Biology 12

Inheritance Organisms inherit characteristics from their parents Characteristics are controlled by DNA In asexual reproduction, organisms inherit DNA from 1 parent In sexual reproduction, organisms inherit DNA from both parents

DNA DNA is found in the nucleus of cells It is organised into segments called chromosomes Chromosomes are only visible when the cell is dividing

DNA controls protein synthesis

Why are proteins important? Roles of proteins in the body include Structural proteins eg collagen, keratin Enzymes (organic catalysts) eg digestive enzymes Transport proteins eg haemoglobin Regulatory proteins eg hormones Protective proteins eg antibodies, clotting factors Therefore proteins determine what you will look like, and how your body functions

Genes and chromosomes The segment of DNA that controls one characteristic is called a gene Genes are found on structures called chromosomes The location of the gene on a chromosome is called its locus

Asexual reproduction One parent No variation in offspring Advantages - low complexity, rapid division Disadvantages – as all offspring identical, have smaller ability to survive change

Sexual reproduction 2 parents Variation in offspring Advantages – variation gives better chance of species survival if change occurs Disadvantages – more complex, takes longer to produce offspring

Cell division for reproduction The process of cell division for asexual reproduction is called mitosis Offspring will have the same number of chromosomes as their parent The process of cell division for sexual reproduction is called meiosis It is necessary in order to reduce the number of chromosomes Gametes will contain half the number of chromosomes – this is called the haploid number

Events of meiosis

Comparing mitosis and meiosis MitosisMeiosis Where it occurs Body cellsGonads (reproductive organs) Why it occurs Cell repair, growth, asexual division Sexual reproduction Number of cells produced 24 Number of divisions 12 Number of chromosomes in daughter cells Same as parent (diploid) Half that of parent (haploid) Amount of variation in daughter cells NoneLots

Comparing mitosis and meiosis 2 MitosisMeiosis Advantages for reproduction Simple Rapid division Allows variation Disadvantages for reproduction No variationMore complex Slower reproduction

Homologous chromosomes Chromosomes in diploid organisms come in pairs called homologous chromosomes Organisms inherit one of each pair from each of their parents Each chromosome of a pair has loci for the same genes That means organisms have at least 2 genes for each characteristic – one from each parent

Alleles Genes can come in alternative forms called a Organisms can carry two identical alleles for a characteristic and be called homozygous Organisms can carry two different alleles for a characteristic and be called heterozygous

Dominant – recessive inheritance If an organism has two identical alleles, they will show the characteristics of that allele If an individual has two different alleles, sometimes they will only show the characteristic of one of the alleles This is called Dominant - recessive inheritance The allele that is expressed is called Dominant The allele that is hidden is called recessive Examples include Tongue rolling, Huntington’s chorea, Purple flower colour in peas

Co-dominant inheritance If an organism has two identical alleles, they will show the characteristics of that allele If an individual has two different alleles, sometimes they will only show a characteristic that is a mixture of both alleles This is called co-dominance, incomplete dominance or blending Examples include flower colour in snap dragons, A & B blood groups, roan colour in cows and horses

Genotype and phenotype The genotype describes the alleles that are present The phenotype describes the characteristic that the organism shows

Chromosome numbers Different species have different numbers of chromosomes In some species the male has a different number of chromosomes to the female The diploid number is the number of chromosomes with homologous pairs (ie found in normal cells) The haploid number is the number of chromosomes with only 1 of each homologous pair (ie found in gametes)

Environmental influences Some inherited characteristics are influenced by the environment eg height and weight are affected by diet & exercise, skin colour is affected by exposure to the sun

Roulette wheel