Environmental Biology & Genetics Factors Affecting Variety in a Species M r G D a v i d s o n

Saturday, August 08, 20152Mr G Davidson Sexual Reproduction  Plants and animals produce offspring in a process called reproduction.  There are 2 types of reproduction:  Asexual reproduction  Sexual reproduction

Saturday, August 08, 20153Mr G Davidson Asexual Reproduction  Asexual reproduction only involves one parent.  In asexual reproduction the offspring are identical to the parent.  In asexual reproduction the offspring are identical to each other.

Saturday, August 08, 20154Mr G Davidson Sexual Reproduction  In sexual reproduction 2 parents are involved.  In sexual reproduction the offspring are similar to the parents but not identical.  Sexual reproduction is the key to variety and biodeiversity.

Saturday, August 08, 20155Mr G Davidson Sexual reproduction in Plants  The sex organs of a plant are found inside the flowers.  Most of these flowers have both male and female parts inside them.  The sex organs produce sex cells called gametes.  A gamete is a cell containing half the total number of chromosomes for that organism.

Saturday, August 08, 20156Mr G Davidson Sexual reproduction in Plants  Flowers have parts called anthers which produce pollen grains containing the male gametes.  The ovary produces ovules which contain the female gametes.

Saturday, August 08, 20157Mr G Davidson Sexual Reproduction in Plants  The nucleus of the pollen and the egg fuse together and this is called fertilisation.  During fertilisation a zygote is produced.

Saturday, August 08, 20158Mr G Davidson Sexual Reproduction in Plants Part of FlowerFunction OvaryMakes ovules OvuleFemale gamete AntherMakes pollen PollenMale gamete

Saturday, August 08, 20159Mr G Davidson Sexual Reproduction in Mammals  The male gametes are the sperm and are produced in the testes.  The sperm travel from the testes along the sperm duct.

Saturday, August 08, Mr G Davidson Sexual Reproduction in Mammals  Eggs are produced in the ovaries.  Sperm swim along the oviduct.  Fertilisation can only take place in the oviduct.

Saturday, August 08, Mr G Davidson Fertilisation in Humans  One sperm joins with one egg and a zygote is formed.  The zygote contains a full set of chromosomes, half from the sperm and half from the egg.

Random Combination of Chromosomes  An male mammal has  one set of chromosomes from the father  one set of chromosomes from the mother  When the gametes are formed these chromosomes are distributed randomly  That is the set of chromosomes in the gamete contains some from the male parent and some from the female parent Saturday, August 08, Mr G Davidson

Saturday, August 08, Mr G Davidson Variation in Humans  Humans have 23 pairs of chromosomes in every cell except the gametes.  There is an enormously large number of combinations of chromosomes to form zygotes because fertilisation is random.  This means that all zygotes are different.

Saturday, August 08, Mr G Davidson Variation in Humans  Human characteristics are controlled by genes.  Genes are found on chromosomes.  Chromosomes are found in the nucleus of every cell.

Saturday, August 08, Mr G Davidson Genetics  A gene is a section of chromosome which carries one piece of genetic information.  The total number of chromosomes in each cell of an organism is called the chromosome complement  (note the first “e” otherwise it means praise).  The genes determine the characteristics of an organism.

Saturday, August 08, Mr G Davidson Genetics  Chromosomes are found in pairs.  Chromosomes are made of DNA bases.  There are four kinds of DNA base  DNA carries coded information.

Saturday, August 08, Mr G Davidson DNA base Backbone Base

Saturday, August 08, Mr G Davidson Function of DNA  DNA carries genetic instructions which allow the cell to make specific protein molecules.  Proteins are built using amino acid molecules.

Saturday, August 08, Mr G Davidson Function of DNA  A DNA molecule contains a sequence of chemical bases which codes for the amino acids.  The order of the DNA bases is code for the order of amino acids in the protein.

Saturday, August 08, Mr G Davidson Function of DNA Amino acid A Sets of bases on the DNA strand code for each……… …….. amino acid which join together to make a protein molecule. Amino acid A Amino acid C Amino acid B

Relationship between proteins and characteristics  The protein haemoglobin gives red blood cells their colour.  Enzymes, used in digestion, are all proteins.  Hormones, used in the control of the body, are proteins. Saturday, August 08, Mr G Davidson

Saturday, August 08, Mr G Davidson Gamete Production  Gametes are sex cells.  Reproduction involves the joining of gametes.  In the sex organs, gametes are formed from gamete mother cells.  This is done by a type of cell division called meiosis.

Saturday, August 08, Mr G Davidson Gamete Production  This reduces 2 sets of double chromosomes in the gamete mother cell to 1 set of single chromosomes in each of the gametes.  When the gametes fuse together at fertilisation, the zygote produced will have 2 matching sets of single chromosomes.

Saturday, August 08, Mr G Davidson Meiosis  Meiosis is a special form of cell division that produces gametes.  The different ways in which the matching chromosomes can pair up during meiosis increases the total number of gamete varieties.

Saturday, August 08, Mr G Davidson Gamete Production  This is called chromosome shuffling.  This is also called random assortment.  It is this shuffling which results in the variation of offspring.

Saturday, August 08, Mr G Davidson Sex Determination  In humans the 23 rd pair of chromosomes are called the sex chromosomes.  In human females the sex chromosomes are X and X.  In human males the sex chromosomes are X and Y.  Each individual inherits one sex chromosome from each parent gamete.

Sex Determination Saturday, August 08, Mr G Davidson

Saturday, August 08, Mr G Davidson Sex Determination Male gametes X or Y Female gametes X or X Y X XX X X If these chromosomes meet, the result is a female zygote.

Saturday, August 08, Mr G Davidson Sex Determination Female gametesMale gametes X or Y X or X Y X XX X Y If these chromosomes meet, the result is a male zygote. If the other male chromosome meets a female chromosome, the following happens.

Saturday, August 08, Mr G Davidson Sex Determination  Sex in humans is determined by the male gamete.  The ratios of males to females is always 1:1 because half the sperm are X and the other half are Y.  Because this process is random, a 1:1 ratio is not always produced, but the greater the number in the sample, the closer it will be to a 1:1 ratio.