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GENETICS > Chromosomal Genetics > Flashcards

Chromosomal Genetics Flashcards

1
Q

What are the key principles of Chromosome Theory?

A
  • Chromosomes are the fundamental carriers of genetic material
  • They are linear structures with genes located at specific loci
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2
Q

What are the 3 key aspects of chromosomal behaviour?

A
  • Are present in pairs in somatic cells
  • Segregate during formation of gametes and rejoin during fertilisation
  • Different chromosomes segregate independently
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3
Q

What was the main proof of Chromosomal Theory?

A

The reciprocal Drosophila crosses of Thomas Hunt Morgan

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4
Q

What characteristic did Morgan focus on?

A

Eye colour. Red is WT. White is mutant.

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5
Q

What was the ratio of F1 and F2 flies eye colour if the parentals were the following:
Red female X White male

A 
F1 = all red 
F2 = all red females, 0.5  red male, 0.5 white male
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6
Q

What was the ratio of F1 and F2 flies eye colour if the parentals were the following:
White female X Red male

A 
F1 = all red females, all white males. 
F2 = 0.5 red female, 0.5 white female, 0.5 red male, 0.5 white male
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7
Q

What was the pattern of inheritance for eye colour in Drosophila?

A

X-linked Dominant. The locus for eye colour only on X chromosome.

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8
Q

Define Sex-linked Inheritance.

A

The inheritance of a gene located on a sex chromosome.

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9
Q

Describe the pattern of inheritance of Sex-linked recessive alleles.

A

The allele lies on the X-chromosome so is transmitted in mainly through females but manifests mainly in males.

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10
Q

Give an example of Sex-linked recessive inheritance.

A

Colour blindness

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11
Q

Give an example of Sex-linked recessive inheritance.

A

Haemophilia.

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12
Q

Define Lyonization.

A

Also known as X-Chromosome Inactivation- early in development one of the Xs in a particular cell switches off.

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13
Q

What is a Barr Body?

A

The inactivated X chromosome that appears as a dark staining blob

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14
Q

Give 3 characteristics of Lyonization

A
  • X-chromosome are inactivated at random
  • In het females, different patches of tissue have one of the other alleles expressed
  • Every patch is a clone descending from an early embryonic cell with one X-chromosome activated
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15
Q

Give an example of Lyonization in humans.

A

Females who are hets for colour blindness have patches of normal colour vision and colour blind cells in the retina.

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16
Q

Give an example of Lyonization in humans

A

Duchenne Muscular Dystrophy (DMD) is X-linked recessive. Het twins- one has the disease (normal X activated early in development) the other normal.

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17
Q

What is the purpose of Lyonization?

A

It equalizes the dose of X-linked alleles in males and females.

18
Q

Give an example of Lyonization in mammals.

A

The tortoiseshell cat- has patches of black and orange. Half of cells have orange allele inactivated the other half black allele.

19
Q

Define Cytogenetics

A

The study of chromosomes

20
Q

What is a Centromere?

A

The section where the chromosome attaches to the spindle during cell division. The centromere separate the chromosome into a short P arm and a long Q arm.

21
Q

Define the terms Metacentric, Acrocentric and Telocentric chromosomes.

A

Meta- centromere is at the centre of chromosome Aneu
Acro- centromere closer to one end
Telo- centromere near the very end

22
Q

What are the 7 classes of Chromosomal Rearrangement?

A

Deletion,

Duplication, Inversion, Translocation, Aneuploidy, Nondisjunction Polyploidization

23
Q

What is involved in a Deletion mutation

A

A deletion involves two breaks and a re-joining of DNA. Only the section of the chromosome containing the centromere survives.

24
Q

Give an example of a deletion.

A

Cri du Chat Syndrome- a deletion in chromosome 5p.

25
Q

How are Deletions used in mapping chromosomes?

A

They can be used to find out where the coded regions on a chromosome are. If deletion genotype produced wild phenotype then the deleted region is unlikely to be coding.

26
Q

What are the important features of Duplication?

A

They have increased the size of the genome, are responsible for Gene Families.

27
Q

Define the term Gene Family

A

Groups of adjacent genes with similar sequence and related function.

28
Q

What is the difference between a Tandem Duplication and a Reverse Duplication?

A

A Tandem = ABCD –> ABCBCD

A Reverse = ABCD –> ABCCBD

29
Q

How are Gene Families likely to have been formed?

A

By duplication of an original gene or short segment of chromosome a long time ago.

30
Q

Give an example of a Gene Family.

A

Globin gene family. A range of globin types present at distinct times in development as embryos demand for O2 changes. Alpha globin cluster on C16 and Beta globin cluster on C11.

31
Q

What is the cause of Tandem Duplication?

A

Unequal Crossing over during meiosis. Mispairing of regions causing uneven chiasma formation.

32
Q

Give an example of Tandem Duplication.

A

Bar Eye in Drosophila- on X chromosome, it reduces the number of facets on eye.

33
Q

Give an example of Tandem Duplication.

A

Huntington’s Disease- is due to an increase in the number of “CAG” repeats codes for glutamine.

34
Q

What is meant by a chromosomal Inversion?

A

A section of chromosome has been rotated and reinserted. ABCD –> ACBD. Involves two simultaneous breaks in two positions - rare occurrence.

35
Q

Why are Inversions known as Crossover Suppressors between inverted and non-inverted chromosomes?

A
  • mechanical strain of making the inversion loop

- crossing over may result in one section having two centromeres and the other having none.

36
Q

What is meant by a Translocation?

A

Where two non-homologous chromosomes exchange parts.

37
Q

How can Translocations cause problems?

A

When a person with translocation mates with a normal there will be unbalanced translocation during crossing over (excess of one C and shortage of another)

38
Q

Give two examples of Translocations

A

Chronic Myeloid Leukemia (C9-C22) and Burkitts Lymphoma (C8-C14)

39
Q

Define Position Effect Variegation.

A

A gene on euchromatin (coding) shifted by translocation next to heterochromatin (non-coding) causing a change in expression of the gene (inactivation)

40
Q

How did work on Drosophila describe PEV

A

Drosophila white eye gene usually recessive on X. Translocated to C4 adjacent to heterochromatin makes dominant red allele lose dominance. - red and white variegation in eyes.

GENETICS (7 decks)

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