COMP 2

• development of male gametes : 1. diploid pollen mother cells undergo meiosis 2. forms a tetrad producing 4 haploid cells 3. inside pollen grain haploid nucleus undergoes mitosis producing generative and tube nucleus 4. generative nucleus then forms male gametes
• development of female gametes : 1. ovary contains ovule which contains megaspore 2. megaspore is surrounded by nucellus making 4 haploid cells 3. 3 cells disintegrate 4. remaining cells undergo mitosis 3x to produce 8 haploid cells 5. 2 haploid nucleus fuse making polar nucleus
• double fertilisation : 1. compatible pollen grain lands on the stigma, mitosis of pollen grain nucleus producing 2 male gametes 2. pollen tube nucleus will produce hydrolases that digests the style 3. pollen tube disintegrates 4. male gametes enter embryo sac and fuse with female gamete to form triploid primary endosperm
• Germination : 1. Water is imbibed through micropyle testa splits to allow more oxygen in for aerobic respiration 2. Food reserves from cotolydons = starch and proteins at hydrolysed 3. Provides energy for respiration
• fruit : a structure made from fertilised ovary
• Seed - structure from a fertilised ovule contains embryo Endosperm and testa
• monoctolydon - testa fuses with the ovary wall , endosperm is and contains 1 cotolydon and vascular bundle is scattered In the stems
• Spermatagenesis - 1. Spermatagonia divide many times by mitosis to make primary spermatocytes and more spermatagonia 2. Primary spermatocytes undergo meiosis to produce secondary spermatocytes 3. Secondary spermatocytes undergo meisosi ii making haploid spermatids 4. Spermatids mature into spermatazoa
• oogenesis - 1. oogonium undergo mitosis to make diploid oogonia and more oogonium 2. Oogonia then divide by mitosis to produce primary oocytes 3. A girl is born with millions of primary oocytes that are in prophase 1 . 4. The primary oocytes undergo meiosis || to produce secondary oocytes And 1st polar body 5. Then the ovum and second polar body are therefore created
• Fertilisation - involves capacitation , Acrosome reaction and cortical reaction . acrosome Secretes proteases which digest the zona pellucida , genetic material from sperm enter the secondary oocyte , they fuse and form a diploid nucleus , corona radiata then prevents polyspermy by producing fertilisation membrane
• Binomial system : a universal naming system used worldwide to show relatedness of species . Consists of Genus (capitals) and species (lower case )
• homologous structures : structures in different species with a similar form but different function . pentadactyl limb . due to convergent evolution
• divergent evolution : where a common ancestral structure has evolved and performs different functions
• convergent evolution : the development of similar features in unrelated organisms over long periods of time (wings)
• analogous structure : structure that has the same function but different structure wings in birds and insects
• If chi squared value is greater than or equal to critical value the null hypothesis is rejected
• If chi squared value is less Than critical value the null hypothesis is accepted
• Linked - genes are on the same chromosome . So independent assortment cannot occur . 3:1 ratio
• Unlinked : genes are on different chromosomes meaning independent assortment can occur . Gives rise to 9:3:3:1 ratio
• monohybrid heterozygous : 3:1 ratio
• Dominant phenotype ratio : 1:1
• Co-dominant or incomplete dominance ratio : 1:2:1
• Test cross : used to determine if an individual with a dominant trait comes from 1 or 2 dominant alleles
• X chromosomes are much larger than Y chromosomes as they contain additional genes that Y chromosome's do not have
• Many X linked recessive conditions are highly prevalent in males due to males having X and Y chromosomes and in order for males to express the phenotype they only need to inherit one of these x chromosomes
• mutagen : a chemical agent taht increases the rate of gene mutation can lead to cancer
• methylation prevents bases being recognised and the genes being turned on due to histone proteins coiling tightly and preventing gene expression . However modification does not effect base sequence of the gene and translation will still produce the same amino acid sequence
• Female spore is the embryo sac
• Generative nucleus then goes to form male gamete
• adavantges of self pollination - it can preserve successful genomes
• Development of fruit and seed : ovule Will contain embryo endosperm and testa which will form the seed , diploid zygote then divides by mitosis to form diploid embryo , Triploid endosperm nucleus divides by mitosis , ovary wall develops into fruit wall enclosing the seed
• Dicotyledon - such as the broad bean will contain most of its mass as a cotyledon
• monocotyledon : such as maize contains endospermic seeds and most of its mass will be the endosperm
• aleurone layer : high protein content layer in endospermic seeds
• effect of gibberellin : giberellin will go to the aleurone layer where it will promote the production of protease and amylase which will hydrolyse amino acids and starch , this will allow glucose and other nutrients to be made for aerobic respiration
• Tube nucleus controls the growth of the pollen tube ALWAYS MENTION
• The pollen tube enters the embryo sac via the micropyle
• Gene pool - all the alleles of all the genes in a population
• Natural selection : mutations can arise which can change allele frequency , variation in phenotypes due to different alleles , some alleles are more advantageous than others meaning this allows for an increase in frequency in these alleles in the gene pool as these advantageous alleles are passed on to the offspring as they are more likely to survive and reproduce , meaning natural selection has occurred
• Hybrid sterility - caused as a result of chromosomes not being homologous , this ensures no separation of homologous pairs during prophase I meaning meiosis cannot occur as a result