BB LEC - Basic Principles of Genetics

Genetics

The scientific study of heredity

Gene

A sequence of nucleotides that represents a functional unit of inheritance; a region of DNA that codes for a product, either RNA or protein

Chromosome

Highly ordered structure composed of DNA and proteins that carries the genetic material

Autosome

All chromosomes other than X and Y chromosomes (make up the Chr 23 / sex chromosomes)

Homologous Chromosomes or Homologs

Sister chromosomes, the members of a pair of chromosomes in which one is inherited from the mother and the other from the father

Locus

The position of a gene on a chromosome

Allele

An alternative form of gene occupying the same locus. An ____ may be the result of a mutation

Mutation

A permanent heritable change in the sequence of genomic DNA

Karyotype

The chromosome constitution of an individual. It is comprised with autosomes and sex chromosomes

Karyogram

A figure showing the paired chromosomes from a cell arrayed in a standard sequence; Maps out all the paired chromosomes

Diploid

The presence of two copies of each unique chromosome per cell

Haploid

One copy of each unique chromosome; Half of the diploid copy of the number of chromosomes per cell

Homozygous

Both alleles at a locus are the same

Heterozygous

The two alleles at a locus are the different

Hemizygous

The presence of only one chromosome or chromosome segment rather than the usual two

Genotype

The genetic constitution/material inherited by an individual or organism (what you inherit)

Phenotype

The appearance of an individual that results from the interaction of environment and genotype; Traits expressed from a genotypic material inherited; The expression of genotype

Dominant Allele

An allele that is expressed when present in only a single dose; Always expressed; alpha allele / trait

Recessive Allele

An allele that is only expressed when homozygous when paired with a dominant allele, it is not expressed. The only way it could be expressed as a trait is when the allele is homozygous (containing two recessive alleles)

Codominant Allele

Alleles that show no dominance or recessive to each other but, when present together, are both fully expressed

Independent Assortment

Random assortment of chromosomes in the gametes; 50:50 chance of inheriting a given chromosome from one parent

Linkage

The presence of two or more genes on the same chromosome that tend to be inherited together

Crossing over

The physical exchange of genetic material between homologous chromosomes

Recombination

The generation of new allelic combination on chromosomes, usually by crossing over

Mitosis

Somatic cell division in which the DNA replicates and is evenly distributed to two equal daughter cells

Meiosis

Cell division in the gonads that produces the gametes

Nondisjunction

Failure of chromosomes or chromatids to separate to opposite poles in cells division

Prophase, Metaphase, Anaphase, Telophase

Phases of Mitosis

Interphase (2N)

Resting stage between cell division wherein during that period cells are synthesizing RNA and proteins, and chromatin is uncondensed

Prophase (4N)

First stage of mitotic cell division. Chromosomes become more visible and condense. Each chromosome has two chromatids from duplication of DNA and chromatids are linked via the centromere; The initial parent cell undergoes mitotic cell division

Metaphase (4N)

Chromosomes move toward the equator of the cell and are held in place by proteins called microtubules attached at the mitotic spindle apparatus

Anaphase (4N)

The two sister chromatids separate. Each one migrates to opposite poles of the cell, and the diameter of the cell decreases at equator

Telophase (2N)

Chromosomes are at the poles of the cell, and the cell membrane divides between the two nuclei. The cell divides, and each cell contains a pair of chromosomes identical to the parent cell.

Meiosis

The process by which cell division results in four unique daughter cells with each cell carrying half the number of chromosomes of their parent cell (haploid).

Gonads

Meiosis takes place in the ___ and aims to produce sex cells or gametes.

Metaphase II, Anaphase II, Telophase II

What are the additional events not present in mitosis that are in meiosis?

Interphase (2N)

Resting stage between cell division; during that period cells are synthesizing RNA and proteins, and chromatin is uncondensed

Prophase I (4N)

First stage of meiotic division. Chromosomes condense Homologous chromosomes pair to become bivalent. Chromosome crossing over occurs at this stage

Metaphase I (4N)

Bivalent chromosomes align at the cell equator. Bivalent chromosomes contain all four of the cell's copies of each chromosome

Anaphase I (4N)

Homologous pairs move to opposite poles of the cell. The two sister chromatids separate

Telophase I (2N)

The cell separates to become two daughter cells. The new cells are now 2N

Metaphase II (2N)

Homologues line up at the equator

Anaphase II (N)

Homologues move to opposite poles of the cell equator

Telophase II (N)

Each cell separates into two new cells. There are now four (N) cells with a unique genetic constitution

Molecular Genetics

Consists of structures which contain the genetic materials that are passed on from the parent cells to the offspring

Chromosomes

Composed of long linear strands of DNA tightly coiled around highly basic proteins

Histones

Proteins coiled around DNA

Nucleosome

The complex of DNA and histone protein is referred to as a?

Chromatid, Centromere

Each double helix is termed as a ____ and the two are held together by an as yet unreplicated region of DNA known as ____ or primary constriction

Metacentric, Submetacentric, Acrocentric, Telocentric

Chromosomes are identified by the location of the centromere:

Autosomes, Sex chromosomes

In a karyogram, 1-22 are called ____ while X and Y are the ____?

Deoxyribonucleic Acid (DNA)

A masterpiece of architectural evolution and is considered the backbone of heredity

4 nitrogenous bases, Deoxyribose, Phosphate group

A nucleic acid composed of:

Adenine, Cytosine, Guanine, Thymine

What are the 4 nitrogenous bases?

Phosphodiester linkages

The backbone of a DNA molecule is joined by?

Hydrogen Bonding and Van der Waals forces

Nitrogenous bases face into each other and are stabilized by?

Basic

Since DNA is a nucleic acid, most proteins that interact with it have to be at what pH?

Anti-parallel

DNA strands are termed ____ because one strand is going to one direction and the opposite or complementary strand is going to the opposite direction

Replication

Process of copying or creating a replica of DNA

True

T or F: The replication of DNA is a complex process involving numerous enzymes, nucleic acid primers, various small molecules, and the DNA helix molecule that serves as its own template for the replication process

Before

DNA must be copied BEFORE/AFTER mitosis can occur and must be copied in such a way that each daughter cell will have the same amount of DNA and the same sequence

Prophase

What do you call the stage wherein the number of DNA is replicated?

Bidirectional

Nearly all DNA replication is done in a ____ manner and is semi-conservative in nature

True

T or F: DNA must be copied exactly or the information it contains will be altered, any mistakes or any alterations result in a decrease in the organism's vitality

Photoreactivation

Becomes active and enzymatically cleaves thymine dimers when formed after exposure to UV light

Excision Repair

aka Cut and Patch Repair. We cut a certain mistake of the DNA replication process and then we patch up. A complex process in which the disrupted region of the DNA is removed

Recombinational Repair

Uses the correct strand of DNA to fill in the strand where the error was deleted

Mismatch Repair

Remove the incorrect nucleotides and insert the correct ones; methyl groups on adenines are used to determine which is correct and which is a mistake

SOS Repair

Induce when DNA and cell damage occur

Mutation

Any change in the structure or sequence of DNA, whether it is physical or biochemical, caused by mutagens

True

T or F: Once a mutation is introduced into a DNA coding strand, the information in that strand is already altered

Point Mutation

Simplest type of mutation; Only one nucleotide in the DNA sequence is changed; includes: substitutions, insertions, and deletions

Transition

One purine is substituted for another purine, or one pyrimidine is substituted for another pyrimidine

Transversion

When a purine is substituted for a pyrimidine or a pyrimidine for a purine

Missense Point Mutation

Result from a change in a codon, which alters the amino acid in the corresponding peptide (e.g. alterations in the hemoglobin molecule at a single base pair, resulting in different types of inherited anemias)

Nonsense Mutation

A point change in one of the nucleotides of a DNA sequence causes the three possible stop codons to be formed

Frameshift Mutation

There is an insertion or deletion of one or more (but never multiplicities of three) nucleotides in the DNA sequence

Ribonucleic Acid (RNA)

A single-stranded structure with Uracil (instead of Thymine) that transmits genetic information (stored as DNA) from the nucleus to the cytoplasm

ribose ; carbon 2

RNA contains a sugar ____ in the backbone structure, which has the hydroxyl group at ______ position

transcription, translation

RNA undergoes what 2 specific processes?

interphase

RNA synthesis happens or occurs during ____ or the resting state

RIBOSOMAL RNA (rRNA)

Most abundant and consistent type of RNA that makes up a large part of the ribosomal structure on the endoplasmic reticulum in the cytoplasm, and is the site where RNA is translated into peptide

MESSENGER RNA (mRNA)

Type or RNA that is transcribed from DNA and undergoes postsynthesis processing before it can be transferred out of the nucleus and translated

TRANSFER RNA (tRNA)

Type of RNA that is involved in bringing amino acids to the mRNA bound on the ribosome for protein synthesis

SMALL RNA MOLECULES

Type of RNA that regulates gene expression

CELLULAR GENETICS

Area of genetics that involves mitosis and meiosis?

MITOSIS

The process by which cells divide to create identical daughter cells

same number

The goal of MITOSIS is to create identical daughter cells containing the ______ or copy of chromosomes from that of the parent cell

MEIOSIS

The process by which cells divide that results in four unique (bc haploid/half the no. of chromosomes from parents) daughter cells

gametes / sex cells

MEIOSIS occurs to produce what?

POPULATION GENETICS

Area of genetics that tackles the law of inheritance

MENDEL'S LAW OF INHERITANCE

A popular scientific theory of how hereditary characteristics are passed from parent organism to their offspring

→ Law of Dominance
→ Law of Independent Segregation
→ Law of Independent Assortment

State the 3 laws under MENDEL'S LAW OF INHERITANCE

LAW OF DOMINANCE

State what law of inheritance:
When an organism has two different alleles for a trait, one allele dominates

Dominant Allele

• represented by a capital letter
• T-Tall
• the allele that is expressed

Recessive Allele

• are presented by a small letter
• t-short
• expressed only when homozygous

LAW OF INDEPENDENT SEGREGATION

State what law of inheritance:
The two coexisting alleles of an individual for each trait segregate during gamete formation so that each gamete gets only one of the two alleles or haploid. Viewed by Punnett Square

LAW OF INDEPENDENT ASSORTMENT

State what law of inheritance:
The genes for different traits are inherited separately from each other, allowing for all possible combinations of gene to occur in the offspring

HARDY-WEINBERG PRINCIPLE

A mathematical formula that allowed the study of Mendelian inheritance in great detail

p2+pq+q2

State the formula of the HARDY-WEINBERG PRINCIPLE