Lecture 17th

DNA

the double-stranded biomolecule that is the unit of heredity for all cellular life

Gene

discrete until of DNA that influences hereditary traits

chromosomes

very long DNA molecules

genome

the full genetic code of an organism (contained in each nucleus)

sister chromatids

2 chromosomes attached at the centromere called “sister chromatids”

What type cells go through mitosis

asexual eukaryotes; our somatic cells

germ cells

meiosis

germ cells - gametes. Sperm and Egg

Haploid (1N) - 2 copies of each chromosome

somatic cells- everything else

Diploid, (2N) - 2 copies of each chromosome

Alleles

Homologous chromosomes contain the same genes

what happens before meiosis

all chromosomes replicate

Prophase I

Homologous chromosomes form pairs

Special proteins ‘glue’ pairs together

what is this

prophase I

Metaphase I

Homologous chromosomes line up and are attached to the spindle

what is this?

metaphase I

Anaphase I

Homologous chromosomes are seperated

what is this?

anaphase I

Telophase I

• 2 haploid (1n) cells

• Each chromosome is still duplicated

• are these genetically identical

what is this

telophase I

Meiosis II

separation of the sister chromatid which leads to 4 daughter cells

Meiosis II end result

four haploid cells that are not genetically identical

meiosis consists of two nuclear divisions DNA is only replicated once true or false

true

the haploid cells produced by meiosis are genetically different from one another and from the parent cell

true

meiosis in females

meiosis begins during fetal development

after puberty meiosis in females

1 egg each month enters meiosis II

creates 4 products, but 3 disintegrate

a single egg is released

Meiosis in males

meiosis doesn’t begin until puberty

spermatogenesis

is biological process by which germ cells transform into mature, haploid spermatoza (sperm cells) inside the male testes.

Fertilization

haploid products of meiosis (usually sperm and eggs) fuse

Form a single diploid cell

zygote

two important ways in which meiosis generates genetic diversity

1. independent assortment

2. crossing over

independent assortment

the way in which chromosomes line up on the metaphase plane in meiosis I is random

when does crossing over occur

prophase I

when does genetic exchange occurs

between non-sister chromatids

chiasmata

chroatids breaks and rejoin to non-sister homologous

what is this

crossing over results in recombinant chromatids and increases genetic variability

Diploid cells of the fruit fly Drosophila have eight chromosomes. How many chromosomes does a Drosophila gamete have?

4

sexual reproduction increases genetic variability through:

crossing over, independent assortment, and random fertilization

when does crossing over occur?

prophase of meiosis I, when homologous chromosomes pair

the chromosome number of each daughter cell is reduced by half during meiosis beacuse

homologous chromosomes separate during anaphase of meiosis I

mutation

the original source of all variation

how many stages does the cell cycle have

four stages

G1

cells carry out normal functions. G1 is an arrested state. Cells remain in the state until receiving cell division signal

S phase

DNA is replicated

G2

cell prepares for mitosis

M phase:

mitosis and cytokinesis

Prokaryotes

usually reproduce by binary fission

single-celled eukaryotes reproduce by

mitosis

n=

number of distinct types of chromosomes

haploid

individuals have 1 version of each chromosome

diploid

individuals have 2 versions of each chromosome

2n=

2 complete sets

what are pairs called

homologous chromosomes