Chapter 9.5

Question 1

How does meisosis generate variability: 3 Mechanisms

( creates new combinations of alleles)

Answer 1

1. Crossing Over
2. Random alignment-Independent assortment
3. Random Fertilization

Question 2

CROSSING OVER

Answer 2

Is a process in which 2 homologous chromosomes exchange genetic material

Question 3

Where does the process of crossing over

Answer 3

Prophase 1 (late)

Question 4

The process of crossing over

Answer 4

1. In Prohase I, the homologs ( repicatid with sister chromatids) align themselves precisely gene by gene ( SYNAPSIS)
2. The chromosomes are attached at a few points ( called CHIASMATA) where homologs exchange genetic material (exchanging alleles)

Question 5

germ cells

Answer 5

are diploid produce gametes that are haploid

Question 6

RECOMBINANT CHROMATID

Answer 6

Resulted from exchanging of alleles of two homologs in crossover process

Question 7

how many chromatids take part in crossover

Answer 7

only 2 ( one sister chromatid from each homolog that is next to each other). ( recombinant)

those that do not experience chiasmata would remain unchanged ( parental)

only half of the chromatids contain allele combination that are new(

Question 8

The result of crossing over

It ensures what

Answer 8

4 genetically different chromatids in place of 2 pairs of identical chromatids

Each will end up in a haplid cell (4)

Question 9

meiosis takes place in which cell

Answer 9

germ cells that are diploid they produce gametes that are hapoid

Question 10

It crossing over ensures what

Answer 10

that each haploid cell will be genetically different from the others

Question 11

Independent assortment or random allignment occurs where

Answer 11

IN METAPHASE I

Where the homologs may align in the equator in any possible combination.

so that when in anaphase and 1/2 of a homolgous pair gets pulled to each pole it may have different genetic combinations of mom and dad

Question 12

The number of possible arrangements in independent assortmnent are related to what

Answer 12

The number of chromosomes

Question 13

the formula for random alignment

Answer 13

2^n ( where n is the haploid number)

eg. If there are 2 pairs of of homologs

(XX xx)= 4 chromosomes

n= 2n=4( the number of chromosomes)

n=2

2^2=4

eg 3. if their are 3 pairs

chromosomes=6

2n=6

n=3

2^3 =8 possibilities/configurations can occur in a gamete

Question 14

The purpose of Random Fertilization

Answer 14

It multiplies diversity

Question 15

Why do identical twin exist

Answer 15

They are a result from just one fertilization event.

The resulting zygot or embryo splits in half creating seperate identical babies

They are (MONOZYGOTIC) resulting from one zygote

Question 16

Fraternal twins are

Answer 16

DIZYGOTIC ( resulting from 2 zygotes) ( non identical )

Question 18

How does crossing over shuffle genes?

Answer 18

Crossing over shuffles genes when part of one chromosome switches places with part of its homologous chromosome.

Question 19

. Explain how events in metaphase I enable a human to produce over 8 million genetically different gametes.

Answer 19

During metaphase I, 23 homologous pairs of chromosomes (consisting of four chromatids) align at the equator of the cell. Each homologous pair can align in either of two ways. For 23 homologous pairs, there are 223 possible alignments (more than 8,300,000).

Question 20

. What is random fertilization

Answer 20

During random fertilization, any one of the 8,388,608 possible combinations of gametes in a woman’s eggs can be fertilized by any one the 8,388,608 possible combinations of gametes in a man’s sperm, producing over 70 trillion offspring combinations.

Question 21

How are identical twins different from fraternal twins?

Answer 21

Identical (monozygotic) twins arise from a single zygote and are therefore genetically identical to each other. Fraternal (dizygotic) twins arise from two separate fertilized eggs and are therefore as similar (or dissimilar) as any two non-identical siblings.

Question 22

how many possibilities can a human cell have of chromosomes combinatiions

Answer 22

2^23 = 8388608 and equally as many gametes for either sex