Lecture 14 - Sexual Reproduction Flashcards
any one of 2^23 possible
sperm can unite with any one of 2^23 possible sperm for 70 trillion unique combinations (crossing over contributes more variability)
random fertilization
2 homologs exchange genetic material resulting in new gene combinations
crossing over
what part of meiosis does crossing over take place
Prophase 1
when are all possible combinations equally probable
random alignment of chromosome pairs in Metaphase 1
what kind of DNA replication is meiosis
single
in meiosis human cells are….
diploid
- 2 full sets of chromosomes
- 1 set from each parent
most body cells do not participate directly in reproduction
somatic cells
specialized cells to produce gametes (eggs and sperm)
germ cells
are eggs and sperm haploid or diploid
haploid
gametes fuse at fertilization to produce…
new diploid zygote
different versions of same gene
alleles
cytokinesis only effects ______ gametes
male
states of meiosis
Meiosis 1
Meiosis 2
stages of Meiosis 1
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1
stages of Meiosis 2
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2
produces haploid nulcei
Meiosis 2
where genetic recombination occurs
Meiosis 1
reduces #’s of chromosomes by half (shuffling of genetic info)
Meiosis 1
when do cells become haploid
Anaphase 1
when, because of crossing over, are the cells not the same
Anaphase 2
the egg won’t finish anaphase 2 and telophase 2 until it…
is fertilized with the sperm
why is it unnecessary for the female eggs to undergo cytokinesis
instead of going through cytokinesis, it just throws one egg out
chromosomes fail to separate at 1st or 2nd meiotic division = gamete with extra or missing chromosome
nondisjunstion
gamete with extra chromosome
trisomy
gamete with missing chromosome
monosomy
most embryos with incorrect chromosome numbers…
cease developing
which causes fewer problems, trisomy or monosomy
trisomy
increasing woman’s age, _______ likelihood of trisomy
increases
difference between homologous chromosomes and sister chromatids
homologous:
- same gene types, different versions(alleles)
- come from different parents (2, get 1 from each parent)
- have the exact same amount of genetic information = same size, # nucleotides, types of genes
sister chromatids
- exact copies of each other that come about through semiconservative DNA replication (interphase)
more than or equal to 1 complete set of extra chromosomes
polyploidy
when does mitotic spindle pull on either side
metaphase 1
single zygote
monozygote
2 separate zygotes
dizygotic
when does meiosis begin in males
puberty
when does meiosis begin in females
before they’re even born
True/False: ultimately, gonads are the only cells that undergo meiosis
True
why do problems with nondisjunction occur earlier in females than males
because of the age of their cells….females cells begin meiosis before they’re born and males begin meiosis at puberty
difference between homologous chromosomes
the alleles
the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring
crossing over
states that the alleles for a trait separate when gametes are formed
independent assortment
NOT genetic recombination, its when a mistake happens
Nondisjunction
when does crossing over occur
prophase 1
when does independent assortment occur
metaphase 1
when does nondisjunction occur
anaphase 1 or 2
when homologous pairs of chromosome errors exchange equal amounts of genetic info(alleles) and recombine what alleles they have
crossing over
how the homologous pairs line up along the middle
- depends randomly what side they line up on = mixes and matches all homologous chromosomes your parents gave you
independent assortment
failure of homologous chromosomes(anaphase 1) or sister chromatids(anaphse 2) to separate from each other
nondisjunction
three types of genetic recombination that occur in sexual reproduction
- crossing over
- independent assortment
- fertilization
when sperm and egg fertilize each other
type of genetic recombination
when does fertilization in females occur
right in the middle of meiosis 2
fertilization in males occur
after meiosis 2, it has to finish before sperm can mature
difference between monozygotic and dizygotic twins
monozygotic:
- have to be same sex
- genetics = exact same
dizygotic:
- 2 separate fertilization events
when either homologous chromosomes or sister chromatids fail to separate = 1 more or 1 less chromosome
nondisjunction
- most of the time = fatal
most common form of autosomal nondisjunction
trisomy nondisjunction/down syndrom
which of the following are examples of trisomy in the autosomes
- kleinfelter syndrome
- down syndrome
- triple x syndrome
- turner syndrome
down syndrome
True/False: nondisjunction is most common in sex cells
True
the only monosomy nondisjunction that we’ve seen to have 1% survival rate
turner syndrome
True/False: you can survive without an ‘“x” chromosome
FALSE! You have to have an x chromosome to live
which of the following is not an example of nondisjunction? - - - - barbody
barbody = x chromosome inactivaton
True/False: After meiosis 1 cells are already haploid
True
