The Chromosomal Basis of Inherit Flashcards
How do scientists tag the location of isolated chromosomes?
Fluorescence in situ hybridization (FISH)
An organisms life cycle
The sequence of stages leading from the adults of one generation to the adults of the next
Why do our chromosomes duplicate?
Sorts new sets of chromosomes into the resulting pair of daughter cells, for reproduction of single-felled organisms, for growth of multicellular organisms from a fertilized egg into an adult, to repair and replace cells, and for sperm/egg production
How many divisions are in Meiosis?
Two sequential divisions
What are the three mechanisms that contribute to genetic variation?
Random fertilization (eg. many sperm competing to fertilize egg), independent assortment of chromosomes, and crossing over
Independent assortment
Homologous pairs of chromosomes orient randomly at metaphase 1 of meiosis. Each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently of the other pairs
What does 2^n stand for?
The number of combinations possible when chromosomes assort independently into gametes (n stands for the haploid number)
Who discovered the first evidence of chromosomal basis for inheritance?
Thomas Hunt Morgan in his fruit fly study - noted wild type and mutant traits - reasoned that the white-eyed mutant allele must be located on the X chromosome due to how it was inherited by only male flies in the second generation
Why use flies?
They produce many offspring, a generation can be bred every two weeks and they have only four pairs of chromosomes
Sex chromosomes
Designated X and Y, determines an individuals sex
What are the four other main types of sex determination
The X-0 system: only have one toe if sex chromosome
The Z-W system: females produce eggs that are either Z or W with males gametes being Z (reversed relative to humans)
The haplo-diploid system: no sex chromosomes, instead, females develop from fertilized eggs while males develop from unfertilized eggs
Environmental temperature: temperature determines the sex of the embryo - males develop in colder temperatures while females develop in warmer temperatures
Sex-linked genes
Located on either of the sex chromosomes - the X chromosome Carrie’s many genes unrelated to sex
Is colorblindness an X-linked recessive trait?
True - all daughters will receive a color blindness allele form their colorblind father making them carriers, sons have a 50% chance of receiving the colorblind allele form their mother (50% chance of being colorblind), and only a daughter born to parents who both carry the color blindness allele could be colorblind
Hemophilia
The Royal Disease - characterized by excessive bleeding because hemophiliacs lack one or more of the proteins required for blood clotting
What does the Y chromosome provide clues about?
Human male evolution - Y chromosomes are passed intact from father to son
Do females make twice as much as males of the products encoded in the X chromosome?
No - one of the X chromosomes is inactivated
Germline tissue
Produces gametes - expresses both X chromosomes
Somatic tissue
Found in females, looks like a mosaic, some express maternal X chromosome and others express the paternal X chromosome
When one of the two X chromosomes in each cell is randomly inactivated during embryonic development is condenses into what?
A Barr body
What triggers the inactivation?
X-inactive specific transcription (XIST) - XIST mRNA covers the chromosome, chromosomal DNA then has methyl groups attached to it to inactivate it
Linked genes
Located close together in the same chromosome, tend to be inherited together, and do not follow Mendel’s law or independent assortment
What produces new combinations of alleles?
Crossing over between homologous chromosomes produces new combinations of alleles in gametes
Recombination frequency
The percentage of recombinant offspring
Map units
Distance between genes as equivalent to a 1% recombination frequency
