10Biology Unit 1: Genetics

Heredity

Passing on traits from parents to offspring

Heritable Trait

A trait which can be inherited

Variation

Differences in genetic profiles in a population

Chromosomes

threadlike structures made of DNA molecules that contain the genes

How many chromosomes are there

46 (23 pairs)

Homologous pairs of chromosomes

consist of two chromosomes the same size and with the same genes

Haploid cells

A cell containing only one set of chromosomes (gametes).

Diploid cells

Cells containing the full set of chromosomes (body cells)

Karyotype

A display of the chromosome pairs of a cell arranged by size and shape.

Gene

A segment of DNA on a chromosome that codes for a specific trait

DNA

Deoxyribonucleic acid

DNA Structure

Double helix

What is DNA made from

Sugar phosphate backbone of deoxyribose sugar and phosphate groups and nitrogenous bases

Nitrogenous bases

Adenine, Thymine, Guanine, Cytosine

What are the base pairs

Adenine - Thymine

Guanine - Cytosine

What are nitrogenous bases bound to

Deoxyribose sugar

What is a nucleotide made from

one phosphate, one deoxyribose sugar, one nitrogenous base

codon

triplet of bases

Allele

Different forms of a gene

Dominant Gene

A gene that is expressed in the offspring whenever it is present

Recessive Gene

Gene that is hidden when the dominant gene is present

Homozygous

Having two forms of the gene

Heterozygous

Having two different forms of the gene

Genotype

An organism's genetic makeup

Phenotype

Actual trait resulting from genetic makeup

Sex determination

An individual's sex is determined by sex chromosomes from each parent

Sex linked genes

Females: XX Males: XY

Where are sex linked genes located

on the sex chromosomes

Pedigree

A diagram that shows the occurrence of a genetic trait in several generations of a family.

Autosomal dominant

Autosomal Recessive

X-Linked dominant

X-Linked recessive

Fertilisation

The process of combining the male and female gamete, producing a zygote

Asexual reproduction

- Does not involve sex cells or fertilisation

- only 1 parent required

- genetically identical offspring

Sexual reproduction

the production of new organisms by the combination of genetic information of two individuals of different sexes

Asexual reproduction advantages

Saves energy, no time needed to find a mate

Asexual reproduction disadvantages

Low genetic variability, can be wiped out by a single change in the environment

Sexual reproduction advantages

highly genetically diverse, better adaptation to changing environment

Sexual Reproduction disadvantages

Energy costly, time needed to find a mate

Role of the cell cycle

Growth and development, repair and replacement, asexual reproduction

Interphase

Cell prepares for division by growing, replicating DNA and producing organelles

Prophase

Chromosomes condense, spindle fibres form, and the nuclear envelope breaks down

Metaphase

Chromosomes align at the cell's metaphase plate, attached to spindle fibres

Anaphase

Sister chromatids are pulled apart to opposite ends of the cell

Telophase

Chromatids reach the ends, nuclear envelope and chromosomes de-condense

Cytokinesis

Cytoplasm divides, forming two separate daughter cells

Prophase 2

A new spindle forms around the chromosomes, nuclear envelope breaks down again

Metaphase 2

Chromosomes line up individually along the equator of each cell, spindle fibres attach to each chromatid

anaphase 2

sister chromatids separate ad move to opposite poles of the cell, each chromatid is considered a separate chromosome

Telophase 2

Chromosomes reach the poles and begin to decondense, nuclear envelopes re-form around each set of chromosomes

cytokinesis 2

the 2 cells divide again, producing 4 genetically unique gamete cells

Mutation

change in DNA code, therefore can alter the protein product

where do mutations occur

in one of the parental gametes

causative agents - induced mutations

x rays, uv radiation, nuclear radiation, chemical substances (mutagenic agents)

non causative agents - spontaneous mutation

occurs more frequently with age

How does DNA code for proteins

proteins are made from amino acids and each codon codes for one amino acid

chromosomal mutations

the individual inherits the wrong number of chromosomes or large parts of chromosomes are altered via crossing over

point substitution mutation

The replacement of one nucleotide by another in the DNA

Frameshift Mutation

An insertion or deletion of one or more bases has occurred, resulting in the disruption of subsequent codons

Inversion mutation

Chromosome rearrangement in which a segment of the chromosome is reversed end to end