Starter • Describe what a gene is. • Describe the three main components of a DNA molecule. You may use the diagram to help you.
Starter • A gene is a sequence of bases / part of a DNA molecule or chromosome, that codes for a characteristic/trait/protein. • Phosphate • Pentose Sugar • Nitrogenous Base
Starter • The sequence of DNA shown was repeated in a larger section of DNA, and it was found that Adenine (A) occurred 300 times. • How many times would Cytosine (C), Thymine (T) and Guanine (G) occur? • C – 600 • T – 300 • G – 600
Starter • Using one or more examples, discuss how DNA determines the characteristics of an individual. • DNA carries information in the order of bases / nucleotide OR Genes / Alleles. • Links code to the production of traits / characteristics. • Discusses how the order of bases AND genes / alleles carry genetic information AND uses an example to show how differences are produced.
Human Chromosomes • Human cells have 23 pairs of chromosomes (homologous pairs) for a total of 46. • One member of each pair comes from the sperm and the other from the egg. • Each chromosome in the homologous pair will contain the same genes (possibly different alleles)
Karyotype • Karyotype - Chromosomal characteristics of an organism.
Mitosis • Mitosis is the process in which a cell duplicates its chromosomes and the nucleus divides to generate two identical cells. • Occurs when organisms grow (i.e. from a zygote to adult) and also in wound healing. • Happens throughout the body, but particularly in bone marrow, skin, hair and nails.
Zygo-whaty? • Zygote is the first cell that is produced after fertilization (when the egg fuses with the sperm).
Cut and Paste Mitosis • For the next few slides, write down the steps and find the picture which best fits the description.
Sequence of Events • Chromatin in the nucleus begins to condense and becomes visible as chromosomes. Chromosome Chromatin
Sequence of Events • Each chromosome forms an identical pairthat remains attached at theCentromere. Centrioles begin moving to opposite ends of the cell. • The nuclear membrane dissolves as centrioles send out spindle fibres to attach to the centromeres.
Centromere Unduplicated Duplicated
Sequence of Events • Spindle fibres align the chromosomes along the middle of the cell nucleus. • The paired chromosomes separate at the centromere and move to opposite sides of the cell. • Chromosomes arrive at opposite poles and the cell begins to divide into two.
46 chromosomes + 46 chromosomes