Meiosis and Errors in MeiosisJanuary 2009

Production of gametes

If a plant carries alleles Aa for a gene, what type(s) of gametes (sex cells) would it produce?

A) AaB) AA and aaC) A and aD) Not enough information

X

Round, Yellow Wrinkled, Green

YYRR yyrr

What are the possible gametes produced by F1 peas?A) yyrr, YyRr, YYRRB) R, r, Y, yC) Rr, Yy, RR, rr, YY, yyD) YR, yR, Yr, yr

P

F1

YyRr

100% Round, Yellow

Meiosis

• Goal: produce a haploid cell that contains half the genetic material of the parent cell.

Which type of cells undergo meiosis?A) somatic cells (any cell in the body that is not a gamete)B) gametes (sex cells that produce eggs or sperm)C) eggs or spermD) all of the aboveE) B and C

Chromosome Alignment

What does this somatic cell look like after DNA replication?

Somatic Cell

Ff

Aa#1

#1

#2#2

A a

fF

fF

A a

A Aa a

FFff

A.

B.

#2 #2

#2 #2

#1 #1#1 #1

#1 #1#1 #1

#2 #2#2 #2

Homologous pair after DNA replication

A A a a

Sister chromatids

Question 3: What does a homologous pair look like before DNA replication?

A a

aa

A)

B)

DNA replication generates identicalsister chromatids (attached). Homologuesare not attached and are not identical.

Chromosome Nomenclature

Homolog vs. Sister Chromatid

A A

a a

FF

ff

Do they have the same set of genes?

A. Yes

B. No

Do they have the same alleles?

A. Yes

B. No

#2 #2

#2 #2

#1 #1

#1 #1

For the following questions, refer to the sister chromatids circled in red.

A A

a a

FF ff

Do the homologous chromosomes circled in red have the same set of genes?

A. Yes

B. No

#2#2#2 #2

#1 #1

#1 #1

What statement is true regarding the differences between a pair of sister chromatids and a pair of homologous chromosomes?

A. Sister chromatids have the same set of genes, homologous chromosomes usually have a different set of genes

B. Homologous chromosomes have the same set of genes, sister chromatids usually have a different set of genes

C. Sister chromatids have the same alleles, homologous chromosomes may have different alleles

D. Homologous chromosomes have the same alleles, sister chromatids may have different alleles

Nondisjunction

A meiotic nondis-junction problem:

The nondisjunction event in Fred that gave rise to child A occurred during:

A. Meiosis I B. Meiosis II C. Either meiosis

Chromosome 21 errors during meiosis II in Fred

Q Qq q

Q Q q q

21 21 21 21

Qq

Child will have sister chromosomes from

Fred with two identical alleles

Q2121

21

Precursor sperm cell after DNA replication before cell division

qEgg cell

QQ q qMeiosis II

nondisjunction

A meiotic nondis-junction problem:

The nondisjunction event in Mary that gave rise to child B occurred during:

A. Meiosis I B. Meiosis II C. Either meiosis

Chromosome 21 errors during meiosis I in Mary

Q Qq q

Qq

Qq

21 21 21 21

QqChild will have

homologous chromosomes from Mary with 2 different

alleles

2121

21

Precursor egg cell after DNA replication before cell division

sperm

Q Q

q q

Meiosis I nondisjunctio

n

Ploidy

A plant species with diploid chromosome number of 6 (2n=6)hybridizes with a plant that has a diploid chromosome number of 4 (2n=4).

How many chromosomes are present in the resulting fertilized egg?

A) 4B) 5C) 10D) 20