ineritance patterns2 Flashcards
what are the rules of mendelian genetics
Alleles are dominant, recessive or codominant
Each gene has two alleles that segregate during meiosis
independent assortjent
Determine the genotypes and phenotypes of the offspring of two parents with blood group A and nail patella syndrome (NPS). The parents are heterozygous at both loci and the allele for NPS is dominant.
what’s the difference between x and y chromosome
y chromosome is the shortest chromosome
- 50 mil base pairs
- contains 70-300 genes
x chromosome,e is larger
155 mil base pairs
contains 1200 genes
why does complete synapsis not occur in prophase 1
structural differences between the x and y chromosomes
what is synapsis
pairing/mathcing of two homologous chromosomes that occurs in propahse 1 in meiosis
occurs before chromosomes are segregated and before crossing over occurs
what are pseudo autosmal regions
homologous regions of the x and y chromosomes
where can synapsis and crossing over occur
between pars located on the sex chromosomes
inheritenve of alleles at loci within pars follow mendelian inheritence
whare are the genes that are locatde outisde of pars
they are sex linked
majorit of sex linked genes are x linked
SRY
sex determining region
found only on y chromosome
is a transcription factor
- stimulates a translation cascade whch results in the expression of others trans factors
- these trans factors trigger the expression of genes that code for men
expression of sry - causes development of seminiferous tubules in th testes
and supresses development of female anatomy
what are the differences on the x chromosome for men and women
Females have two alleles of each gene on the two Xs
Female inheritance of genes on the X is the same as for autosomes
Males have only one copy of most genes on the X - hemixygous but some of the y overlaps
mary lyon hypothesis
FEMALES HAVE 2 Xs BUT HAVE THE SAME NUMBER OF X LINKED PROTEINS AS MALES
states that one copy is inactivated in every cell of the female body - leads to dosage compensation
some cells have inactive maternal x but othrs have inactive paternal x
these is no x inactivation in men
what are barr bodies
inactivated x chromatin
how do barr bodies upport he lyon hypothesis
Inactive X is highly condensed
Barr body number is Xs minus one
XX females have one (i.e. 2X-1X= 1)
XY males have none
X females (Turner’s) have none as have only one X chromosome
XXY males (Klinefelter’s) have one
when and how does x inactivation occur
occurs 7-10 days after fertilisation
when the inner cell mass is just a few dozen cells
occurs randomly in cells and is permanant
why does varitation in disease severity occut in females with the same disorder
number of inactivated paternal and maternal x chromosomes
x linked dominnat inheritence
no father to son transmission
daughters of affected fathers must be affected
heterozygous females have 50% transmission to both sons and daughters
doesnt skip generations
charecteristics of x linked recessive inheritence
no father to son transmission
affected female homozygotes are rare
penetrance variability menas heterozygous females maybe ne affected
traits may skip gens through female carriers
y linked inheritence
only father to son transmission
ALL sons must be affected
no daugthers are affectdee
present in ALL generations
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