Biology 1A03 Theme 5

DNA polymorphisms

one of two or more alternative forms(alleles) of a gene at a chromosomal region that differs in either a single nucleotide base or have variable numbers of tandem nucleotide repeats

Tandem repeats

are patterns of one or more nucleotides that are repeated (these repetitions are directly adjacent to each other and can

How are alleles detected?

microarray analysis, PCR, southern blot, and even dna sequencing

Single Nucleotide Polymorphisms (SNPs)

most common type of genetic variation and come from single nucleotie base changes or substitutions that can occur in a significant portion of a population and are usually found in non coding and coding region

How often are SNPs?

about once every 350bp

DNA markers

if an SNP if found close to a particular gene, they can be used as DNA markers for that specific gene (if the SNP is close enough of linked to a gene of interest, then every time that gene is passed on from a parent to a child, then the SNP is also passed on)

Silent variations

variations that happen in non coding regions of DNA and has no effect

Genotype

representation of the pair of alleles the person has

phenotype

the cell or bodily physical representation of the genotype (blue eyes, sickle cell shaped blood)

Beta Globin gene in sickle cell anemia

it is found in chromosome 11 and every person has two copies, one from each parent

HbA

the homozygous genotype and will express normal blood cells

HbS

the sickle allele brought about by SNPs

Homozygous HbS

leads to sickle cell anemia with blood that cant take oxygen properly

HbA/HbS

heterozygous allele will produce normal and sickle blood cells but they will make more normal blood cells and thus there is no sickle cell effect that will occur

Variation in populations

sickle cell anemia is found in many populations with different alleles or haploytypes emerging independently across many poplulations

Among nations with the highest prevalence of sickle-cell anemia, it has been found that there are a possible 5 distinct beta-globin haplotypes found across different patients that correlates with regional distribution of distinct sickle cell anemia single nucleotide polymorphism

Variation in gene copy number

gene copy number can contribute to genetic difference between individuals and result in a region that many be normally present in one copy per chromosome but may be duplicated or deleted (Ex. AMY1 gene for amylase)

Inheritence of chromosomes

done through mieosis

Gamete

cells in the body that are not produced through mitosis (sperm and egg)

Male gamete

4 haploid sperm cells

Female gamete

one large egg

Meiosis

similar to mitosis is the division of gamete cells

Interphase

allows for duplication of chromosomes by two consecutive cell divisions wich results in the production of four haploid daughter cells by the end which contain half the amount of chromosomes of the parent cell

Prophase 1

it is the first meiotic division wher ethe chromosomes condense and the nuclear envelope begins to degrad ealong side with the chromosomes undergoing synapsis

Synapsis

pairing of and physical connection of homologous chomosomes along their length

Synaptonemal complex

forms between homologous chromosomes which hold them together during synapsis

Chiasmata

the cross over and exhchange of corresponding segments of DNA molecules between homologous chromosome pairs

Recombiant Chromatids

all homologous chromosomes will pair with eachother during synapsis which allows for the formation of a bivalent unit which consists of a pair of synapsed chromosomes to form a a four stranded sturcutre

non sister chromatids

replicas of different chromosomes which are genetically similar but not identical

metaphase I

homologous chromosomes line up at metaphase plate

Anaphase I

synaptonemal complex breaks down and allows simple fibers to pull each homologous pair on opposite poles

Telophase I

allows the division of the cell into two haploid cells

the parent diploid of 46 chromosomes will now split into two haploid cells with 23 chromosomes each

Prophase II

23 different duplicated sister chromatids and nuclear envelope breaks down and chromosomes condense

Metaphase II

chromosomes positioned at center and since crossing over occured in Meiosis I, the two sister chromatids are not identical

Anaphase II

proteins holding the sister chromatids toether at the centromere broken down and allows chromatids to seperate and move to opposite poles of the cell as individual chromosomes

Telophhase II

reforming of nuclear envelope and chromosomal decondesing which is followed by cytokinesis

Nondisjunction

When gametes have an extra chromosomes or other have a missing chromosomes due to failures in meiosis

Gregor Mendel

Identified and documented two laws that would explain principles of inheritence

What did mendel do?

he bred true breeding plants and bred the first generations and saw what would happen

Law of Segregation

states that two alleles of a gene separate into two different gametes during gamete formation in both parents

Monohybrid

cross between two traits

heterozygous

Aa or Bb, when there is a dominant and recessive trait the dominant trait takes over

Heterozygous dominant

when there are two alleles and the dominant takes over

Homozygous Dominant

AA when both alleles are dominatn

Homozygous recessive

when both alleles are recessive (aa) they take over

Monohybrid Phenotype ratio

3:1

Monohybrid genotype ratio

1:2:1

Law of independent assortment

Applies to genes that are located different chromosomes stating that allele pairs seperate independant during the formation of gametes, thus traits are transmitted to offsprint independently of eachotehr

Dihybrid cross

cross between two parents of a two genes taht are linked

Mendel -from gene to protein

B gene in SBE1 gene (starch branding enzyme)

without this enzyme, sucrose contest was higher and caused swelling of the seed, and when the seed matured it lost its water and went wrinkled --> physical wrinkled seeds

Pedigrees

family trees that allow for a visual representation of the segregartion of s specific trait

Sex chromosomes

the X and Y chromosomes

Male sex chromosome

XY

female sex chromosome

XX

how do the sex chromosomes pair and segregate like homologous ones during meisis

they have small regions at the tips that are similar to allow pairing

Sex linked gene

gene that is on the sex chromosomes even if it has nothing to do with the sex of the organism because the expression depends on the sex of the individual

p arm

short arm of chromosome

q arm

long arm of chromosome

Colourblindness

an ishihara colour test is the most common way to test for red/green colour blindness, and it is a hemizygous state, the rule of dominance and recessiveness no longer apply

Linked genes on the X chromosome

genes positioned close together on the same chromosome are referred to as linked because they usually inherit together and do not segregate

Recombination of Alleles

- If two genes are far apart, during crossing over, there is a high chance that alleles can be switched from each chromosomes creating recombinant chromosomes

- But if the genes are close to each other, we see very little chance to switch alleles during crossing over

- Recombination frequency is higher with alleles that are farther apart than closer together

- Recombination frequency can be used to determine the distance between genes along the same chromosome

Linkage maps

shows you the distance between chromosomes but also the order the genes along the chromosome

What is recombination frequency used for?

to determine the distance between genes along the same chromosome

genes closer together

do not segregate

genes farther apart

segregate

The ABO blood system

variation in genetics contributes to the system. red blood cells all have the same function but different types exist and the blood type depends on the presence or absence of specific inherited cell surface proteins

glycosyltransferase enzyme

catalyzes the formation of speicific A or B agglutinogens that are expressed on the cell surfaceIn addition, the AB blood type has several SNP polymorphisms that leads to the formation of slightly different transferases

HIV resistance mutation

some mutations such as those by some people in the mid-14th century