ECU BIO 1050 EXAM 3 | VERIFIED STUDY | QUESTIONS
AND ANSWERS | 2026 UPDATES
What are the two types of cell division in eukaryotes? - ANSWER- mitosis and meiosis
What types of cells does meiosis create? - ANSWER- sperm and eggs
What happens if there are errors during meiosis? - ANSWER- nondisjunctions (ie.
disorders like Down Syndrome)
Describe meiosis. - ANSWER- The process that produces haploid gametes in diploid
organisms
How many cell divisions occur during meiosis and how many cells are produced? - ANSWER-
2 cell divisions
Meiosis 1- homologous pairs separate
Meiosis 2- sister chromatids separate, resulting in 4 haploid cells, each containing a copy of each
chromosome instead of a homologous pair
What is a life cycle? - ANSWER- Diploid organisms undergo meiosis to create haploid
gametes
Sperm fertilizes an egg to create a zygote which undergoes mitosis to grow
What is a zygote? - ANSWER- a fertilized egg (diploid)
Describe the life cycle of a human. - ANSWER- Meiosis --> Fertilization --> Mitosis
What are the male sex chromosomes? - ANSWER- XY
What are the female sex chromosomes? - ANSWER- XX
Explain why fathers determine the sex of their offspring, instead of mothers. - ANSWER-
Women have 2 X chromosomes, so an X is always present in every egg (half of eggs get a
copy of one X, the other half get the other X) whereas men have each (half of sperm get X, half
get Y). The type of sperm that reaches the egg determines the sex.
Do all animals have the same system of sex determination as humans? - ANSWER- No. In
birds, mom determines sex in a way similar to human dads. In insects, males are haploid and
females are diploid. In turtles, sex determined by temperature at which eggs are incubated.
,What are 2 reasons why offspring from sexual reproduction are genetically different from their
parents & each other? - ANSWER- random fertilization and crossing over
random fertilization - ANSWER- source of genetic variation caused by the unlimited
number of possible sperm & egg combinations (64 trillion genetically different options)
What is crossing over? - ANSWER- exchange of genetic material between homologous
chromosomes (each individual chromosome becomes a mix of info from mom and dad)
Why is crossing over important? - ANSWER- -creates gene combinations different from
those carried by the parents' chromosomes
-main reason offspring of sexual reproduction are genetically unique
What is a nondisjunction? - ANSWER- -members of a chromosome pair fail to separate in
meiosis
-causes abnormal chromosome numbers
-we don't know what causes them
What happens if a sperm fertilizes an egg with an abnormal chromosome number? - ANSWER-
Every cell resulting from this initial error (including the zygote) will also have the wrong
chromosome number
Can nondisjunctions lead to abnormal chromosome numbers in autosomes, sex chromosomes,
or both? - ANSWER- BOTH
What happens to a human embryo born with an abnormal # of autosomes? - ANSWER-
Generally catastrophic and results in miscarriage or survival with a syndrome
What is a syndrome? - ANSWER- A characteristic set of symptoms that different people
have to varying extents
Down syndrome - ANSWER- have an extra copy of chromosome 21 (also called trisomy
21)
How does the age of the mother influence the likelihood of a baby having Down syndrome? -
ANSWER- Incidence of down syndrome increases with age of mother, especially after 35
(increases from less than 0.05% to greater than 1%)
Explain what we know about why the likelihood of Down syndrome increases with the mother's
age. - ANSWER- Likely has to do with the "pause" in egg's process in meiosis-- longer lag
time means higher chance of errors
, Do offspring with abnormal numbers of sex chromosomes usually survive? - ANSWER-
Yes, but every cell has different combo of sex chromosomes.
Can cause Turner syndrome (just X, no Y), Klinefelter syndrome (XXY), XYY Male, XXX Female
Describe the general rules for which chromosomes produce "maleness" versus what creates
"femaleness". - ANSWER- -"default" condition is female
-single Y present turns embryo to males
What process is used to make sperm? - ANSWER- meiosis
Why are males always able to make more sperm? - ANSWER- Spermatagonium will always
undergo mitotis before meiosis-- every time it divides to make sperm, it makes a backup copy
that can be used to make sperm in the future
What does the head of a sperm contain? - ANSWER- the nucleus with DNA
What does the body (midpiece) of a sperm contain and why? - ANSWER- many
mitochondria, with generate ATP energy so it can swim
What is the function of the tail of a sperm? - ANSWER- propels the sperm forward
What is semen? - ANSWER- fluid with sperm and sugars to aid in cellular respiration
What happens during ejaculation? - ANSWER- approximately 300 million sperm cells are
expelled as part of semen
When does egg formation begin? - ANSWER- Begins in the female fetus and pauses until
puberty
What happens in a female's body from puberty until menopause? - ANSWER- ovulation:
an egg part way through meiosis is released from the ovary every month
When does ovulation generally occur? - ANSWER- monthly
Describe the ovarian cycle. - ANSWER- Eggs are formed through meiosis in ovaries
1 matures enough to be released into fallopian tubes (halfway through monthly cycle)
Corpus luteum where egg used to be disintegrates unless fertilized
What happens if sperm are present in the female's ducts during ovulation? - ANSWER-
eggs are fertilized and egg will undergo meiosis (fertilization occurs here- cannot happen
if egg is already in uterus)
AND ANSWERS | 2026 UPDATES
What are the two types of cell division in eukaryotes? - ANSWER- mitosis and meiosis
What types of cells does meiosis create? - ANSWER- sperm and eggs
What happens if there are errors during meiosis? - ANSWER- nondisjunctions (ie.
disorders like Down Syndrome)
Describe meiosis. - ANSWER- The process that produces haploid gametes in diploid
organisms
How many cell divisions occur during meiosis and how many cells are produced? - ANSWER-
2 cell divisions
Meiosis 1- homologous pairs separate
Meiosis 2- sister chromatids separate, resulting in 4 haploid cells, each containing a copy of each
chromosome instead of a homologous pair
What is a life cycle? - ANSWER- Diploid organisms undergo meiosis to create haploid
gametes
Sperm fertilizes an egg to create a zygote which undergoes mitosis to grow
What is a zygote? - ANSWER- a fertilized egg (diploid)
Describe the life cycle of a human. - ANSWER- Meiosis --> Fertilization --> Mitosis
What are the male sex chromosomes? - ANSWER- XY
What are the female sex chromosomes? - ANSWER- XX
Explain why fathers determine the sex of their offspring, instead of mothers. - ANSWER-
Women have 2 X chromosomes, so an X is always present in every egg (half of eggs get a
copy of one X, the other half get the other X) whereas men have each (half of sperm get X, half
get Y). The type of sperm that reaches the egg determines the sex.
Do all animals have the same system of sex determination as humans? - ANSWER- No. In
birds, mom determines sex in a way similar to human dads. In insects, males are haploid and
females are diploid. In turtles, sex determined by temperature at which eggs are incubated.
,What are 2 reasons why offspring from sexual reproduction are genetically different from their
parents & each other? - ANSWER- random fertilization and crossing over
random fertilization - ANSWER- source of genetic variation caused by the unlimited
number of possible sperm & egg combinations (64 trillion genetically different options)
What is crossing over? - ANSWER- exchange of genetic material between homologous
chromosomes (each individual chromosome becomes a mix of info from mom and dad)
Why is crossing over important? - ANSWER- -creates gene combinations different from
those carried by the parents' chromosomes
-main reason offspring of sexual reproduction are genetically unique
What is a nondisjunction? - ANSWER- -members of a chromosome pair fail to separate in
meiosis
-causes abnormal chromosome numbers
-we don't know what causes them
What happens if a sperm fertilizes an egg with an abnormal chromosome number? - ANSWER-
Every cell resulting from this initial error (including the zygote) will also have the wrong
chromosome number
Can nondisjunctions lead to abnormal chromosome numbers in autosomes, sex chromosomes,
or both? - ANSWER- BOTH
What happens to a human embryo born with an abnormal # of autosomes? - ANSWER-
Generally catastrophic and results in miscarriage or survival with a syndrome
What is a syndrome? - ANSWER- A characteristic set of symptoms that different people
have to varying extents
Down syndrome - ANSWER- have an extra copy of chromosome 21 (also called trisomy
21)
How does the age of the mother influence the likelihood of a baby having Down syndrome? -
ANSWER- Incidence of down syndrome increases with age of mother, especially after 35
(increases from less than 0.05% to greater than 1%)
Explain what we know about why the likelihood of Down syndrome increases with the mother's
age. - ANSWER- Likely has to do with the "pause" in egg's process in meiosis-- longer lag
time means higher chance of errors
, Do offspring with abnormal numbers of sex chromosomes usually survive? - ANSWER-
Yes, but every cell has different combo of sex chromosomes.
Can cause Turner syndrome (just X, no Y), Klinefelter syndrome (XXY), XYY Male, XXX Female
Describe the general rules for which chromosomes produce "maleness" versus what creates
"femaleness". - ANSWER- -"default" condition is female
-single Y present turns embryo to males
What process is used to make sperm? - ANSWER- meiosis
Why are males always able to make more sperm? - ANSWER- Spermatagonium will always
undergo mitotis before meiosis-- every time it divides to make sperm, it makes a backup copy
that can be used to make sperm in the future
What does the head of a sperm contain? - ANSWER- the nucleus with DNA
What does the body (midpiece) of a sperm contain and why? - ANSWER- many
mitochondria, with generate ATP energy so it can swim
What is the function of the tail of a sperm? - ANSWER- propels the sperm forward
What is semen? - ANSWER- fluid with sperm and sugars to aid in cellular respiration
What happens during ejaculation? - ANSWER- approximately 300 million sperm cells are
expelled as part of semen
When does egg formation begin? - ANSWER- Begins in the female fetus and pauses until
puberty
What happens in a female's body from puberty until menopause? - ANSWER- ovulation:
an egg part way through meiosis is released from the ovary every month
When does ovulation generally occur? - ANSWER- monthly
Describe the ovarian cycle. - ANSWER- Eggs are formed through meiosis in ovaries
1 matures enough to be released into fallopian tubes (halfway through monthly cycle)
Corpus luteum where egg used to be disintegrates unless fertilized
What happens if sperm are present in the female's ducts during ovulation? - ANSWER-
eggs are fertilized and egg will undergo meiosis (fertilization occurs here- cannot happen
if egg is already in uterus)
