Genetics II
Mini Study Guide!
By Alex Z
Let’s start off this study guide with some vocabulary words that will help us
explain some stuff!
THY WORDS!
Fitness - The ability to survive, reproduce, and pass on traits. (This is crucial in
anything that is biotic!)
Chromosome - A tightly coiled form of DNA
Gamete - A sex cell that carries chromosomes to a baby (the egg is a gamete and the
sperm is a gamete)
Fertilization - When the egg and sperm meet
Zygote - This is just a fancy term for a fertilized egg
Now, let’s move onto the actual stuff… genetics!
- Chromosomes are big coils of DNA that all humans have. Typically we have 46
chromosomes, but there could be people with a few additional chromosomes
(typically additional sex chromosomes.)
- Chromosomes are usually sorted into pairs of the same size and shape. Since
every chromosome in the human body is paired up with another chromosome,
this gives the average human 23 pairs of chromosomes.
- When parents pass on their genes to their offspring, they pass it on via a haploid
called a gamete!
Already confused? Me too! Let’s get some vocab in here again!
Haploid - A cell or nucleus that has a bunch of unpaired chromosomes
Diploid - A cell or nucleus with a bunch of paired chromosomes (REMEMBER: Di = two
chromosomes. Haploid, HAP for HALF the amount in diploids)
Meiosis - A type of cell division in sexual reproducing organisms that reduces the
number of chromosomes in gametes.
, Homologous chromosomes - Two chromosomes that carry the same traits, but may
have different alleles for it. These are NOT identical!
Sister chromatids - Two ATTACHED pieces of DNA that have the EXACT same trait and
alleles. They are shaped sort of like an X and are connected by a centromere.
- Initially, each parent has their own diploid cells which then create copies of
themselves and each homologous chromosome creates an identical copy of itself.
- This identical copy is attached onto its identical chromosome via something
called a “centromere.”
- These two identical copies are known as SISTER CHROMATIDS. (Think twin
sisters!)
- As you can see in the image shown above, the red and blue chromosomes
carry the same trait based on their size and shape, but they carry different
variations or alleles for the trait and are NOT connected by a centromere
(yellow circle), so they are homologous chromosomes!
- The other two chromatids in the image shown above are attached by a
centromere and look the exact same and carry the exact same trait and
alleles! This means that they are sister chromatids!
- Now, let’s get back on track, the new sister chromatids that are formed are
able to now cross over with their homologous chromosomes! (I know that
sounds confusing right now, so let me elaborate!)
❖ Now that there are two identical copies of the homologous
chromosomes, these two copies are able to exchange DNA with
their homologous chromosome!
❖ Here is a visual representation which can help you understand
better:
Mini Study Guide!
By Alex Z
Let’s start off this study guide with some vocabulary words that will help us
explain some stuff!
THY WORDS!
Fitness - The ability to survive, reproduce, and pass on traits. (This is crucial in
anything that is biotic!)
Chromosome - A tightly coiled form of DNA
Gamete - A sex cell that carries chromosomes to a baby (the egg is a gamete and the
sperm is a gamete)
Fertilization - When the egg and sperm meet
Zygote - This is just a fancy term for a fertilized egg
Now, let’s move onto the actual stuff… genetics!
- Chromosomes are big coils of DNA that all humans have. Typically we have 46
chromosomes, but there could be people with a few additional chromosomes
(typically additional sex chromosomes.)
- Chromosomes are usually sorted into pairs of the same size and shape. Since
every chromosome in the human body is paired up with another chromosome,
this gives the average human 23 pairs of chromosomes.
- When parents pass on their genes to their offspring, they pass it on via a haploid
called a gamete!
Already confused? Me too! Let’s get some vocab in here again!
Haploid - A cell or nucleus that has a bunch of unpaired chromosomes
Diploid - A cell or nucleus with a bunch of paired chromosomes (REMEMBER: Di = two
chromosomes. Haploid, HAP for HALF the amount in diploids)
Meiosis - A type of cell division in sexual reproducing organisms that reduces the
number of chromosomes in gametes.
, Homologous chromosomes - Two chromosomes that carry the same traits, but may
have different alleles for it. These are NOT identical!
Sister chromatids - Two ATTACHED pieces of DNA that have the EXACT same trait and
alleles. They are shaped sort of like an X and are connected by a centromere.
- Initially, each parent has their own diploid cells which then create copies of
themselves and each homologous chromosome creates an identical copy of itself.
- This identical copy is attached onto its identical chromosome via something
called a “centromere.”
- These two identical copies are known as SISTER CHROMATIDS. (Think twin
sisters!)
- As you can see in the image shown above, the red and blue chromosomes
carry the same trait based on their size and shape, but they carry different
variations or alleles for the trait and are NOT connected by a centromere
(yellow circle), so they are homologous chromosomes!
- The other two chromatids in the image shown above are attached by a
centromere and look the exact same and carry the exact same trait and
alleles! This means that they are sister chromatids!
- Now, let’s get back on track, the new sister chromatids that are formed are
able to now cross over with their homologous chromosomes! (I know that
sounds confusing right now, so let me elaborate!)
❖ Now that there are two identical copies of the homologous
chromosomes, these two copies are able to exchange DNA with
their homologous chromosome!
❖ Here is a visual representation which can help you understand
better:
