Chapter 10

 Father of genetics – the branch of biology that studies heredity.  Mendel did his experiments on pea plants

 Mendel carried out the first important studies of heredity (the passing on of characteristics from parent to offspring)  Mendel controlled the pollination of the pea plants in his experiments.  Characteristics that are inherited are called traits.

 Each organism has two factors that control each of its traits.  These factors are called genes.  Genes exist in alternate forms called alleles (you have two alleles for each of your traits – one coming from your mom and one from your dad)

 Dominant – the observed trait (represented by a capital letter)  Recessive – the trait that disappeared (represented by a lower case letter) Ex. Tall plant (T) short plant (t)

 The dominant trait always wins out and is the trait to show up if it is present.  An uppercase letter represents dominant traits Ex. Tall plant (T) TT = ? short plant (t) Tt = ? tt = ?

 The appearance of an organism is called its phenotype (ex. Tall plant, brown hair)  The gene combination of an organism is called its genotype (ex. TT, Tt, tt)  You cant always know an organism’s genotype by looking at its phenotype.

 If both alleles for a trait are the same then the organism is homozygous. ex. TT = homozygous dominant tt = homozygous recessive  An organism is heterozygous for a trait if its two alleles are different. ex. Tt

 Crosses involving only “one” trait  P generation = parents F 1 generation = first filial generation F 2 generation = second filial generation

 Cross two parents to get the F 1 generation  Cross two F 1 to get the F 2 generation  Put the alleles for each parent on the outside of the box.

Chapter 10.2

 In the body cells of animals and most plants, chromosomes occur in pairs.  One chromosome came from the male parent, and the other came from the female parent.  A cell with two of each kind of chromosome is called a diploid (2n) cell.

 This pairing supports Mendel’s conclusion that organisms have two factors – alleles – for each trait.  Organisms produce gametes (sperm and egg) that contain one of each kind of chromosome.  A cell with one of each kind of chromosome is called a haploid (n) cell.

 Human diploid cells have 46 chromosomes (23 from mom and 23 from dad)  Human haploid cells have 23 chromosomes  If a dogs diploid cells had 78 chromosomes, how many chromosomes would its haploid cells have?

 Meiosis is the division of diploid cells to produce gametes containing half the number of chromosomes (haploid).  If meiosis didn’t occur, then the offspring would have twice as many chromosomes as the parents.  23 chromomes (sperm) + 23 chromosomes (egg) = 46 chromosomes (zygote)

 Consists of two separate divisions known as Meiosis I and Meiosis II.  Meiosis starts with one diploid cell and ends with 4 haploid cells.  Everything happens the same in the stages just like mitosis, but what happens to the chromosomes is different.

 The exchange of genetic material between chromosomes.  Crossing over can occur at any location on a chromosome (happens randomly)  Crossing over results in new combinations of alleles on a chromosome