Topic 2 - Chromosomal Basis of Inheritance

SRY gene

Helps with the development of testes

if the SRY gene is not present than ovaries will be developed

abnormalities → XY females and XX males

Name Y-linked genetic disorders

1. Swyer Syndrome

2. XX male Syndrome

Swyer Syndrome

XY gonadal dysgenesis (XY females)

mutation in the SRY gene

so basically we have, male individuals with female characteristics

XX male syndrome

This is caused by the translocation of part of the Y chromosome

the SRY gene is on the X chromosome

basically we have females with male characteristics

What is Translocation?

it’s the exchange of chromosomal fragments between non-homologous chromosomes

Mammalian Females

XX

one of the two X chromosomes is inactivated during embryotic development and condenses into Barr body

Aneuploidy

Abnormal chromosome number

Polyploidy

More than 2 complete sets of chromosomes

Autosomal Trisomies

Trisomy 21 - Down Syndrome

Trisomy 18 - Edward’s Syndrome

Trisomy 13 - Patau Syndrome

Aneuploidy Conditions

1. Klinefelter Syndrome (XXY)

2. Turner’s Syndrome (XO)

Klinefelter Syndrome

Males with females characteristics (i.e gynecomastia)

What do Structurally Altered Chromosomes cause?

1. Cri du chat syndrome

2. Certain cancers

Cri du chat syndrome

Deletion at chromosome 5

Certain cancers

Chronic myelogenous leukemia (CML)

Reciprocal translocation (exchange of fragments between non-homologous chromosomes

Genomic imprinting

Only affects a small fraction of mammalian genes (1%) - mammalian genes : imprinted genes critical for embryotic development

It is the silencing of the maternal or paternal allele

Beckwith - Wiedemann Syndrome (BWS) and symptoms

Abnormal activation of maternal IgF2 allele

symptom : overgrowth, increased risk of childhood cancer

Mitochondrial Disorders

1. Mitochondrial Myopathy

2. Leber’s hereditary optic neuropathy

Homozygous Woman and an Affected Male

Female children : heterozygous

Male children : normal

Heterozygous Woman and a Normal Male

Female children : 50% normal, 50% heterozygous

Male children : 50% normal, 50% affected

Heterozygous Woman and Affected Man

Female children : 50% female, 50% affected

Male children : 50% normal, 50% AFFECTED

Completely Linked Genes

→ Relative Position

→ RF

Position : same chromosome (very close)

RF : 0%

Incompletely Linked Genes

→ Relative Position

→ RF

Position : same chromosome (distance between them)

RF : 0<RF<50%

Physically Linked but Genetically Unlinked Genes

→ Relative Position

→ RF

Position : same chromosome (far away)

RF : close to 50%

Unlinked Genes

→ Relative Position

→ RF

Position : different chromosomes

RF : 50%