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Midterm 3: Meiosis learning objectives
Terms in this set (34)
trace individual chromosomes from parent cells to gametes through the process of
Process of gamete (reproductive cell: sperm and eggs) formation
How many chromosomes do gamete cells have relative to "parent" cells?
Half as much (22 autosomal and 1 sex)
The process of 2 gametes coming together to restore the full chromosome number (46), results in a new unique organism
Different versions of a specific gene
Can homologous chromosomes carry different versions of genes?
Yes, homologs are just a pair of the same type of chromosomes but not identical chromosomes. (EX: two 22 chromosomes, one from each parent)
Identifies number and types of chromosomes present in a species
Two alleles of each gene (can be same or different EX: RR)
One allele for each gene (EX: R)
What is the haploid number (n) for humans?
What is the diploid number (2n) for humans?
How many cell divisions occur in meiosis?
Two. Meiosis I and Meiosis II.
What occurs during meiosis I?
Two homologs of each chromosome pair separate into two daughter cells. Each daughter cell has one set of chromosomes. Diploid parents produce two haploid daughter cells.
What occurs during meiosis II?
Sister chromatids for each chromosome separate into two daughter cells. Each of the daughter cells from meiosis I divide, resulting in four haploid cells.
Describe what happens meiosis.
A diploid parent cell replicates into two diploid daughter cells and then divides into two four haploid cells. These four haploid cells can develop into four gametes through a process called gametogenesis.
What is a zygote?
A fertilized diploid cell
What is a paternal chromosome?
A chromosome coming from a father's haploid cell.
What is a maternal chromosome?
A chromosome coming from a mother's haploid cell.
If an organism has three or more versions of each type of chromosome, what is it referred to as?
What does a cell's ploidy indicate?
The number of complete chromosome sets it contains
When replication is complete, how many identical sister chromatids does each chromosome have?
What are non-sister chromatids?
Chromatids belonging to homologs
Contrast mitosis and meiosis
Mitosis produces two diploid daughter cells that are genetically identical to the parent cells. Meiosis produces four haploid gamete daughter cells that are genetically unique from each other and from the parent cell.
Compare mitosis and meiosis
Both start as diploid cells and then their DNA condenses in order to replicate
What is "crossing over"?
Sections of the maternal and paternal DNA are randomly exchanged between their homologs producing unique chromosomal combinations.
In what phase does crossing over occur?
Late Prophase 1
What is the principle of independent assortment?
The random separation of homologous chromosomes during meiosis 1 can result in a variety of combinations of maternal and paternal chromosomes. (Possible combinations 2^n EX: Humans N=23 so 2^23= 8*10^6)
Describe what happens in Meiosis 1
Meiosis 1 results in two daughter cells with only one chromosome of each homologous pair. They are haploid but still contain replicated chromosomes.
How does Meiosis promote genetic variation?
Meiosis results in four gametes all with unique chromosome compositions. These variations are caused by the independent assortment of maternal and paternal chromosomes and crossing over during meiosis 1.
Does fertilization introduce variations? If so, how?
Yes because fertilization combines a unique sperm cell and a unique egg to create a unique offspring.
Describe what happens in Meiosis 2
Each of the two daughter cells from meiosis 1 divides which results in four haploid daughter cells that are all genetically distinct from each other and the parent cells.
How is DNA altered?
DNA is altered by crossing over and independent assortment.
How is DNA organized?
How is DNA divided to form haploid gametes from diploid parent cells
In meiosis 1 the diploid parent cell is divided into two haploid cells by spindle apparatus attaching to the chromosomes then pulling them apart. These haploid cells divide into four genetically different daughter cells
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