Genet 302 lec 51 & 52
What does metacentric mean?
The centromere is in the middle of the chromosome
What does acrocentric mean?
The centromere is toward one end of the chromosome
What does telocentric mean?
The centromere is at one end of the chromosome
What kind of inversion can change centromere location?
A pericentric inversion
Why can pericentric inversions change chromosome type?
Because they include the centromere and can move it relative to the chromosome ends
What other chromosome changes can convert telocentric and metacentric forms?
Translocations, chromosome fusions, and chromosome fissions
Why can mice have telocentric chromosomes while humans have metacentric chromosomes?
Chromosome rearrangements during evolution can shift centromere position and convert one chromosome type into another
What is the key difference between meiosis in spermatogenesis and oogenesis for chromosome competition?
In spermatogenesis all 4 meiotic products become sperm, but in oogenesis only 1 product becomes the egg and the others become polar bodies
Why does oogenesis allow chromosome evolution by meiotic drive?
Because only one chromosome arrangement gets into the egg, so biased transmission can be favored
In rodents, which chromosome type tends to win during oogenesis in the lecture model?
The telocentric chromosome
In primates, which chromosome type tends to win during oogenesis in the lecture model?
The metacentric chromosome
Why can some animals have telocentric chromosomes while others have metacentric chromosomes according to this lecture?
Different chromosome types can be favored during female meiosis in different lineages, driving karyotype evolution
Why are some human chromosome arms wider than others during mitosis?
Longer chromosome arms are wider
What correlation was emphasized for human chromosome arms?
Chromatid width increases with arm length
What staining method was used in the HeLa metaphase image for the width study?
Giemsa
Why do longer chromosome arms tend to be wider in the lecture model?
They take up more space in the interphase nucleus and are better at recruiting condensins
What proteins were emphasized as helping make longer chromosome arms wider?
Condensins
What is the main idea explaining differences in chromosome-arm width?
Arm length plus a species-specific factor helps determine arm width
Why do some mammals have many shorter chromosomes while others have fewer longer chromosomes?
Different lineages evolved different ways to pack chromosomes into the interphase nucleus
What chromosome pattern was emphasized for marsupials?
Relatively few long chromosomes
What chromosome pattern was emphasized for placental mammals?
Relatively many short chromosomes
What nuclear-organization strategy was emphasized for marsupials?
Centromere clustering
What nuclear-organization strategy was emphasized for placental mammals?
Chromosomal territories
Why might fewer longer chromosomes work well with centromere clustering?
Long chromosomes can be organized by clustering their centromeres together
Why might many shorter chromosomes work well with chromosomal territories?
Many short chromosomes are easier to keep in separate territories
What is the overall explanation for why elephants can have many shorter chromosomes while wallabies have fewer longer chromosomes?
Different mammalian lineages evolved different chromosome-packing strategies in the nucleus, favoring either many short chromosomes or fewer long chromosomes
How can human DNA and chromosomes be obtained for testing?
From preimplantation embryos, amniotic fluid, blood samples, or affected tissue samples
What is the first step of preimplantation genetic diagnosis?
In vitro fertilization
What 2 IVF methods were mentioned in this lecture?
Co-incubation of eggs and sperm and intracytoplasmic sperm injection
In PGD, what is removed from the embryo for testing?
One cell from an 8-cell morula
What is done after a cell is removed in PGD?
It is tested for mutation(s)
When are cells obtained in amniocentesis?
At about 15–20 weeks
What sample can provide either DNA or metaphase chromosomes directly?
A blood sample
What tissue samples are hard to obtain?
Neurons and heart cells
What tissue samples are easy to obtain?
Blood and skin