IB Biology Topic 3

chromosome

A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins.

difference between dna in eukaryotes and prokaryotes

→Prokaryotic- one chromosome, ring shaped, in cytoplasm, made of dna

→Eukaryotic- many chromosomes, made of dna, in strands, in nuclei

what is sickle cell anemia

The hemoglobin molecule, resulting in crescent shaped RBCs which have a difficult passing through blood vessels. Occurs from a base substitution mutation where valine is produced instead of glutamine.

how to determine sex by karyogram

x is longer than y. if it is xx, it is female, if it is xy, then it is

describe first phase of meiosis→Interphase (s-phase)

Interphase (s-phase)

→In the S-phase of the interphase before meiosis begins, DNA replication takes place.

→Chromosomes are replicated and these copies are attached to each other at the centromere.

→The attached chromosome and its copy are known as sister chromatids.

Prophase I

* DNA supercoils and chromosomes condense
* nuclear membrane dissolves
* nuclear membrane dissolves
* centrioles migrate to the poles of the cell.
* Crossing-over between chrimosomes can take place. This results in recombination of alleles and is a source of genetic variation in gametes

Metaphase I

* bivalents line up at the equator
* Random orientation occurs - each bivalent aligns independently and hence the daughter nuclei get a different mix of chromosomes.
* This is a significant source of genetic variation: there are 2n possible orientations in metaphase I and II. That is 223 in humans - or 8,388,068 different combinations in gametes

Anaphase I

* Homologous pairs are separated and pulled to opposing poles.
* Spindle fibres contract
* This is the reduction division - the bivalent is split and half the chromosomes move towards each pole.

Telophase I

* Cytokinesis
* New nuclei membrane forms
* Chromosomes decondense

how does down syndrome occur

3 copies of chromosomes on chromosome 21

genome size

The amount of DNA contained in one copy of a genome

difference of karyotype and karyogram

* A karyogram is A diagram or photograph of the chromosomes present in a nucleus (of a eukaryote cell) arranged in homologous pairs of decreasing length
* A karyotype is A property of the cell described by the number and type of chromosomes present in the nucleus (of a eukaryote cell)

Explain why meiosis is described as a reduction division.

because it reduces the number of chromosomes from 46 chromosomes or 2n to 23 chromosomes or n (n describes a single chromosome set).

why does crossing over occur

to create diversity, bigger allele pool

Disjunction

the separation of homologous pairs of chromosomes following meiotic synapsis

Compare and constrast between the outcomes of non-disjunction in anaphase I with anaphase II

-both spiral and use endoflagellum to cause diseas

Chorionic Villus Sampling

sampling of placental tissues for prenatal diagnosis of potential genetic defects

Amniocentesis

A technique of prenatal diagnosis in which amniotic fluid, obtained by aspiration from a needle inserted into the uterus, is analyzed to detect certain genetic and congenital defects in the fetus.

chromatid

one of two identical "sister" parts of a duplicated chromosome

symptoms of sickle cell anemia

Causes blood to sickle so it is unable to carry as much oxygen to the cells of the body and can get stuck in vessels. Pain in the hands, feet, anemia, fatigue, yellowing of skin and eyes, rediced life span

advantages in technology that made human genome project possible

¥ Biotechnology techniques such as PCR are used to prepare samples: the DNA needs to be copied to prepare a sufficiently large pure samples to sequence

¥ Computers automate the sequencing process

¥ Fluorescent labeling techniques enable all four nucleotides to be analysed together

¥ Lasers are used to fluoresce the dye markers

¥ Digital camera technology reads the dye markers

Computers are used to assemble the base sequence

John Cairn

grew bacteria in media containing radioactive nucleotides, isolated the dna, and placed it on a electron-microscope grid covered with photographic emulsion

chromosome

made of DNA and protein; contains genes; structural units that are made up of DNA and proteins; by coiling DNA around proteins many times, large amount of information can be stored inside nucleus

genes

* heritable factors that control specific characteristics; various specific forms of a gene (ex: 2 forms of gene that influences height=tall or short); different alleles are due to a slight variation in the base sequence;
* multiple alleles: more than 2 alleles for one gene (ex: blood type), occupy same locus on one chromosome

alleles

different forms of a specific gene

gene locus

specific position of a gene on a chromosome

What do all individuals of a species carry?

same genes at same loci on same chromosome

human body cell (somatic cells)

have 46 chromosomes

human sex cells (gametes)

have 23 chromosomes

members of a species have...

same number of chromosomes each with same genes in sane gene loci (number of chromosomes varies between species)

mutations

new alleles are formed by mutation--\> random changes, base substitution (change in one base in sequence of a gene which may or may not change amino acid sequence), neutral or harmful, can be lethal, mutations in somatic cells are not passed on but mutations in gametes are

Sickle cell disease

single base substitution leads to production of valine instead of glutamine; leads to production of abnormal red blood cells

gene mutations (gene wrongly expressed)

mutation is a permanent change in the base sequence of DNA; it is cumulative effects of millions of mutations and natural selection that have allowed all organisms to evolve from simpler ancestors; not all mutations cause disease;

mutations more likely to occur when....

exposed to mutagens like radiation and some chemicals

malaria

parasitic disease caused by a plasmodium cell; cannot infect sickle cells so people with sickle cell trait are resistant to malaria (sickle cell more prevalent in areas where malaria is endemic\=natural selection)

genome

whole of the genetic information of an organism; humans: all DNA in nucleus & mitochondria; plant: all DNA in nucleus, mitochondria, & chloroplast; prokaryotes: smaller circular DNA & plasmids

human genome project

23,000 protein encoding genes; highly repetitive sequences (satellite DNA) important to gene expression

bacterial chromosomes

circular DNA molecule consisting of one chromosome (not associated with proteins, one copy of each gene)

plasmids

* some prokaryotes contain them; extra DNA molecules (small and circular), not associated with proteins, not needed for basic life functions, multiple copies may be present, not always passed on in cell division, can be transferred from one cell to another (transformation)

eukaryote chromosomes

linear DNA associated with histone proteins; different chromosomes carry different genes (different in size & location of centromere, 23 types of chromosomes in human cells, each chromosome can carry thousands of genes); homologous chromosomes (carry same gene sequences, but not necessarily same alleles, allows for interbreeding, 1 from mom & 1 from dad)

sister chromatids

exact replicas

haploid

one chromosome of each type, humans\=23, ex: gametes, end result of meiosis (4 haploid cells)

diploid

pairs of homologous chromosomes-2 copies of every gene; humans 26 chromosomes, ex: somatic cells, end result of mitosis (2 genetically identical diploid cells)

sex chromosomes

XX=female (all offspring inherit one X chromosome from mother)

XY=male (offspring inherit either an X or a Y chromosome from their father; determines sex of offspring)

X Chromosome

carries genes essential for males and females; one X chromosome is silenced in females during embryonic development

Y Chromosome

mostly carries genes only necessary for male development; houses the SRY gene (initiates development of male features); smaller

karyograms

shows chromosomes of an organism in homologous pairs of decreasing length (chromosomes are best seen during metaphase with a stain, some stains provide distinctive banding pattern for each chromosome)

arrangement of chromosomes that allow for distinctions to be made

size and structure, position on centromere, pattern of banding

karyotypes

property of an organisms studied through observations of a karyogram (can determine sex, detect down syndrome and other chromosomal abnormalities in fetal cells); chromosomes arranged in pairs according to size and structure

meiosis

two cycles of cell division (1 cell--\>2 cells--\>4 cells); reduces chromosome \# by half (diploid--\>haploid); reduction division

homologous chromosomes

in pairs (inherited maternally & paternally); have same genes (but may different alleles); will have same size, centromere location

non-disjunction

can happen in anaphase; spindle fibers fail to separate chromosomes (both go to one pole); results in abnormal chromosome \# (too few/many)

trisomy 21

down syndrome is a chromosomal condition that is associated with intellectual disability

klinefelter syndrome

a chromosomal condition that affects male physical and cognitive development

turner's syndrome

chromosomal condition that affects development in females; most common feature is short stature

crossing over

occurs during prophase 1; equivalent pieces of chromosomes are traded; new combinations of alleles; genetic diversity

random orientation of maternal & paternal chromosomes

a maternal chromosome line up with the homologous paternal chromosome but the side of the cell is random

genetic diversity

recombination: combinations of alleles different from the parents'; due to: random orientation of chromosomes, crossing over; benefit because diversity leads to flexibility in a changing environment

Mendel's Laws

discovered the basic laws of genetics although no one knew the shape of DNA; wrote his laws based on the # and type of peas that each pea plant produced

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1. traits are inherited as discrete units
2. law of segregation (each parent has two copies of each trait; each parent passes on one copy-caused by reduction division in meiosis)
3. independent assortment (allele inherited for one trait does not determine the alleles inherited for other traits-caused by random assortment and crossing over)

gametes

haploid cells that result from meiosis (contain one allele of each gene); sperm or egg (fuse to form a diploid cell)

zygote

start of life; fusion of gametes results in diploid \#, 2 alleles of each gene present (same or different), 1 from mom and 1 from dad, combination of alleles depends on type and \# of alleles present

genotype

combination of alleles present (TT, Tt)

phenotype

physical expression of genotype (tall, short)

codominant

two alleles are equally strong so both are expressed; ex: AB Blood

ABO blood system

controlled by tri-allelic gene; generates 6 genotypes; alleles control production of antigens on surface of red blood cells; allele I^A produces antigen A; I^B produced antigen B; I produced no antigen

blood types and transfusions

blood types carry and immune system recognizes own blood type as being self; other types recognized as non-self; if blood which is incompatible with body is transfused it will result in agglutination of foreign red blood cells (except Type O does not carry any antigens for the ABO system\=universal donor; AB\=universal recipient)

incomplete dominance

one allele not dominant over other so phenotype of heterozygote is blend between two alleles (pink four o'clock flowers)

autosomal chromosomes

body chromosomes that both genders have in their cells

sex chromosomes

chromosomes that determine gender of an individual

autosomal trait

will occur in both sexes equally

sex-linked trait

will appear more often in males; found of X chromosome; male needs only one copy of recessive allele to exhibit phenotype; females needs two copies; ex: baldness

sex-linked genes

genes on sex chromosomes ( Y chromosome genes in mammals are responsible for male characteristics; X chromosome genes in mammals affect many traits)

autosomal genetic disorder

cystic fibrosis (heterozygote for a recessive disorder is a carrier)

polygenic inheritance

single characteristic is controlled by multiple genes; gives rise to continuous variation in phenotypes (skin color)

pedigrees

biological family tree that shows interrelationships between parents and children across generations; helps illustrate pattern of inheritance for a single trait through that family

biotechnology

use of living organisms or other biological systems in manufacture of drugs or other products or for environmental management

Human Genome Project

international project completed in 2003; sequenced the human genome; around 25,000 genes; improved sequencing technology; identified some disorders

Goals of HGP

identify all 20,000-25,000 genes in human DNA; determine sequences of 3 billion chemical base pairs that make up human DNA; store this info in databases; improve tools for data analysis; transfer related technologies to private sector; address ethical, legal, and social issues that may arise from project

Bioinformatics

using computers to store and analyze data generated from sequencing genomes

pharmacogenomics

looks at differences in genomes in different populations to differences in their response to drug treatment

Advantages of HGP

diagnosis of disease; medicines; gene therapy

Polymerase Chain Reaction (PCR)

* when only small sample of DNA is available; amplifies 'copies' the DNA millions of times, creating a large useful DNA sample;
* fluorescent dyes are attached to all the STR copies that get made—one type of dye for each STR region—so that all of the DNA copies from a given region can be distinguished from the others in the mix.

Gel electrophoresis

process where DNA fragments are separated by charge or size due to an electric field; stained, separated, visualized, and analyzed; small more further and opposite charge move further

Application of Electrophoresis

DNA profiling; paternity testing; crime scenes

ABO blood types

O is the most common with no antigens, A and B are equally common with A antigen or B antigen, AB is the most rare with both A and B antigens.

hemophilia

An X-linked recessive disorder in which blood fails to clot properly, leading to excessive bleeding if injured.

dna profiling

The process of testing to identify DNA patterns or types. In forensic science this testing is used to indicate parentage or to exclude or include individuals as possible sources of bodily fluid stains (blood, saliva, semen) and other biological evidence (bones, hair, teeth)

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PCR is an example of DNA profiling.

color blindness

A sex-linked trait in which an individual cannot perceive certain colors.

how can sex linked (x linked) disorders be carried by women that don't show the trait and still affect their male offspring?

the women may have only one x chromosome that is affected, and pass that x chromosome down to their male offspring. Since a male only has one x chromosome, if it is affected with a disorder, the male is affected.

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\-sex linked traits more common in males than females because a reccesive ~~allele~~ on the X chromosome will always produce the trait in a male

how to transcribe dna

DNA to rna

A-U, G-C, C-G, T-A

test cross

the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype

Huntington's Disease

is a brain disorder that affects a person's ability to think, talk, and move. HD is caused by a mutation in a gene on chromosome 4.

Dominant

Autosomal, caused by mutation on gene 4

why can some mutations be silent?

This occurs because several DNA codons can code for the same amino acid

examples of mutagens

\-high energy radiation

\-UV light

\-carcinogens

1. Distinguish between mutations that can affect an individual during their lifetime and those which can lead to genetic diseases.

\-Mutations in the gamete cells can be inherited by an offspring leading to genetic diseases

\-Mutations in the somatic cells stay with an individual for their lifetime.

PCR

What test uses very small amounts of DNA that can be amplified and analyzed

stages of PCR

1. Denaturation- DNA samples are heated to separate into two strands
2. Annealing- DNA primers attach to opposite ends of target sequence
3. Elongation- heat tolerant DNA polymerase (Taq) copies the strands

gel electrophoresis steps

The separation of nucleic acids or proteins, on the basis of their size and electrical charge, by measuring their rate of movement through an electrical field in a gel.

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uses-

a. Determining paternity

b. Evidence in criminal cases

c. Identify species

gene transfer

When a gene from one organism is inserted into the genome of another organism

gene transfer steps

\-Restriction enzymes cut the desired gene from genome

\-E.Coli bacteria contains plasmids which are small circles of DNA that can be removed

\-The same restriction enzyme cuts into plasmid. Because it is the same restriction enzyme the same bases are exposed which leaves 'sticky ends'.

\-Ligase joins the sticky ends fixing the gene into the E.coli plasmid.

\-The recombinant plasmid is inserted into the host cell, and proceeds to express the new gene. Ex: human insulin production.