exam 4

BIO 101

Unit 4

Lecture

Notes

(To be used along with lecture presentations)

Chapter 9: The Cell Cycle and Cellular Reproduction

Remember that The Cell Theory states that all cells come from pre-existing cells .

Asexual reproduction occurs when 1 parent makes offspring that are genetically identical to

that parent (unless a mutation occurs).

Binary fission: the method of reproduction used by prokaryotes (Domain Archaea

and Domain Bacteria) and in some protists (Domain Erotista

Kingdom Eukarya)

Method by which one cell is split into two cells

The single, circular chromosome is duplicated

The chromosome and it’s copy attach to the plasma membrane

The cell stretches in length and the 2 chromosomes are separated

A new plasma membrane and cell wall form

Produces offspring that are genetically identical to the parent cell

The Cell Cycle:

Interphase: stage between divisions (first)

G1: growth

S:DNA replication

G2: prep for cell division

Mitotic Phase: End of cell cycle

Mitosis: Division of the nucleus

Cytokinesis: Division of the cytoplasm

First, you need some words…

Chromatin – refers to the loose, unraveled DNA and its associated proteins, visible when the cell is NOT dividing

Chromosomes – consists of the highly condensed (packed) structure of the DNA; visible when the call is Dividing

Sister chromatids – a pair of chromosomes, consisting of an original

chromosome and it’s copy (made during the S stage of interphase) o Held together by a centromere

Homologous chromosomes -Chromosomes of the same number from each parent

Diploid – Two sets of chromosomes (2N)

Sister Sister

chromatid chromatid

Haploid –One set of chromosomes (N)

Centrioles – Always in organelle used in cell division

Centrosome - Area where centrioles are found

Reasons for Mitotic Cell Division:

Some organisms use it in sexual reproduction, single-celled organisms (see beginning of notes)

Growth from one cell to multiple cells in multicellular organisms

You are now made up of approximately seventy trillion cells

Replacement of dead cells such as skin cells (dead skin) and blood cells.

Repair an injury

Stages of Mitosis:

Prophase

1.Chromatin condenses into chromosomes forming sister chromatids

2. Nuclear envelope and nucleolus disappear

3.Duplicated centrioles start moving to opposite sides of the cell (start producing spindle fibers)

Metaphase

Sister chromatids line up in the middle of the cell

Anaphase

1.Sister chromatids start to separate from each other

1.Chromosomes collect to either end. (Back to be chromatin)

Telophase

Nuclear envelope and nucleoli come back. (2) (2 because we now have 2 sets of DNA) Reform around each set of chromosomes

3. Spinde fibers break down (because they did their job)

Draw it!

Cytokinesis - division of the cytoplasm

Begins during Telophase or sometimes Early Anaphase

Animal cells - Cytoplasm splits from the outside

to Inside by creating a cleavage furrow (pinch)

Plant cells - Cytoplasm splits from the Inside

to outside by creating a cell plate

G1 checkpoint – Checks for errors

in the DNA

G2 checkpoint – Checks that the DNA

has properly Replicated

M checkpoint - mitosis will

not continue unless

The chromosomes

have correctly aligned

along the metaphase plate

*Some texts include a fourth checkpoint during the S stage to check for DNA errors during replication.

If there are errors in the cell that cannot be fixed, the cell will be programmed to

die by a process called apoptosis.

o An organism begins as a single cell that repeatedly undergoes the cell cycle to produce

multiple cells, but eventually some cells must die for the organism to take shape.

Examples: Tadpoles to frogs.

Cell division and apoptosis are two opposing processes that keep the number of cells in the body at an appropriate level. In other words, cell division increases

the number of body cells and apoptosis decreases the number of body cells.

The checkpoints of the cell cycle are controlled by internal and external signals. These signals are typically molecules that increase or decrease cellular functions.

Example: contact inhibition - Stop dividing when they contact other cells

Inhibition: To stop

Many cells seem to “remember” the number of times they have already divided, and they stop when they have reached a certain number of cell divisions. The aging of cells, called Senescence, can be likened to an internal battery-operated clock that runs down and then stops. We now know that senescence is due to the shortening of telomeres, a series of repeating DNA nucleotides (TTAGGG) located at the end of chromosomes. Telomeres have been likened to the protective caps on the ends of shoelaces because they stabilize the chromosomes. Each time a cell divides, a small portion of a

Telomere is lost. When telomeres become too short, the cell is identified as being “old” and is destroyed by the process of apoptosis.

G0 – cells continue normal daily function but do not replicate

May occur after interphase

Many cells in the G0 phase can reenter the cell cycle and divide again to repair the damage

Some cells do not have the ability to divide

muscle cells typically remain in G0, and cell division does not occur

nerve cells almost never divide again once they have entered G0

The Cell Cycle and Cancer

Cancer - Uncontrolled cell growth/division

The development of cancer is called carcinogenesis

The accumulation of cancerous cells forms a tumor

Blood vessels grow and supply the enlarging tumor through the process of angiogenesis

Enzymes allow the tumor to invade surrounding tissues

If cancerous cells enter the bloodstream or lymph, they can spread to other areas of the body and grow new tumors, a process called metastasis

Characteristics of Cancer Cells

carcinogenesis: development of cancer

Cancer cells lack differentiation and do not contribute to body function.

Cancer cells have abnormal nuclei and may have abnormal chromosomes.

Cancer cells do not undergo apoptosis

Cancer cells can form tumors because they do not respond to contact inhibition signals. There are two general types of tumors:

Benign: contained within a capsule and don’t spread, usually easier to remove

malignant: do not have a capsule, spread to other tissues

Some cancer cells can undergo metastasis (spread to different body tissues) and trigger angiogenesis (form new blood vessels to nourish themselves)

[READ The Immortal Henrietta Lacks in your eBook, pg. 75.]

When cancer develops, the cell cycle occurs repeatedly, typically due to mutations in two types of genes:

Proto-oncogenes - code for proteins that promote (increase) the cell cycle and inhibit (prevent)

apoptosis

o Mutations can cause them to become oncogene

cancer- causing genes

Promote the cell cycle

Tumor suppressor genes - code for proteins that inhibit the cell cycle and promote

apoptosis

o Mutations can cause them to STOP inhibiting the cell cycle or promote apoptosis

tumors may occur when mutations cause these genes to become nonfunctional

Cancer Development:

Some cancer cells and certain adult cells, such as stem cells and germ cells, have an enzyme, called telomerase, that can rebuild telomeres. The gene that codes for telomerase is turned on in cancer cells. If this happens, the telomeres do not shorten, and cells divide repeatedly.

The p53 tumor suppressor gene produces a protein that checks the DNA for damage before it proceeds through the G1 checkpoint.

o Failure of the p53 gene to perform this function allows cells with DNA damage to rapidly divide, potentially leading to cancer.

What does this have to do with elephants? Elephants have 20 pairs of p53 genes in the genome, which means that it is very likely that their cells will lose all of these genes’ functionality

BRCA1 and BRCA2 - two oncogenes on the chromosomes, if inherited, increase the chances of developing breast cancer

Ch. 10: Meiosis and Sexual Reproduction

Is there another YOU out there?

In humans, more than 70 trillion different genetic combinations are possible from the mating of just

two individuals!

Meiosis serves two major functions:

Reducing the number of chromosomes from diploid (2 sets of chromosomes) to diploid (2 sets of chromosomes)

Produces genetically unique gametes

Homologous chromosomes (aka homologues)

Members of a pair of chromosomes of the same number

Contain the same genes for the same traits

Gene — segment of DNA that holds instructions for making a protein

A child receives one member of each homologous pair from each parent.

Homologous pairs may contain different versions of the same gene

Alleles – alternate forms of genes

Examples: ear lobes

All humans have 23 pairs of homologous chromosomes, totaling 46 chromosomes

Typical body cells (called somatic cells) have the diploid number of chromosomes, 46 total chromosomes

22 pairs of autosomes

1 pair of sex chromosomes

XX female or XY male

Visible on a Karyotype -

Gametes (sperm and eggs) have the haploid number of chromosomes; 23 total chromosomes, made up of one of each homologous pair

Where do new alleles come from? Mutations

Sexual Life Cycle

Involves both sperm and egg

Mitosis involved in growth (from a single-celled zygote to a multicellular adult), repairing and replacing of tissues throughout life

Meiosis reduces the number of chromosomes from

haploid to diploid.

spermatogenesis produces sperm in the testes

oogenesis produces egg cells in the ovaries

Fertilization: sperm and egg cells join to form a zygote (diploid)

(From here, mitosis begins again.)

Examples:

A quokka has 11 pairs of chromosomes. The somatic cells are all diploid and contain 11

Homologous pairs for a total of 22 chromosomes.

The gametes are haploid and contain only 1 of each homologous pair

for a total of 11 chromosomes.

A hermit crab has 127 pairs of chromosomes. The somatic cells are all diploid and contain

127 homologous pairs for a total of 254 chromosomes.

The gametes are haploid and contain only 1 of each homologous pair

for a total of 127 chromosomes.

Causes of genetic variation:

Crossing over (genetic recombination) -Prophase I

Independent assortment - Chromosomes line up (randomly) in metaphase, they are independent of each other

Fertilization – Sperm fertilizes the egg first = Genetic variation (final result)

Human Life Cycle

Meiosis produces gametes, which are eggs in females and sperm in males.

These cells are (diploid / haploid) with 23 chromosomes. Fertilization occurs as the

sperm enters the egg to form a zygote, which is (diploid/haploid) with 46

chromosomes. The zygote grows by mitosis into a mature adult.

Spermatogenesis:

1 to 4 ½’s

Oogenesis: 1 to 1 ½‘s

Changes in chromosome number and structure:

Euploidy – true number of chromosomes (correct)

Nondisjunction – Chromosomes do not separate correctly

Aneuploidy – incorrect (unusual) number of chromosomes (either 1 extra or 1 less)

Monosomy – When there is a single chromosome from a homologous pair. (turner syndrome)

Trisomy – when a parent gives an extra chromosome (down syndrome)

Changes in sex chromosome number:

Turner Syndrome – XO

Affects females who have only one X chromosome instead of two. This can lead to developmental issues and infertility.

Klinefelter Syndrome – XXY

Affects males who have an extra X chromosome. This can result in reduced testosterone levels, infertility, and some physical and cognitive differences.

Poly-X Syndrome – XXX

Affects females who have an extra X chromosome. Most individuals have few or no symptoms, but some may experience taller stature and learning difficulties.

Jacob’s Syndrome – XYY

Affects males who have an extra Y chromosome. This can lead to taller stature and sometimes learning difficulties or behavioral issues.

Changes in a single chromosome:

Deletion – Missing a piece of a chromosome

Duplication – Repeated (duplicated) chromosome piece

Inversion – a section gets flipped

Translocation – 2 chromosomes swapped from different numbers

Chapter 11: Mendelian Patterns of Inheritance

Section 10.1 Gregor Mendel

Common belief at the time…

Blending concept of inheritance - parents of contrasting appearance always produced offspring of intermediate appearance

BUT that did not account for the presence of variations among members of a family.

Gregor Mendel

Highly intelligent Austrian monk

Studied math and science(particularly prob and stats)

Had no knowledge of DNA

Worked with garden peas, pissum sativa in 1860’s

Used the scientific method and kept very accurate data

Mendel’s Experimental Procedure

Garden pea, Pisum sativa

Easy to grow, short generation time, easily recognizable traits

Chose true-breeding varieties — offpsring were like the parent plants

Developed his Particulate Theory of Inheritance:

genetic traits are passed from parents to offspring as discrete units, called "particles" (now known as genes), rather than blending together in a continuous mixture, meaning offspring inherit distinct characteristics from each parent, not a blend of both

Alleles - alternate forms of a gene

dominant allele - typically masks the expression of the recessive allele

recessive allele – typically masked by the dominant allele

For the most part, an individual’s traits (phenotypes) are determined by the alleles (genotypes)

inherited.

Alleles occur on chromosomes at a particular location called the gene locus.

Homologous chromosomes have similar alleles at the same locus

Genotype Versus Phenotype

Genotype — pairs of alleles

Homozygous—two identical alleles

Homozygous dominant - 2 dominant alleles: AA

Homozygous recessive - 2 recessive alleles: aa

Heterozygous—two different alleles (1 dominant; 1 recessive)

Phenotype – visible physical expressions of a gene

Dominant or Recessive

One-Trait Inheritance

Original parents = P generation

First-generation offspring = F1 generation

Second-generation offspring = F2 generation

Punnett square - shows all possible combinations of alleles that might be passed

on to an offspring

Examples: eye color, hair color.

The possible offspring from a cross of a homozygous dominant parent and a homozygous recessive parent will be:

Genotypic Ratio:

Phenotypic Ratio:

The possible offspring from a cross of two heterozygous parents will be:

Genotypic:

Phenotypic:

Monohybrid cross – combining one trait

Dihybrid cross – combining two traits

One-Trait Testcross

Testcross

Used to determine the genotype of an individual with the dominant phenotype (aka if that individual has the heterozygous dominant genotype or the

heterozygous genotype)

The unknown is crossed with an individual that has the recessive phenotype (the

Homozygous recessive genotype)

IF any of the resulting offspring have the recessive trait, then the unknown parent genotype must be Heterozygous. Why? It allows for recessive alleles to be shown

IF all the resulting offspring show only the dominant trait, then the unknown parent genotype is likely Homozygous dominant. Why? homozygous dominant masks any other trait

Section 10.2 Mendel’s Laws

Mendel’s Law of Segregation

Basis for his Particulate Theory of Inheritance

States that…

o Each individual has 2 factors for each trait

o The factors segregate (separate) during the formation of the meiosis

o Each gamete contains only 1 factor from each pair of factors.

o fertilization gives each new individual 2 factors for each trait.

We now know that the “factors” are called genes and their alternate versions are alleles.

They separate from each other during the process of meiosis, so that each gamete

contains only 1 of each allele. Fertilization of the meiosis by a gamete unites the two

alleles so the new individual has 2 alleles for each trait.

NOTE:

It is important to remember that parents do not just pass on an allele for one trait. Each parent gives the offspring one allele for EVERY trait.

A two-trait cross looks at just that – 2 traits in the offspring.

You could continue to look at a 3-trait cross, 4-trait cross, etc., but it will get tricky!

Mendel’s Law of Independent Assortment

Each pair of factors segregates (assorts) independently (randomly) of the other pairs.

All possible combinations of factors can occur in the gametes.

Section 10.3 Human Disease

Autosomal dominant disorders – the dominant allele is causes the disorder

individual with the homozygous dominant ( DD ) or Heterozygous

( Dd ) genotype has the disorder

individual with the homozygous recessive (dd ) genotype does not have the disorder

Autosomal recessive disorders – the dominant allele causes the disorder

individual with the homozygous recessive ( dd ) genotype has the disorder

individual with the homozygous dominant( DD) or Heterozygous

( Dd ) genotype does not have the disorder

Pedigree - shows the pattern of inheritance for a particular condition

In a human pedigree, males are designated by squares and females by circles

o Shaded circles and squares are the effective individuals. o A line between a square and a circle represents a union.

o In the patterns below, a vertical line leads to a single child. If there are more children, they are lined up horizontally.

Use A and a to answer the following:

In pattern I, the offspring is affected, but neither parent is.

The condition is caused by the recessive allele and both parents are Dd.

Their child is a male who (has / does not have) the condition.

the parents are carriers, because they do not express the trait but are

capable of having offspring with the genetic disorder

In pattern II, the offspring is unaffected, but the parents are affected

The condition is caused by the dominant allele and the parents are DD.

Their child is a male who (has / does not have) the condition.

Why do these not involve carriers? Because they have an allele and show them (pass them because they have it)

Read about the following in Section 11.3 of your eBook.

Autosomal recessive disorders:

Methemoglobinemia

Cystic fibrosis

Phenylketonuria

Autosomal dominant disorders:

Osteogenesis Imperfecta

Huntington’s Disease

Hereditary Spherocytosis

Section 11.4 Beyond Mendelian Inheritance

Incomplete dominance

Heterozygote has an intermediate phenotype

Example 1: Curly hair genetics - Cc

Example 2: Familial hypercholesterolemia - Persons with one mutated allele have an abnormally high level of cholesterol in the blood, and those with two mutated alleles have a higher level still.

ABO blood group inheritance has 3 alleles; determines part of your blood type

o IA = A antigen on red blood cells

o IB = B antigen on red blood cells

o i = neither A nor B antigen on red blood cells

Each person has only 1 of the three alleles

Both IA and IB are both dominant to i

IA and IB are codominant — both will be expressed together in the blood cells

Polygenic Inheritance

A single trait is governed by 2 or more genes that have additive effects on the phenotype

Result in a gradual variation— bell-shaped curve

Examples:

Epistasis — one gene interferes or overrides the instructions of another

Pleiotropy – a single gene affects multiple traits

Sex-Linked Inheritance

Sex Chromosomes are the 23 pair of homologous chromosomes, determine genetic gender of an

individual

Females are XX

All eggs contain an X

Males are XY

Sperm contain either an X or a Y

Y carries SRY gene — determines maleness

X-Linked Traits — genes found only on the X-chromosomes

Males always receive X from female parent, Y from male parent

A female who carries an X-linked trait but does not express it is considered a carrier. Can a male be a carrier? Why or why not? A male cannot be a carrier because there dominant to that gene making them be forced to express that gene

X-Linked Recessive Disorders

Red-Green Color blindness

About 8% of Caucasian men have red-green color blindness & can’t distinguish the two colors.

Duchenne muscular dystrophy

Absence of protein(dystrophin) causes wasting away of muscles

Therapy—immature muscle cells injected into muscles

Hemophilia

Blood clotting disorder

Was a problem in royal families of England, Spain, Russia, Germany for centuries