9.2 - Meiosis And Genetic Variation Flashcards
(28 cards)
Meiosis produces what?
Four daughter cells, each with half the number of chromosomes as the parent cell
Why do gametes not have a full set of chromosomes (diploid number) in meiosis?
If games had the full 46 chromosomes when they fused the cells of the offspring would have 92 chromosomes. So in order to maintain a constant number of chromosomes they must be halved at some point in the life cycle, this halving happens in meiosis
When does meiosis occur?
During the formation of gametes
What is non - disjunction?
Failure of a pair of chromosomes to separate during meiosis
Why does every diploid cell have 2 complete sets of chromosomes in meiosis?
One set from each parent
What happens to the homologous pair during meiosis
They separate so that only one chromosome from each pair enters a daughter cell - this in known as the haploid number of chromosomes which in humans in 23
Where are homologous chromosomes held together?
A bivalent crossing point of sister chromatids - chiasmata
Whats produces at the end of meiosis 2?
The chromosomes have segregates into chromatids producing 4 gametes
How many cell types are produced if recombination occur?
4 different cell types
What is a gene
A length of DNA that codes for a polypeptide
What is a allele?
One of a different form of a particular gene
Why does the independent assortment of the chromosomes produce new genetic combinations?
Although each chromosomes in the homologous pair has exactly the same genes and determines the same characteristic, the alleles differ
What happens if there is no recombination by crossing over?
Only 2 different types of cells are produced
What are homologus chromosomes?
A pair of chromosomes, one maternal and one paternal, that have the same genes loci
What happens during meiosis 1?
This is the first division, homologous chromosomes pair up and their chromatids wrap around each other. Equivalent portions of these chromatids may be exchanged in a process called crossing over. By the end of this division the homologous pairs have separated with one chromosome from each pair going into one of the 2 daughter cells
What is recombination?
The process of the broken off portions of chromatids recombining with another chromatid
What is mendel’s law of independent segregation?
When gametes are formed the separation of one pair of alleles into daughter cells is independent of the separation of another pair of alleles
Explain independent segregation of the homologous chromosomes?
During meiosis 1, each chromosome lines up alongside its homologous pair, randomly. One of each pair will pass to each daughter call - which one of the pairs and with which ones of any pairs depends on how the pairs are lined up in the parent cells is. Since the pair line up is random, the combination of chromosomes of maternal and paternal origin that go into the daughter cell at meiosis 1 is a matter of chance.
How many nuclear divisions occur in meiosis?
2 - which occur immediately one after the other
What happens during meiosis 2?
The chromosomes move apart. At the the end of meiosis 2, 4 cells have been formed. In humans these each contain 23 chromosomes
Why cant the same parents produce multiple offspring with variety?
As each gamete has a different make up. There random fusion produce variety
How do the haploid gametes restore their diploid state?
During fertilisation - they fuse randomly
What is produced at the end of meiosis 1?
The homologous pair has segregated into 2 separate cells
What is a locus?
The position of a gene on a chromosome or DNA molecule
