Unit 11 of Genetics

How did Mendel discover some fundamental principles of hereditary or inheritance?

By cross-breeding garden peas from stamen to carpel

Character

Heritable feature that varies (variables)

Trait

The variants for each character

True breeding

Offspring of same variety over many generation of self-pollination

F1 Generation

First filial generation (4x Pp)

F2 Generation

Second filial generation (1x PP, 2x Pp, 1x pp)

Law of Segregation

Alleles that account for different characteristics separate during meiosis when gametes inherit 1 allele of each that are either dominant to override or recessive.

What hypothesis did the Law of Segregation refute? Why?

Blending Hypothesis because the genotype did not vanish

How many traits of peas did Mendel observe?

7: color of flower, seed, pod, shape of seed and pod, height, and flower position

Homozygous vs. Heterozygous

Having different vs. identical allies

Allele

Alternative versions of gene

Punnet square

Diagrammatic devices that predicts allele composition of all offspring

Phenotype

Appearance or physiology

Genotype

Genetic makeup

Testcross

Breeding with unknown genotype but known phenotype (from observation) with homozygous recessive

Monohybrid

Heterozygous organism begotten from homozygous parents with respect to single gene of interest

Monohybrid cross

To follow a trait by mating 2 heterozygotes

Carrier

Phonetically normal individual who may transmit recessive allele to their offspring

Dihybrid

Heterozygous organism for or of two different traits

Law of Independent Assortment

Alleles/genes for different traits separate independently during meiosis (on non-homologous chromosomes)

Simple Principles of Mendelian model

A gene that influences one characteristic has either dominant or recessive allele on different locations of chromosomes.

What about the peas did not fit in the Mendelian model?

Pleiotropy from purple flowers always with gray coated seeds

Incomplete dominance

Neither completely dominant (e.g. snapdragons of C(red) x C(white) making pink

Codominace

Equally dominant and distinct phenotypically (e.g. Camellia flowers and blood types)

Tay-Sachs disease

Metabolism for some lipids not affecting those with recessive homozygotes but half of molecules are dysfunctional

Multiple allele

More than two alleles for gene

Pleiotropy

One gene for multiple traits (e.g. sickle-cell anemia: mishaped RBC and cystic fibrosis: no Cl- channel so thick mucus)

Epistasis

Expression of 1 gene at 1 locus altering expression of second gene at second chromosome

Polygenic trait

Multiple gene affecting 1 phenotype

Quantitative characters

Gradation of characteristic along a continuum

Phenotype plasticity

Genotype’s ability to produce different phenotype from or under different environments (e.g. Himalayan rabbits and hydrangeas: red in basic soil while blue in acid soil)