Intro to Cytogenetics Flashcards
Human chromosomes in a pair are called what? How many pairs of autosomes are there? Sex chromosomes?
Homologous chromosomes (homologs); 22; 1
For somatic division what process is used? For germ cell division what process is used? What about N and C?
Mitosis (2N –> 4C –> 2N)
Meiosis (2N –> 4C –> 2N –> N)
Five steps of mitosis?
Interphase, prophase, metaphase, anaphase, telophase
When can you see shortened and thickened chromosomes? How could you view them?
Metaphase; light microscope
When do centromeres divide and chromosomes separate?
Anaphase
In germ cells, what process occurs during prophase I?
Recombination of linked alleles leading to gene reassortment
What process occurs during anaphase I?
Reduction division, leading to products that are N
When do you see crossover?
Between two HOMOLOGOUS chromosomes!
In the reduction division, what occurs regarding N and C?
Given A1, A2, B1, and B2, how would they segregate?
2N –> N; 4C –> 2C
One A, B in one cell; the other A, B in the other cell
What type of division occurs in meiosis II?
Division similar to mitotic division, but NO DNA REPLICATION!!
Are there pairs of chromosomes remaining after meiosis II?
No, meaning that they have half the DNA content (C) and half the original chromosomes (N, or usually 23)
What error can occur related to anaphase I?
Nondisjunction, with failure of the chromosome or chromatids to disjoin properly; e.g. A1, A2, and B1 go to one cell, but only B2 goes to the other cell after reduction division
What is disomy?
Normal condition, two chromosomes per pair
What is isodisomy?
Having 2 chromosomes from the same source (ie duplication of 1 chromosome)
What is heterodisomy?
Having 2 different chromosomes!
If you were to have nondisjunction during the first division, with A1, A2, B1, and B2 as examples, what would you expect to see in the four gametes?
An example would be heterodisomy of A (A1 and A2) in two of the gametes, but nullosomy of A in the other two gametes even with the second division occurring properly; in general, you would still have disomy of A in those two gametes
If nondisjunction occurred at meiosis II, what might you expect in the gametes given A1, A2, B1, B2?
Now, when the centromeres divide and chromatids separate, you might not have separation of e.g. the A2 chromatid, and this would affect two of the gametes as A2 would be present in only one of those, leading to ISODISOMY!!!
In males, trace out sperm production from spermatogonia to spermatids
Spermatagonia (2N, 2C) –> one chosen –> DNA replication –> primary spermatocyte (2N, 4C) –> reduction division –> secondary spermatocyte (2N, 2C) –> second division –> spermatids (N, 4 of these; C)
In females, trace out oogenia to ovum
Oogenia (2N, 2C) –> DNA replication –> Primary oocyte (2N, 4C) –> reduction division –> first polar body (could give daughter polar bodies possibly) and secondary oocyte (2N, 2C; latter with more cytoplasm) –> meiosis II –> second polar body and ovum (N, C)
What is the bottom line with oogenesis and spermatogenesis in terms of gamete production?
Primary spermatocyte = 4 gametes
Primary oocyte = 1 gamete
When in meiosis completed for the oocyte?
Not until fertilization!!
When does the oocyte complete meiosis I?
At ovulation, becoming a secondary oocyte
What results in human zygote formation?
Fusion of the male and female pronuclei
What are a couple differences between spermatogenesis and oogenesis besides gamete production?
- Spermatocytes made throughout repro life; oocytes all present at birth
- Spermatocytes made continually; oocytes once a month
Who is homogametic? Heterogametic?
Females (XX); males (XY)
Besides between homologous chromosomes, where can recombination occur?
Pseudoautosomal region of the X and Y chromosomes
What does TDF/SRY mean for males with respect to certain proliferation and degeneration?
It means proliferation of the Wolffian ducts due to testosterone present (Leydig cells); also due to AMH it means degeneration of the Mullerian ducts (which proliferate in females)
Can you affect one’s sex by e.g. losing a sex chromosome once it’s been determined? Is TDF the only factor that defines sex?
No; no
Why are males not at a deficit by having just one X chromosome?
X inactivation (dark spot in one X of the female chromosomes)
What is the total number of inactive X’s equal to?
Total number of X’s - 1
What is needed to determine a normal female? When does inactivation occur? Can you reverse inactivation in somatic tissues? What results from X-inactivation?
You NEED TWO X chromosomes that are ACTIVE; it occurs 3-7 days after fertilization; IRREVERSIBLE!!
Dose compensation!
What happens with somatic mosaicism, especially given that one is heterozygote for a certain trait?
Half of the father’s X chromosomes are inactive, and half of the mother’s X chromosomes are inactive, meaning you could get e.g. black and yellow patches of fur
How can inactivation be protective?
Non-random inactivation of abnormal X, that could otherwise cause problems
How does X inactivation occur? What type of modification is this? Where does it start? What site can escape X inactivation?
Methylation; epigenetic; XIST (X inactivation center); pseudoautosomal regions
What must happen in order to transmit X chromosomes to offspring?
Reactivate the inactive X at meiosis!!!
What are some effects of chromosomal abnormalities?
Phenotype change, fetal loss, genetic disease, malignancy
What are some examples of chromosomal anomalies for post-natal cases?
Features of a known chromosomal disorder; ambiguous genitalia (chromosomal defect); multiple congenital anomalies (chromosomal defect)!!
How can chromosome abnormalities manifest later in life?
Features of known chromosomal disorder (e.g. trisomy 13); FH of chromosomal disorder; infertility; mental retardation, malignancies
What type of chromosomal abnormalities are we looking for?
Numerical (change in total number of chromosomes)
Structural (deletion, translocation)
How can we acquire specimens for analysis?
Blood (easiest); bone marrow (oncology); chorionic villi, amniotic fluid (prenatal); tissue (skin biopsies)
How to identify chromosomal abnormalities?
Metaphase: 1. Size 2. Centromere pattern 3. Binding pattern
What are metacentric, submetacentric, acrocentric chromosomes?
Metacentric: centromere found about equal from both ends
Submetacentric: centromere closer to one end
Acrocentric: modified short (p) arms that have rRNA genes and modified telomere called a satellite
What is the banding pattern?
Pattern of alternating light and dark regions, usually using Giemsa staining
What is a chromosomal polymorphism? How are they inherited?
Presence of two or more alternative structural forms for a chromosome within a population; inherited as Mendelian characters
How can you arrange chromosomes from metaphase?
In a karoyogram
