biology exam 3: sexual reproduction/ meiosis

gametes

sperm and egg cells

what is meiosis

nuclear division that leads to halving of chromosome number in gametes to become haploids

homologs/ homologous chromosomes

similar in size and structure, contain same traits but not same DNA, carry different alleles of gene, on mom one dad

autosomes

numbered chromosomes in karyotype

what are germ cells

produce gametes during meiosis

what does meiosis do

DNA replicates once, then the DNA/ nucleus content divides twice

prophase 1

chromosomes pairs with homologous pair and crossover occurs

metaphase 1

homologous pairs line up in middle of cell, microtubules connect to kinetochore

anaphase 1

homologous pairs separate to opposite sides of cell, the sister chromatids remain together

telophase 1

nuclear envelope forms, spindle fibers disappear, chromosomes decondense

cytokinesis 1

cell separates into two cells

prophase 2

spindle fibers form, consists of chromosomes (two chromatids)

metaphase 2

chromosomes line up in the middle

anaphase 2

sister chromatids separate and move to opposite sides

telophase 2

chromosomes fully on opposite sends, nuclei form, chromosomes decondense, spindle fibers disappear 

cytokinesis 2

cell seperates, now 4 cells

nondisjunction

failure of chromosomes to properly separate

what does nondisjunction cause

abnormal number of a specific chromosome

aneuploidy is what

wrong number of specific chromosomes

when does nondisjunction occur

anaphase 1 or 2

mendel’s 1st law

two versions of each gene (alleles)

monohybrid cross

crossing of two heterozygous individuals

mendel’s 2nd law

law of independent assortment, segregation of alleles for one gene does not influence segregation of other alleles 

when do mendel’s laws not apply for single genes

incomplete dominance, codominance, pleiotropy 

pleiotropy

gene mutation that causes multiple effects on phenotype

when do mendel’s laws not apply to two or more genes

epistasis and polygenic inheritance

what is epistasis

one genes masks the phenotypic expression of another gene