T3L4 - Inheritance and Genetic Disorder Flashcards
Sexual reproduction
Beneficial combinations of genes to come together
Deleterious combinations of genes to be removed
Genetic diversity
Genetic variation via
- Mutation (errors in DNA replication and repair)
Diploid cells (inherit one set of chromosomes from each parent)
Homologous recombination (HR) between chromosomes during meiosis
Meiosis I
Prophase
Metaphase
Anaphase
Telophase
Meiosis I - Prophase
Early Prophase - Chromatin begins to condense following interphase
Mid Prophase - Synapsis aligns homologs and chromosomes condense more
Late Prophase I - Promometaphase - Chromosomes coil and shorten. Crossing over and nuclear envelope breaks down.
Meiosis I - Metaphase
Homologous pairs line up on equatorial metaphase plate
Meiosis I - Anaphase
Homologous chromosomes each with 2 chromatids move to opposite pole
Meiosis I - Telophase
Chromosome gather into nuclei and cell divides
Meiosis II
Prophase - condense
Metaphase - Centrosome of paired chromatids line up at equator plate of each cell
Anaphase - Chromatids finally separate and pulled to opposite poles
Telophase
Homologous recombination
Occurs during long prophase of meiosis I
2-3 crossover events/chromosome/meiosis
Highly similar DNA sequence binds to complementary sequence on homologous chromosome
Non fatal trisomy
21, 13 or 18
Trisomy 21
Down's syndrome 1 in 750 live births Non-specific effects Mental retardation Broad flat face, slanting eyes Congenital heart disease Intestinal blockage Enlarged colon
Trisomy 13
Patau’s Syndrome
Trisomy 18
Edward’s Syndrome
Monsomy: Turner’s
- Female
- Pubertal failure
- Infertile
- Normal intelligence
- May have:
- neck webbing, heart defects and horseshoe kidneys
Monosomy fatal except X chromosome
Sex chrome syndromes
• XXY: Klinefelter syndrome (male, reduced fertility, lower IQ) May go undiagnosed
• XXX: undiagnosed
XYY: undiagnosed
Sickle cell disease: Heterozygous advantage
Autosomal Incomplete Recessive SCD
Sickle cell disease common in African/Caribbean families
SCD carriers more resistant to malaria
Positive selection for HbS allele in malaria endemic areas
Malaria parasites unable to replicate as well inside heterozygote (carrier) red blood cells…therefore SCD allele retained in the population
X-linked recessive disease: Haemophilia A
Blood clots slowly: Bleeding, Easy bruising, Joint and muscle haemorrhages & Problem after surgery or trauma
Lack of blood clotting factor VIII
X-linked recessive trait: Deletions or inversions in F8 gene & Resulting in loss of function
Other X-linked recessive disorders
Duchenne muscular dystrophy
Red-green colour-blindness