Unit 3 Chapter 12: Meiosis Flashcards
What must happen before sexual reproduction
homologs must be reduced by half
What is fertilization
when and egg and sperm unite
What is meosis
- sexual reproduction
- a reduction division
- nuclear division that leads to halving the chromosome number
- precedes the formation of eggs and sperm in animals
What are autosomes
chromosomes that are not x/y sex chromosomes
What are homologous chromosomes (homologs)
- 2 chromosomes of the same type
- carry the same genes but each may have different alleles
What is a gene
a section of DNA that influences some hereditary trait in an individual
What is a trait
a characteristic
What is an allele
different versions of the same gene
What does diploid mean
2 copies of each chromosome ie. human body cells
What does haploid mean
1 copy of each chromosome ie. human gametes
How does the ploidy of meiosis work
after meiosis 1: diploid parent cell makes 2 haploid daughter cells (each chromosome is replicated though ie. 2 sister chromatids)
after meiosis 2: 4 haploid cells produced (each chromosome in unreplicated though)
What is a zygote
diploid cell produced from fusion of 2 haploid gametes
What is meiosis 1
- begins after chromosomes have been replicated during S phase
- interphase
- early prophase 1
- late prophase 1
- metaphase 1
- anaphase 1
- telophase/cytokinesis 1
What is synapsis
-occurs during early prophase 1, homologous chromosome pairs come together forming tetrads
What are tetrads
- form from synapsis
- 2 homologous chromosomes which each has 2 sister chromatids
What is crossing over
- occurs during late prophase 1
- when paternal and maternal chromatids break and rejoin at each chiasma (x shaped structure) producing chromatids that have a mix of maternal and paternal segments
What happens during early prophase 1
- replicated chromosomes condense
- spindle forms and nuclear envelope disappears
- synapsis of homologs forms tetrads
- kinetochore microtubules attach to kinetochores
What happens during late prophase 1
-crossing over
What happens during metaphase 1
tetrads line up at metaphase plate
What happens during anaphase 1
homologs separate and move to opposite poles
What happens in telophase 1
homologs finish moving to poles, sometimes nuclear envelope reappears, cell divides
What happens during prophase 2
-spindle forms (kinetochore microtubules attach to each side of every chromosome-one per sister chromatid)
What happens during metaphase 2
-replicated chromosomes line up at metaphase plate
What happens during anaphase 2
-sister chromatids separate, and unreplicated chromosomes move to poles of the cell
What happens in telophase 2
- chromosomes finish moving to opposite poles
- nuclear envelope reforms
What is the synaptonemal complex
a network of proteins that hold 2 pairs of non-sister chromatids together
When do most mitotic divisions in plants occur
after meiosis 2
What is the principle of independent assortment
when pairs of homologs line up in meiosis 1 and the separate, a variety of combinations of maternal and paternal chromosomes can result
How do you determine how many combinations of maternal and paternal chromosomes are distributed to daughter cells
2^n where n=number of chromosomes
What is recombination
any change in the combination of alleles on a given chromosome
-ie. crossing over produces combination that were not present in either parent
What is trisomy
3 copies of a chromosome, ie. down syndrome
What is nondisjunction
if both homologs or sister chromatids move to the same pole of the cell during meiosis
What is Klinefelter syndrome
XXY in males
What is Turner syndrome
XO females (missing an x); female and sterile
What is a consequence of odd ploidy
tend to be sterile as there is are unpaired homologs in metaphase 1
Meiosis 2 is similar to which process
mitosis in haploid cells
