Review: Reproduction & Genetics

• Why do organisms reproduce?– For the continuation of the species

• How do organisms reproduce?– Sexual reproduction: two organisms produce a

new unique organism– Asexual reproduction: one organism produces a

new nearly identical organism = no variability!

Cell Division

• Before a cell becomes too large, it divides to form two cells.• The two new cells are called daughter cells.• The process by which the cell divides into two new daughter

cells is called cell division.• At this very moment, group of cells in your body are growing,

dividing, and dying.• Worn out skin is being replaced and bruises are healing.• Red blood cells are being produced in your bones at a rate of

2 to 3 billion to replace those that wear out.

Cellular Reproduction• Reproduction – the life process by which living things

produce other living thing of the same species• It is necessary for the survival for the species• Two types of Reproduction through cell division:

– Sexually reproducing organisms go through mitosis and meiosis– Asexually reproducing organisms only go through mitosis

Chromosomes• Pass genetic information

from one generation of cells to the next

• Made up of DNA (which carries the cell’s coded genetic information) and proteins

• The cells of every organisms have a specific number of chromosomes – Human somatic (body) cells

= 46 chromosomes– Human gametes (sex cells) =

23 chromosomes

Asexual reproduction• Your body (somatic) cells

– Cellular asexual reproduction (mitosis and cytokinesis): Organisms with eukaryotic cells use mitosis and cytokinesis to create cells with the same genetic information (DNA) as the parent cell.

• Some organisms– Binary fission– Budding– Sporulation (spore formation)– Regeneration– Vegetative Propagation

Sexual Reproduction• What is an inheritance?

– Something passed from one generation to the next.• How is it determined?

– Your genes from your parents!• Since the hereditary material comes from two parents it

resembles both parents in some ways, but is also different from both in others.

• It has all the characteristics of its species, but at the same time has its own individual characteristics that distinguish it from all other members of that species.

• Genetics = The branch of biology that is concerned with the ways in which hereditary information is transmitted from parents to offspring.

• Hereditary information is contained in genes, located in the chromosomes of each cell.

• An inherited trait of an individual can be determined by one or by many genes, and a single gene can influence more than one trait.

• A human cell contains many thousands of different genes in its nucleus.

Genes

Dominant vs. Recessive

• An organism with a dominant allele for a particular trait will always have that form– The characteristic shows up

• An organism with a recessive allele for a particular trait will have that form only when the dominant allele for the trait is not present– The characteristic only shows up when the dominant

allele is not present, otherwise it is carried

• Alleles are separated (segregated) during gamete (sex cell) formation.

Mendel’s Principles• Inheritance is determined by genes passed from

parents to offspring• Some forms of genes are dominant and others are

recessive• Each offspring has two copies of a gene (alleles),

one from each parent because they are segregated during game formation

• The allele for different genes usually segregate independently of one another during gamete formation

• Chromosomes come from both the male parent and female parent

• Homologous pairs: each of the chromosomes coming from one parent have corresponding chromosomes from the other parent

• Diploid: a cell that contains both sets of homologous chromosomes = “two sets” (2N)– Diploid cells contain two complete sets of

chromosomes and two complete sets of genes– Human somatic (body) cells have 46 chromosomes or

23 homologous pairs

Diploid cells

• Haploid: contain only one set of chromosomes and one set of genes = “one set” (N)

• Gametes of sexually reproducing organisms are haploid containing one complete sets of chromosomes and one complete sets of genes

• Human gametes have 23 chromosomes

• Sperm (23) + Egg (23) = Zygote (46)

• How are haploid gamete produced from diploid cells?

Haploid cells

The process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell

The four daughter cells contain haploid (N) chromosomes

Meiosis

• However, crossing-over sometimes separates gene that are usually found on the same chromosome, so genes may not be linked together forever!

• Crossing-over is soooo important because it helps generate genetic diversity – new combinations of allele are constantly produced

• Increasing the variability of a species increases the possibility that some individuals of that species will be better adapted than others to survive both short-term and long-term changes in the environment.

Importance of crossing-over

Mitosis vs. Meiosis

• Mitosis – produces 2 genetically identical diploid cells

• Meiosis – produces 4 genetically different haploid cells

DNA• Genes are made of DNA = deoxyribonucleic acid• DNA codes for the function of genes• Its a long molecule made of units called

nucleotides• Each nucleotide is made of 3 basic parts:

– A 5-carbon sugar called deoxyribose– A phosphate group– A nitrogenous base (There are 4 kinds…)

A (Adenine) T (Thymine)G (Guanine) C (Cytosine)Purines Pyrimidines

A Single DNA Nucleotide

PhosphateGroup

DeoxyriboseSugar

Nitrogenous Base

DNA StructurePhosphate

Group Deoxyribose Sugar

Nitrogenous Base

Weak Hydrogen Bonds

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Structure of DNA

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Figure 12-10 Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

Section 12-2

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Eukaryotic DNA

• DNA is found in the nucleus in chromosomes (the number of chromosomes varies widely of different species)

• DNA is very long!... but it is highly folded packed tightly to fit into the cell!– For example, a human cell contains more than 1 meter of DNA made of more

than 30 million base pairs!

Eukaryotic Chromosomes

• Contain DNA and proteins called histones• Tightly packed DNA and proteins form

chromatin• During mitosis, the chromatin condenses to

form tightly packed chromosomes

DNA Replication• The process of making a copy of the DNA• Occurs inside the nucleus of the cell• Occurs when the cell is going to divide so

each resulting cell will have a complete set of DNA

• During DNA replication, the DNA separates into two strands, then produces two new complementary strands following the rules of base pairing.

• Each strand serves as a template, or model, for the new strand.

• Replication occurs in both directions• The site where separation occurs is called

the replication fork

DNA Replication• The two strands of DNA unwind or “unzip”

breaking the hydrogen bonds and separating. Then each strand becomes the guide or “template” for the making of a new strand.

• A protein called an enzyme called DNA polymerase breaks the nitrogen base bonds and the two strands of DNA separate, polymerizes individual nucleotides to produce DNA and “proof reads” the new DNA.

• The bases on each strand pair up with new bases found in the cytoplasm

• Then the sugar and phosphate groups form the sides of each new DNA strand

• Each new DNA molecule contains an original DNA strand and a new DNA strand

DNA Replication

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Growth

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous basesReplication fork

Original strand

New strand

Mutations

• Changes in the DNA sequence the affect genetic information• Mistakes occur every now and then• There are many different types of mistakes:

– Inserting the wrong base– Deleting a base– Skipping a base

• Gene mutations result from changes in a single gene• Chromosomal mutations involve changes in whole

chromosomes

Chromosomal Mutations• There are four chromosomal mutations:

– Deletion: loss of all or part of a chromosome– Duplication: segment of a chromosome is repeated– Inversion: orient part of chromosome in reverse direction– Translocation: part of one chromosome breaks off and

attaches to another, non-homologous, chromosome.

Deletion

Duplication

Inversion

Translocation

How are genes expressed?

• Genes are coded DNA instructions that control the production of proteins within the cell.

• The 1st step in decoding the DNA is to copy part of the nucleotide sequence into RNA

• RNA = ribonucleic acid• RNA assembles amino acids

into proteins

RNA

• RNA consists of a long chain of nucleotides (like DNA)– A sugar called ribose– A phosphate group– A nitrogenous base

Adenine (A) Uracil (U) … not Thymine (T)Cytosine (C) Guanine (G)

• RNA is single-stranded

RNA Nucleotide

Phosphate Group

Ribose Sugar

NitrogenousBase

RNA StructurePhosphate

GroupNitrogenous Base

Ribose Sugar

Types of RNA

• Messenger RNA copies instructions in genes and serves as a “messenger” from the DNA to the ribosome

• Ribosomes make proteins• Ribosomal RNA passes through the ribosome

• Transfer RNA transfer amino acids to the ribosome

How is RNA made?• RNA is made by transcription: DNA to RNA• Transcription uses an enzyme RNA polymerase• During transcription, RNA polymerase binds to DNA and

separates the DNA strands, RNA polymerase then uses one strand of DNA as a template (stencil) from which nucleotides are assembled into a strand of RNA

• For example: DNA: ACTGTGGACCTRNA: UGACACCUGGA

TRANSCRIPTION

RNADNA

RNApolymerase

Figure 12–14 TranscriptionSection 12-3

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

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How are proteins made?• Proteins are made by translation: RNA to protein• During translation, the cell uses information from mRNA to

make proteins.• mRNA instructs amino acids on tRNA to join together in the

ribosome containing rRNA• Remember: Proteins are chains of amino acids called

polypeptides• The order of the amino acids and shape of the chain determines

the properties of the protein• The instructions for making different

amino acids are in the mRNA = the genetic code

• The genetic codes is read 3 letters at a time, • so each “word” is 3 bases long = codon

Messenger RNA Messenger RNA is transcribed in the nucleus.

Transfer RNAThe mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon.

mRNA Start codon

Ribosome

Methionine

Phenylalanine tRNALysine

Nucleus

Figure 12–18 TranslationSection 12-3

mRNA

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The Polypeptide “Assembly Line”The ribosome joins the two amino acids—methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids.

mRNARibosome

Translation direction

Lysine tRNA

tRNA

Ribosome

Growing polypeptide chain

mRNA

Completing the PolypeptideThe process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

Figure 12–18 Translation (continued)Section 12-3

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Genetic Engineering

• Genetic engineering changes the arrangement of DNA that makes up a gene.

• Genes can also be inserted into cells to change how the cell performs. • For example, large volumes of medicines, such as insulin,

can be produced or plants resistant to diseases can be developed.

Uses of Genetic Engineering• In the past, people breed for organisms with desired traits by selective

breeding• Now people can insert genes (DNA) into cells to produce organisms with

those same desired traits by genetic engineering (Cell Transformation)• Gene therapy is a form of genetic engineering that inserts a normal

allele into a virus that attacks a target cell and inserts the normal allele into the body.

• Cloning is the process of making a new identical copy of an organism from a single adult cell. Cloning can occur naturally as twins, or to genetically engineer plants and animals, endangered or extinct species, a deceased pet or human, or stem cells.• Stem cells are the cells that all of your cells “stem” from. Stem cells

can be used to determine the function of specific genes, manipulate genes, or make new cells or tissue to treat injuries or diseases.

Transforming Bacteria• Bacteria can be transformed using recombinant DNA.• Foreign DNA joins to a small circular DNA called a plasmid, which are

naturally found in some bacteria.

Pedigrees are used to study how traits are passed from one generation to the next.However, most human traits are impossible to trace as single genes. Remember:

Many human traits are polygenic = many genes control a single traitPhenotypes are influenced by genotypes and the environment.

Karyotype = picture of organized chromosomesHuman cells contain 46 chromosomes (23 pairs)44 chromosomes are autosomal chromosomes or autosomes2 chromosomes are known as sex chromosomes, because they determine an individual’s sex.

Females have two X chromosomes (46XX)Males have one X and one Y chromosome (46XY)

Sex-linked Genes

• Genes located on the X or Y chromosomes are said to be sex-linked.– Many sex-linked genes are found

on the X chromosome, the smaller Y chromosome contains only a few genes.

– Since males have just one X chromosome, X-linked alleles are expressed in males, even if their recessive

• Colorblindness• Hemophilia• Duchenne Muscular Dystrophy

Father(normal vision)

ColorblindNormal vision

Mother (carrier)

Daughter(normal vision)

Son(normal vision)

Daughter(carrier)

Son(colorblind)

Section 14-2

Male

Female

Figure 14-13 Colorblindness

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Human Genes

• The human genome includes tens of thousands of genes and the DNA sequence on these genes determines many characteristics.

• Gene mapping is the process of identifying the trait each gene is responsible for on each chromosome.

• Since no two individuals have the exact same genome, biologist can use DNA fingerprinting to identify individuals– For example, if blood, sperm or hair is found at a crime

scene, DNA from the tissue can be cut using restriction enzymes and fragments can be separated using gel electrophoresis, resulting in a unique pattern that can be compared to a suspect’s DNA

Restriction enzyme

Chromosomes contain large amounts of DNA called repeats that do not code for proteins. This DNA varies from person to person. Here, one sample has 12 repeats between genes A and B, while the second sample has 9 repeats.

Restriction enzymes are used to cut the DNA into fragments containing genes and repeats. Note that the repeat fragments from these two samples are of different lengths.

The DNA fragments are separated according to size using gel electrophoresis. The fragments containing repeats are then labeled using radioactive probes. This produces a series of bands—the DNA fingerprint.

Section 14-3

Figure 14-18 DNA Fingerprinting

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DNA Fingerprinting

Gene Therapy• Gene therapy = an absent or faulty gene is replaced by a

normal, working gene, but it can’t be inherited unless a reproductive cell is altered!– Some researchers insert a DNA fragment containing a

replacement gene into viral DNA, and then infect the patient with the modified virus, which should carry the gene into cells and correct the genetic disorder.