SBI 3U Biology: Grade 11 University Preparation

Genetics

Heredity: The passing of traits from parents to offspring.

Genetics: The scientific study of heredity and variations.

Genetic information is contained in a molecule of DNA. Each thousands of chemical subunits that act as a set of chemical instructions. The instructions occur as distinct sequences of information along the DNA molecules- this is called a gene. Each gene occupies a specific location- locus/loci, on a chromosome. A typical chromosome carries information for hundreds or thousands of genes.
Chromosomes are found in the nucleus of all eukaryotic cells. Different organisms have different numbers of chromosomes- humans have 46. In most multicellular organisms chromosomes occur in sets or chromosomes. Haploid cells have half the normal number of chromosomes. Polyploids have three or more sets of chromosomes.

Asexual Reproduction: A form of reproduction in which a new individual is produced from a single parent by cell division- MITOSIS. This results in two new cells that are genetically identical.
Cell Division
MITOSIS: process through which the genetic material in the nucleus is divided into two new nuclei
→ Prophase: chromosomes shorten and thicken, centrioles move to opposite poles of the cell, nuclear membrane starts to divide.
→ Metaphase: each chromosome, composed of sister chromatids, pull towards the centre of the cell.
→ Anaphase: centromeres divide and sister chromatids move to opposite poles.
→ Telophase: chromosomes reach opposite poles and unwind, spindle fibre dissolves and nuclear membrane form around the chromosomes.
Cytokinesis: process in which a eukaryotic cell divides its cytoplasm into two new daughter cells.
Interphase: the part of the cell cycle in between divisions, genetic material is duplicated so that when the cell divides both new cell have the right number of chromosomes.

Chromatin: the tangled strands on DNA and protein within a eukaryotic nucleus,
Sister Chromatid: the identical copy of a single chromosome that remains attached to the original chromosomes at the centromere.

Sexual Reproduction: the form of reproduction in which individuals are produced from a fusion of two sex cells. They form offspring that are not genetically identical to the parents and rarely to each other.

Meiosis 1-
Prophase 1: nuclear membrane dissolves, centriole splits and its parts move to opposite ends of the cell. Spindle fibres are formed. Chromosomes come together in homologous pairs- each chromosome is composed of a pair of sister chromatids- whole structure is refereed to as a tetrad- the coming together of a tetrad is called synapsis. As they synapse, chromatids often intertwine and sometimes break and exchange segments- this referred to as crossing over, it permits the exchange of genetic material between homologous pairs of chromosomes.
Metaphase 1: homologous chromosomes attach to spindle fibres and line up along the equatorial plate.
Anaphase 1: segregation- at this point diploid parent cells become 2 haploid daughter cells.
Telophase 1: nucleus divides, chromosomes in each nuclei are not identical- each nuclei contains one member of chromosomes pair. Division of the cytoplasm follows this stage.

Meiosis 2: * no replication of chromosomes prior to cell division.
Prophase 1: nuclear membrane dissolves, spindle fibres begin to form.
Metaphase 2: chromosomes move to equatorial plate. Chromatids remain pinned by centromere.
Anaphase 2: centromere splits- each chromatid moves to opposite poles. Stage ends when nuclear membrane begins to form.
Telophase 2: second nuclear division completed. Second division of cytoplasm occurs. 4 haploid daughter cells are produced.

Karyotypes are used to look at the chromosomes that make up an individual.

Homologous Chromosomes: are similar in size, shape and genetic makeup.

The X and Y chromosomes determine the sex of an offspring; XX- female, XY- male.

Non-disjunction: the failure of