9.1 Flashcards
Why has meiosis evolved (importance of meiosis)? (2)
(1) To maintain a constant number of chromosomes in adults of a species
(2) Without meiosis, the chromosome number would double in each generation.
What occurs during the first meiotic division (meiosis I)? And what does it lead to? (2+1)
(1) Homologous chromosomes pair up…
(2) and may exchange equivalent portions through crossing over
(3) This exchange increases genetic variation.
What are the two ways meiosis increases genetic variation? (2)
(1) Independent segregation of homologous chromosomes
(2) Recombination of homologous chromosomes by crossing over
What are homologous pairs? (2)
(1) Pairs of chromosomes that… carry the same genes…
(2) but may have different alleles
What process produces new genetic combinations during meiosis l? What is this process? (2)
(1) Independent segregation of chromosomes
(2) This process is when homologous chromosomes line up randomly.
How many different combinations of alleles can be produced from independent segregation? How do you calculate that? (2)
(1) Over 8 million different combinations
(2) This is due to the 2^23 combinations possible from the 23 pairs of chromosomes.
Explain the significance of the random arrangement of homologous chromosomes during meiosis. (2)
(1) It leads to genetic variation in gametes
(2) The random distribution of chromosomes results in different combinations of alleles in offspring.
What is an allele? (1)
different forms of the same gene
Define locus in genetics. (1)
The position of a gene on a chromosome or DNA molecule
What occurs in meiosis 1? What does it lead to? (2)
(1) Homologous chromosomes segregate into two separate cells AFTER being duplicated
(2) This reduces the chromosome number by half, preparing for gamete formation.
What occurs during meiosis 2? (2)
(1) Sister chromatids are separated into different cells
(2) This results in the formation of four gametes from each original cell.
How does independent assortment contribute to genetic diversity? (1)
(1) By allowing different combinations of alleles to be passed to each gamete
Describe the process of genetic recombination by crossing over in meiosis. (3)
(1) chromatids of each pair become twisted around each other
(2) during the twisting, tensions are created & equivalent portions of the chromatids break off
(3) these broken portions may then rejoin or exchange with the chromatids of their homologous partner
Why is the process called recombonation? (1)
(1) because broken off portions of chromatids recombine with another chromatid
What happens if NO recombination occurs? What happens if recombonation occurs? (1+2)
(1) NO recom. : only 2 different TYPES of cells are produced
(2) recom. : 4 different TYPES of cells are produced…
(3) Each w different allele combinations
