IB Genetics

chromosome

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)

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

• 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)

plasmid used in bacterial 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

Punnett square

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

Downs Syndrome karyogram

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

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