genetics

Gene

a section of DNA that carries the code to make a protein

genome

Houses all the genetic information needed to build and maintain an organism

allele

A variation of a gene

Locus

the specific area on a chromosome where the same traits are found.

Metacentirc

centromere is in the middle

Submetacentric

centomere is 3/4 up

acrocentic

centromere is almost at the top

Telocentric

centromere is at the very top.

criteria for homologous chromosome

same size and length, same centromere position, share the same genes at the same loci.

homologous chromosome

a pair of chromosomes, one is paternal one is maternal.

karyotype

a visual representation of an organism's genome

what does a human karyotype display

22 pairs of autosomes, 1 pair of sex chromosomes

44 autosomes, 2 sex chromosomes

xx sex chromosmes

female

xy sex chromosomes

male

Aneuploidy

incorrect number of total chromosomes caused by the addition of loss of an individual chromosomes. in humans, more or less the 46.

organism has one missing chromosome

monosomy (2n-1)

organism has one extra chromosome

trisomy (2n+1)

Polyploidy

an abnormal number of chromosomes in each set. only in plants

example of monosomy

Turner syndrome, individual has only 1 X chromosome. symptoms: infertility, short stature, fused neck.

example of trisomy

Down syndrome (trisomy 21). extra copy of chromosome 21. symptoms: delayed physical growth, possible heart defects, moderate intellectual disability.

tetrasomy

organism has four copies of a particular chromosome instead of the normal two. (2n+2)

diploid cell

cell containing pairs of chromosomes (2n) somatic cell

haploid cell

A cell containing only one set of chromosomes (n). gamete

what does meiosis produce

4 genetically different haploid cells, gametes

crossing over

the exchange of genetic material between non sister chromatids during prophase 1. results in new combinations of alleles in the daughter cells

prophase 1

chromosomes condense and line up in homologous pairs. crossing over occurs.

metaphase 1

chromosomes line up randomly across the equator of the cell. microtubules attach.

Anaphase 1

Homologous chromosomes separate. sister chromatids remain attached at the centromere.

Telophase 1

2 daughter cells are formed, each haploid with double stranded chromosomes. cleavage furrow forms and cell seperates.

independent assortment

the random orientation of homologous chromosomes across the equator in metaphase 1.

prophase 2

The duplicated chromosomes condense and spindle fibers reappear in each new cell.

metaphase 2

Chromosomes line up at the equator. spindle fibres attach

anaphase 2

sister chromatids separate and move to opposite poles

telophase 2

nuclear membrane forms. chromosomes begin to decondense.

cytokinesis

chromosomes split resulting in 4 haploid daughter cells with single stranded chromosomes.

non disjunction

occurs when homologous chromosomes fail to separate properly during anaphase 1. one gamete receives two of chromosome type and the other receives none.

genotype

genetic composition of an organism at a particular locus.

phenotype

the visual representation of the genotype combined with epigenetic and environmental factors.

homozygous dominant (with Aa)

AA

Homozygous recessive (with Aa)

aa

Heterozygote (with Aa)

Aa

epigenetics

factors within the body that can control gene expression without altering the DNA sequence.

types of epigenetics

DNA methylation and histone modification

DNA methylation

A methyl group attaches to cytosine bases, often preventing that gene being expressed.

histone modification

Chemical changes to histones affecting the tightness of the DNA coil and therefore altering gene expression.

things that lead to epigenetic modifications

exposure to UV, chemicals and toxins, and harmful radiation.

example of environmental factors

uv, nutrition, exposure to chemicals toxins and radiation, predators, pathogens, competition for reasources.