Openstax Biology Chapter 11

23 pairs

Human somatic cells have ___ ____ of chromosomes

homologous

The two chromosomes in each pair are called ________ chromosomes.

length, shape, inherited characters

Chromosomes in a homologous pair are the same ____ and ______ and carry genes controlling the same ______ _______.

sex chromosomes

x and y chromosomes

female

homologous pair of XX chromosomes

male

x and y chromosome

autosomes

non-sex chromosomes, remaining 22.

parent

Each pair of homologous chromosomes includes one chromosome from each

46, 23

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

diploid cell

has two sets of chromosomes, in humans 2n = 46

karyotype

an ordered display of the pairs of chromosomes from a cell

fertilization

union of gametes (the sperm and the egg)

zygote

fertilized egg

undifferentiated cells

gametes

only types of human cells produced by meiosis rather than mitosis

meiosis

results in one set of chromosomes in each gamete

diploid to haploid

Meiosis reduces the number of chromosome sets from ____ ___ _____.

replication of chromosomes

Like mitosis, meiosis is preceded

Meiosis I, Meiosis II

Two sets of cell divisions for meiosis.

four

The two cell divisions result in ____ daughter cells, rather than the _____ daughter cells in mitosis.

Prophase I

Chromosomes begin to condense

Prophase I

Homologous chromosomes loosely pair up, aligned gene by gene (synapsis)

Prophase I

Non-sister chromatids of one homologous chromosome exchange DNA segments with the other by crossing over.

chiasmata

point where crossing over has occurred.

Prometaphase I

Spindle fiber microtubules attach to kinetochore of chromosomes. i

Metaphase I

the paired chromosomes (tetrads) randomly line up at the metaphase plate, with one chromosome facing each pole

tetrads

paired chromosomes

Anaphase I

Pairs of homologous chromosomes separate- not the sister chromatids.

Anaphase I

One chromosome moves toward each pole, sister chromatids remain attached at the centromere and move together.

Telophase I and Cytokinesis

Cleavage furrow forms

Cytokinesis usually occurs simultaneously,

Prophase II

Spindle apparatus forms

Prometaphase II

Spindle fiber microtubules attach to kinetochore of chromosomes

Metaphase II

Sister chromatids are arranged at the metaphase plate

Anaphase II

Sister chromatids separate and move toward opposite poles

Telophase II and Cytokinesis

Nuclei form

Cytokinesis occurs

four, haploid

At the end of meiosis, there are ____ daughter cells, each with a ____ set of chromosomes

Independent Assortment of Chromosomes

During Metaphase I, the chromosomes line up completely randomly,

There are more than 8 million possible combinations of chromosomes possible when chromosomes assort independently into gametes

Crossing over

in prophase I combines DNA inherited from each parent

Homologous portions of two nonsister chromatid trade places

contributes to genetic variation by combining DNA, producing chromosomes with new combinations of maternal and paternal alleles

Random Fertilization

adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg)

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 combinations