Semester 2 Week 2

Question 1

Why are X linked disorders more common in males?

Answer 1

X linked disorders are more common in males because for a recessive trait to be expressed, a female needs 2 copies of allele but males only need 1.

Question 2

Give an example of a gene that is on the Y chromosome.

Answer 2

One gene that’s on the Y chromosome is the SRY gene, which codes for the development of testes.

Absence of SRY gene leads to development of gonads into ovaries.

Question 3

What is Swyer syndrome?

Answer 3

Mutations in the SRY gene leads to XY females with gonadal dysgenesis. SRY gene is responsible for maleness, so if it’s inactivated then XY individuals will have female characteristics.

Question 4

What is genetic recombination?

Answer 4

Genetic recombination is the exchange of chromosomal fragments BETWEEN homologous chromosomes. This is normal

Question 5

What is translocation?

Answer 5

Translocation is the exchange of chromosomes between non-homologous chromosomes. This is abnormal.

Question 6

What is XX male syndrome?

Answer 6

Translocation of part of Y gene containing SRY gene to X chromosome. X chromosome carries male SRY gene, so females have male characteristics.

Question 7

What happens when one of the 2 X chromosomes is inactivated during embryonic development?

Answer 7

When 1 of the 2 X chromosomes is inactivated during embryonic development, the inactive X chromosome condenses into a Barr body, which lies in nuclear envelope.

Question 8

What is gene linkage?

Answer 8

Genes located near each other on the same chromosome tend to be inherited together are called linked genes.

Question 9

What is offspring that matches one of the parental phenotypes called?

Answer 9

Offspring that matches one of the parental phenotypes is called parental types.

Question 10

What is offspring with non-parental phenotypes called?

Answer 10

Offspring with non-parental phenotypes are called recombinant phenotypes.

Question 11

What is genetic recombination?

Answer 11

Genetic recombination is the crossing over of non-sister chromatids of homologous chromosomes during meiosis I.

Question 12

What is aneuploidy?

Answer 12

Aneuploidy is the presence of an abnormal chromosome number, caused from fertilisation of gametes in which nondisjunction occured.

Question 13

What is nondisjunction?

Answer 13

Nondisjunction is the abnormal separation of homologous chromosome pairs during meiosis I or sister chromatids during meiosis II.

Question 14

What is polyploidy?

Answer 14

Polyploidy is when an organism has more than 2 complete sets of chromosomes.

Triploidy (3n) is three sets of chromosomes

Tetraploidy (4n) is four sets of chromosomes.

Question 15

What are the 4 types of changes that can be caused by breakage of a chromosome?

Answer 15

The 4 types of changes caused by breakage of a chromosome are:
Deletion - removal of chromosome segment
Duplication - repetition of a segment
Inversion - reversal of a segment within a chromosome.
Translocation - exchange of segments between non-homologous chromosomes

Question 16

What is Trisomy 21?

Answer 16

Trisomy 21 is Down Syndrome

Question 17

What is Trisomy 18?

Answer 17

Trisomy 18 is Edwards Syndrome

Question 18

What is Trisomy 13?

Answer 18

Trisomy 13 is Patau Syndrome

Question 19

What is Klinefelter syndrome?

Answer 19

Klinefelter is when males have an extra X chromosome (XXY individuals). This causes males to have some female characteristics, such as gynecomastia.

Question 20

What is Turner Syndrome?

Answer 20

Turner Syndrome is when a female has a missing or incomplete X chromosome.

Question 21

What is Cri du Chat syndrome?

Answer 21

Cri du chat syndrome is when part of chromosome 5 is deleted. Children born with this syndrome are mentally retarded and have a cat-like cry. They usually die in early childhood.

Question 22

What is Genomic Imprinting?

Answer 22

Genomic imprinting is the silencing of either maternal or paternal genes (alleles) of certain genes at the beginning of development.

Question 23

How are genes silenced?

Answer 23

Genes are silenced by “stamping” them with an imprint (methylation - addition of CH3) during gamete production.

Question 24

What is Igf2?

Answer 24

Igf2 is a growth factor essential for embryonic/fetal development. It’s inactivated by methylation.

Question 25

What is Beckwith-Wiedemann Syndrome?

Answer 25

Beckwith-Wiedemann Syndrome is abnormal activation of the maternal Igf2 allele during egg formation/ early development. This increases risk of childhood cancer.

Question 26

What are extranuclear genes and why are they inherited maternally?

Answer 26

Extranuclear genes are genes found in organelles in the cytoplasm, such as mitochondria.

These genes come maternally because zygote’s cytoplasm comes from the egg.

Question 27

What do defects in mitochondrial genes cause?

Answer 27

Defects in mitochondrial genes prevent cells from making enough ATP and cause serious neuromuscular disorders such as mitochondrial myopathy (muscle deterioration) and Leber’s hereditary optic neuropathy (nerve deterioration).

Question 28

How can defects in mitochondrial genes be prevented?

Answer 28

Defects in mitochondrial genes can be prevented by ‘Three person IVF’. 2 eggs allow women with mitochondrial DNA disorders to have healthy children.