Cellular Control Unit 1 Communication, Homeostasis and Energy
Cellular Control Unit 1 Communication, Homeostasis and Energy Meiosis Module 1: Cellular Control Learning outcomes describe, with the aid of diagrams and photographs, the behaviour of chromosomes during meiosis, the associated behaviour of the nuclear envelope, cell membrane and centrioles. (Names of the main stages are expected, but not the subdivisions of prophase); Reproduction and variation Asexual reproduction Single organism divides by mitosis New organism is genetically identical to the parent Sexual reproduction Meiosis produces haploid gametes Which fuse at fertilisation to form a diploid zygote This produces genetic variation amongst offspring Human Life Cycle Diploid Zygote 46 fertilisation Mitosis Haploid Sperm 23 Haploid Egg 23 Meiosis Adult 46 Self assessment questions The fruit fly Drosophila melangaster has eight chromosomes in its body cells. How many chromosomes will there be in a Drosophila sperm? The symbol n is used to indicate the number of chromosomes in one set – the haploid number of chromosomes. For example in humans n = 23, in a horse n = 32. How many chromosomes are there in a gamete of a horse? What is the diploid number of chromosomes (2n) of a horse? Meiosis Meiosis is a reduction division Resulting daughter cells have half the original number of chromosomes Daughter cells are haploid Can be used for sexual reproduction Source of genetic variation Meiosis has two divisions meiosis I and meiosis II Each division has 4 stages Prophase, metaphase, anaphase, telophase Meiosis You can view an animation of Meiosis at http://www.cellsalive.com/meiosis.htm Meiosis I Prophase I Chromatin condenses Homologous pairs form a bivalent Nucleolus disappears Spindle forms Anaphase I Homologous chromosome in each bivalent are pulled to opposite poles Metaphase I Bivalents line up on equator of cell Telophase I Two new nuclear envelopes form Cell divides by cytokinesis Early Prophase 1 Late Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Cytokinesis 1 Meiosis II Prophase II Metaphase II Anaphase II Telophase II Nucleolus disappears Chromosomes condense Spindle forms Centromeres divide Chromatids pulled apart to opposite poles Chromosomes arrange themselves on equator Attach by centromere to spindle fibres nuclear envelopes reform around haploid nuclei Cell divides by cytokinesis Prophase II Metaphase II Anaphase II Telophase II Cytokinesis II Learning outcomes explain how meiosis and fertilisation can lead to variation through the independent assortment of alleles Key words Allele Locus Crossing over Maternal chromosome Paternal chromosome Alleles, locus and homologous chromosomes Meiosis and variation Meiosis enables sexual reproduction to occur by the production of haploid gametes. Sexual reproduction increases genetic variation Genetic variation increases the chances of evolution through natural selection Meiosis and Variation Crossing over – prophase I Independent assortment of chromosomes – metaphase I Random assortment of chromatids – metaphase II Random fertilisation Chromosome mutations Number of chromosomes ▪ Non-disjunction - polysomy or polyploidy Structure of chromosomes ▪ Inversion, deletion, translocation Crossing over During metaphase I During metaphase I No crossing over Crossing over – new combinations of alleles Independent Assortment Learning Outcomes explain the terms allele, locus, phenotype, genotype, dominant, codominant and recessive; explain the terms linkage and crossingover; Glossary Gene Locus Allele Genotype Phenotype Heterozygous Homozygous Monohybrid cross Dominant allele Recessive allele Genetics Genetics is the study of inheritance Allele different varieties of the same gene Locus position of a gene on a chromosome Genetics Dominant An allele whose effect is expressed in the phenotype if one copy present Recessive An allele which only expresses as a homozygote Co-dominant Both alleles have an effect on the phenotype Genotype genetic constitution of the organism Phenotype appearance of character resulting from inherited information Homozygous Individual is true breeding Possesses two alleles of a gene e.g. RR or rr Heterozygous Two different alleles for a gene e.g. Rr Monohybrid inheritance Mendel’s First Law principle of segregation “The alleles of a gene exist in pairs but when gametes are formed, the members of each pair pass into different gametes, thus each gamete contains only one of each allele.” Inheritance of height in pea plants gene Height of pea plants Allele relationship Symbol Tall Dominant T dwarf recessive t Follow out the following cross to the F2 generation Homozygous tall pea plant with a homozygous dwarf pea plant Write out the genotypic and phenotypic ratios from the F2 generation Inheritance of height in pea plants Laying out the cross P phenotype P genotype Gametes F1 genotype F1 phenotype F1 self-fertilised Gametes Random fertilisation F2 genotypic ratio F2 phenotypic ratio Pupil Activity Answer the questions on monohybrid inheritance Remember to write out each cross in full. Cystic Fibrosis Cystic Fibrosis is caused by a mutation to a gene on one of the autosomes. Mutation Changes the shape of the transmembrane chloride ion channels (CFTR protein) The CFTR gene is found on Chromosome 7 The faulty gene is recessive Genetic Cross conventions Use symbols to represent two alleles Alleles of the same gene should be given the same letter Capital letter represents the dominant allele Small letter represents the recessive allele Choose letters where the capital and small letter look different The examiner needs to be in no doubt about what you have written Inheritance of cystic fibrosis Three possible genotypes FF Ff ff unaffected unaffected cystic fibrosis Remember gametes can only contain one allele for the CFTR gene At fertilisation, any gamete from the father can fertilise any gamete from the mother This can be shown in a genetic diagram Genetic diagram showing the chances of a heterozygous man and a heterozygous woman having a child with cystic fibrosis. Phenotype ratio of offspring Genotype ratio 1FF:2Ff:1ff Phenotype ratio 3 unaffected:1cystic fibrosis Can also be expressed as 25% chance of the child having cystic fibrosis Probability of 0.25 that a child will inherit the disease Probability that 1 in 4 that a child from these parents will have this disease. Learning Outcome Use genetic diagrams to solve problems involving sex-linkage and codominance. Sex-Linkage Sex-linked genes are genes whose loci are on the X or Y chromosomes The sex chromosomes are not homologous, as many genes present on the X are not present on the Y. Examples Haemophilia Fragile X syndrome Red green colour blindness Sex Chromosomes Factor VIII and Haemophilia Haemophilia is caused by a recessive allele of a gene that codes for a faulty version of the protein factor VIII XH Xh normal allele haemophilia allele possible genotypes and phenotypes Inheritance of Haemophilia Pedigree for a sex linked recessive disease Codominance Codominance describes a pair of alleles, neither of which is dominant over the other. This means both have an effect on the phenotype when present together in the genotype Codominance example Flower colour in plants CR Cw red white Genotypes CRCR CRCW CWCW red flowers pink flowers white flowers Write out a genetic cross between a pure breeding red plant and a pure breeding white plant. Carry out the cross to the F2 generation. Write out the genotype and phenotype ratio for the F2 generation Revision Question Coat colour in Galloway cattle is controlled by a gene with two alleles. The CR allele produces red hairs and therefore a red coat colour. The Cw allele produces white hairs. A farmer crossed a true-breeding, red-coated cow with a true-breeding white-coated bull. The calf produced had roan coat colouring (made up of an equal number of red and white hairs). Explain the result and draw a genetic diagram to predict the outcome of crossing two roan coloured animals. Inheritance of A, B, AB and O blood groups Human blood groups give an example of codominance and multiple alleles There are 3 alleles present ▪ IA ▪ IB ▪ Io IA and IB are codominant Io is recessive Remember each human will only have two alleles Blood Groups Genotype Phenotype IAIA IA Io IAIB IBIB IB Io Io Io Blood Group A Blood Group A Blood Group AB Blood Group B Blood Group B Blood Group o Inheritance of blood groups Carry out genetic crosses for the following examples Two parents have blood groups A and B, the father is IAIo and the mother is IBIo Father has blood group AB and the mother has blood group O Mother is homozygous blood group A and the father is heterozygous B. Learning Outcome Describe the interactions between loci (epistasis). Predict phenotypic ratios in problems involving epistasis. Dihybrid Inheritance Monohybrid cross Inheritance of one gene Dihybrid cross Inheritance of two genes Example – dihybrid cross Tomato plants Stem colour A purple stem a green stem d potato leaves Leaf shape D cut leaves NOTE In the heterozygote AaDd due to independent assortment in meiosis there are 4 possible gamete combinations AD Ad aD ad Crosses Cross a heterozygous plant with a plant with a green stem and potato leaves Cross two heterozygous tomato plants Dihybrid Inheritance A woman with cystic fibrosis has blood group A (genotype IAIo). Her partner does not have cystic fibrosis and is not a carrier for it. He has blood group O. Write down the genotypes of these two people. With the help of a full and correctly laid out genetic diagram, determine the possible genotypes and phenotypes of any children that they may have. Autosomal linkage Each Chromosome carries a large number of linked genes If two genes are on the same chromosome then independent assortment can not take place. The genes are transmitted together and are said to be linked. Linked Genes Where linked genes are involved the offspring of a dihybrid cross will result in a 3:1 ratio instead of the 9:3:3:1 ratio. Example: In peas, the genes for plant height and seed colour are on the same chromosome (i.e. linked) Learning Outcome Describe the interactions between loci (epistasis). Predict phenotypic ratios in problems involving epistasis. Flower colour in sweet pea Flower colour Colourless precursor of a pigment C Gene that controls conversion of this pigment to purple P Both dominant alleles need to be present for the purple colour to develop Cross Cross two white flowered plants with the genotypes CCpp and ccPP Follow this cross through to the F2 generation Interactions of unlinked genes A single character maybe influenced by two or more unlinked genes. E.g. determination of comb shape in domestic poultry Dominant allele P pea comb Dominant allele R rose comb Two dominant alleles walnut comb No dominant alleles single comb Genetic Crosses Carry out a genetic cross between a true-breeding pea comb and a true breeding rose comb Follow this cross through to the F2 generation Inheritance of coat colour in mice Wild mice have a coat colour that is referred to as “agouti”. Agouti (A) is dominant to black (a) C is a dominant gene required for coat colour to develop A homozygous recessive cc means that no pigment can be formed and the individual is albino Inheritance of coat colour in mice Carry out a cross between a purebreeding black mouse (aaCC) and an albino (AAcc) Follow this cross through to the F2 generation. Epistasis This is the interaction of different gene loci so that one gene locus masks or suppresses the expression of another gene locus. Genes can Work antagonistically resulting in masking Work complementary Epistasis ratios 9 : 3 : 4 ratio Suggests recessive epistasis 9 : 7 ratio Suggests epistasis by complementary action 12 : 3 : 1 ratio or 13 : 3 ratio Suggests dominant epistasis Predicting phenotypic ratios Read through pages 132 and 133 of your textbook Answer questions 1 – 7 Complete the stretch and challenge question on “eye colour in humans” Read through and complete the worksheet provided for you on epistasis Learning outcome Use the chi-squared (χ2) test to test the significance of the difference between observed and expected results. χ2 (chi-squared) test Allows us to compare observed and expected results and decide if there is a significant difference between them. χ2 (chi-squared) test Where Σ = the sum of O = observed value E = expected value χ2 (chi-squared) test Compare the χ2 value to a table of probabilities The probability that the differences between our expected and observed values are due to chance. If the χ2 value represents a probability of 0.05 or larger, the differences are not significant If the χ2 value represents a probability of less than 0.05, it is likely that the results are not due to chance and there is a significant difference. Degrees of freedom The degrees of freedom takes into account the number of comparisons made. Degrees of freedom = number of classes of data - 1 Table of χ2 values Degrees of freedom 1 2 3 4 Probability greater than 0.1 0.05 0.01 0.001 2.71 4.60 6.25 7.78 10.83 13.82 16.27 18.46 3.84 5.99 7.82 9.49 6.64 9.21 11.34 13.28 Critical value 95% certain that the results are not due to chance Table of χ2 values Degrees of freedom 1 2 3 4 Probability greater than 0.1 0.05 0.01 0.001 2.71 4.60 6.25 7.78 10.83 13.82 16.27 18.46 3.84 5.99 7.82 9.49 Accept null hypothesis There is no significant difference, results have occurred due to chance 6.64 9.21 11.34 13.28 Table of χ2 values Degrees of freedom 1 2 3 4 Probability greater than 0.1 0.05 0.01 0.001 2.71 4.60 6.25 7.78 10.83 13.82 16.27 18.46 3.84 5.99 7.82 9.49 6.64 9.21 11.34 13.28 Reject null hypothesis: accept experimental hypothesis Difference is significant, not due to chance Mammal question χ2 value = 51.8 Degrees of freedom = 3 Critical value (p=0.05) = 7.82 Reject the null hypothesis There is a significant difference between observed and expected results Suggestions? The two genes are linked Variation What did you learn at AS level? Learning Outcomes Define the term variation. Discuss the fact that variation occurs within as well as between species. Describe the differences between continuous and discontinuous variation, using examples of a range of characteristics found in plants, animals and microorganisms. Explain both genetic and environmental causes of variation. Variation Variation is the differences that exist between individual organisms. Interspecific variation (between species) ▪ Differences that are used to assign individuals to different species Intraspecific variation (within a species) ▪ Individuals of the same species show variation Variation can be inherited or influenced by the environment. Types of variation There are two main types of variation Continuous variation Discontinuous variation There are two main causes of variation Genetic variation Environmental variation Continuous variation Existence of a range of types between two extremes Most individuals are close to a mean value Low numbers of individuals at the extremes Both genes and the environment interact in controlling the features Examples Height in humans Length of leaves on a bay tree Length of stalk of a toad stool Continuous variation Use a tally chart and plot results in a histogram Discontinuous variation 2 or more distinct categories with no intermediate values Examples Earlobes Blood groups Bacteria Flowers attached or unattached A, B, AB or o flagella or no flagella colour of petals Genetically determined The environment has little or no effect on discontinuous variation Discontinuous variation Causes of variation Genetic Variation Genes inherited from parents provide information used to define our characteristics Environmental Variation Gives differences in phenotype (appearance) but not passed on by parents to offspring Examples ▪ Skin colour tans with exposure to sunlight ▪ Plant height determined by where the seed lands Variation What you need to know for A2!! Learning outcomes Describe the differences between continuous and discontinuous variation. Explain the basis of continuous and discontinuous variation by reference to the number of genes which influence the variation. Explain that both genotype and environment contribute to phenotypic variation. Explain why variation is essential in selection. variation Variation can be: Discontinuous ▪ Each organism falls into one of a few clear-cut categories, no intermediate values ▪ Qualitative differences between phenotypes Continuous ▪ No definite categories ▪ A continuous range of values between two extremes ▪ Quantitative differences between phenotypes Genes and variation Discontinuous (qualitative) variation Monogenic inheritance Different alleles at same gene locus Different gene loci have different effects Epistasis, codominance, dominance and recessive patterns of inheritance Genes and Variation Continuous (quantitative) variation Polygenic inheritance Two or more genes Each gene has an additive effect Unlinked genes Polygenic Inheritance Example –length of corn cobs Three genes – A/a, B/b and C/c Each dominant allele adds 2 cm length Each recessive allele adds 1 cm length So AABBCC aabbcc Hmmm!! = 12 cm long = 6 cm long How long would AaBBCc be? How long would aaBbCc be? Genotype, environment and phenotype The environment can affect the expression of the genotype examples AABBCC has the genetic potential to produce cobs 12cm long ▪ This could be affected by ▪ Lack of water, light or minerals Obesity in humans ▪ Affected by diet and exercise Genotype, environment and phenotype The environment influences the expression of polygenic traits more than monogenic traits. Learning Outcomes Use the Hardy–Weinberg principle to calculate allele frequencies in populations. Population genetics What is a population? Group of individuals of the same species that can interbreed Populations are dynamic The set of genetic information carried by a population is the gene pool. Allele Frequency To measure the frequency of an allele you need to know Mechanism of inheritance of that trait How many different alleles of the gene for that trait are in the population Hardy-Weinberg principle The Hardy-Weinberg principle is a fundamental concept of population genetics It makes the following assumptions Population is very large Random mating No selective advantage No mutation, migration or genetic drift The equations p frequency of the dominant allele q frequency of the recessive allele The frequency of the allele will be in the range 0 – 1. 0 – no one has the allele 0.5 – half the population has the allele 1 – only allele for that gene in the population Ok – the equations Equation 1 p+q=1 Equation 2 p2 + 2pq + q2 = 1 Where ▪ p2 frequency of genotype DD ▪ 2pq frequency of genotype Dd ▪ q2 frequency of genotype dd Calculating the frequency of cystic fibrosis in the population 1 in 3300 babies are born with cystic fibrosis All babies with cystic fibrosis have genotype nn Calculate q2 Calculate q Calculate p Calculate frequency of genotype Nn If we have 30,000 people in our population how many will be carriers of the cystic fibrosis allele Question Phenylketonuria, PKU, is a genetic disease caused by a recessive allele. About one in 15 000 people in a population are born with PKU. Use the hardy-Weinberg equations to calculate the frequency of the PKU allele in the population. State the meaning of the symbols that you use, and show all your working. The Answer Calculate q2 = 1 / 15000 = 0.000067 Calculate q = 0.0082 Another question Explain why the Hardy-Weinberg principle does not need to be used to calculate the frequency of codominant alleles. Pupil Activity Answer the Hardy-Weinberg practice question. You have 10 minutes Starting NOW!! The Answers q2 = 0.52 / q = 0.72 p = 1 – 0.72 = 0.28 p+q=1 p2 + 2pq + q2 = 1 Answer = 2pq / use of appropriate numbers; Answer = 40%; The other answers Any three from: Small founder population / common ancestor; Genetic isolation / small gene pool / no immigration / no migration / in-breeding; High probability of mating with person having Hallele; Reproduction occurs before symptoms of disease are apparent; Genetic argument – Hh x hh = 50% / Hh x Hh = 75% affected offspring; No survival / selective disadvantage; Learning Outcomes Explain, with examples, how environmental factors can act as stabilising or evolutionary forces of natural selection. Explain how genetic drift can cause large changes in small populations. Variation and Natural Selection The set of alleles in a population is it’s gene pool Each individual can have any combination of alleles in the gene pool producing variation Some individuals more likely to survive They reproduce and pass genes on to offspring Advantageous alleles become more frequent in the population Environmental Resistance Environmental factors that limit the growth of a population offer environmental resistance These factors can be biotic or abiotic Selection pressures An environmental factor that “selects” for some members of a population over others Confers an advantage onto certain individuals Stabilising Selection If the environment stays stable The same alleles will be selected for in successive generations Nothing changes, this is called stabilising selection Stabilising Selection Stabilising Selection Directional Selection Change in the environment resulting in a change in the selection pressures on the population Previously disadvantageous alleles maybe selected for Change in the genetically determined characteristics of subsequent generations of the species A.k.a. evolution Directional Selection Directional Selection Genetic Drift A change in the gene pool and characteristics within the population. This change has occurred by chance rather than as the result of natural selection. Genetic Drift and Islands Genetic drift is thought to happen relatively frequently in populations on islands. Small populations Geographically separated from other members of their species Evidence Many isolated islands have their own endemic species of plants and animals Genetic Drift Reduces genetic variation Reduce the ability of the population to survive in a new environment May contribute to the extinction of a population or species Could lead to the production of a new species Genetic Drift – Frog Hoppers The colours of the common frog-hopper are determined by seven different alleles of a single gene. The range of colours and their frequencies, on different islands in the Isles of Scilly, are very variable, There are different selection pressures on the different islands Genetic Drift – Frog Hoppers The answers Learning Outcomes Explain the role of isolating mechanisms in the evolution of new species, with reference to ecological (geographic), seasonal (temporal) and reproductive mechanisms. Speciation Speciation is the formation of a new species. Species Group of organisms, with similar morphology and physiology, which can interbreed with one another to produce fertile offspring. Speciation In the production of a new species, some individuals must Becomes morphologically or physiologically different from members of the original species No longer be able to breed with the members of the original species to produce fertile offspring. Isolation Splitting apart of a “splinter group” Geographical isolation Organisms are separated by a physical barrier Reproductive isolation Two groups have become so different that they are no longer able to interbreed They are now a different species Isolating Mechanisms Large populations may be split into sub-groups by Geographic barriers Ecological barriers Temporal barriers Reproductive barriers Geographical Barriers (AS recap) Geographical barrier separates two populations of a species Two groups evolve along different lines Different selection pressures Genetic drift If barrier breaks down and two populations come together again, they may have changed so much that they can no longer interbreed They are now two different species Isolating Mechanisms Speciation occurs when organisms live in the same place The barriers which can prevent two closely related species from interbreeding include Ecological Temporal Reproductive Ecological Barriers Ecological barriers exist where two species live in the same area at the same time, but rarely meet. Example Two different species of crayfish, Orconectes virilis and orconectes immunis, both live in freshwater habitats in North America Meet the Crayfish Orconectes virilis Not good at digging, can’t survive summer drying Lives in streams and lake margins Orconectes immunis Lives in ponds and swamps, Can easily burrow into the mud when the pond dries up In streams and lake margins O. virillis is more aggressive and will drive O. immunis out of crevices where it tries to shelter Temporal Barriers Two species live in the same place, and may even share the same habitat Do not interbreed as they are active at different times of the day, or reproduce at different times of year Example – flowering shrubs in Western Australia Meet the shrubs Banksia attenuata flowers in the summer Banksia menziesii flowers in the winter They can not interbreed Reproductive barriers Even if species share the same habitat and are reproductively active at the same time, they may not be able to interbreed Different courtship behaviours Mechanical problems with mating Gamete incompatibility Zygote inviability Hybrid sterility Meet the Mallards Different courtship behaviours A male mallard duck will only mate with a female who displays the correct courtship behaviour Although the pintail female looks similar to the Mallard female, her courtship behaviour will only attract a pintail male. Learning Outcomes Explain the significance of the various concepts of the species, with reference to the biological species concept and the phylogenetic (cladistic/evolutionary) species concept. The Species Concept In AS biology you defined a species as “a group of organisms, with similar morphological, physiological, biochemical and behavioural features, which can interbreed to produce fertile offspring, and are reproductively isolated from other species” The two species concept Group of organisms Capable of interbreeding Capable of producing fertile offspring Reproductively isolated from other groups This is the Biological Species concept Group of organisms showing similarities in characteristics Morphological Physiological biochemical Ecological Behavioural This is the phylogenetic species concept Biological Species concept Group of organisms that can interbreed and produce fertile offspring. Clear cut definition Limitation Can only be used for organisms that reproduce sexually Phylogenetic species concept Also known as the Evolutionary species concept Cladistic species concept Different morphology between the two groups and certain that they evolved from a common ancestor Not rigorous but allows decisions to be made Comparing the genetics Closely related organisms have similar molecular structures for DNA, RNA and proteins. Biologists can compare specific base sequences (haplotypes) The number of differences caused by base substitutions can be expressed as the % divergence Cladistics Clade Group of organisms with similar haplotypes In cladistic classification systems is assumes that the taxa are monophyletic, this means that it includes an ancestral organism and all it’s descendents. Cladistic classification Focuses on evolution Places importance on using molecular analysis Uses DNA and RNA sequencing Uses computer programmes Makes no distinction between extinct and still existing species Learning Outcomes Compare and contrast natural selection and artificial selection. Describe how artificial selection has been used to produce the modern dairy cow and to produce bread wheat (Triticum aestivum). Selection Natural Selection Mechanism for evolution Organisms best adapted to their environments more likely to survive to reproductive age Favourable characteristics are passed on Produces organisms that are well adapted to their environment Artificial Selection Humans select the favourable characteristics Humans allow those organisms to breed Produces populations that show one characteristic to an extreme Other characteristics retained may be disadvantageous Artificial Selection and the modern dairy cow Breeds of cows with higher milk production have been artificially selected for Milk yield from each cow is measured and recorded Test progeny of bulls Elite cows given hormones to produce many eggs Eggs fertilised in vitro Embryos implanted into surrogate mothers A few elite cows produce more offspring than they would naturally Disadvantage to high milk yields Health costs for artificially selected cows is higher due to Mastitis Ketosis and milk fever Lameness Respiratory problems Artificial selection and bread wheat (Triticum aestivum) Polyploidy Nuclei contain more than one diploid set of chromosomes Wild species of wheat have a diploid number (2n) of 14 Modern bread wheat is hexaploid (6n), It has 42 chromosomes in the nucleus of every cell Getting from the ancestors to modern bread wheat Wild einkorn AUAU 2n = 14 Domestication and artificial selection Einkorn AUAU 2n = 14 x Wild Grass BB 2n = 14 Einkorn AUAU 2n = 14 x Wild Grass BB 2n = 14 Sterile hybrid P AuB Mutation that double chromosome number Emmer Wheat AUAUBB 4n = 28 x Wild Grass DD 2n = 14 Emmer Wheat AUAUBB 4n = 28 x Wild Grass DD 2n = 14 Sterile hybrid Q AuBD Mutation that double chromosome number Common Wheat AUAUBBDD 6n = 42 Continuing selection in wheat Breeders are continuing to try and improve wheat varieties Resistance to fungal infections High protein content Straw stiffness Resistance to lodging Increased yield
© Copyright 2024