Basic Genetics Flashcards
Number of autosomes in somatic cells
22 pairs = 44
Number of sex chromosomes in somatic cells
1 pair = 2 (XX or XY)
Normal chromosome complement is known as- ?
Diploid
Genomes with a single copy of each chromosome are known as-?
OR
Half of full set of genetic material in the gamete (egg/sperm) -?
OR
Single set of chromosomes in the gamete (egg/sperm) -?
Haploid
Three copies of each chromosome are known as-?
Triploid
A karyotype with too many or too few chromosomes + total is NOT multiple of 23 >> is known as-?
Aneuploid
What does divide chromosome into long arm & short arm?
Centromere
Short arm symbol
p (= petit)
Long arm symbol
q
If centromeres are located at one end, the chromosomes are known as-?
Acrocentric chromosomes
What are the acrocentric chromosomes?
13, 14, 15, 21, 22
If a cell contains more than one X chromosome, but only one is active >> known as -?
Lyonisation
In lyonisation, which X is selected as active?
Random selection
In lyonisation, inactivated X chromosome is seen as-?
Barr body on microscopy
A region of DNA that encodes protein
Gene
Complete set of gene of an organism + the intervening DNA sequences
Genome
Site of a gene/particular DNA region in a chromosome
Locus
Self replicating genetic structure of cells containing the cellular DNA that bears the linear array of genes in its nucleotide sequence
Chromosome
Alternative form of gene found at the same locus on a chromosome >> known as-?
Alleles
Sequence of amino acid-known as?
Codon
Number and appearence of chromosome in the nucleus
Karyotype
Karyotype of a normal person
46 XY or 46XX
Any chromosome other than sex chromosome
Autosome
Diploid to diploid cell division
= mother diploid cell to daughter diploid cells
Nuclear chromosomes are genetically identical both to each other & to the original parent cell
Mitosis
Diploid to haploid cell division
= Diploid mother cells to haploid daughter cells
= Nuclear chromosome in daughter cells are half than the mother cells & genetically different from each other
Meiosis
Another name of meiosis
Reduction division
Where does Meiosis occur?
Germ cells of the gonads
Number of produced cells and chromosomes in Meiosis
4 haploid daughter cells, each containing one set of chromosome pair
Division of Meiosis
Meiosis I and meiosis II
When are the chromosomes reduced in number? Meiosis I or Meisosis II?
Meiosis I
Exchange of chromosome segments between homologous chromosomes - is called?
Crossing over
When does Crossing over occur? in Meiosis I or Meiosis II?
In Meiosis I, before chromosomes are reduced in number
All four daughter cells are genetically identical to each other or different?
Different to each other
Why are all 4 haploid daughter cells in Meiosis genetically different to each other?
Due to recombination from crossing-over during meiosis I
Time of onset of meiosis in male
Meiosis and spermatogenesis both start at puberty
Time of onset of meiosis in female
Meiosis (replication of the chromosomes and crossing over) starts in foetal life
Oocytes remain suspended before the first cell division, until just before ovulation
Exchange of genetic material between non-homologous chromosomes- is called?
Reciprocal translocation
Fusion of two acrocentric chromocomes at their centromeres- is called?
Robertsonian translocation
If no chromosomal material has been lost or gained overall- is called?
Balanced translocation
If chromosomal material has been lost or gained overall- is called?
Unbalanced translocation
Common sex chromosome aneuploidies
Turner syndrome (45, XO)
Triple X syndrome (47, XXX)
Klinefelter syndrome (47, XXY)
47XYY males
Common autosomal chromosome aneuploidies
Down syndrome (trisomy 21)
Edward syndrome (trisomy 18)
Patau syndrome (trisomy 13)
(These 3 are also example of non-dysjunction/trisomies)
(These 3 aneuploides are compatible of life)
(21, 18, 13 are the least gene-rich chromosomes)
Trisomy vs monosomy in autosomal chromosome aneuploidy
Trisomy is well tolerated than monosomy
3 trisomies are there which are compatible with life, but no whole autosome monosomies are compatible with life
Why are trisomies 21, 18, 13 compatible with life?
Because chromosome 21, 18, 13 are 3 least gene rich chromosomes
Common Microdeletion syndromes
DiGeorge syndrome
Williams syndrome
What are the Mendelian inheritances?
Autosomal dominant
Autosomal recessive
X-linked dominant
X-linked recessive
For most genes, both copies (maternal/paternal) are expressed.
But for some genes, either the maternal or paternal copy is used- this phenomenon is known as?
Genomic imprinting
Common examples of genomic imprinting
The most commons:
Prader Willi syndrome
Angelman syndrome
Other commons:
Albright’s hereditary osteodystrophy
Beckwith-Wiedemann syndrome
Russell-Silver syndrome
Familial paraganglioma
