Topic test science

Structure and function (role) of DNA

Codes for our traits (proteins)

Nucleotide

Phosphate, Deoxyribose sugar, Nitrogenous base

Gene

Section of DNA that codes for an amino acid (protein)

Chromosome

Somatic cell = 46

Sperm and Egg = 23

Homologous chromosomes

a pair of chromosomes that contain the same genes

one chromosome is inherited from the mother and the other from the father

Chromatid

an individual copy of a chromosome that has duplicated but has not yet separated from its identical copy.

Centromere

the specialized, constricted region of a chromosome that holds sister chromatids together after DNA replication

Karyotype

is a visual representation of an organism’s chromosomes, including their number, size and shape.

It can also refer to the complete set of chromosomes in an individual’s cells.

Complementary base pairing (AT, CG)

Adenine pairs with Thymine

Cytosine pairs with Guanine

The process of DNA replication

Mutation types

Point mutations

Silent mutations

Missense mutations

Nonsense mutations

Frameshift mutations

Point Mutations

Genetic mutations that involve a physical change to one nitrogenous base within a base sequence

Type of point mutation - substituation

A different base in the same sequence

Type of point mutation - insertion

A new base is added in the sequence

Type of point mutation - deletion

A base is removed from the sequence

Silent Mutations

Occurs due to a substitution mutation - replacement of one base for another

There is no effect on the protein formed

Missense Mutations

Occurs due to a substitution mutation

The shape of the protein may be affected

May affect the function of the protein

Nonsense Mutations

Occurs due to a substitution mutation

New triplet codes for a STOP instruction - the amino acid sequence is shortened

Good chance it will cause a loss of protein function

Frameshift Mutation

Occurs due to an addition or deletion of a nitrogenous base

Causes a complete shift in the reading frame of the triplet bases

All amino acids coded for are changed - results in totally different protein (most likely non-functioning) being formed

Genotype

a set of alleles of a gene in our DNA responsible for a particular trait (e.g. GG/Gg/gg)

Phenotype

physical appearance of the trait resulting from genotype (e.g. Green or yellow peas)

The cell cycle

The sequence of events that takeplace during the life of a cell

These are continuous

Cell cycle - Interphase

Longest section of a cell cycle’s life

Cell growth and copying of chromosomes to prepare for cell division (90% of the cell cycle)

Interphase - Gap 1 stage (G1)

Cell grows in size and organelles double

Interphase - Synthesis stage (S)

DNA replication (each chromosome doubles)

Interphase - Gap 2 stage (G2)

More growth of cell and preparation for Mitosis

Cell cycle - Mitosis Phase (M)

Mitosis otherwise known as Nuclear division

Mitosis consists of three phases (PMAT)

PMAT.- Prophase

Chromosomes condense

PMAT - Metaphase

Chromosomes align in the equator

PMAT - Anaphase

Chromosomes pulled to separate sides (pulled apart)

PMAT - Telophase

The new nuclei has formed and about to separate

Cytokinesis

Cytoplasm splits resulting in the parent cell dividing into two daughter cells

Meiosis - Crossing over

Happens in prophase I

Chromosomes exchange genetic information

Gametes

Haploid sex cell

Inheritance

the process by which genetic information is passed from parents to offspring through DNA

Alleles

version of a gene

Dominant trait

only needs one allele in the genotype for the trait to be expressed in the pheonotype

Recessive trait

only expressed in the phenotype when there are two copies present

Homozygous

both alleles in a pair are the same

Heterozygous

One dominant and one recessive allele in a pair

Haploid

cells containing a single set of unpaired chromosomes

Diploid

contains two complete sets of chromosomes, one inherited from each parent

Punnett squares

a table in which all of the possible outcomes for a genetic cross between two individuals with known genotypes are given

Test cross

used in genetics to determine whether an organism with a dominant phenotype is homozygous dominant (AA) or heterozygous (Aa)

Carrier

an individual who possesses and can pass on a recessive, disease-causing allele (genomic variant) without expressing the disease themselves

Type of inheritance - Autosomal dominant

gene coding is located on one of the autosomes

only one copy is needed for the trait to be observed in the phenotype

Type of inheritance - Autosomal recessive

gene coding for the trait is located on one of the autosomes

Two copies need to be inherited for the condition to be observed in the phenotype

Type of inheritance - X-linked Dominant conditions

gene coding for the trait is located on the X-chromosome

For both males and females, only one copy is needed to be seen in the phenotype

Type of inheritance - X-linked recessive conditions

gene coding for the trait is located on the X-chromosome

For females, two copies are needed for the trait to be in the phenotype

For males, only one copy is needed as they only have one X-chromosome

MAINLY IN MALES