Environmental Biology & Genetics

1. Environmental Biology & Genetics Factors Affecting Variety in a Species Mr G Davidson

2. Sexual Reproduction • Plants and animals produce offspring in a process called reproduction. • There are 2 types of reproduction: • Asexual reproduction • Sexual reproduction Mr G Davidson

3. 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. Mr G Davidson

4. 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. Mr G Davidson

5. 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. Mr G Davidson

6. 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. Mr G Davidson

7. 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. Mr G Davidson

8. Sexual Reproduction in Plants Mr G Davidson

9. 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. Mr G Davidson

10. Sexual Reproduction in Mammals • Eggs are produced in the ovaries. • Sperm swim along the oviduct. • Fertilisation can only take place in the oviduct. Mr G Davidson

11. 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. Mr G Davidson

12. 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 Mr G Davidson

13. 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. Mr G Davidson

14. Variation in Humans • Human characteristics are controlled by genes. • Genes are found on chromosomes. • Chromosomes are found in the nucleus of every cell. Mr G Davidson

15. 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. Mr G Davidson

16. Genetics • Chromosomes are found in pairs. • Chromosomes are made of DNA bases. • There are four kinds of DNA base • DNA carries coded information. Mr G Davidson

17. DNA base Backbone Base Mr G Davidson

18. Function of DNA • DNA carries genetic instructions which allow the cell to make specific protein molecules. • Proteins are built using amino acid molecules. Mr G Davidson

19. 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. Mr G Davidson

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

21. 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. Mr G Davidson

22. 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. Mr G Davidson

23. 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. Mr G Davidson

24. 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. Mr G Davidson

25. Gamete Production • This is called chromosome shuffling. • This is also called random assortment. • It is this shuffling which results in the variation of offspring. Mr G Davidson

26. Sex Determination • In humans the 23rd 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. Mr G Davidson

27. Sex Determination Mr G Davidson

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

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

30. 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. Mr G Davidson