Genetics & Plant Breeding

1. Genetics & Plant Breeding

2. DNA Gene Chromosome Ploidy Haploid (N) Diploid (2N) Polyploid (3N, 4N, 6N) RNA Mitosis Meiosis Things to Know

3. The word genetics comes from the word “gene”, and genes are the focus of the subject • So we can say that genetics: is the study of genes The science of the transmission of characteristics between generations What is a gene? A gene is a section of the (DNA) deoxyribonucleic acid

4. DNA

5. DNA structure • Made of repeating units called nucleotides • Each nucleotide made of: • A sugar named deoxyribose • A phosphate • A base

6. Four different bases are present in DNA: • adenine (A) • thymine (T) • cytosine (C) • guanine (G)

7. Thymine NH2 CH3 Adenine N N N O O O O NH NH N N N N N N O NH2 NH2 Guanine Cytosine NH2 N N Purines Pyrimidines

8. The particular order of the bases arranged along the sugar-phosphate backbone is called the DNA sequence • The two DNA strands are held together by weak bonds between the bases on each strand, forming base pairs (bp). • Genome size is usually stated as the total number of base pairs; the human genome contains roughly 3 billion bp

10. Variation in Chromosome Number and Arrangement

11. Cromatids Cromatids Centromere Centromere What is a chromosome? The structure within cells that contains the genes. What it looks like?

12. X: the basic chromosome number the basic chromosome number • n: is the gametic or haploid chromosome number for a particular species. is the gametic or haploid chromosome number for a particular species. • 2n: the somatic or diploid chromosome number. • a genome contains the basic chromosome number. • The gametic chromosome number for a plant is the same as its haploid chromosome number. • The somatic (and diploid) chromosome number is double the haploid number.

13. Diploid: Having two sets of chromosomes, which are referred to as homologues. Animals and plants are diploid in the dominant phase of their life cycles. Haploid: Having only one set of chromosomes. Gametes, certain animals, protests and fungi, and certain stages in the life cycle of plants are haploid.

14. Euploidy: organisms having multiples of complete sets basic to a species. The addition or deletion of specific chromosomes. Aneuploidy:

15. Polyploidy • Polyploid individuals have more than two sets of chromosomes • Many important commercial plants are polyploid: • Roses • Navel oranges • Seedless watermelons • Polyploid individuals usually result from some sort of interruption during meiosis

16. Polyploidy:are euploids in which the somatic cells possess multiples of the basic chromosome sets. • How can we get a polyploidy plant or species? • Chromosome duplication (autoploidy) • Combining complete chromosome genomes from two or more species. (alloploidy).

17. Polyploidy is of special significance because: • It permits greater expression of existing genetic diversity in the plant kingdom. • Provides the breeder with the opportunity of bringing about changes in the character of a plant by altering the number of chromosome sets. • Changing the number of genes within a single cell.

18. The Autoploids May arise spontaneously, or they may arise by induced doubling of the chromosomes in a plant with lower ploidy. Spontaneous: when unreduced gametes (each with the diploid chromosome number) fuse producing an individual with four basic sets or genomes of chromosomes. Induced: by environmental shock or with chemicals.

19. 8n 2n 2n 4n Polyploidy • Very common in plants • associated with origin of new species • may positively correlate to size and vigor • e.g. alfalfa, coffee, peanuts are tetraploid • e.g large apples, pears, grapes are tetraploid • e.g. large strawberries are octaploid • Derived from diploid ancester • Result: fertile, larger fruits and vegetables than wild relatives

20. The Alloploids • They are polyploids created by combining genomes from two or more species. • The basic set of chromosomes of one species is A so the diploid parent will be AA • The basic set of chromosomes of the second species is B so the diploid parent will be BB • The doubled F1 hybrid progeny would be AABB

21. Naturally occurring alloploids (wheat) • Artificially induced alloploids (Triticale from wheat and rye) • Characteristics of alloploids: (larger cells and stockier plants)

22. How alloploidy serves plant breeding? • Identify genetic origin of polyploidy plant species (like wheat) • Facilitate the transfer of genes from related species. • Facilitate the substitution of individual chromosomes or pairs of chromosomes (in situ) • Produce new plant genotypes and plant species (Triticale).

23. Monoploid Applications • Monoploid plants can be created by culturing pollen grains (n = 1), • the population of haploid organisms is then screened for favorable traits, • the plants are then treated with colchicine which generates a 2n plant homozygous for the favorable traits.

24. Monoploidy

25. Mendel and Pea Experiments

26. Dominant vs Recessive S = smooth s = wrinkled

27. Principle of Segregation Mendel's first law Each pair of factors of heredity (‘alleles’) separate during gamete formation so that each gamete receives one member of a pair

28. Some genetic terms • An organism with two identical alleles for a character is homozygous for that character. • Organisms with two different alleles for a character is heterozygous for that character. • A description of an organism’s traits is its phenotype. • A description of its genetic makeup is its genotype.

29. Homozygotes vs. heterozygotes • Homozygote • True-breeding; pure breeding • Heterozygote • Hybrid

30. Phenotype vs. genotype • SS and Ss • Two different genotype • The same phenotype • How do you distinguish these two genotypes experimentally (like Mendel)?

31. Test cross breeding a homozygous recessive with dominant phenotype to determine the geneotype

32. Backcross Mating of an individual to a type like one of the parents Testcross Mating of an individual to one that expresses the recessive phenotype for a trait being followed Backcross vs. Testcross The two terms are often used interchangeably, although they do not always mean the same. When a monohybrid is crossed to the the recessive parent, this is a backcross and also a test cross. When the hybrid is crossed to the dominant parent, it is a backcross, but not a test cross (not being diagnostic).

33. One-factor (monohybrid) cross • F1: all dominant trait • Dominant vs. recessive traits • Dominant: S - Smooth • Recessive: s – rough • Self (self cross) of F1 • What would happen?

34. Two-factor (dihybrid) cross 315 smooth yellow 108 smooth green 101 wrinkled yellow 32 wrinkled green

35. Principle of Independent Assortment • Mendel's second ‘law’ During gamete formation, alleles in one gene pair segregate into gametes independently of the alleles of other gene pairs. • True only in certain cases • When the genes are on different chromosomes • When the genes are distantly separated on the same chromosomes

36. Explainations • Incomplete or codominance • Multiple alleles for a single gene • Epistasis • X-linkage • Sex influenced or limited genes, where expression is influenced or limited by gender or environment