Bio - EOYT.

Mitosis

A form of cell division resulting in two daughter cells from a mother cell - identical

Chromosomes

Condensed forms of DNA located in the nucleus of a cell

Chromatid

One half of a chromosome

Centromere

The region of a chromosome where the two sister chromatids are joined and where spindle fibers attach during cell division.

• spindle

• cell pole

• equator

• Come from centrioles (used to separate chromatids)

• opposite sides of a cell

• the mid plain of a cell

Homologous chromosomes

Chromosome pairs, one from each parent, that are similar in shape, size, and genetic content.

Meiosis

A type of cell division that reduces the chromosome number by half, resulting in four genetically diverse gametes, crucial for sexual reproduction. - except for 3 polar bodies in oogenesis

Diploid vs haploid

• double vs half (full chromosome set vs half set)

Cell cycle - interphase

• G1 phase - initial growth phase + copying of organelles

• S phase - DNA duplication phase - centrosomes duplicated

• G2 phase - further growth

Prophase - mitosis

Prophase - meiosis

Metaphase

• chromosomes align at the equator (homologous if meiosis)

Anaphase

Chromosomes or chromatids pulled apart by spindle fibers from centrioles (in the centrosomes)

Telophase

Variation

• Crossing over

• Random arrangement

• Random assortment

• Non-disjunction/other mutations

• Fertilization

Gene

Small segment of DNA that codes for a specific trait

Alleles

Alternate forms of one trait (brown hair and ginger hair)

Homozygous

Two of the same characteristics

Heterozygous

Two different alleles for one trait

Genotype

The gene composition of an individual

Phenotype

Physically visible characteristics of a certain genotype

Law of segregation

When gametes form, alleles are separated so that each gamete carries only one allele for each gene

Law of independent assortment

The segregation of alleles for one gene occurs independently to that of any other gene

Law of dominance

Recessive alleles will be masked by dominant alleles

Autosomal traits

Traits that are located on any chromosome except for the sex chromosomes

Both parents affected, child unaffected

Dominant trait, heterozygous parents

All affected individuals…

..must have an affected parent - dominant trait

Both parents are unaffected, then children also unaffected

Parents would be homozygous recessive and trait dominant

If both parents are unaffected and child is affected..

Trait must be recessive (parents are heterozygous carriers)

If both parents show trait, child must too

Homozygous recessive for trait

Co-dominance

Both genotypes are dominant and are equally represented in the phenotype

Incomplete dominance

Both genes mix together to create a new and unique phenotype

Sex-linked traits

Sex linkage refers to when a gene controlling a characteristic is located on a sex chromosome (X or Y)

Rule 1:

Only females can be carriers (a heterozygote for a recessive disease condition), males cannot be heterozygous carriers (they have only 1 X-chromosome)

Rule 2:

Males will always inherit an X-linked trait from their mother (they inherit a Y chromosome from their father)

Rule 3:

Females cannot inherit an X-linked recessive condition from an unaffected father (must receive his dominant allele)

• so he is unaffected and therefore doesn’t have the recessive gene, so daughter wouldn’t inherit it from him but perhaps would from mother

Unlinked genes

Gene loci on different chromosomes and are independent of one another

Di-hybrid cross

Determines the genotypic and phenotypic rations of two unlinked traits (so hair colour and eye colour)

Discontinuous variation

• Organism either has it or not

• Qualitative

• Only determined by genes

• eg. blood type or sex

Continuous variation

• determined by genes and environmental influence

• every organism shows gene but to different extent

• several genes acting together

• quantitative

• use di-hybrid cross to express

Causes of mutation

• Mistake in copying DNA

• DNA damage

• eg. radiation, chemicals, etc.

Adaption

An organism that is well –suited to make the most out of the limited resources within its environment is said to show adaptation

Process of evolution

• Over production/genetic variation

• Struggle for existence/environmental pressure

• Variation/adaption

• Natural selection/survival of the fittest

• speciation

Evidence of evolution

• analysis of fossils - compare to existing creatures and create family tree

• bio-geographical location - continental drift

• comparative anatomy - homologous(same structure different function) + analogous (different structure, same function)

• DNA (mitochondrial) - passed down from mother and can analyse tree line