Heredity and Reproduction The Nature of Heredity

Genetic Material Genetics is the study of heredity and variation. Chromosomes are made of DNA (deoxyribonucleic acid) A gene is a segment of a DNA molecule that codes for a specific trait and is always found at the same spot (locus) on a chromosome.

Asexual Reproduction A new individual is created from a single parent by cell division. Genes are identical to parent. Advantages: parent does not have to find a mate, no specialized mating behaviours, no need for complex anatomy.

Types of Asexual Reproduction Runners: above ground stems that extend and produce a new plant Budding: a new individual is an outgrowth of the parent before it buds off and becomes it’s own body. Binary fission: parent splits into two Fragmentation: fungi do this; a fragment of the parent develops into a mature individual.

Cell Division Mitosis happens for growth and development, tissue repair replacing cells that have aged Cell division happens at different rates depending on where the cell is located in the body, the age of the organism and even which organism it is. Mitosis occurs when a parent cell divides into 2 daughter cells (which are genetically identical to each other and the parent cell)

Because the genetic material is the same, we call it genetic continuity. DNA --> chromatin (DNA + protein)--> chromosome (condensed and folded) Occurs in all of our body cells: somatic cells Each human cell has 46 chromosomes, which we call the diploid number. After Mitosis cells will go through differentiation where they will specialize and have different forms and functions within the organism. Mitosis and Cancer: cancer is basically mitosis gone out of control. There are many types of therapy to help combat cancer.

Cloning Is the process of producing one individual that is genetically identical to another using a single cell or tissue. Biotechnology is the use of organisms for applications in engineering, industry, and medicine. Cloning of plants is widely used today. In 1996, the world’s most famous sheep, “Dolly” was born. She was the first mammal cloned from an adult body cell.

Applications of Cloning Mass production of livestock and crop plants –Improve livestock and crop production –May be very expensive –Unnatural/unethical –Vulnerability to disease Clone genetically modified organisms (GMOs) –Commercial insulin –GM bananas: have genes for hepatitis vaccine –GM pigs: production of omega-3 fatty acids Cloning endangered species –Genetic variability is still a problem

Sexual Reproduction Individuals are produced from the fusion of two cells. Sex cells usually come from two different parents. Offspring are genetically different from parents.

Meiosis A two-stage cell division in which the resulting daughter cells have half the number of chromosomes as the parent cell; results in the formation of gametes or spores. The number of chromosomes in somatic (body) cells any organism has is referred to as the diploid number (2n). We have 23 pairs of homologous chromosomes making 46 chromosomes in total. We have 23 chromosomes from our mother, and 23 from our father. Each gene has its own specific position on the DNA strand, this is called its locus.

Because we have homologous pairs of chromosomes, the genes will be found at the same locus on each of the pairs. Sometimes both chromosomes will not have the identical genes on them, when they have these differences they are called alleles. Meiosis produces gametes that contain one of each of the homologous pairs of chromosomes and therefore will have only 23 chromosomes in a gamete. This is called the haploid number. (n) When fertilization happens, the male gamete (the sperm that is made by the spermatogonia in the testes) and the female gamete (the egg that is made by oogonia in the ovaries) join together, resulting in a diploid cell called the zygote.

Meiosis produces genetic variability in two ways: –By random assortment of the maternal and paternal sets of chromosomes during Metaphase I. –By the crossing over during Prophase I.

Prophase II Prophase I Metaphase IAnaphase I Telophase I Interphase Metaphase II Anaphase II Telophase II

Random Assortment During meiosis I, homologous pairs line up in pairs and separate. The number of possible combinations depends on the number of chromosome pairs. For the same couple mating, with only three chromosome pairs it would be 2 3 = 8 different possibilities. Since we have 23 pairs, it would be 2 23 = different possibilities!! This variation doesn’t even include crossing over! That’s why we look so different!

Female Meiosis The formation of egg cells is a bit different because only one egg is made each month, but more energy goes into making that egg. –Telophase I: the cytoplasm does not divide equally and the parent cell (primary oocyte) divides into one large haploid cell and one small haploid cell. –larger cell: secondary oocyte; the smaller cell: polar body. –Meiosis II: large cell divides unequally again, making a larger cell (egg or ovum) and a smaller cell (polar body.) –The polar body produced after meiosis I may also divide and make two small polar bodies or it may just deteriorate. –End result: only 1 functional cell, but it has a lot more cytoplasm and nutrients. Hence the difference in size between the egg and sperm.

Karyotypes The chromosomes of an individual that have been sorted and arranged according to size and type. Numbers 1 to 22 are autosomal chromosomes Number 23 are the sex chromosomes (XX or XY)