Chromosomal abnormalities

Question 1

DNA

Answer 1

A DNA moleculeis composed of two polynucleotide chains ( DNA strands) held together by hydrogen bonds between the paired bases. The arrows on the DNA strands indicate thepolarities of the two strands, which run antiparallel to each other in the DNA molecule. -> a double helix

Question 2

What are the 3 major components (building blocks) of a nucleotide?

Answer 2

nitrogen-containing base and a five-carbon sugar, to which is attached one or more phosphate groups

Question 3

Name the 4 nucleotides that are in DNA

Answer 3

adenine (A), cytosine (C), guanine (G), or thymine (T)

Question 4

What is it about a DNA strand that gives it polarity, i.e. a 3’ and 5’ end?

Answer 4

linkage at 3-OH and 5-Phosphate to the sugar

Question 5

Base pair

Answer 5

Each purine–pyrimidine pair is called a base pair

(A)-(T)

(G)-(C)

Question 6

DNA Functions

Answer 6

• Encoding genetic information/instructions
• storage of information

Question 7

Genome

Answer 7

the total genetic information carried by all the chromosomes in a cell or organism constitutes its genome.

Question 8

Chromosome

Answer 8

• In eukaryotic cells, very long double-stranded DNA molecules are packaged into chromosomes.
• Chromosomes comprise of both DNA and protein. DNA is packaged by the protein component and is allowed to fit and organized within the cell.
• Some of the proteins play a role in replication , repair and transcription.

Question 9

Chromatin

Answer 9

• The complex of DNA and protein is called chromatin

Question 10

Karyotype

Answer 10

An ordered display of the full set of 46 human chromosomes is called the human karyotype

Question 11

Gene

Answer 11

• segment of DNA that contains the instructions for making a particular protein or RNA molecule.
• functional units of DNA
• Majority encode for proteins

Question 12

Diploid

Answer 12

each cell contains two sets of chromosomes—one inherited from each parent (germ-line cell)

Question 13

Haploid

Answer 13

they each contain only one set of chromosomes ( gametes)

Meiosis generates haploid

Question 14

Sister chromatids

Answer 14

The twin copies of each duplicated chromosome

Question 15

Homologous chromosomes/homologs

Answer 15

the marternal and parternal chromosomes of a pair are called homologs.

all of which are ‘identical’

Question 16

Recombination/crossing-over

Answer 16

a process in which two identical or very similar nucleotide sequences exchange genetic information

during meiosis

Question 17

2 mechanisms that are generated by meiosis

Answer 17

1. Independent assortment
2. Crossing over

Question 18

Change in the amount of genetic material in a cell leads to

Answer 18

Deletions and duplications

Question 19

Rearrangements of genetic material within or between chromosomes

Answer 19

inversions and translocations

Question 20

Heterochromatin

Answer 20

condensed region, shows up as dark bands (more difficult to transcribe)

Question 21

Euchromatin

Answer 21

Light bands; less condensed region (easier to transcribe)

Question 22

Nonhomologous chromosomes

Answer 22

paired sex chromosomes, X = maternal and Y = paternal, they are not ‘identical’

Question 23

Independent assortment

Answer 23

After replication in meiosis I, allocation of maternal or paternal homologs to each daughter cell is random = reshuffling of maternal and paternal chromosomes into different combinations

Question 24

Crossover (recombination)

Answer 24

Crossing-over occurs between the maternal and paternal chromatids – they swap homologous sections between the chromatids. The locations at which crossingover occurs are held together by chiasmata.

Crossover (recombination) between non‐sister chromatids in the bivalent in meiosis I allows for genetic variation of gametes.

Question 25

Euploidy

Answer 25

term used to describe a cell which contains the same number of chromosomes within each set of chromosomes and that is normal for that organism (diploid organisms contain 2 chromosomes per set).

Question 26

Aneuploidy

Answer 26

is when one or more of the sets of chromosomes within a cell contains a different number of chromosomes compared to the other sets. Aneuploidy can occur during meiosis I, meiosis II (and during mitosis).

• when 1 or more sister chromatids fail to segregate properly ⇒ nondisjunction
• or due to chromosome loss because sister chromatid not properly attaching to the mitotic spindle, i.e. to a kinetochore microtubule, and because it is unattached it is rapidly degraded

Question 27

Polyploidy

Answer 27

is when all of the sets of chromosomes have additional chromosomes to what is considered ‘normal’ for a particular organism, for example a human cell, which should be diploid, that contains 4 of each chromosome per set. Polyploidy results when cytokinesis does not occur.

Question 28

5 types of chromosomal abnormalities

Answer 28

deletion, duplication, inversion, simple translocation, reciprocal translocation ⇒ these all occur because of ds breaks in DNA

• Deletions and duplications result in a change in the amount of genetic material in a cell,
• inversions and translocations result in rearrangements of genetic material within or between chromosomes

Question 29

Can daughter somatic cells be aneuploidy?

Answer 29

Yes. Because Nondisjunction and loss of chromosomes can also occur during mitosis

Question 30

Chromosomal abnormalities : variation in chromosome structure

Answer 30

Causes: Recombination errors and DNA damaging agents, e.g. x-rays, that cause double strand breaks in DNA

Question 31

Complementary base pairing

Answer 31

• G forms 3 H-bonds with C
• A forms 2 H-bonds with T/ (Or U in RNA)

Question 32

Human somatic cells

Answer 32

• contain 2 copies of each chromosome (they are diploid); 1 maternal and 1 paternal homolog.
• They are generated via mitosis.

Question 33

Human germ cells (gametes; sperm and egg cells)

Answer 33

have only 1 copy of each chromosome (they are haploid), they are generated via meiosis.

Question 34

telomeres

Answer 34

The DNA located at the end of chromosomes

Question 35

centromere

Answer 35

The DNA sequence that links sister chromatids and ensures each is apportioned correctly to daughter cells

Question 36

nucleosome

Answer 36

DNA that is packaged around histones

Question 37

first step in meiosis

Answer 37

• chromosomes are replicated to generate sister chromatids
• there are 2 maternal chromatids and 2 paternal chromatids for each chromosome that the organism has.
• During meiosis I the replicated maternal and paternal chromosomes line up adjacent to each other on the spindle and form bivalents

Question 38

5’‐GCATCA‐3’

Answer 38

complement sequence is; 3’‐CGTAGT‐5’

Reverse complement sequence is; 5’‐TGATGC‐3’