basic plant genetics
DESCRIPTION
BASIC PLANT GENETICS. Structures Controlling Inheritance. Chromosomes - contained in nucleus - carry most of the genetic information - number/cell usually 2n, or diploid - sex cells are 1n, or haploid - chromosome numbers are known for most plant species. Chromosome Makeup. - PowerPoint PPT PresentationTRANSCRIPT
BASIC PLANT GENETICS
Structures Controlling Inheritance
Chromosomes
- contained in nucleus
- carry most of the genetic information
- number/cell usually 2n, or diploid
- sex cells are 1n, or haploid
- chromosome numbers are known for most plant species
Chromosome Makeup
DNA – deoxyribonucleic acid RNA – ribonucleic acid Various proteins
DNA replicates and transmits genetic information throughout the cell
DNA Makeup
NucleotideA DNA/RNA subunit made up of a sugar, a
phosphate, and a nitrogenous baseRepeating nucleotides vary by which base
is usedDNA bases are:Cytosine(C), Guanine(G), Adenine(A), Thymine(T)
DNA Makeup (cont)
Two spiral strands comprise DNA“Backbone” of strands is the repeating
sugar-phosphate linkage (identical)Bases attach to sugars (vary)Phosphate-sugar-base = nucleotideNucleotides of two strands are joined
at bases by hydrogen bondsBases are specific for bonding
Base Bonding
Adenine with Thymine Cytosine with Guanine
Referred to as “complementary pairs”Because the hydrogen bond between
bases is relatively weak, DNA can “unzip” at this point to facilitate replication
RNA Makeup
Similar to DNA Makeup Important variations:
RNA is a single strandSugar is RiboseBase Uracil replaces ThymineRNA is complementary to DNAThree forms of RNA:
Messenger, Transfer, Ribosomal
RNA Forms
Messenger (mRNA)
Copies DNA (transcription)Carries copy out to cytoplasmMoves to ribosomes
RNA Forms (cont)
Transfer (tRNA)
Reads mRNA (translation)Brings Amino Acids to ribosomesProtein is synthesized
RNA Forms (cont)
Ribosomal (rRNA)
A chief component of RibosomesThe site of protein synthesis
GENES
Gene definitions gene: (cistron) Structurally, a basic unit of hereditary material; an ordered sequence of nucleotide bases that encodes one polypeptide chain (via mRNA).
GENES (cont)
The gene includes, however, regions preceding and following the coding region (leader and trailer) as well as (in eukaryotes) intervening sequences (introns) between individual coding segments (exons).
GENES (cont)
Gene “facts”Part of chromosomeDetermine characteristicsToo small to be seenThousands per plant cellSome act independent, some togetherGenes on the same chromosome are
said to be “linked”
GENES (cont)
LinkageGenes move from one cell generation
to the next as a unitLinkage may be broken during
meiosis
HOMOLOGOUS CHROMOSOMES
Definition: Chromosome pairs that have alleles for the same genesAlleles occupy the same position (loci)
on homologous chromosomes and affect the same trait
Genes may have two or more allelesAllelic genes can be dominant or
recessive to each other
MITOSIS
Definition: The process of nuclear division in which chromosomes are first duplicated, followed by the separation of daughter chromosomes into two genetically identical nuclei
MITOSIS (cont)
Figures 1 through 6 illustrate the stages of mitosis in onion (Allium cepa) as viewed with light microscopy.
Microtubule dynamics in mitosis & cytokinesis
A Interphase: Cortical microtubules are aligned within the inside of the cell wall.
B Pre-prophase: Microtubules form a band around the equatorial region of the cell marking the plane of future cytokinesis.
C Prophase: Cytoplasmic microtubules disappear and a mitotic spindle of microtubules is formed.
D Metaphase: Chromosomes are aligned on an equatorial plate of the spindle.
E Anaphase: Interzonal fibers extend from one pole to the other. Chromatids are moved to opposite poles of the spindle. Dictyosomes (two are shown) begin to produce vesicles which will fuse laterally initiating the cell plate.
F Telophase: The spindle microtubules disappear and a phragmoplast is formed whose component microtubules are concentrated at the periphery of the cell plate which grows centrifugally towards the parent cell wall. The phragmoplast microtubules remain at the edge of the cell plate until it reaches the parent cell wall, and then they disappear.
Illustration from: Ledbetter & Porter, 1970, Introduction to the Fine Structure of Plant Cells, Springer-Verlag
MITOSIS (cont)
Results of Mitosis:Vegetative cells usually contain two
sets of homologous chromosomes – the 2n or diploid number
Daughter cells are genetically identical to the mother cell
MEIOSIS
Definition: Nuclear division in which chromosomes are doubled and then divided twice
MEIOSIS (cont)
Meiosis facts:occurs in the flowerin plants, meiosis forms sporesIn angiosperms, forms pollen and eggthe daughter nuclei from meiosis have
half the number of chromosomes of the parent nucleus (1n or haploid)
Crossing over of homologous chromosomes can occur
FERTILIZATION
Definition: the fusion of sperm and egg in sexual reproduction
Definition (Angiosperms):Double Fertilization: the process by
which one sperm cell fertilizes the egg to form a zygote and another sperm cell fertilizes the polar nuclei to form a primary endosperm nucleus
Double Fertilization (cont)
Double fertilization: One of the two sperm nuclei fertilizes the egg cell; the other fertilizes the central cell
Pollen tube discharges sperm into one of the synergids
A typical picture of the double fertilization process. The pollen tube (pt) enters through the micropyle, one of the synergids (s) discharges its contents. Then the sperm nuclei traverse the synergid, one enters the egg cell (e) and the other enters the central cell (cc). Thereafter, their nuclei (unlabeled arrows) fuse with the egg nucleus (yellow) and the polar nuclei (red).
ii = inner integument; n = nucellus
MUTATIONS
Definition: a sudden, heritable change appearing in an individual as the result of a change in genes or chromosomes
MUTATIONS (cont)
Mutation statements:Mutations can and do occur during
replication of DNAAltered genes may result in changes
in plant characteristicsMost mutations go unnoticedMany mutations are subtly harmfulSome provide a source of genetic
variability for developing new cultivars
MUTATIONS (cont)
Hereditary modifications from chromosome number or structure changeDoubling of chromosomesAddition or subtraction of
chromosomesStructural change in chromosome
POLYPLOIDY
Plant has more than two sets of homologous chromosomes in their vegetative cellsNormal Diploid (2n)Triploid (3n)Tetraploid (4n) etc.Common in cultivated crops like oats,
wheat, and tobacco (Table 14-1, text)
CLASSICAL GENETICS
View video:Understanding Basic Genetics
Complete Study Guide
Complete Lessons 1, 2, 3, 4, and 5 from your DNA websight
http://www.dnaftb.org/dnaftb/