L-15 Flashcards by Lucy Fenton

What is Down syndrome represented by in a karyotype

3rd copy of 21st chromosome

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What is Aneuploidy? Give an example

To possess an abnormal amount of a particular chromosome

Down syndrome

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How common is Down syndrome?

Occurs in 1/750 live births

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What is the risk factor for down syndrome? What are the stats to back this up?

maternal age

- 40% of cases occur when mothers are older than 45

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What causes Down syndrome? Which version of this is more common

nondisjunction during meiosis

- 95% of cases have 2 maternal chromosomes (2nd division)

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What is nondisjuction?

Failure of chromosomes to separate properly during meiosis

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What is Klinefelter syndrome?

Genetic condition where male has an extra X chromosome (XXY)

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What are the symptoms of Klinefelter syndrome?

infertility
small poorly functioning testicles

In worse cases:

weaker muscles
greater height
less body hair
breast growth
lower libido

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How common in Klinefelter syndrome?

Occurs in 1-2/1000 live male births

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Is Klinefelter syndrome more likely to be a result of maternal or paternal nondisjuction?

Neither is more likely

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What is Turner syndrome?

Genetic condition where females may be partially of fully missing a sex chromosome (XO)

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What are the symptoms of Turner syndrome?

skin folds around neck
intellectual impairment
infertility
individuals do not naturally develop breasts of a menstrual cycle

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How common is Turner syndrome?

1/2000-5000 live female births

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What is polyploidy?

Possession of multiple sets of chromosomes

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What is polyploidy caused by?

Meitotic error resulting in unreduced gametes with the 2n number of chromosomes

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What can self-fertilisation of polyploids lead to?

An auto plaid zygote with the 4n number of chromosomes

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Can offspring with polyploid karyotypes be variable?

Yes in plants

What is an example of polyploidy in animals ?

Triploid pathogenic lizard- New Mexico Whiptail

How are offspring of the New Mexico Whiptail produced?

Asexually

- New indivuals produced by mating of parent species in a process that prevents the formation of healthy males

What can other chromosomal abnormalities be caused by?

deletions
inversions
duplications
translocations

What is a deletion mutation?

Removal of a chromosomal segment

What is an inversion mutation?

Reversal of a segment within a chromosome

What is a duplication mutation?

A repeat of a segment within a chromosome

What is a translocation mutation?

Moving a segment from one chromosome to another nonhomologous chromosome

What is cri du chat syndrome?

Genetic condition caused by the deletion of the tip of the short arm of chromosome 5

What are the symptoms of cri du chat syndrome?

- severe intellectual imparement - most offspring wont reach adulthood - problems with larynx + nervous system give affected infants a meow like cry

What is the Philadelphia translocation?

A segment of chromosome 9 is translocated onto chromosome 22 and a segment of chromosome 22 is translocated onto chromosome 9

What does the Philadelphia translocation cause?/ what condition is the Philadelphia translocation highly correlated with?

95% of patients with chronic myeloid leukaemia have the Philadelphia translocation

What is familial Down syndrome also known as?

Translocation down syndrome

What percentage of recorded Down syndrome cases do familial Down syndrome patients make up?

4.5%

What is the cause of familial Down syndrome?

- robertsonian translocation | - long arm of chromosome 21 is attached to chromosome 14

What is the phenotype of an individual with the robertsonian translocation?

Normal but act as carrier

How many possible zygotes are formed from mating of an individual with the robertsonian translocation with a normal individual? Name their associated phenotypes

- 6 - 3 lethal - 1 Down syndrome - 1 normal - 1 carrier

What is the change of an offspring having familial Down syndrome when the mother has the robertsonian translocation? Father?

- 15% | - >5%

What is a Barr body?

Visible dense region in the nucleus which is a condensed and inactivation X chromosome

What is the name for the process of X inactivation?

Lyonisation

What genotypes will have a Barr body?

- XX - XXY - XXX

What genotypes will not have a Barr body?

- XY - XO - XYY

Why can women with the genotype XXX live near normal lives and have limited symptoms

They will have 2 Barr bodies so the genetic material is not interfering with each other

What is a visible example of mosaic lyonisation?

Fur colour in cats

What is a condition in women effected by lyonisation? How?

- anhidrotic ectodermal dysplasia ( no sweat glands) - If only present in one X chromosome then random inactivation in early cells will lead to mosaic patterning of skin with and without sweat glands

Why does lyonisation not affect all X linked genetic conditions?

gene products can travel around the body and have effects everywhere