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.• Stem 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 are classified into 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

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.

• Stem cells come from adults and embryos.– Adult stem cells can be hard to isolate and grow.– The use of adult stem cells may prevent transplant

rejection.– The use of embryonic

stem cells raisesethical issues

5.5 Multicellular Life

• The use of stem cells offers many currently realized and potential benefits.

– Stem cells are used to treat leukemia and lymphoma.– Stem cells may cure disease or replace damaged

organs.– Stem cells may revolutionize the drug development

process.

5.5 Multicellular Life

KEY CONCEPT Gametes have half the number of chromosomes that body cells have.

6.1 Chromosomes and Meiosis

You have body cells and gametes. • Body cells are also called somatic cells.• Sex cells = Germ cells develop into gametes.

– Germ cells are located in the ovaries and testes.– Gametes are sex cells: egg and sperm.

body cells sex cells (sperm) sex cells (egg)

6.1 Chromosomes and Meiosis

Body cells are diploid; • Fertilization between egg and sperm occurs in

sexual reproduction. • Diploid (2n) cells have two copies of every

chromosome.– diploid – Somatic cells– Human 2n = 46

6.1 Chromosomes and Meiosis

• Haploid (n) cells have one copy of every chromosome.

Human n = 23

6.1 Chromosomes and MeiosisGametes are haploid.

n (sperm cell) + n (egg cell) =2n (fertilized egg)

Haploid + Haploid = Diploid

Gamete + Gamete = Zygote

6.1 Chromosomes and Meiosis

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 doublehelix

DNA andhistones

Chromatin SupercoiledDNA

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• To keep the chromosome

from unwinding

5.2 Mitosis and Cytokinesis

Anatomy of a Chromosome

XTelomere

Telomere

Centromere

Chromatid Chromatid

Telomere

Telomere

Chromosome

5.2 Mitosis and Cytokinesis

QTL – Quantitative Trait Locus: address of a geneEx: 6p24.q2

P-short arm

Q-long arm

5.2 Mitosis and Cytokinesis

• Chromosomes contain many genes.– The farther apart two genes are located on a

chromosome, the more likely they are to be separated by crossing over.

– Genes located close together on a chromosome tend to be inherited together, which is called genetic linkage.

• Genetic linkage allows the distance between two genes to be calculated.

6.6 Meiosis and Genetic Variation

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

• Your body cells have 23 pairs of chromosomes.– 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

6.1 Chromosomes and Meiosis