(02) Cytogenetics

Question 1

What is more dense - DNA during metaphase or interphase?

Answer 1

• DNA during metaphase

Question 2

What is the process of capturing dividing cells at metaphase to examine chromosomal characteristics called?

Answer 2

• karyotyping

Question 3

(Karyotyping)

What does G banding detect? What is used? What did this allow?

What does R banding detect?

What does C Banding Detect? What is used?

Answer 3

• High A and T – trypsin + Giemsa Stain – allowed for differentiation using banding (in addition to size and shape)
• Reversed Patterns (reversed G bands)
• identifies heterochromatin (repetitive DNA such as centromeres - so mostly the centromere just stains darks) – BaOH and Giesma

Question 4

• Somatic cells in diploid organisms have ___ copies of each autosomal chromosome. One from the ___ and one from the ____.

What is the diloid number? What is it?

How much variety in total chromosome number across species? Genes? DNA?

Answer 4

• 2, father, mother
• 2N – the total chromosomes in a somatic cell
• a lot (dogs have 78, cats have 38) – very similar (~20,000) – very different (1.1 - 3 billion bp (haploid))

Question 5

(Chromosome Nomenclature)

• Chromosomes have a ___ and a ____ arm. Where they join is called the _____. The two pairs of identical chromosomes (left and right side of X) are called _____.

Name from left to right

Answer 5

• short (p), long (q) – centromere – sister chromatids
• metacentric, submetacentric, acrocentric, telocentric

Question 6

How many sex chromosomes does each individual have?

• in mammals?
• in birds?
• Reptiles?

Answer 6

• 2 sex chromosomes
• XX females and XY males
• ZZ males and ZW females
• a bunch of different stuff (temperature dependent sex differentiation sometimes - temp of an egg)

Question 7

(Fluroescence in situ Hybridization)

What is it?

How is it done?

What combines with DNA easier - large or small fragments?

How far has this advanced (in humans)?

Answer 7

• A technique that allows you to take a known piece of DNA, tag it with a fluorescent probe, and hybridize to a chromosome to see where it goes
• DNA (of chromosome) is denatured (heat or acid) – then a apply a small piece of DNA that you have designed with a fluorescent tag on it - then it will hybridize and you can follow it
• small (don’t have as much steric hindrance)
• Now possible to color entire chromosomes one color (to pair them or see if they recombine) - called Multi-color fish?

Question 8

What can cytogenetic abnormalities that affect the integrity of a chromosome be referred to as?

What are the two types of chromosomal abnormalities?

What does each type include?

Answer 8

• structural aberrations
• Balanced and unbalanced (transolcations)
• balanced - no net gains or loss of DNA (as in peri- or paracentric inversions and reciprocal translocations)
• unbalanced - duplication, deletions, and non-reciprocal translocations

Question 9

What can cryogenetics be used for in a clinical setting?

Answer 9

Investigation of infertility/reproductive disorders and evaluation of tumors

Question 10

• If a chromosome change causes a problem it is either the result of something that occurred during ______, or the problem is that it causes problems with _____.

In meiosis starts out with a ____ cell, produces ______ by way of ___ divisions

What separates in first division? second?

Answer 10

• meiosis, meiosis
• diploid, haploid gametes, two
• homologous chromosomes - sister chromatids

Question 11

(Abnormal Chromosome Number)

What is Aneuploidy? What is it most commonly seen in? What causes it? What is the percentage of this occuring?

• What have monosomy and trisomy of autosomes been observed in (what animals)?

What is down syndrome in humans?

Answer 11

• karyotypes with more or fewer than the normal euploidy state – most commonly seen with sex chromosomes (or small autosomes) – non-disjuction during meiosis – 5% of all meioses have a disjunction (these are usually destroyed)
• cattle and horses
• trisomy of Hsa21

Question 12

(Inter-species crosses)

• Female Horse + Male Donkey =
• do the parents have the same number of chromosomes?
• does mitosis occur normally?
• Does the mule have an even number of homologous pairs? Why or why not?

What is the result?

Answer 12

• infertile mule
• no (horses 64 and donkeys 62)
• yes
• no - has 63 chromosomes (cause his parents had different numbers)
• meiosis is disrupted and viable eggs and sperm are not formed

Question 13

(Nondisjuction of Sex Chromosomes)

• If you have a non-disjuction in the first division what do you end up with? In the second?
• What is XO called? symptoms?
• XXX?
• XXY?
• Which animal does this occur in?

Answer 13

• (XY) XXY, (XY) XXY, (O) XO, (O) XO – (XX) XXX, (O) XO, (Y) XY, (Y) XY (normal)
• Turner’s syndrome - normal appearing but sterile
• often fertile - Kleinfelter’s syndrome (predominantly male, sterile)
• alpaca (XXX) - infertile

Question 14

What is the deal on reciprocal translocation?

Result in individual?

Gametes?

Answer 14

• portion of one chromosome gets stuck onto another
• often normal phenotype (still has balanced chromosomal material)
• Unbalanced gametes form during meiosis

Question 15

What occurs in a Roberstian Translocation?

Can it have an effect on fertility?

Answer 15

• 2 acrocentrics form a metacentric and one centromere fragment (for example) – have one less chromosome but still have balanced amount of DNA
• yes

Question 16

(Meiosis)

What is a ribbon-like protein structure that forms between homologous chromosomes during prophase 1 of meiosis?

What does this structure help do?

Answer 16

• synaptonemal complex
• mediate chromosome pairing (synapsis) and recombination (crossing over) (maybe)

Question 17

_:_ centric fusion in cattle

what happens?

• do you go through normal disjuction (balanced gamete)?

Will chromosomal rearrangement always affect fertility?

Answer 17

• 1:29
• one 1 and one 29 pair up
• no
• not always, depends on how organism deals with it

Question 18

(Inversion)

• What one is on top? on bottom?

example?

How are these a problem? What does this result in?

Answer 18

• paracentric inversion (does not involve centromere)
• pericentric inversion (involves centromere)
• tobiano coat color
• during meosis need to get homologous genes paired up correctly - so one of these has to loop a bunch for this to work
• One chromosome with deletions and one with duplications

Question 19

• Chromosome problems are problematic if they ______ or if they ______.

Answer 19

• change amount of DNA, interrupt meiosis

Question 20

Is it possible to get XX male or XY female?

How?

Answer 20

• yes
• SRY (sex determining region on Y) makes someone male - if this gets sent to X during recombination fuck up can result in that

Question 21

What is the small region of X and Y that are homologous? where? Significance?

How does this cause XX male?

Answer 21

• pseduo-autosomal region (PAR) – one on short and one on long arm – behaves as though autosomal - recombination occurs here (has to meisos to occur)
• SRY is close to PAR - if there is a mess up the SRY can get sent to X

Question 22

How are mosaics and chimeras similar? different?

Examples of this?

Is tortoiseshell coat color an example of this? what is it?

Answer 22

• Both have more than one genetically distinct population of cells
• mosaics - arise from one zygote
• chimeras - arise from more than one zygote
• intersex chicken (female on side, male on other)
• not really - different inactivation of X - one that codes for orange - one for black or whatever

Question 23

What is freemartinism in cattle?

How does this occur?

What does this result in ?

Answer 23

• if you have twin cattle - one male and female - the female will be sterile
• exchange of hormones and hemotopoetic cells
• masculization of tubular female reproductive tract, lack of female gonad development, ovatestes