Chromosome Variation and Sex Determination Flashcards
What is the name for organisms with multiples of the basic chromosome set (genome)?
Euploid
What can vary among closely related species when euploid is involved?
Chromosome number
Give an example of euploid:
Chinese muntjac and Indian muntjac
Have different number of chromosomes but same number of genes
Define aberrant euploid:
Organisms that have more or fewer than the normal number of chromosome
Give examples of aberrant euploid:
Polyploids Triploid Tetraploid Pentaploids Monoploids
Define polypoid:
have more than two chromosome sets
Define monoploid:
An individual of a typically diploid species that has only one set of chromosomes
Finish the sentence:
Eukaryotes haploid with…
one chromosome
Finish the sentence:
Eukaryotes diploid with…
two chromosomes
Are polyploids common in plants or mammals?
plants
Define aneuploid:
Individuals whose chrosumse number differ by one or a small number of chromosomes
Finish the sentence:
An aneuploid can have a chromosome number either greater or smaller than that of the…
wild type
Define trisomic:
2n + 1
Define monosomic:
2n - 1
Define nullisomic:
2n - 2
What can O stand for?
Absence chromosome
How can cells end up with two many or too few chromosomes?
Non-disjunction event at meiosis or mitosis
What does the risk of non-disfunction rise with?
Maternal age
Why do extra chromosomes affect phenotype so drastically?
- Gene balance - genes have evolved to function in a diploid genetic background and disrupting that background disrupts their function
- Expression of deleterious alleles on monosomic autosomes
What does duplication play an important role in?
Evolution of the genome
How can chromosomes have extra pieces?
duplication
How can chromosomes have missing pieces?
Deletion
Finish the sentence:
Deletions can be small…
only covering a part of one gene
Finish the sentence:
Deletions can be large, with chromosomes missing pieces large enough to be visualised on a …
karyotype
What does FISH stand for?
Fluorescent in situ hybridisation
What is copy number variation?
Chromosomes can have missing or extra pieces on one chromosome
How can chromosomes have mixed-up pieces?
Inversion or translocation
How do you create and inversion?
A segment of the chromosome is cut out, flipped and reinserted into the chromosome in the opposite orientation
Are inversion balanced rearrangements?
Yes
Why are inversions balance rearrangements?
They don’t gain or loss of genetic material
When can inversion lead to duplication or deletion?
during meiosis
What is translocation?
Rearrangement involving a part of one chromosome that has broken off and reattached to a different chromosome
What sex determination system do mammals have?
XY
Are males XY or XX?
XY
Are females XY or XX?
XX
Who discovered the Y chromosome?
Netti Stevens in 1905
Describe the Y chromosome:
- Determine maleness
- Mostly repeated sequences
- Very few genes
- SRY maleness- determining gene
- inherited father to son
Describe the X chromosome:
- Many genes: unrelated to sex-determination
- Males are homozygous for X-linked genes
Examples of X-linked traits in humans:
- Red-green colour vision deficiency
- Haemophilia
- Duchenne muscular dystrophy
What prevents X-chromosome gene dosage differences having significant phenotypic effect?
- Between XY males and XX females
- In cases of X-chromosome aneuploidy
What is lynosiation?
In female mammals one X chromosome is epigenetically inactivated early in development
Define reciprocal translocation:
Part of arms from one chromosome are switched with another
Define robertonian translocation:
Arm of chromosomes fuse around a single centromere
Finish the sentence:
X and Y chromosomes contain very little…
homology
What do inactive X chromosomes look like?
Highly condensed ‘Barr’ body
Are all species in the world XX for female and XY for male?
No, sometimes it is switched round
How can X-linked recessive traits be deduced?
- More males than females express trait
- Skips a generation
- If female expresses the characteristics, all male offspring will express trait
In humans, there is a recessive, sex-linked allele for night-blindness (the inability to see in poor light). The wild-type allele, XN, results in typical night-vision. Curly hair is caused by a dominant allele of the gene W, while the recessive allele results in straight hair.
If a straight-haired, night-blind woman married a man with normal night-vision and curly hair, whose father had straight hair, what would be the probability that their first child would be a straight-haired, night-blind boy?
A) 0.00
B) 0.25
C) 0.50
D) 0.75
B
