Breeding Horticultural Plants

Flashcards covering key concepts from lecture notes on plant genetics, Mendel's laws, cross breeding, polyploidy, tissue culture, and genetic engineering methods.

What are the three main types of genetics outlined in plant breeding?

Mendelian genetics, Molecular genetics, and Population genetics.

According to the Central Dogma of Molecular Genetics diagram, what is the complete pathway from DNA replication to protein synthesis?

Replication reproduces DNA, which undergoes Transcription to form RNA (mRNA, rRNA, tRNA), which is then translated at the Ribosome to produce Protein.

What is the key difference between a somatic mutation and a germ-line mutation?

A somatic mutation occurs in a body cell, whereas a germ-line mutation occurs in tissues that produce sex cells and is passed on to future generations.

How does an aneuploid organism differ from a polyploid organism?

An aneuploid carries one or more extra chromosome(s) or is missing one or more chromosome(s), whereas a polyploid has at least one complete extra set of chromosomes.

In Gregor Mendel's crosses of tall and short pea plants, what phenotypic ratio was observed in the second filial ($F_2$) generation?

A ratio of three tall individuals to one short individual ($3:1$).

What does the Law of Dominance state?

For any given pair of alleles, one (dominant) may mask the expression of the other (recessive).

What are the expected genotypic and phenotypic ratios produced by intercrossing $F_1$ plants in a monohybrid cross?

A $1:2:1$ genotypic ratio and a $3:1$ phenotypic ratio.

What is the Law of Independent Assortment, and what phenotypic ratio does a dihybrid cross produce?

The Law of Independent Assortment states that factors (genes) controlling two or more traits segregate independently of each other. A dihybrid cross produces a $9:3:3:1$ phenotypic ratio.

What is the difference between linked genes and unlinked genes?

Linked genes are on the same chromosome and do not segregate independently, while unlinked genes are on different chromosomes.

What is a testcross, and what is its main purpose?

A testcross is a cross between a plant having a dominant phenotype with a homozygous recessive plant. Its purpose is to determine whether the plant with the dominant phenotype is homozygous or heterozygous.

What occurs in incomplete dominance (absence of dominance)?

The heterozygote displays a phenotype that is intermediate to the two homozygotes.

What are quantitative trait loci (QTL's)?

QTL's are chromosomal fragments identified by molecular geneticists that contain genes influencing quantitative traits and behave like Mendelian genes.

Why is extranuclear DNA in mitochondria and chloroplasts passed on via maternal inheritance?

Sperm rarely carry mitochondria and chloroplasts, so extranuclear DNA is passed to the next generation only by the female parent.

What is the fundamental formula for phenotype in plant breeding, and why is changing the genotype preferred?

$\text{Phenotype} = \text{Genotype} + \text{Environment}$. Changing the genotype creates a permanent change, whereas changing phenotype via environment is temporary and requires repeated intervention.

What is heritability, and how does trait complexity affect it?

Heritability is the degree of phenotypic expression of a trait that is under genetic control. Simply inherited (qualitative) traits are more heritable than complex (quantitative) traits.

How do breeders produce seedless watermelons?

Breeders cross a tetraploid ($4n$) parent with a diploid ($2n$) parent to yield a triploid ($3n$) offspring, which is sterile due to abnormal meiosis.

How is a 2nd generation pluot created according to the provided breeding process?

A $1001\%$ plum parent is crossed with a 1st generation plumcot ($50\%$ plum / $50\%$ apricot) to produce a 2nd generation pluot ($75\%$ plum / $25\%$ apricot).

How do self-pollinating and cross-pollinating plants differ in genetic nature?

Self-pollinating plants tend to be highly homozygous because genes come from the same parent, whereas cross-pollinating plants tend to be highly heterozygous.

What causes inbreeding depression when cross-pollinating plants are forced to self-pollinate?

Inbreeding depression is caused by the expression of deleterious recessive alleles.

What is protoplast fusion and how does it work?

Cells of two sexually incompatible species are grown in liquid solution and chemically stripped of their cell walls to form protoplasts, which are then stimulated to fuse using an electric current or chemical solution to form somatic hybrids.

How do bacterial restriction enzymes assist in recombinant DNA technology?

They cut DNA into fragments with one DNA strand longer than the other, creating "sticky ends" that base-pair with tails of other fragments cut with the same enzyme.

How is Agrobacterium tumefaciens used to produce transgenic plants?

It inserts transfer DNA (T-DNA) containing a gene of interest from its plasmids into the plant's chromosomes.

How do particle guns introduce foreign genes into plant cells?

They shoot tungsten or gold pellets coated with the cloned gene directly into plant cells.