Biology

IB MYP 5 Biology

Allele

These are the different forms of a single gene. Characteristics like colour are coded for by ___, which can be dominant or recessive.

Carrier

In genetics, this is an individual who is heterozygous for a recessive condition; they possess one copy of the recessive allele but do not show symptoms of the disease.

Chromatin

This is uncoiled DNA that is spread throughout the nucleus during the interphase of the cell cycle. It eventually warps around histone proteins and condenses into chromosomes during mitosis.

Chromosome

A thread-like structure found within the nucleus, made of DNA and protein. Humans typically have 46 ____ in normal cells, consisting of 22 pairs of autosomes and one pair of sex ____.

Codominance

A genetic scenario where both alleles in the genotype affect the phenotype, such as in snapdragon flowers where red and white allels can result in pink offspring.

Complementary Base Pairing

The specific rule in DNA where Adenine (A) only pairs with Thymine (T) and Guanine (G) only pairs with Cytosine (C).

Diploid (2n)

Cells that contain two copies of each chromosome. In humans, this refers to the 46 chromosomes found in normal body cells.

DNA (Deoxyribonucleic acid)

The chemical substance that genes are made of, appearing as a double-helix composed of a sugar-phosphate backbone and four nitrogenous bases.

Dominant

An allele that is always expressed in the phenotype, even if only one copy is present in a heterozygote.

Evolution

Defined as the gradual change of a species of living organisms over a

long period of time.

Gene

A specific length of DNA that acts as the basic unit of inheritance by coding for the production of a particular protein.

Genotype

The specific combination of alleles an organism possesses for a particular characteristic.

Haploid (n)

Cells that contain only one copy of each chromosome, specifically sex cells known as gametes.

Helicase

The enzyme responsible for separating the DNA double helix into single strands by breaking the hydrogen bonds between complementary bases.

Heterozygous

A genotype consisting of two different alleles for a specific gene.

Homozygous

A genotype consisting of two of the same alleles for a specific gene.

Meiosis

A type of cell division used to make gametes; resulting in four genetically different daughter cells with a haploid number of chromosomes.

Mitosis

A cell division process that produces two genetically identical daughter cells, ensuring each receives a full set of DNA for growth and tissue repair.

Mutation

A change in the DNA molecules of a cell, which can be caused by external factors like radiation or errors during DNA replication. Examples of DNA ____ include insertion, deletion, and substitution mutations (which can be silent, missense, or nonsense).

Natural Selection

The process where individuals with favourable traits are more likely to survive and reproduce, passing those traits to the next generation.

Nucleotide

The building block of DNA, consisting of a pentose sugar, a phosphate group, and a nitrogenous base.

Nucleus

A cell organelle that contains chromosomes. It controls the cell's activities.

Phenotype

The physical appearance or expressed traits of an organism resulting from its genotype.

Recessive

An allele that is only expressed in the phenotype when the genotype is homozygous (no dominant allele is present).

Selective Breeding (Artificial Selection)

The process where humans choose specific organisms with desirable traits to breed together to produce offspring with those characteristics.

Species

A group of organisms that can interbreed to produce fertile offspring.

Test Cross

Testing a suspected heterozygote by crossing it with a known homozygous recessive.

Variation

The differences in characteristics between individuals (for example, physical traits, physiology, behaviour etc.) within a population, caused by both genetic and environmental factors.

Prophase

Chromosomes condense; spindle forms.

Metaphase

Chromosomes align at the equator.

Anaphase

Sister chromatids separate to opposite poles.

Telophase

The two groups of chromosomes reach the opposite ends of the cell, new nuclear envelope forms around each group.

Cytokinesis

Not classified as a stage in Mitosis. Cell divides into two genetically identical daughter cells.

Fertilisation

The process in which an egg cell (ovum) and sperm cell (spermatozoa) join together.

Double-Helix

The physical, twisted-ladder structure of DNA, composed of two antiparallel strands of nucleotides that coil around a central axis.