Chapter 13

Question 1

Heredity

Answer 1

the transmission of traits from one generation to the next

Question 2

variation

Answer 2

is demonstrated by the differences in appearance that offspring show from parents and siblings

Question 3

Genetics

Answer 3

is the scientific study of heredity and variation

Question 4

How are genes passed to the next generation?

Answer 4

via gametes

Question 5

Humans have how many chromosomes and where are they?

Answer 5

46 chromosomes in their somatic cells

Question 6

Locus

Answer 6

genes specific position along a chromosome

Question 7

asexual reproduction

Answer 7

a single individual passes all of its genes to its offspring without the fusion of gametes

Question 8

sexual reproduction

Answer 8

two parents give rise to offspring that have unique combinations of genes inherited from the two parents

Question 9

life cycle

Answer 9

is the generation-to-generation sequence of stages in the reproductive history of an organism

Question 10

Homologous chromosomes

Answer 10

• same length
• same shape-
• carry genes controlling the same inherited characters

Question 11

sex chromosomes

Answer 11

which determine the sex of the individual, are called X and Y
Human females (XX)
Human males (XY)

Question 12

autosomes

Answer 12

remaining 22 pairs of chromosomes after the sex chromosomes

Question 13

diploid cell

Answer 13

2n has two sets of chromosomes

For humans, the diploid number is 46 (2n = 46)

Question 14

haploid

Answer 14

contains a single set of chromosomes (gamete, sperm or egg)
For humans, the haploid number is 23 (n = 23)
22 autosomes
single sex chromosome

Question 15

sex chromosome in sperm and unfertilized egg

Answer 15

In an unfertilized egg (ovum), the sex chromosome is X

In a sperm cell, the sex chromosome may be either X or Y

Question 16

zygote

Answer 16

fertilized egg

The zygote produces somatic cells by mitosis and develops into an adult

Question 17

fertilization

Answer 17

union of gametes

Question 18

at sexual maturity the ovaries and testes produce what?

Answer 18

haploid gametes

Question 19

what human cells are produced by meiosis?

Answer 19

Gametes

Question 20

Independent Assortment of Chromosomes

Answer 20

Homologous pairs of chromosomes orient randomly at metaphase I of meiosis
In independent assortment, each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently of the other pairs

Question 21

how many possible combinations of chromosomes

Answer 21

The number of combinations possible when chromosomes assort independently into gametes is 2n, where n is the haploid number
For humans (n = 23), there are more than 8 million (223) possible combinations of chromosomes

Question 22

crossing over

Answer 22

• Crossing over produces recombinant chromosomes, which combine DNA inherited from each parent
• Crossing over contributes to genetic variation by combining DNA from two parents into a single chromosome
• In humans an average of one to three crossover events occurs per chromosome

Question 23

random fertilization

Answer 23

The fusion of two gametes (each with 8.4 million possible chromosome combinations from independent assortment) produces a zygote with any of about 70 trillion diploid combinations
-Crossing over adds even more variation
Each zygote has a unique genetic identity