Meiosis and Sexual Life Cycles

Variations on a thme

heredity is the transition of traits from one generation to the next.

Genetics is the scientific study of heredity and hereditary variation

INHERITANCE OF GENES

Units are called genes

reproductive cells are called gametes

46 chromosomes in somatic cells

genes specific location along the length of a chromosome is called the genes locus.

COMPARISON OF ASEXUAL AND SEXUAL REPRODUCTION

asexual reproduction a single individual passes all its genes to its offspring giving birth to a clone

Sexual reproduction is made between two parents and the intercourse of their genes.

FERTILIZATION AND MEIOSIS ALTERNATE IN SEXUAL LIFE CYCLES

a life cycloe is the generation-to-generation sequence of stages in the reproductive history of an organism

SETS OF CHROMOSOMES IN HUMAN CELLS

each somatic cell has 46 chromosomes

chromosome pairs are called karyotype

If the two chromosomes of a pair have the same length contromere and staining paterna are called homolohous chromosomes or homolohs.

X and Y chromosomes are called sex chromosomes

Other chromosomes are called autosomes

any cell with two chromosome sets ic alled a diploid cell

BEHAVIOUR OF CHROMOSOME SETS IN THE HUMAN LIFE CYCLE

union of gametes culminating in the fusion of their nuclei is called fertilization

zygote is a fertilized egg

the only cells fo the human body not produced by mitosis are the gametes

germ cell in the gonads

THE VARIETY OF SEXUAL LIFE CYCLES

Plants and some species of algae exhibit a second type of life cycle called alternation of generations

In this cycle, they alternate between a diploid sporophyte phase that produces spores and a haploid gametophyte phase that produces gametes, allowing for genetic diversity.

MEIOSIS REDUCES THE NUMBER OF CHROMOSOME SETS FROM DIPLOID TO HAPLOID

THE STAGES OF MEIOSIS

sister chromatid cohesion is two copies associated closely.

different version of genes is called alleles.

PROPHASE I

centrosome movement, creation of spindle fiber and breakdown of the nuclear envelope.

xshaped regions called chiasmata

METAPHASEI

paris of hmologous chromosomes

noth chrimatids are attached to kinetochore microtubules.

ANAPHASEI

breakdown of proteins that are responsible for sister chromatids

moves toward opposite poles

sister chromatid cohesion persists only at the centromere

TELOPHASE AND CYTOKINESIS I

complete haploid set of duplicated chromosomes

cytokinesis

a cleavage furrow forms

PROPHASE II

spindle aparatus forms

METAPHASE II

the chromosomes are positioned at the metaphase plate

not genetically identical

ANPHASE II

breakdown of proteins holding the sister chromatids together

TELOPHASE AND CYTOKINESIS II

Nuclei forms meiotic division of one parent cell produces 4 daughter cells

genetically distinct

CROSSING OVER AND SYNAPSIS DURING PROPHASE I

chromatids are held together by proteins called cohesins

SYNAPTONEMAL COMPLEX holds on molog tighlty to the other

A COMPARISON OF MITOSIS AND MEIOSIS

Synapsis and crossing ober

duplicated homologs pair up and crossing over occurs

Homologous pairs at the metaphas plate

Separation of hmologs→ homolohous pair move toward opposite poles

Meiosis I is called the reductional division because it reproduces the number of chromosome sets from two to one

Meiosis iI is called the equational division because sister chromatids separate.

INDEPENDENT ASSORTMENT OF CHROMOSOMES

random orientation of pairs of homolohous chromosomes at metaphase of meiosis ni

there is 50% chance that a particular daughter cell of meiosis I will get the maternal chromosome of a cetain homologous pair an =d a 50% chance that it will get the paternal chromosome

Crossing over

produces recombinant chromosomes

RANDOM FERTIZILIZATION