Lecture 9 plant genetics part 2: mendelian genetics

Gregor Johann Mendel

Studied garden pea plants by breeding

Self-fertilization

when pollen encounters ova within the same flower, the flower petals remain sealed tightly until pollination is completed to prevent the pollination of other plants.

Hybridization

Involves mating two true-breeding individuals that have different traits.

1. Unit factors occur in pairs

2. Dominance and recessiveness

3. Segregation

4. Independent Assortment

Mendel’s Four Postulates

Allele

one of the two alternative states of a gene

Dominant allele

an allele of a gene that is expressed and masks the effect of the other.

Recessive allele

allele of a gene whose effect is masked by the presence of a dominant allele.

Genotype

refers to the alleles or variants an individual carries in a particular gene or genetic location (locus); genetic makeup.

Phenotype

is the observable trait

Unit Factors Occur in Pairs

“Genetic characters are controlled by unit factors that exist in pairs in individual organisms”

Dominance and Recessiveness

When two unlike unit factors responsible for a single character are present in a single individual, one unit factor is dominant to the other, which is said to be recessive.

Segregation

During the formation of gametes, the paired unit factors (alleles) segregate randomly so that each gamete receives one or the other. This happens during metaphase of Meiosis.

Independent Assortment

Pairs of heritable factors assort independently during gamete formation.

Monohybrid Cross

The simplest crosses performed by Mendel

Punnett Square

method used to predict the outcomes of a cross

Punnett Square

named after the person who first devised it, Reginald C. Punnett

Reginald C. Punnett

punnet square is named after the person who first devised it, _

Test Cross

simple method devised by Mendel to know the genotype of an individual by crossing it to another individual with known genotype.

Dihybrid Cross

An extension of monohybrid cross where two characters are examined simultaneously. It is also known as two-factor cross.

two-factor cross

An extension of monohybrid cross where two characters are examined simultaneously. It is also known as _ .

selfed

the pollen lands onto its own stigma and fertilizes its own ovule

Incomplete Dominance

heterozygous individual clearly shows the effect of both alleles

Co-dominance

Two dominant alleles are expressed since neither allele is recessive.Both phenotypes appear in heterozygotes.

Multiple Alleles

When there are more than two alleles for one trait

Pleiotropy

property where a gene has more than one effect on the phenotype of an organism.

Quantitative Trait Loci (QTL)

are specific regions in DNA where multiple genes influence a quantitative trait. Are genetic neighborhoods where multiple genes work together to influence complex,quantitative traits, such as height, weight, or intelligence.

Quantitative Trait Loci (QTL)

Are genetic neighborhoods where multiple genes work together to influence complex,quantitative traits, such as height, weight, or intelligence.

Epistasis

from the Greek word for stopping –one gene can alter the phenotypic expression of another gene.

Environmental Effects

Some traits can be affected by the environment.

e.g. Exposure to sunlight affects skin color in humans, Nutrition affects height in humans, and Soil acidity affects color in Hydrangea macrophylla flowers.

Mutation

Change in the genetic sequence of the genome of an organism or extrachromosomal genetic element.

Mutation

Result of unrepaired damage to DNA or RNA, errors in the replication process or insertion or deletion of DNA by mobile genetic elements.

Change in nucleotide sequence, Alterations of Chromosome Structure(Gene level), and Alterations in Chromosome Number

Types of Mutation

Point mutation

single base substitution; causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA.

Frameshift mutation

caused by indels (insertions or deletions) of a number of nucleotides in a DNA sequence that is not divisible by three.

Indels

Frameshift mutation is caused by _ (insertions or deletions) of a number of nucleotides in a DNA sequence that is not divisible by three.

Deletion

Removes chromosonal segment in the gene

Duplication

repeats a segment

Inversion

Reverses a segment within a chromosome

Translocation

moves a segment from one chromosome to another, nonhomologous one.

Reciprocal Translocation

the most common tyep nonhomologous chromosomes exchange fragments.

Nonreciprocal Translocation

In which a chromosome transfer a fragment without recieving a fragment in return.

Euploidy

An addition or deletion of a whole set of chromosomes.

Polyploidy

is the condition where there are more than 2 complete sets of chromosomes.

Triploid

3 sets of chromosomes

Tetraploid

4 sets of chromosomes

Aneuploidy

Errors in meiosis or mitosis may lead to one extra or one less chromosome.

Trisomic

3 copies of a chromosome

Monosomic

only 1 copy of a chromosome

Turner Syndrome

Inheritance of only one X (XO), 98% spontaneously aborted, and Survivors are short, infertile females.

Down Syndrome

Trisomy of chromosome 21

Klinefelter Syndrome

XXY condition, Results mainly from nondisjunction in mother (67%). Phenotype is tall males.

XYY Condition

Taller than average males, Most otherwise phenotypically normal, Some mentally impaired, and Once thought to be predisposed to criminal behavior, but studies now discredit.