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Why do cells in an organism divide?
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Cell Cycle—Draw the cell cycle below
How Do Cells Divide?
Cells go through a cycle called the ________________. There are 3 parts to this cycle:
1. _______________ --DNA ___________________ (replication) and the cell __________________
2. _________________________________ divides (which contains DNA)
3. ____________________________________ divides to make 2 new cells
The cell cycle is divided into three distinct phases:
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Interphase (I)
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Mitosis (M)
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Cytokinesis (C)
In which phase does
the cell spend most of
its life? ___________________________________________
What would happen if DNA is not copied during interphase?
Daughter cells would have only ½ the required chromosomes
A human cell would have 23 instead of the normal 46
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Cell Division Mitosis
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The two exact copies that make up the chromosome are called ____________________________. They are both
attached at the center at a point called the ____________________________
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Each of the 23 pairs consists of two _____________________________________________
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Homologous chromosomes are similar in size, shape and genetic content. One is from the mother, and one
from the father.
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All of the cells in the body other than gametes are considered ______________________________, in that they
contain two sets of DNA, they are said to be ______________________
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In the case of gametes the cells are __________________________, containing only half the DNA.
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22 of those chromosomes are referred to as ___________________________
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The last pair of chromosomes is called a sex chromosome because they determine the sex of the individual
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XX- female
XY- male
Cells with special functions, such as the nerve cell or cheek cell might look different but each one has 46
chromosomes in the human
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After Mitosis each daughter cell must have 46 chromosomes or 23 pairs
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Replication-process of making exact copies of the DNA strand
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Stages of Cell Division
1. _________________________- the cell grows and copies DNA
2. _______________________-(cell division)
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Stage 1:prophase-spindle _____________________ form
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Stage 2:metaphase-sister chromatids line up in the _________________ of the cell
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Stage 3:Anaphase-chromosomes move to opposite ______________________of the cell
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Stage 4:Telophase-the cell begins to ___________________ in half
3. ______________________________- the cytoplasm is split in half to form ____________________
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Key Players in the Mitotic Phase
1. Nucleus – Control center that holds _____________________
2. DNA – Can exist in several forms
1. Chromatin – refers to all the DNA in a cell. DNA is called chromatin when it is _________ coiled.
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2. Chromosomes – Rod shaped structure that forms when DNA is _____________ coiled. Humans
have _________ Chromosomes
3. C. Sister chromatids. When DNA has copied itself, there are __________ of each chromosome.
The copies attach to each other and form sister chromatids.
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Sister chromatids are attached in the _____________________ at a region called the centromere.
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Centrioles – 2 ___________ _____________ proteins that help move chromosomes (Only found in eukaryotes).
*Centrosomes are regions that help organize the spindle fibers
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Spindle Fibers – a set of _________________ that form between the centrioles to help the chromosomes move.
*Made of microtubules
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Meiosis
Why is it important?
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You could not have been created without it!
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Cell division to produce gametes (egg and sperm)
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These cells are haploid (N)= They contain only half the chromosomes of somatic (body) cells.
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One chromosome from each homologous pair.
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Humans contain 22 pairs of autosomes and two sex chromosomes.
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The sex chromosomes determine the gender of an individual.
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Females can only contribute an X to their egg.
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Males can contribute either an X or a Y to the sperm.
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Therefore, males determine the sex of a baby.
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Meiosis occurs only in the reproductive tissue
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Ovaries and testes
Has same 4 phases of mitosis ( prophase, metaphase, anaphase, telophase)
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Meiosis creates variety in the genes of living organisms
Independent assortment:One chromosome from each homologous pair is randomly given to each gamete
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The way is which the homologous pair lines up is random
Meiosis in males is different than in females
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Draw the chart
Female Meiosis OOGENESIS
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The fetus develops primary oocytes which have 46 chromosomes (diploid).
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DNA is replicated and meiosis stops in prophase. Restarts at puberty.
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At puberty females have about 400,000 primary oocytes.
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Each month one primary oocyte completes meiosis I
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Secondary oocyte starts meiosis II but stops at metaphase. Then ovulation occurs.
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If fertilization occurs then meiosis II continues. Meiosis II results in one haploid 23 chromosome egg (OVA) and
a polar body.
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Fertilization occurs when the egg and sperm fuse to form a diploid zygote.
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MALE Meiosis Spermatogenesis
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Spermatogonia develop in the fetus and rest until puberty.
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At puberty these cells develop into primary spermatocytes (diploid).
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After mieosis I two secondary spermatocytes are produced.
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Meiosis II results in two spermatids which are haploid, n=23.
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Spermatids undergo spermiogenesis to become mature sperm.
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The whole process from primary spermatocyte to sperm takes about 74 days. Sperm can live in the female
reproductive tract for about 48 hours.
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The volume of semen in a single ejaculation may vary from 1.5 to 6.0 ml. There are usually between 50 to 150
million sperm per milliliter of semen.
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Meiosis – Making sex cells
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REMEMBER: humans have 23 PAIRS of chromosomes. Both chromosomes in a pair carry similar information.
These are called ____________________________________. (Homo = same)
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Each sex cell needs to have ___________________________ in order to function correctly. Homologous
chromosomes have different versions of the same genes. A version of a gene is called an ____________.
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One cell divides into ________ cells, each with __________ the number of chromosomes as the original cell.
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REMEMBER: Humans have 23 pairs of chromosomes. Both chromosomes in a pair carry similar information.
These are homologous chromosomes. Each sex cell needs to have one chromosome from each pair in order to
function correctly.
***How would the effect of a mutation in a body cell be different than the effect of a mutation in a gamete?
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