meiosis

alleles

each copy of chromosomes in a diploid cell has the same sequence of genes, but the genes may have different forms

congugation

transferring pieces of genes to other bacteria that they contact. one bacterium connects itself to another through a pilus. Genes are transferred from one bacterium to the other.

budding

organism grows a small bud that splits off to become its own organism (plants, sea creatures, single celled eukaryotes)

fragmentation

entire organism is split into fragments and each fragment grows and matures into its own organism

advantages of asexual reproduction

• establish/re-establish population quickly

• low investment for energy and time

disadvantages

• low genetic diversity

• cannot easily adapt to change in environment

sexual reproduction advantages

• increased genetic variation

• variation allows for resistance to environmental changes

sexual reproduction disadvantages

• fewer offspring

• time, energy, and competition for mate

mitosis summary

• produces body/somatic cells

• parent and daughter cells are diploid

• parent and daughter cells are identical

meiosis

purpose is to produce gametes

during the process, 4 daughter cells are produced, each of which are haploid

prophase 1

homologus chromosomes pair up an exchange fragments (crossing over)

2n

metaphase 1

homologus pairs line up at the metaphase plate. independent assortment occurs

2n

anaphase 1

homologus chromosomes separate to opposite ends of the cell

sister chromatids stay together

2n

telophase 1

newly forming cells are haploid (n)

each chromosome has two sister chromatids

at the end of meiosis 1….

homologus chromosomes have been separates

prophase 2

starting cells are the haploid cells made in meiosis 1

chromosomes condense

spindle apparatus forms

n

metaphase II

chromosomes line up at the metaphase plate

n

anaphase II

sister chromatids separate to opposite ends of the cell

n

telophase II

newly forming gametes are haploid

each chromosome has just one chromatid

n

at the end of meiosis II…

the sister chromatids have separated

origins of genetic variation

mutation, independent assortment of chromosomes, crossing over, random fertilization

nondisjunction meiosis 1

homologus chromosomes do not move apart properly which leads to the production of aneuploid gametes

nondisjunction meiosis II

sister chromatids fail to separate

duplication

broken fragments become reattached as an extra segment to a sister or non-sister chromatid

deletion

chromosome fragment is lost

inversion

fragment may attach in reserve order

translocation

fragment may join nonhomologus chromosome

karyotyping

the general appearance of the complete set of chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes

multiple y

why is it not a problem?

• y chromosomes are the smallest human chromosome

• contains very few genes

• major function is to direct testes formation in early development

crossing over in increasing genetic diversity

exchange of DNA segments between non-sister chromatids

independent assortment in exchange of DNA segments between non-sister chromatids

random orientation of homologus pairs, maternal and paternal chromosomes are sorted into gametes randomly

random fertilization

any one sperm can fuse with any one egg which creates a massive number of potential genetic combinations

recombination frequency

number of recombination offspring/total number x 100

restoration of a diploid number

diploid number 2n is restored through fertilization. when a haploid sperm (N) fuses with a haploid egg, the resulting zygote possess a full set of homologus pairs (2n)

aneuploidy

abnormal number of chromosomes

trisomy

having three copies of chromosome

monosomy

having only one copy of a chromosome (turner syndrome)