Unit 5: Heredity

Question 1

Where do homologous chromosomes come from?

Answer 1

One from mom, one from dad
These are the same genes, but possibly different versions (alleles)

Question 2

What is ploidy? How many are in diploid versus haploid?

Answer 2

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

Question 3

Haploid + haploid = diploid
Egg cell + sperm cell = ___

Answer 3

Zygote (a diploid sex cell)

Question 4

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 ___

Answer 4

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

Question 5

Why does meiosis yield 4 haploid cells?

Answer 5

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

Question 6

Meiosis is divided into what two stages? What comes before both?

Answer 6

Meiosis I
Meiosis II
Interphase is before both

Question 7

What happens in meiosis I?

Answer 7

Prophase I (just like mitosis), EXCEPT crossing over occurs

Question 8

What is “crossing over”?

Answer 8

An unequal exchange of DNA between homologous chromosomes during prophase I

Question 9

What are the chromatids called that have taken part in crossing over?

Answer 9

Recombinant chromatids

Question 10

What happens in Metaphase I?

Answer 10

Same as in mitosis, EXCEPT there’s independent assortment (ex. all chromosomes from mom doesn’t necessarily go to the same pole)

Question 11

What happens in anaphase I?

Answer 11

Same as mitosis

Question 12

After meiosis I, does meiosis II immediately start?

Answer 12

No, there is a brief interphase where centrosomes are duplicated

Question 13

What is the major difference between meiosis II and mitosis?

Answer 13

Cells start and finish meiosis II as haploids, while in mitosis cells start and finish as diploids

Question 14

What’s unique in prophase II?

Answer 14

There is no synapse or crossing over

Question 15

What’s unique in metaphase II?

Answer 15

Chromosomes are unpaired

Question 16

What are the 3 processes that make it so offspring can be genetically varied?

Answer 16

Crossing over in meiosis
Independent assortment in meiosis
Random fertilization (random sperm meets random egg)

Question 17

How many chromosomes do humans have (normally)? How many pairs?

Answer 17

46 chromosomes with 23 pairs

Question 18

What are the two types of chromosomes?

Answer 18

Sex chromosomes and autosomes

Question 19

How many chromosomes do egg and sperm cells each carry?

Answer 19

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

Question 20

Who studied genetics using peas? What did he look at?

Answer 20

Gregor Mendel; pea traits of color and texture

Question 21

What is “true breeding”?

Answer 21

Cross a plant to itself over many generations and a specific trait doesn’t change (ex. always making green peas)

Question 22

What are loci?

Answer 22

The location on a chromosome. Loci refers to where genes/traits are found on the chromosome.

Question 23

What are alleles?

Answer 23

Possible versions of a gene

Question 24

Dominant versus recessive?

Answer 24

Dominant traits will always win (RR, Rr)
Recessive traits will only show when they are the only ones present (rr)

Question 25

Is the most common allele dominant?

Answer 25

Not necessarily
Some dominant traits are very rare or even lethal

Question 26

Relation between allele and phenotype?

Answer 26

Genotype : trait/characteristic
Aa : brown eyes

Question 27

Hh
hh
HH

Answer 27

Heterozygous dominant
Homozygous recessive
Homozygous dominant

Question 28

What are Punnett squares used for?

Answer 28

Crossing genes to see genetic probabilities for each individual offspring

Question 29

What are the probabilities of the offspring for Aa x Aa?

Answer 29

A a
A AA Aa

a Aa aa

= 75% dominant, 25% recessive

Question 30

What is codominance?

Answer 30

When both alleles are dominant, so both are shown

Question 31

How are codominant alleles represented?

Answer 31

Using superscripts

Question 32

What’s an example of codominance?

Answer 32

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

Question 33

Is type O blood dominant or recessive?

Answer 33

Recessive! A and B are both dominant to O.
A and B are codominant to each other

Question 34

What is it called when both copies of a chromosome go to the same cell during cell division?

Answer 34

Nondisjunction

Question 35

What is monosomy? Trisomy?

Answer 35

Monosomy: 1 chromosome when it should be 2
Trisomy: 3 chromosomes when it should be 2

Question 36

What’s an example of trisomy?

Answer 36

Down syndrome has 3 copies of chromosome 21 in each cell

Question 37

What are the sex chromosomes?

Answer 37

X and Y
XX: typically female
XY: typically male

Question 38

What characteristics are shown for someone with these sex chromosomes?
X
XXY

Answer 38

X: Shows female characteristics; called “Turner syndrome”
XXY: Shows male characteristics; called “Klinefelter syndrome”

Question 39

A picture of what phase of meiosis would show chromosomes lined up double-file in the middle of the cell?

Answer 39

Metaphase I