Biology Exam Revision

Alleles

Alternate forms of a gene for a particular characteristic

autosomes

non-sex chromosomes

carrier

an individual heterozygous for a characteristic who does not display the recessive trait

cell

the smallest unit of life and the building blocks of living things

centromere

section of a chromosome that links sister chromatids

Chargaff’s rule

a rule that states the pairing of adenine with thymine and cytosine with guanine

chromatid

one identical half of a replicated chromosome

complementary base pairs

In DNA, specific base pairs will form between the nitrogenous bases adenine (A) and thymine (T) and between the bases cytosine (C) and guanine (G)

complete dominance

a type of inheritance where traits are either dominant or recessive

deoxyribonucleic acid (DNA)

a substance found in all living things that contains its genetic information

deoxyribose

the sugar in the nucleotides that make up DNA

diploid

the possession of two copies of each chromosome in a cell (2n) 46 in a human

DNA replication

process that results in DNA making a precise copy of itself

dominant

a trait (phenotype) that requires only one allele to be present for its expression in a heterozygote

gametes

reproductive or sex cells such as sperm or ova

gene

segment of a DNA molecule with a coded set of instructions in its base sequence for a specific protein product; when expressed, may determine the characteristics of an organism

genome

the complete set of genes present in a cell or organism

genotype

genetic instructions (contained in DNA) inherited from parents at a particular gene locus

haploid

the possession of one copy of each chromosome in a cell (n) 23 in a human

heterozygous

a genotype in which the two alleles are different

homologous

chromosomes with matching centromeres, gene locations, sizes and banding patterns

homozygous

a genotype in which the two alleles are identical

homozygous dominant

a genotype where both alleles for the dominant trait are present

homozygous recessive

a genotype where both alleles for the recessive trait are present

inheritance

genetic transmission of characteristics from parents to offspring

karyotype

an image that orders chromosomes based on their size

locus

position occupied by a gene on a chromosome

meiosis

cell division process that results in new cells with half the number of chromosomes of the original cell

transfer RNA (tRNA)

Molecules of tRNA are responsible for matching amino acids with the appropriate codons in mRNA.

messenger RNA (mRNA)

single‑stranded RNA transcribed from a DNA template that then carries the genetic to a ribosome to be translated into a protein

mitosis

cell division process that results in new genetically identical cells with the same number of chromosomes as the original cell, for non sex cells

monosomy

a condition where there is only one copy of a particular chromosome instead of two

mutations

changes to DNA sequence, at the gene or chromosomal level

nitrogenous base

a component of nucleotides that may be one of adenine, thymine, guanine, cytosine or uracil

nucleic acids

molecules composed of building blocks called nucleotides, which are linked together in a chain

nucleotides

compounds (DNA building blocks) containing a sugar part (deoxyribose or ribose), a phosphate part and a nitrogen-containing base that varies

nucleus

roundish structure inside a cell that contains DNA and acts as the control centre for the cell

pedigree chart

diagram showing the family tree and a particular inherited characteristic for family members

phenotype

characteristics or traits expressed by an organism

Punnett square

a diagram used to predict the outcome of a genetic cross

recessive

a trait (phenotype) that will only be expressed in the absence of the allele for the dominant trait

ribose

the sugar found in nucleotides of RNA

ribosome

organelle found in the cells of all organisms in which translation occurs, made of RNA and proteins

sex chromosomes

chromosomes that determine the sex of an organism

sex-linked inheritance

an inherited trait coded for by genes located on sex chromosomes

sister chromatids

identical chromatids on a replicated chromosome

somatic cells

cells of the body that are not sex cells

transcription

the process by which the genetic message in DNA is copied into a mRNA molecule

translation

the process by which mRNA is translated into proteins.

trisomy

a condition where there are three copies of a particular chromosome instead of two

interphase

Stage of the cell cycles where the cell grows, performs its normal functions, and prepares for division including DNA replication; consists of G1 (organelles growth), S (DNA synthesis), and G2 (growth and preparation for mitosis, checks if everything is ready)

prophase

first and longest phase of mitosis, during which the chromosomes become visible and the centrioles separate and take up positions on the opposite sides of the nucleus

metaphase

phase of mitosis in which the chromosomes line up across the centre of the cell

anaphase

Phase of mitosis in which the chromosomes separate and move to opposite ends of the cell

telophase

the final phase of mitosis, in which the chromatids or chromosomes move to opposite ends of the cell and two nuclei are formed.

cytokinesis

Division of the cytoplasm during cell division

crossing over

Process in which homologous chromosomes exchange portions of their chromatids during meiosis.

independent assortment

the random distribution of the pairs of genes on different chromosomes to the gametes

differences between animal and plant cells

plant cells have a cell wall, and a much larger vacuole.