Presentation on theme: "Genetics. Heredity- passing of traits from parent to offspring Traits- hair color, eye color, height, etc. (are like your parents) -characteristics that."— Presentation transcript:
Heredity- passing of traits from parent to offspring Traits- hair color, eye color, height, etc. (are like your parents) -characteristics that are inherited Genetics- the study of heredity
Gregor Mendel Gregor Mendel- Austrian Monk (mid 1800’s) is considered the “Father of Genetics” -studied pea plants (Pisum sativum) to explain heredity
Why study pea plants? 1. Pea plants have easy traits to identify (32 varieties of traits, he chose 7 to study) ex. Flower color, seed color, seed shape 2. Pea plants are small, easy to grow, and produce large number of offspring -allowed Mendel to have something to count (used ratios)
Why Study Pea Plants 3. Pea plants have the ability to self-pollinate (both male and female parts on same flower) or cross-pollinate
Self-Pollination Involves having the pollen (male sperm) be directly deposited on the female section of the flower
Cross- Pollination Requires the removal of the male stamen (makes pollen) on 1 st flower and transferring the pollen from a different flower to the first one
Mendel’s Pea Plant Experiments -he studied 3 generations of pea plants (parents, kids, grandkids) 1. Parents had to be true breeding (pure plants) in which the same trait is expressed in all offspring when pea plant is self-pollinated -called the parental generation (P1)
Mendel’s Pea Plant Experiments 2. Mendel cross-pollinated 2 varieties (1 true breeding tall and 1 true breeding short plant) from the P1 generation 3. This produced the F1 (“filial” or kids) generation *It was amazing to Mendel that all of the kids were tall and none of them were short! -it appeared as if the short parent had never existed!
Mendel’s Pea Plant Experiments 4. He then allowed the F1 generation to self- pollinate which produced the F2 (grandkids) generation *He noticed that some of the grandkids were tall and others were short (he counted them and found that there was a 3:1 ratio of tall to short plants in the F2 generation) *The short trait reappeared as if from nowhere!
Results of Mendel’s cross of true breeding short with a true breeding tall pea plant
Mendel saw the same results in different traits
Mendel’s Theory of Heredity 1. Parents pass on units of information to offspring. He called “traits”= genes. -don’t pass trait directly because only the unit is passed 2. 1 unit from mother + 1 unit from father (gene in egg) (gene in sperm) 2 units for each trait
Alleles on homologous chromosomes *These alternative forms of a gene that code for a trait are called alleles. There are 2 alleles for each trait; 1 allele for a trait is from mom and 1 allele is from dad.
Homozygous vs. Heterozygous Homozygous- if the 2 alleles for a trait are the same TT (homozygous dominate) tt (homozygous recessive) Heterozygous- if the 2 alleles for a trait are different -Tt
Genotype Genotype- the allele combination an organism has for a trait -ex. TT is the genotype (genetic formula) of a tall plant that has 2 alleles for tallness
Phenotype Phenotype- “physical appearance” of an organism or the way it looks and behaves -determined by the genotype -the phenotype of a tall plant is tall whether it is TT or Tt and the phenotype of a short plant is short only if it is tt.
3. The presence of an allele does not guarantee it will be expressed. -Only the dominant allele is expressed in heterozygous individuals and the recessive allele is not expressed Ex. a Tt individual will appear tall
Law of Segregation Alleles are passed from one generation to the next by the Law of Segregation which says that the 2 alleles (genes) for each trait must separate when gametes are formed.
Also, the Law of Independent Assortment is followed which says the pairs of alleles for different traits separate independently of one another during gamete formation. In other words the inheritance of one trait has no influence on the inheritance of another trait.