BIO1101 week 3

Explain the causes and types of genetic changes.

Mutations

Change in chromosome number

Cause: nondisjunction in which the members of a chromosome pair fail to separate. Trisomy 21, the most common chromosome number abnormality, results in a condition called Down syndrome.

If an abnormal gamete produced by nondisjunction unites with a normal gamete during fertilization, the result is a zygote with an abnormal number of chromosomes. If the organism survived, it would most likely display a syndrome of disorders caused by the abnormal number of genes. Nondisjunction is estimated to be involved in 10–30% of human conceptions and is the main reason for pregnancy loss.

Change in chromosome structure

Causes: errors in meiosis or damaging agents such as radiation can cause a chromosome to break, which can lead to

4 types of change in chromosome structure:

→ Deletion: a chromosomal fragment (along with its genes) becomes detached.

→ Duplication: a “deleted” fragment may become attached as an extra segment to its sister chromatid or a homologous chromosome.

→ Inversion: a chromosomal fragment may reattach to the original chromosome but in the reverse orientation.

→ Translocation: the fragment joins a nonhomologous chromosome.

Explain the basic organization of eukaryote life cycles.

The large, complex chromosomes of eukaryotes duplicate with each cell division. A eukaryotic cell has many more genes than a prokaryotic cell, and they are grouped into multiple chromosomes in the nucleus. Each chromosome contains one long DNA molecule. Individual chromosomes are visible under a light microscope only when the cell is in the process of dividing; otherwise, chromosomes are thin, loosely packed chromatin fibers too small to be seen. Before a cell starts dividing, the chromosomes duplicate, producing sister chromatids (containing identical DNA) that are joined together along their lengths. Cell division involves the separation of sister chromatids and results in two daughter cells, each containing a complete and identical set of chromosomes.

Core Processes in All Eukaryotic Life Cycles

1. Fertilization (Syngamy) → Fusion of two haploid gametes → forms a diploid zygote (2n).

2. Meiosis → Diploid cells undergo reduction division → produce haploid (n) cells.

3. Mitosis → Can occur in either the haploid or diploid phase (or both), enabling multicellular development or clonal growth.

p.174

Describe the mechanisms by which prokaryotes can horizontally exchange genes.

10.22 - 10.23 : Horizontal Gene Transfer

→ how bacteria produces new combinations of genes

3 mechanisms by which genes can move from one cell to another: 

Transformation

→ The uptake of foreign DNA from the surrounding environment

Transduction

→ The transfer of bacterial genes by a phage 

Conjugation

→ The  physical union of two bacterial cells—of the same or different species—and the DNA transfer between them

Explain how genes are inherited in eukaryotes, including both Mendelian and non-Mendelian patterns.

Heredity = the transmission of traits from one generation to the next.

Gene = nucleotide sequence = discrete unit of hereditary information.

Mendelian pattern

Law of segregation: alternative versions (alleles) of genes account for the variations in inherited characters. For each character, two alleles are inherited (one from each parent) → homozygous (PP)/heterozygous (Pp). Alleles can be dominant (P) /recessive (p).

Law of independent assortment: the alleles of a pair segregate independently of other allele pairs during gamete formation. Monohybrid/dihybrid.

Variations on Mendel’s laws

• Incomplete dominance

• Codominance

• Pleiotropy

• Polygenic inheritance + the effect of environment

• Linkage/crossing over

• Sex-linked genes

• The effect

p.212

Calculate the probabilities of different genotypes and phenotypes of offspring in a given cross.

skill

Use knowledge of genetic technologies to discuss their importance in modern biology as well as controversies surrounding their use.

Biotechnology: the manipulation of organisms or their components to make useful products.

List of genetic technologies:

• Gene cloning and editing

• PCR

• Reverse transcription

• CRISPR - Cas9 system

• GMOs

• DNA profiling

• DNA sequencing

Positive aspects:

GMOs: produce drugs, diagnose diseases, produce vaccines, gene therapy, agriculture - food security

DNA profiling: determines whether two samples of DNA come from the same individual → helps solve crimes and identify individuals

Sequencing and PCR allow rapid detection of diseases and deeper understanding of genetics.

Negative aspects:

Ethical concerns about gene editing (e.g., “designer babies”) and altering genomes.

Safety risks such as off-target mutations and ecological impacts of GMOs.

Privacy issues and potential misuse of genetic data from DNA profiling.

Social inequality due to unequal access to advanced genetic technologies.

Explain the purpose and steps of the polymerase chain reaction and compare it to natural DNA replication.

Purpose: amplify specific DNA sequences. PCR makes use of specific DNA primers that flank the desired DNA sequence.

CYCLE - 3 steps:

1. Denaturation → heat separates DNA strands

2. Annealing → primers bond with ends of target sequences

3. Elongation/extension → DNA polymerase adds nucleotide

DNA // PCR

RNA primers made by primase // DNA primers (forward and reverse)

Helicase // Heat (denaturation)

Proteins to stabilize unwound DNA // Buffer

Amplifies complete chromosome // Amplifies specific DNA sequence