Lesson 15- Life Cycles and Meiosis

Life Cycle

generation-to-generation sequence of stages in the reproductive history of an organism

Human Life Cycle starts with ____

two haploid gamete cells

Fertelization

fusion of the two nuclei of the gametes

A fertilized egg is called a ____, is also what ploidy?

zygote, diploid

In Meiosis there are ___ rounds of cell division and ___ round of DNA replication

two, one

Meiosis Overview

• Starts with a diploid cell

• DNA is duplicated within the S phase

• two cell divisions produce, four daughter cells

Homologous Chromosome Characteristics

• same size

• same shape

• same genes

Maternal/Paternal = ….

grandparents

Before Meiosis., what must be done before the process starts?

a copy of every chromosome

In Meiosis, going from a diploid to a haploid cell is called….

reduction division

What 4 things happen in Prophase I:

chromosomes condense, nuclear envelope breaks down, centrosomes separate, spindle fibers attach to kinetochore

Prophase I: Homologous chromosomes pair up (synapsis) to form ____

tetrads/bivalents

Crossing over occurs to create or causes ___ what phase does this occur in?

genetic variation, prophase I

Synapsis

homologous chromosomes physically connect to each other along their lengths

During synapsis, chromosomes are held together by ___

synaptomeal complex, zipper-like protein structure

Synapsis occurs in what phase?

prophase I

Cross Over

genetic swap between homologous, non-sister chromatids

How often does human crossing over occur in a tetrad?

1-3 times

Chiasma

the point where crossing over occurs

What phase do the tetrads line up at the metaphase plate?

metaphase I

In Metaphase I, chromosomes are joined at the ___

chiasmata

What is different in Metaphase I in Meiosis then Mitosis?

Kinetochores in one X are attached to microtubules from the SAME spindle core

What happens in Anaphase I?

• homologous chromosomes separate and move to separate poles

• sister chromatids remain attached 

In Telophase I/Cytokinesis what happens?

• each new daughter cell is now a haploid

  • has one set of duplicated chromosomes

Both new cells enter ___ after telophase I/Cytokinesis?

interkinesis

What is interkinesis?

like interphase but no DNA replication

Where do the cells go after Interkinesis?

Meiosis II

Are sister chromatids genetically identical once single file lining up at the metaphase plate in Metaphase II?

no

What happens in Anaphase II?

sister chromatids separate and move toward the opposite spindle poles

In meiosis you go from what to what?

one diploid parent cell to four daughter haploid cells

Nondisjunction

improper segregation of chromosomes

What happens with the spindle fibers in Nondisjunction?

they don;t attach properly to the kinetochores 

Euploidy

correct number of chromosomes for each species 

Aneuploidy

change in chromosome number resulting from nondisjunction

What phase does Nondisjunction occur in?

Anaphase I or Anaphase II