Unit 5: Heredity Flashcards
Where do homologous chromosomes come from?
One from mom, one from dad
These are the same genes, but possibly different versions (alleles)
What is ploidy? How many are in diploid versus haploid?
The number of copies of each chromosome.
Diploid non-sex cells have 2 copies of each chromosome
Haploid sex cells have only 1 copy of each chromosome
Haploid + haploid = diploid
Egg cell + sperm cell = ___
Zygote (a diploid sex cell)
In mitosis, a diploid cell makes __ diploid cells and the resulting cells are ___
In meiosis, a diploid cell makes __ _______ cells and the resulting cells are ___
In mitosis, a diploid cell makes 2 diploid cells and the resulting cells are identical
In meiosis, a diploid cell makes 4 haploid cells and the resulting cells are different from one another
Why does meiosis yield 4 haploid cells?
Cells undergo 2 rounds of division. After the initial round, there is a diploid germ cell. After the final round, there is a haploid sex cell/gamete
Meiosis is divided into what two stages? What comes before both?
Meiosis I
Meiosis II
Interphase is before both
What happens in meiosis I?
Prophase I (just like mitosis), EXCEPT crossing over occurs
What is “crossing over”?
An unequal exchange of DNA between homologous chromosomes during prophase I
What are the chromatids called that have taken part in crossing over?
Recombinant chromatids
What happens in Metaphase I?
Same as in mitosis, EXCEPT there’s independent assortment (ex. all chromosomes from mom doesn’t necessarily go to the same pole)
What happens in anaphase I?
Same as mitosis
After meiosis I, does meiosis II immediately start?
No, there is a brief interphase where centrosomes are duplicated
What is the major difference between meiosis II and mitosis?
Cells start and finish meiosis II as haploids, while in mitosis cells start and finish as diploids
What’s unique in prophase II?
There is no synapse or crossing over
What’s unique in metaphase II?
Chromosomes are unpaired
What are the 3 processes that make it so offspring can be genetically varied?
Crossing over in meiosis
Independent assortment in meiosis
Random fertilization (random sperm meets random egg)
How many chromosomes do humans have (normally)? How many pairs?
46 chromosomes with 23 pairs
What are the two types of chromosomes?
Sex chromosomes and autosomes
How many chromosomes do egg and sperm cells each carry?
23! Think about it…We have a total of 46, and we get half from each parent. That means 23 from an egg, 23 from a sperm
Who studied genetics using peas? What did he look at?
Gregor Mendel; pea traits of color and texture
What is “true breeding”?
Cross a plant to itself over many generations and a specific trait doesn’t change (ex. always making green peas)
What are loci?
The location on a chromosome. Loci refers to where genes/traits are found on the chromosome.
What are alleles?
Possible versions of a gene
Dominant versus recessive?
Dominant traits will always win (RR, Rr)
Recessive traits will only show when they are the only ones present (rr)
Is the most common allele dominant?
Not necessarily
Some dominant traits are very rare or even lethal
Relation between allele and phenotype?
Genotype : trait/characteristic
Aa : brown eyes
Hh
hh
HH
Heterozygous dominant
Homozygous recessive
Homozygous dominant
What are Punnett squares used for?
Crossing genes to see genetic probabilities for each individual offspring
What are the probabilities of the offspring for Aa x Aa?
A a
A AA Aa
a Aa aa
= 75% dominant, 25% recessive
What is codominance?
When both alleles are dominant, so both are shown
How are codominant alleles represented?
Using superscripts
What’s an example of codominance?
People with blood type AB
Blood types have 3 alleles in humans, but each person only carries 2.
Example alleles for blood type: I^A, I^B, i
Is type O blood dominant or recessive?
Recessive! A and B are both dominant to O.
A and B are codominant to each other
What is it called when both copies of a chromosome go to the same cell during cell division?
Nondisjunction
What is monosomy? Trisomy?
Monosomy: 1 chromosome when it should be 2
Trisomy: 3 chromosomes when it should be 2
What’s an example of trisomy?
Down syndrome has 3 copies of chromosome 21 in each cell
What are the sex chromosomes?
X and Y
XX: typically female
XY: typically male
What characteristics are shown for someone with these sex chromosomes?
X
XXY
X: Shows female characteristics; called “Turner syndrome”
XXY: Shows male characteristics; called “Klinefelter syndrome”
A picture of what phase of meiosis would show chromosomes lined up double-file in the middle of the cell?
Metaphase I
