Oct 16th Lecture notes epigenetics

Alleles

Different forms of a gene that arise by mutation and are found at the same place on a chromosome.

Homozygous Alleles

Both alleles at a given locus are identical.

Heterozygous Alleles

Alleles are different at a locus.

Maximum gene copies in diploid organisms

2

Minimum gene copies

1 (single copy gene)

Single Copy Genes

Genes that have only one copy in the genome, approximately 40% of protein-coding genes.

Biallelic Expression

Both alleles can be expressed, assuming no mutation.

Mendel's Law of Segregation

Alleles separate during gamete formation.

Genotype vs. Phenotype

Genotype determines phenotype (e.g., tall vs. dwarf pea plants).

Mutation Definition

Changes in nucleotide sequence compared to a normal or wild type, including substitutions, deletions, and insertions.

Germline Mutations

Mutations that can affect future generations.

Somatic Mutations

Mutations that are not inherited by the next generation.

Mendel's Law of Independent Assortment

Genes located on different chromosomes assort independently.

Honeybee Queen Bee

Female and diploid (two sets of chromosomes, 2n).

Honeybee Worker Bee

Female and diploid (2n), sterile.

Honeybee Drone Bee

Male and haploid (n), one set of chromosomes.

Epigenetics

Modifications that affect gene expression without altering DNA sequences.

Histone Acetylation

An epigenetic mark that leads to gene activation by loosening chromatin structure.

DNA Methylation

An epigenetic mark often associated with gene silencing (tightens chromatin).

Euchromatin

Loosely packed chromatin, transcriptionally active.

Heterochromatin

Tightly packed chromatin, transcriptionally inactive.

X Inactivation

Process in females where one X chromosome is randomly chosen to be inactivated to balance gene dosage, forming a Barr Body.

Barr Body

The inactivated X chromosome found in female somatic cells.

Genomic Imprinting

Involves monoallelic expression of certain genes, influenced primarily by DNA methylation.

IGF2 gene in mice example (paternal allele)

Active paternal allele leads to normal size.

IGF2 gene in mice example (maternal allele)

Silenced due to methylation; if only the mother's mutant allele is inherited, a dwarf phenotype arises.

Number of copies of a single copy gene in a diploid organism

Two

Repetitive genes

Genes that may have multiple loci.

Control of human traits by single genes

Few traits in humans are controlled by a single gene.

Assumption regarding genes' stability in Mendelian inheritance

Genes are passed unchanged from generation to generation (mutations are rare).

Additional characteristics of a Queen Bee (beyond being female and diploid)

Larger size and ability to lay thousands of eggs.

Additional characteristic of a Worker Bee (beyond being female, diploid, and sterile)

Lifespan in weeks.

What determines the differences in honeybee castes?

Nutrition (specifically royal jelly).

Another example of an epigenetic mark besides histone acetylation and DNA methylation

Histone methylation.

Randomness of X inactivation

Either the paternal or maternal X chromosome is randomly inactivated in different cell lineages.

Factors contributing to the complexity of gene expression

Genetics, epigenetics, and environmental factors (e.g., nutrition).