive  Dominant alleles will ALWAYS cover up recessive allelles Represented by a CAPITAL letter Dominant allele is always written First (Pp)  Recessive allele will only show up when 2 are present (pp) Represented by a lower case letter  Scientist use the same letter for the different alleles of the same trait Flower color of pea plants Purple = P (dominant) White = p (recessive) homgous chromoloosomes

Genotype vs. Phenotype  Genotype Refers to the “gene” allele combination that is producing the phenotype Pea flower color (PP, Pp, pp)  Phenotype Refers to what you “PHysically” see The expression of the genotype You can NOT always determine genotype Pea flower color (purple or white) Explain Mendel’s results using …dominant & recessive …phenotype & genotype F1F1 P X purplewhite all purple

Genotypes homozygous dominant homozygous recessive heterozygous Homozygous = same alleles (PP, pp) True breed Pure breed Heterozygous = different alleles (Pp) Hybrid

Phenotype  2 organisms can have the same phenotype but have different genotypes homozygous dominant PPpurplePpPp heterozygous purple How do you determine the genotype of an individual with with a dominant phenotype? Can’t tell by lookin’ at ya!

Mendel’s 1 st law of heredity  Law of segregation  all organisms have a pair of alleles for each trait  each parent passes on 1 randomly selected allele for trait to the offspring  The offspring in turn has its own pair of alleles for the trait

Mendel’s 2 nd law of heredity  Law of independent assortment  Separate genes for separate traits are passed down independently of one another from parents to offspring For example, just because you have brown hair does not mean you will have blue eyes

Review: Mendel’s laws of heredity  Law of segregation  monohybrid cross single trait  each allele segregates into separate gametes  Law of independent assortment  dihybrid (or more) cross 2 or more traits  genes on separate chromosomes assort into gametes independently

Punnett squares : (used to make predictions) Pp x Pp Pp P p PP 75% 25% 3:1 25% 50% 25% 1:2:1 % genotype % phenotype PPPpPp PpPppp PpPp PpPp ratio Probability