Meiosis and Sexual Life Cycles

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Chromosomes in a homologous pair are the same length and carry genes controlling the same inherited characters

Slide 11

Fig. 13-3

APPLICATION

TECHNIQUE

Pair of homologous

replicated chromosomes

5 µm

Centromere

Sister

chromatids

Metaphase

chromosome

Slide 12

Fig. 13-3a

APPLICATION

Slide 13

Fig. 13-3b

TECHNIQUE

Pair of homologous

replicated chromosomes

Centromere

Sister

chromatids

Metaphase

chromosome

5 µm

Slide 14

The sex chromosomes are called X and Y

Human females have a homologous pair of X chromosomes (XX)

Human males have one X and one Y chromosome

The 22 pairs of chromosomes that do not determine sex are called autosomes

Slide 15

Each pair of homologous chromosomes includes one chromosome from each parent

The 46 chromosomes in a human somatic cell are two sets of 23: one from the mother and one from the father

A diploid cell (2n) has two sets of chromosomes

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

Slide 16

In a cell in which DNA synthesis has occurred, each chromosome is replicated

Each replicated chromosome consists of two identical sister chromatids

Slide 17

Fig. 13-4

Key

Maternal set of

chromosomes (n = 3)

Paternal set of

chromosomes (n = 3)

2n = 6

Centromere

Two sister chromatids

of one replicated

chromosome

Two nonsister

chromatids in

a homologous pair

Pair of homologous

chromosomes

(one from each set)

Slide 18

A gamete (sperm or egg) contains a single set of chromosomes, and is haploid (n)

For humans, the haploid number is 23 (n = 23)

Each set of 23 consists of 22 autosomes and a single sex chromosome

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

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

Slide 19

Fertilization is the union of gametes (the sperm and the egg)

The fertilized egg is called a zygote and has one set of chromosomes from each parent

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

Behavior of Chromosome Sets in the Human Life Cycle