Sex and Meiosis Flashcards
Which cells would be described as haploid?
the basic number of chromosomes found in gametes is referred to as haploid
What are referred to as diploid cells?
the somatic cells which contain TWO copies of each chromosome
How many different stages of meiosis are there? and what are they?
There is one round of chromatid replication followed by two successive divisions
Explain the 1st division phase of meiosis.
a reduction division which halves the chromosome number
Explain the 2nd division phase of meiosis
an equational division which halves the number of chromatids per chomosome
What happens during Meiosis 1: Prophase?
chromatin condenses, chromosomes pair up with their homologues and crossing over may occur
chromatids break and rejoin over the synaptonemal complex.
What happens during Meiosis 1: Metaphase?
The chromosome pairs are lined up on the central plane of the cell
What happens during Meiosis 1: Anaphase?
The spindle microtubules pull the homologues apart
What happens during Meiosis 1: Telophase?
the original diploid cell is now two haploid nuclei, chromosomes still have 2 chromatids
What are chiasmata?
Points of crossover
What happens during Meiosis 2: Metaphase?
the chromosomes are aligned at the central plane of the cell by the spindle microtubules
What happens during Meiosis 2: Anaphase?
sister chromatids are segregated, they are not always identical as crossing over may have occurred. Note that after this, the ploidy has not changed but there is now only one chromatid per chromosome.
What happens during Meiosis 2: Telophase?
The nuclear envelope reforms and the chromatin decondenses.
What is Mendel’s Law of Segregation?
when an organism forms gametes, only one of a pair of alleles enters each gamete
What is Mendel’s Law of Independent Assortment?
During the formation of gametes, the alleles of one gene segregate from each other independently of those for another gene.
Explain crossing over
Crossing over breaks linkage, without it there would be no variation in the offspring.
It depends on the distance between linked genes, the further apart, the more likely they are to cross over
What is it called when the two sexes of an organism have different chromosome compliments?
Karyotypes
What are autosomes?
If most of the chromosomes occur in pairs and are physically indistinguishable from their partners.
What does hymeroptera mean?
No sex chromosomes, fertilised egg = female, unfertilised egg = male
What does sex linked refer to?
The other genes on the sex chromosomes are said to be sex linked and show unusual patterns of inheritance.
