biology sciences

test 3 term 2

DNA 

Deoxyribonucleic acid - the chemical compound that carries the inherited information in the cell, codes for protein production 

Nucleotide

The basic structural unit of DNA, consisting of a deoxyribose sugar, a phosphate and a nitrogen base. 

Gene

A section of DNA, that codes for a particular trait 

Chromatin

Highly coiled DNA molecule 

Chromosome

Super coiled chromatin (DNA) to form a rod-like structure that contains the genes of an individual 

DNA Replication 

to carry the genetic code accurately and be able to pass it onto future generations, every cell must have identical DNA to the original body cell.

1.A representative portion of DNA, which is about to undergo replication

2.the two strands of the DNA separate. The hydrogen bonds between the bases break

3.Free nucleotides are attracted to their complementary bases

4.Once the new nucleotides have lined up, they are joined together by the enzyme DNA polymerase

5.finally, all the nucleotides are joined to form a complete polynucleotide chain using DNA polymerase. In this way, two identical strands of DNA are formed. As each strand retains half of the original DNA material, this method of replication is called the semi-conservative method

Protein 

An organic compound made of amino acids that controls chemical reactions in the body.  

Helicase 

Enzyme responsible for separating the two sides of the  
DNA molecule 

DNA Polymerase 

Enzyme involved in attaching loose nucleotides  
to the exposed DNA strand 

DNA Ligase 

Enzyme involved in repairing the bonds that hold the backbone of the nucleotides together to form DNA 

Allele

An alternative form of a gene that occurs at a given point in a chromosome 

Dominant

Where one allele masks the effect of the alternative allele 

Recessive 

The allele which is only shown if it is not masked by the effects of a dominant allele 

Genotype 

The genes present in an individual, usually represented by letters eg. RR, Rr, rr 

Phenotype

The physical appearance of an individual as determined by its genotype. eg. Tongue rolling and non tongue rolling

Homozygous 

Where an individual has two identical alleles for a given gene 

Heterozygous 

Where an individual has two different alleles for a given gene 

Punnett square 

A table used to solve genetic problems 

Sex-linked trait 

A trait controlled by a gene found on a sex chromosome (usually the X chromosome). 

X chromosome

One of the sex chromosomes; carries many genes. 

Y chromosome 

The smaller sex chromosome; carries fewer genes. 

X-linked inheritance 

When a gene is located on the X chromosome. 

Carrier 

A person who has one copy of a faulty gene but does not show symptoms. 

Affected 

A person who shows the trait or disease. 

Dominant 

A gene that only needs one copy to be expressed. 

Recessive 

A gene that needs two copies to be expressed (in females). 

Pedigree 

A diagram that shows how a trait is passed through a family. 

Generation 

A level in a pedigree (e.g. grandparents, parents, children). 

Individual 

One person in the pedigree. 

Trait 

A characteristic that can be inherited. 

Inheritance pattern 

The way a trait is passed from parents to offspring. 

Cell cycle 

The series of stages a cell goes through as it grows and divides. 

Mitosis

The process where one cell divides to make two identical cells. 

Interphase

The stage before mitosis where the cell grows and copies its DNA. 

Chromosome 

A structure made of DNA that carries genetic information. 

Chromatid

One half of a duplicated chromosome (two identical halves joined together). 

Sister chromatids 

The two identical copies of a chromosome joined in the middle. 

Centromere

The point where sister chromatids are attached. 

Cytokinesis

The cell splits into two identical daughter cells. 

Daughter cells 

The two new cells formed after mitosis (genetically identical). 

Nucleus

The part of the cell that contains DNA. 

Spindle fibres 

Thin structures that pull chromatids apart during mitosis. 

Prophase 

Chromosomes become visible and the nucleus starts to break down. 

Metaphase

Chromosomes line up in the middle of the cell.