Lecture 18 - Behaviour of Chromosomes and Alleles

Question 1

Differ between karyotype and karyogram.

Answer 1

Karyotype: sorted chromosomes

Karyogram: a drawing of chromosomes with banding shown

Question 2

In karyotyping, chromosomes can be sorted on the basis of: _____ (4)

Answer 2

size, centromere position, presence of satellites, and banding pattern

Question 3

(Extra) Human chromosomal centromere position are never _______. There are 5 acrocentric chromosomes in humans: Chromosome no. _______

Answer 3

telocentric

13, 14, 15, 21, 22

Question 4

Differ aneuploidy and euploidy.

Answer 4

Aneuploidy: +/- a chromosome (or a few, but less than a set)

Euploidy: +/- a complete haploid set/s of chromosomes (more than 1 called polyploidy)

Question 5

Describe the variable phenotype of someone with Klinefelter Syndrome (XXY).

Answer 5

small testes, reduced testosterone, delayed puberty, breast enlargement, infertility

Question 6

Explain why older women have a higher rate of aneuploidy.

Answer 6

Older women tend to have a more chromosomally abnormal egg,, where the chromosomes line up erratically, making non-disjunction more likely.

There is also a higher likelihood on the non-disintegration of the protein cohesin by separase (which binds sister chromatids together).

Question 7

In the case of aneuploidy, non-disjunction can occur at three stage of the cell cycle. What are they?

Answer 7

Anaphase I and Anaphase II of Meiosis, and Anaphase of Mitosis

Question 8

What is mosaicism? Explain how a specific kind of aneuploidy may lead to the phenomenon of mosaicism in an individual.

Answer 8

Mosaicism involves the presence of two or more populations of cells with different genotypes in an individual. Non-disjunction occurring during mitosis at blastocyst stage may lead to differing cell lines.

Question 9

Other than changes to chromosomal number, there can be structural changes to chromosomes. This event is called _______

Answer 9

Translocation.

Question 10

Define translocation.

Answer 10

Chromosome translocation is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes

Question 11

Give examples of diagnostic tests to detect chromosomal abnormality.

Answer 11

preimplantation diagnosis (with IVF), ultrasound, triple test of maternal blood (checks level of AFP, hCG, and Oestriol), Cell-free DNA in maternal blood, Chorionic villus sampling, Amniocentesis