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5.5 Multicellular Life
KEY CONCEPT
Cells work together to carry out complex
functions.
5.5 Multicellular Life
Multicellular organisms depend on interactions
among different cell types.
• Tissues are groups of cells that perform a similar
function.
• Organs are groups of tissues that perform a specific or
related function.
• Organ systems are groups of organs that carry out
similar functions.
CELL
TISSUE
ORGAN
5.5 Multicellular Life
Specialized cells perform specific functions.
• Cells develop into their mature forms
through the process of cell differentiation.
• Cells differ because different combinations of
genes are expressed.
• A cell’s location in an embryo helps
determine how it will differentiate.
Outer: skin cells
Middle: bone cells
Inner: intestines
5.5 Multicellular Life
Stem cells are unique body cells.
• have the ability to
– divide and renew themselves
– remain undifferentiated
– develop into a variety of specialized cell types
5.5 Multicellular Life
• Stem cells - three types.
– Totipotent - grow into any other cell type
– Pluripotent - grow into any cell type but a totipotent cell
– Multipotent - grow into cells of a closely related cell
family
5.5 Multicellular Life
• Stem cells come from adults and embryos.
– Adult stem cells can be hard to isolate and grow.
– adult stem cells may prevent transplant rejection.
– embryonic
stem cells raises
ethical issues
First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner
cell mass. These cells are then removed and grown with nutrients. Scientists try to control
how the cells specialize by adding or removing certain molecules.
5.5 Multicellular Life
• The use of stem cells offers many currently
realized and potential benefits.
– used to treat leukemia and lymphoma.
– may cure disease or replace damaged organs.
– may revolutionize the drug development process.
6.1 Chromosomes and Meiosis
• Body cells - somatic cells.
• Sex cells = Germ cells develop into gametes.
– located in the ovaries and testes.
– egg and sperm.
body cells
sex cells (sperm)
sex cells (egg)
6.1 Chromosomes and Meiosis
Gametes are haploid.
• Haploid (n) cells have one copy of every chromosome.
Human n = 23
6.1 Chromosomes and Meiosis
Somatic cells are diploid
• Diploid (2n) - cells have two copies of every
chromosome.
• Human 2n = 46
• Fertilization between egg and sperm occurs in
sexual reproduction.
6.1 Chromosomes and Meiosis
n (sperm cell)
Haploid
Gamete
+
+
+
n (egg cell)
Haploid
Gamete
=2n (fertilized egg)
=
Diploid
=
Zygote
5.2 Mitosis and Cytokinesis
Chromosome – rod-shaped structures made of
DNA & protein
• Histones – (protein) help maintain the shape of
the chromosome and aid in the tight packing of
DNA
DNA double
helix
DNA and
histones
Chromatin
Supercoiled
DNA
5.2 Mitosis and Cytokinesis
• One half of a duplicated
chromosome is a chromatid.
• Sister chromatids are held
together at the centromere.
• Telomere – (4) the tips of the
chromatids
• keep the chromosome
from unwinding
5.2 Mitosis and Cytokinesis
Anatomy of a Chromosome
Telomere
Telomere
Centromere
Telomere
Telomere
Chromatid
Chromatid
Chromosome
5.2 Mitosis and Cytokinesis
P-short arm
QTL – Quantitative Trait Locus:
address of a gene
Ex: 6p24.q2
Q-long arm
6.1 Chromosomes and Meiosis
Sex chromosomes – determine the sex of an organism
• Sex chromosomes, X and Y, determine gender in
mammals.
• May also carry genes for other characteristics
• 2 sex chromosomes
• Normal Females XX
• Normal males XY
Autosomes – all of the other chromosomes
•44 autosomes
•Two sets of each autosome
•Receive one copy of an autosome from each parent
6.1 Chromosomes and Meiosis
• Homologous - pairs of
autosomes
– have the same size and
shape and carry genes
for the same traits
• Karyotype –
photomicrograph of
chromosomes in a
dividing cell
6.6 Meiosis and Genetic Variation
• Chromosomes contain many genes.
– The farther apart two genes are located on a
chromosome, the more likely they are not to be
inherited together
– Genes located close together on a chromosome
tend to be inherited together - genetic linkage.
• allows the distance between two genes to be
calculated.