Campbell Biology Chapter 13

Living organisms are distinguished by

their ability to reproduce their own kind

The scientific study of heredity and variation

Genetics

The transmission of traits from one generation to the next

Heredity

Variation is demonstrated by

the differences in appearance that offspring show from parents and siblings

Children do not inherit particular physical traits from their parents

It is genes that are actually inherited

Units of heredity, and are made up of segments of DNA

Genes

Genes are passed to the next generation via reproductive cells called

Gametes (Sperm & eggs)

Each gene has a specific location called a _____ on a certain chromosome

Locus

DNA is packaged into

Chromosomes

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

Asexual reproduction

A group of genetically identical individuals from the same parent

Clone

2 parents give rise to offspring that have unique combinations of genes inherited from the 2 parents

sexual reproduction

Human somatic cells have _____ pairs of chromosomes

23

Somatic cells are

any cell other than a gamete

An ordered display of the pairs of chromosomes from a cell

karyotype

the 2 chromosomes in each pair are called

Homologous chromosomes, or homologs

The sex chromosomes which determine the sex of the individual are called

X and Y chromosomes

Human females have what specific chromosomes

homologous pair of X chromosomes (XX)

Human males have what specific chromosomes

one X and one Y chromosome

The remaining 22 pairs of chromosomes are called

Autosomes

Each pair of homologous chromosomes includes

one chromosome from each parent

There are ____ chromosomes in a human somatic cell

2 sets of 23; one from the mother and one from the father

A diploid cell (2n) has how many sets of chromosomes

two

For humans the diploid number is

24 (2n=46)

Each replicated chromosome consists of ____ identical sister chromatids

two

A gamete contains how many sets of chromosomes and what is it called

A single set

Haploid (n)

For humans the haploid number is

23 (n=23)

Each set of 23 consists of

22 autosomes and a single sex chromosome

At sexual maturity, germ line cells in the ovaries and testes produce

haploid gametes

____ are only types of human cells produced by meiosis, rather than mitosis

Gametes

Meiosis results in

one set of chromosomes in each gamete

Like mitosis, meiosis is preceded by

the replication of chromosomes

Meiosis takes place in two sets of cell divisions called

Meiosis l and meiosis ll

The two cell divisions result in

four daughter cells rather than the 2 daughter cells in mitosis

Each daughter cell has _____ as many chromosomes as the parent cell

half

The union of gametes (The sperm and the egg)

Fertilization (syngamy)

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

zygote, one

What does the zygote produce

somatic cells by mitosis and develops into an adult

After chromosomes duplicate, two divisions follow

Meiosis l (reductional division) 2 haploid daughter cells with replicated chromosomes

Meiosis ll (equational division) sister chromatids separate

The result after Meiosis l & ll

4 haploid daughter cells with unreplicated chromosomes

Division in meiosis l occurs in 4 phases

Prophase

Metaphase

Anaphase

Telophase & Cytokinesis

Sister chromatids are genetically ______ & are joined at the ______

Identical

Centromere

tetrad is a

group of four chromatids

Each tetrad usually has one or more _______

Chiasmata (X-shaped regions where crossing over occurred)

Prophase l

Chromosomes condense

homologous chromosomes loosely pair up, aligned gene by gene

synapsis

metaphase l

tetrads line up at metaphase plate

microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad

Telophase l

Each half of the cell has a haploid set of chromosomes; still consists of 2 sister chromatids

Cytokinesis usually occurs simultaneously, forming 2 haploid daughter cells

Anaphase l

pairs of homologous chromosomes separate

Sister chromatids remain attached at the centromere

In animal cells what forms

cleavage furrow

In plant cells what forms

cell plate forms

NOTE

no chromosome replication occurs b/t the end of meiosis l and the beginning of meiosis ll because the chromosomes are already replicated

Prophase ll

spindle apparatus forms

chromosomes move toward the metaphase plate

Metaphase ll

Sister chromatids are arranged at the metaphase plate

Sister chromatids are no longer identical

Anaphase ll

Sister chromatids separate

Sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite poles

Telophase ll

Chromosomes arrive at opposite poles

Nuclei form, chromosomes begin decondensing

Cytokinesis

Separates the cytoplasm

Three events that are unique to meiosis and all occur in meiosis l

Synapsis and crossing over in prophase l

At the metaphase plate, there are paired homologous chromosomes instead of individual replicated chromosomes

At anaphase l, it is homologous chromosomes instead of sister chromatids that separate

The original source of genetic diversity

Mutations (Changes in an organism's DNA)

Mutations create different versions of genes called

Alleles

Reshuffling of alleles during reproduction produces genetic variation

3 mechanisms contribute to genetic variation

Independent assortment of chromosomes

Crossing over

Random fertilization

Homologous pairs of chromosomes orient randomly at

metaphase l of meiosis

In independent assortment, each pair of chromosomes sorts maternal and paternal homologs into

daughter cells independently of the other pairs

The number of combinations possible when chromosomes assort independently into gametes is ____

2n (n=haploid number)

Crossing over produces ______ __________, which combine DNA inherited rom each parent

Recombinant chromosomes

Crossing over begins very early is what phase?

Prophase l

NOTES

Crossing over contributes to genetic variation by combining DNA from two parents into a single chromosome

In crossing over, homologous portions of two non sister chromatids trade places

Why does random fertilization add to genetic variation?

Any sperm can fuse with any ovum (unfertilized egg)