biology

Autosomal dominant:

• all affected individuals have at least one affected parent

• once the trait disappears, it cannot reappear in later generations

• affects both males and females, and can be transmitted via any sex (male/female)

Autosomal recessive:

• both males and females can be affected

• two unaffected parents can have an affected child

• all children of two affected parents must also show the condition

• the trait can disappear & reappear through generations

A DNA molecule is in a double helix shape — two strands, bonded in the middle, twisted into a spiral

Nucleotide:

• basic building block of RNA and DNA

• consists of phosphate group, pentose sugar, nitrogenous base

• DNA is made into RNA by ribosomes

• nitrogenous bases are connected by hydrogen bonds

• bases (adenine & thymine, cytosine & guanine)

chromosome - compacted DNA, a human has 46 in each body cell

G1 — Growth occurs as organelles double (cell repair, growth, reproduction preparation)

S — DNA replication occurs as chromosomes duplicate

G2 — Growth occurs as cell prepares to divide

M — Mitosis & cytokinesis occurs

Prophase:

Think — chromosomes physically condenses

• chromatin (DNA + protein) shortens and thicken to form chromosomes (can be observed through microscope)

• chromosome is made up of two identical threads called sister chromatids

• sister chromatids are joined at the centromere

Metaphase:

Think — middle is where the chromosomes line up

• microtubules pull chromosomes to align at the equator of the cell

• centrosomes at the opposite poles of the cell extend spindle fibres, connect to centromeres and align chromosomes in a row (equator)

• metaphase ends when the centromere starts to divide

Anaphase:

Think — chromatids comes apart

• the centromere divides into two, the sister chromatids seperate

• spindle fibres shorten & contract

• chromatids are pulled to the opposite poles of the cell

Telophase:

Think — two new nuclei form

• the chromatids at the opposite ends are now called daughter chromosomes

• chromosomes are formed

• spindle fibres disappear

• new nucleus membranes are formed

Cytokinesis (both mitosis & meiosis):

• the very last step of cell division

• the physical process of cell division

• cytoplasm of parental cell divides into two daughter cells

Variation

genetic variation:

• variation between each of the genomes’ variation in the DNA sequence

  • genome 1 - genome 46

• makes everyone unique

• evolution ensures more individuals in a population to likely have variations

• increases chance of more of the population surviving when conditions change

be careful when saying

“the organism’s genetic variation is caused by the environment”

rather say

“organisms with these genetic variations were more successful in surviving & reproducing in this environment”

meiosis:

• creates gametes (sex cells)

• two ‘cycles’ of the mitosis phases

• one parental cell separates into two, then four daughter cells

• 23 chromosomes in each daughter cell

• daughter cells are gametes, or haploids

• chromosomes cross over when first aligned together in the middle of the cell

• in the process of crossing over, parts of the mother and father’s chromosomes containing different forms of the same gene is switched

• crossing over increases variety in genes, aiding more population within a species pass natural selection

Traits & Alleles

Dominant traits

• represented by capital letter (e.g. T)

• a single copy of the allele is enough to observe the phenotype

Recessive traits

• represented by lower case letter (e.g. t)

• two copies of the allele is necessary to observe the phenotype

Homozygous dominant = two dominant alleles

Homozygous recessive = two recessive alleles

Heterozygous = one dominant, one recessive allele

The dominant allele is always written before the recessive allele.

Each individual has a karyotype - their complete set of chromosomes

The chromosomes for sex determination are chromosomes X & Y

→ Male XY

→ Female XX