Week 2 - Meiosis and Genetic Variation Flashcards
What are genes?
Specific locations on a chromosome/strand of DNA that code for a particular trait or traits
What is a locus?
A specific location where a gene is located on a certain chromosome
What are gametes?
Reproductive cells that pass on genetic information to their offspring
What are sister chromatids?
Two genetically identical chromosomes formed after DNA replication bound together by a centromere
How many chromosomes do humans have?
46
How many pairs of chromosomes do humans have?
23
How many chromosomes do we inherit from each parent?
23
When are chromosomes most condensed?
Metaphase
What is a karyotype?
The number, sizes, and shapes of the entire set of condensed chromosomes
What are some examples of staining methods for karyotyping?
Q, R, and G banding
What is G Banding?
A type of dying used in karyotyping. Most common in human cytogenetics.
Heterochromatin stains are dark compared to light staining euchromatin.
What is ploidy?
Refers to the number of chromosomes in a set. I.e. diploid = 2n, haploid = 1n, triploid = 3n
How many sets of chromosomes do human somatic cells contain?
2 (2n)
How many sets of chromosomes do human gamete cells contain?
1 (1n)
What’s the difference between homologous chromosomes and sister chromosomes?
Sister chromosomes are identical copies of a chromosome that is made after DNA replication
Homologus chromosomes are similar chromosomes that are genetically different, each inherited from a different parent.
What are three events that are unique to meiosis over mitosis?
1
Synapsis and crossing over in prophase 1
In metaphase 1, chromosomes are paired in
2 homologous pairs (tetrads), instead of individual replicated chromosomes
3
At anaphase 1, homologous chromosomes instead of sister chromosomes separate
Outline the steps in crossing over
After interphases, sister chromatids are held together by proteins called cohesion.
Each pair of homologs associated along their lengths
DNA molecules of two non-sister chromatids are broken at precisely corresponding points
The chromatin of the chromosomes begins to condense
A protein called synaptonemal completed forms and attached one homolog to the other
Each homolog swaps over and DNA from each homolog is swapped over
Chromosomes remain slightly attached and move towards the metaphase plate.
What three events during meiosis and fertilisation contribute to the genetic variety of offspring?
Crossing over
Independent assortment of maternal and paternal chromosomes
Random union of gametes
What is independent assortment? Why is it important?
The arrangement of homologus pairs during metaphase 1.
Occur randomly and have many possible arrangements, therefore there are many different possible gametes that can be produced, leading to great genetic variation.
