Mendelian Genetics

Mendel's 1st Experiment

Self-pollinating plants: Flower color-1 purple and 1 white (Parent)
100% purple (F1)
75% purple and 25% white for (F2)

1 value of the characteristic disappeared in F1 plants and reappeared in F2. Law of Segregation: there are 2 factors controlling a given charac.(one that dominates the other) and these factors separate and go to different gametes in reproduction

Theory of Heredity

4 Hypothesis-explain inheritance where 2 alleles of a gene are inherited and result in 1 of any traits in offspring

Allele: alternative form of a gene Ex) Bb

Gene: segment of DNA with info. to encode a polypeptide or RNA molecule (heritable factors/units)

  1. There are different versions of genes (account for variations in charcteristics)
  1. When 2 different alleles (HF) are inherited together, 1 may be expressed, while the other is silenced (Dominant/Recessive)
  1. For each characteristic, an organism inherits 2 allells (1 from each parent; gender is irrelevant when expressed genes are supplied)
  1. When gametes are formed, 2 alleles of each gene are separated (In meiosis, each male or female gamete receives 1 allele for a trait. At fertilization, resulting zygote has 2 alleles of each gene)

Heritable factors are segregated during gamete formation. A pair of alleles is segregated during formation of gametes. During meiosis, homologous chromosomes are randomly separated. Each resulting gamete has an equal probability or chance of receiving either of the two alleles.

Mendel's 2nd Experiment

Crossed plants: yellow round seeds and plants with green wrinkled seeds (Dihybrid Cross)-
Where two traits are examined together
RY + ry= RrYy
RY, rY, Ry, ry

Plants in F1 were alike (Yellow and Round/wrinkled seeds) F2 showed combinations of green(y) and Yellow Rryy and rrYy, rryy

Law of Independent Assortment-Factors controlling different characteristics are inherited independently of each other

Linked genes are close together on a chromosome

Inheritance of 1 trait wont affect the inheritance of another

Genetics of Inheritance

Characteristics of organisms are controlled by genes on chromosomes. Locus: position of a gene on a chromosome

Genotype and Phenotype

Genotype: made up by the individual's alleles

Homozygote: BB/bb Heterozygote: Bb

Phenotype: Produced by expression of an organism's genotype

Purple flowers/ white flowers

Allele: B (purple) b (white)

Punnett Squares=Bb Bb---BB, Bb, Bb, b*b,

Testcross- used to determine organism's genotype. Individual with unknown genotype is crossed with a homozygous recessive individual