Unit 2 biology topic 14: karyotypes and chromosomal abmormalties

Autosomes

- chromosomes that's not a sex chromosome 22 pairs which are matched according to : -banding patterns -centromere position -length -presence of satellites

Aneuploidy

-Aneuploidy is the presence of an abnormal number of chromosomes in a cell, -changes in total number of chromomses -This is a condition in which the chormomses number is more or less than the normal diploid or haploid cell -During meiosis, sometimes the normal separation of homologous chromomses does not occur during meiosis 1 or sister chromatids fail to separate during meiosis 2. -Gametes can end up with more or less than the normal number of chromomses -This type of error is called non-disjunction

Non-disjunction of homologous chromosomes (or sister chromatids )can result in.

-Gametes that lack one member of a homologous pair. If a gamete lacks an autosomes and it's involved in fertillisation, the zygote is not viable -Gametes that contain two cheomomses of the homologous pair -If a gamete with the wrong number of chromosomes is fertilizes, the resulting zygote will also have an abnormal number of chromomses, which has deleterious effects on development, resulting in a 'syndrome' -For mostly chromosomal abnormalities, death occurs and baby is micarried

Sex chromomses

1 pair which determines the sex of the individual

During meiosis, mistakes can occur which may cause changes in....

1. The total number of chromomses 2. Chromomses structure or arrangement

Karyotype

A visual display of an individual's chromosomes set out in homologous pairs- pairs are arranged in order of length, usually longest to shortes

In a karyotype, the chromosome image are organized in a pattern according to....

An international convention

Hybrid

An offspring produced as a result of a mating between two different species. The chromomses are not in homologous pairs but the 2 sets of genes are sufficiently similar that a hybrid organism is produced

Sex chromomses, X and Y, act like homologous chormomses during meiosis in that their pair, but..... does not occur between them

Crossing over. -Each chormomses then segregate to opposite poles during anaphase 1. Failure to segregate can result in gametes that lack a sex chormomses or have 2 sex chromosomes.

An Organised picture of chromosomes produced by....

Cutting out and organizing pictures of stained chromosomes of somatic cells photographed during metaphase of mitosis -SUch as arrangement enables any abnormality in either number or structure of the chromosomes to be quickly identified.

Outline a technique that may be used in conjunction with karyotyping that allows geneticists to arrange and interpret chromomses with greater accuracy

DNA sequencing- find the exact order of bases and compare to the order of bases for that gene

Example of Hybrid

Geep/ shoat - offspring of goat and sheep, it has 57 chromosomes -Goat 2n=60, therefore their gametes contain 30 chromosomes -sheep 2n=54, therefore their gametes contain 27 chromosomes At fertillisation the zygote will contain 57 chromomses. Mitosis occurs many times producing geep/shoat with each cell containing 57 chromomses.

The homologous chromosome are arranged in order from....

Largest to smallest with sex chromosomes on the end -The 22 matched pairs of chromosomes present in both males and females are termed autosomes

Example of Hybrid

Mule- offspring of a horse and a donkey -horse 2n = 64, therefore their gametes contain 32 chromomse Donkey 2n=62, therefore their gametes contain 31 chromomses The mule has 63 chromosomes in each cell

Trisomy

Number of chromomses: 3 Trisomy refers to the presence of three copies, instead of the normal two, of a particular chromomse. The presence of an extra chromomse 21, which is found in Down syndrome, is called trisomy 21. Trisomy 18 and Trisomy 13, known as Edwards Syndrome and Palau Syndrome, respectively, are the two other autosomal trisomies recognized in live-born humans. Trisomy of the sex chromomses is also possible, for example (47, xxx), (47,xxy ), and (46, xyy )

Disomy

Number of chromosome: 2 Disomy is the presence of two copies of a chromosome. For organisms such as humans that have two copies of each chromomse (those that are diploid), it is a normal condition

Testrasomy/Pentasomy

Number of chromosome: 4 or 5 Tetra Sony and pentasomy are the presences of four or five copies of a chromomse, respectively. Although rarely seen with autosomes, sex chromomse tetrasomy and pentasomy have been reported in humans, including XXXX, XXYY, XXXXX,XXXXY and XYYYY

Monosomy

Number of chromosomes:1 Monosomy refers to lack of one chromosome of the normal complement. Monosomy of the sex chromosomes (45, x) causes Turner syndrome

WHat kind of genetic information is not available from karyotype analysis?

Point mutations cannot be identified

Cytogeneticists

Scientists who specialize in the study of human karyotypes

To obtain viable gametes in the mule, all the donkey chromosomes would have to ....

Segregate to the same pole and all the large chromomse would have to segregate to the opposite pole. -The gametes produced would contain one complete set of chromomses, Eiter the donkey's or the horse's, and therefore would also contain one set of genes, -The chance of this happening in a mule is very small so the likely result will be that the gametes will not contain one complete set of chromosomes. -Therefore, the mule is unfertile

What factors determines the sex of an offspring in reptiles

Sex of offspring in same reptiles is determined by the incubation temperature of eggs E.g in turtles- above 31 degrees =male offspring -below 27 degrees= female offspring = 29 degrees, equal female or male

Describe the kind of information that karyotyping provides about an individual

Sex- whether there are any chromomse mutation i.e. whether there are any extra or missing chromomses

What happens during meiosis in hybrids?

Some or all of the chromosomes will not pair up as they are not homologous with another chromosome. The chromomse will then segregate independently of other chromomses -The gametes will be genetically unbalanced and therefore not viable. The organism is said to be unfertile

What are karyotypes used for?

To assist in the analysis of the chromosomes that are present in cells

What factors determines the sex of an offspring in birds?

WZ- female ZZ-male

Female sex chromomses

XX

Male chromosome

XY

What factors determines the sex of an offspring in mammals

Xx- female XY-male