Mendel and Meiosis Basic Genetics

Gregor Mendel’s Peas Gregor Mendel’s Peas Genetics is the scientific study of heredity. Gregor Mendel was an Austrian monk. His work was important to the understanding of heredity. Considered to be “Father of Genetics” Mendel carried out his work with ordinary garden peas. Copyright Pearson Prentice Hall

Mendel observed the phenomenon of inheritance Heredity is the transmission of traits from parents to offspring. Mendel knew that the male part of each flower produces pollen, (containing sperm). the female part of the flower produces egg cells.

Characteristics Mendel Studied Seed texture Seed color Seed coat color Pod appearance Pod color Position of flowers along stem Stem length A trait is a specific characteristic that varies from one individual to another

Pollination The transfer of pollen is known as pollination The transfer of pollen within a single plant OR fertilization that occurs with a single plant is known as self-pollination An organism that has the same genes for a particular trait is known as pure-bred The transfer of pollen from one plant to another OR fertilization that occurs between two individual plants is known as cross pollination

Each original pair of plants is the P (parental) generation. The offspring are called the F1, or “first filial,” generation - Offspring of our parents The offspring of crosses between parents with different traits are called hybrids. Mendel crossed the F1 generation with itself to produce the F2 (second filial) generation. – Our children

Mendel's first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next. Today, scientists call the factors that determine traits genes.

Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait. The different forms of a gene are called alleles.

Mendel’s second conclusion is called the principle of dominance. The principle of dominance states that some alleles are dominant and others are recessive.

Meiosis – 2 nuclear divisions Definition – cell division Occurs in the Sex cells – gametes 4 Daughter Cells are formed with HALF of the number of chromosomes Humans have 46 Chromosomes; 23 in egg and 23 in sperm 2 Stages of Meiosis

Meiosis I – 1St Stage 4 Stages – Prophase I, Metaphase I, Anaphase I, Telophase I Prophase I - Homologous chromosomes pair to form tetrads – “crossing over” may occur Metaphase I – Tetrads line up at the equator Anaphase I – Separation occurs and each homologous chromosome goes to a pole Telophase I – Original cell divides into two and each cell has one of the homologous chromosomes

Meiosis II – 2nd Stage- NO DNA replication Prophase II, Metaphase II, Anaphase II, Telophase II Prophase II – nuclear membrane disappears Metaphase II – Chromosomes line up at equator Anaphase II – Separation occurs however, this time sister chromatids separate at the centromere Telophase II – Original cell is divided into 4 haploid cells, each containing HALF the number of chromosomes

More About Meiosis Sexual reproduction – 2 cells unite to form 1st cell of an organism Zygote – fertilized egg Haploid – (N); ½ number of chromosomes (sex cell number) ex: N=23 chromosomes Diploid – (2N) Original number of chromosomes (body cell number) ex: 2N=46 Gametes – sex cells

Advantages and Disadvantages of Sexual and Asexual Reproduction   Advantages Disadvantages Asexual Reproduction It produces a large number of offspring quickly, which may increase chances of survival in a favorable and stable environment. It requires only one parent organism. Offspring are genetically identical to parent organism, which may limit their ability to survive a changing environment. Sexual Reproduction Offspring are genetically different from each parent, which may help the organism to adapt and survive a changing environment. It produces a smaller number of offspring more slowly, so fewer offspring may survive. It usually requires two parents, one male and one female.