Human Genetics 4 & 5 Flashcards
Describe crossing over
- During Prophase 1: crossing over of non-sister chromatids
- Exchange genetic material
- Pairing structure of homologous chromosome:
- Tetrad (4 chromatids) = synapsis- bivalent
Define chiasmata
points of crossing over
describe independent assortment
in anaphase 1 and 2, either homologous chromosome or either cromatid drawn to different poles at random
which gametes are motile
sperm
what are the names of the male and female sex cells
o male = spermatozoa
female = ova
what are chromosomes ordered by in karyotypes
- length and location
of centromer
female male karyotypes
Female karyotype: 46, XX
Male karyotype: 46, XY
cause is the cause of numerical chromosome aberrations
: failure of segregation= non disjunction (in meiosis I or II)
what occurs at normal segregation
- Homologous chromosomes get ‘separated’ = drawn to different poles in anaphase I
- Sister chromatids get separated= drawn to different poles in anaphase II
define aneuploidy
abnormal number of individual chromosomes in a cell
what trisomy and what ones are possible for humans
extra chromo
13 18 21
what are four non disjunction syndrome for sex chromosomes
- Monosomy X (Turner Syndrome)
- Trisomy X- Triple X syndrome
- Klinefelter Syndrome
- 47 XYY males
describe features of Turner syndrome
- Karyotype 45X
- Only viable monosomy (missing one chromosome) in humans
- Genetically female
describe features of triple x syndrome
- 47 XXX female
- ## Healthy and fertilePhenotypically normal
describe features of klinefelter
• 47 XXY
• Breast enlargement, other feminine characteristics
• Unusually small testes
- male
describe features of 47 XYY males
- Nondisjunction in second meiotic division (of father)
* Phenotypically normal but taller than average
describe sex determination in mammal embryos
- Humans: f/m embryos phenotypically identical till 7th week
Sexual differentiation when sex determining region on y chromosome directs bipotential gonad to turn into testes not ovaries
• Differentiation and dimorphism arises from circulation of sex steroid
• Absence of Y chromosome the embryo will develop female characteristics
describe the compensation mechanism for x chromosome inactivatation
- Inactivation of one X chromosome (16 days post fertilization by packaging heterochromatin
- Becomes silenced = transcriptionally inactive)
- Inactive= Barr bodies
- All descendent cells keep same inactive X
what are 3 non disjunction syndrome for autosomes chromosomes
Patau syndrome (c13)
Edwards syndrome (trisomy 18)
• Down Syndrome (trisomy 21)
describe Patau syndrome (c13)
- Karyotype 47, +13
- Trisomy of 13: extra copy
- Severe disabilities
describe Edwards syndrome (trisomy 18)
- Karyotype: 47, +18
- Trisomy 18
- Lethal
describe Down Syndrome (trisomy 21)
Karyotype: 47, 21+
• Altered phenotype
describe the age effect of trisomy 21
- Highly correlated with age of mother
- Risk associated with delay in competition of prophase I in female gametes
- Paternal age important too (1/4 cases originate from paternal non disjunction)
describe polyploidy
Presence of two or more complete sets of chromosomes (tetraploids 4n)
• Often due to duplication of the genome without subsequent mitosis/cell division
what can cause polyploidy in humans
- Dispermic fertilization of the egg
1. Failure to extrude one polar body from the oocyte
what are symptoms of inborn errors of metabolism due to
- Accumulation of substrate (e.g. alkaptonuria)
- Deficiency of product (e.g. albinism)
- Disturbance of related pathways (e.g. PKU)
