Ch. 7 The Cellular Basis of Inheritance - OpenStax Concepts of Biology

Sexual reproduction

The production by parents of haploid cells and the fusion of a haploid cell from each parent to form a single, unique diploid cell.

Meiosis

the process that produces haploid sex cells

Advantages of asexual reproduction

(1) Offspring that can successfully occupy same habitat as parents

(2) Don't need a mate

(3) All members can produce offspring

Mutation

only source of variation in asexually reproducing organisms

During meiosis and when gametes combine in fertilization

When variation is introduced in sexually reproducing organisms

It provides a way to keep up with other organisms

Why variation is important

Fertilization

the union of two cells from two individual organisms

Meiosis

Nuclear division that reduces the number of chromosome sets

Somatic cells

"Body" cells or nonreproductive cells that reproduce by mitosis and contain homologous chromosome sets

Homologous chromosomes

Matched pairs of chromosomes containing genes for the same traits in the same locations; they are similar, though not identical.

Mitosis

Begins with a diploid cell and ends with two new diploid cells that are identical to the original cell

Meiosis

Begins with a diploid cell and ends with 4 new haploid cells, through 2 rounds of nuclear and cell division, that are different from the original cell

Meiosis I

The first round of meiotic division that reduces the number of chromosome sets from 2 to 1 and during which the genetic information is recombined in the chromosomes.

Meiosis II

The second round of meiotic division that is similar to mitosis.

Same

How does Interphase before Meiosis compare with Interphase before Mitosis?

Meiosis I stages/phases

Prophase I

Metaphase I

Anaphase I

Telophase I

Prophase I

Chromosomes condense, nucleus breaks down, synapsis and crossing over occur

Synapsis

Homologous chromosomes come close to each other

Crossing over

Segments of the homologous chromosomes exchange with each other

Synapsis and crossing over picture

Metaphase I

Chromosomes are lined up in the middle of the cell

Anaphase I

Homologous chromosomes are separated from each other

Randomly

How homologous chromosomes are separated from each other during Anaphase I

Telophase I

Two haploid sets of chromosomes are formed at opposite ends of the cell

Cytokinesis I

The cell divides into two.

Prophase II

Chromosomes condense, nucleus breaks down (if one is made in Telophase I), spindle fibers contact chromosomes

Metaphase II

Chromosomes line up in the middle of the cell

Anaphase II

Doubled chromosomes are separated into individual chromosomes and pulled to opposite ends of each cell.

Telophase II

Two haploid sets of chromosomes are at opposite ends of each cell and a new nucleus forms around each set.

Cytokinesis II

The second cell division.

Mitosis

Single nuclear division resulting in two nuclei, genetically identical to the original, and partitioned into two new cells having the same number of sets of chromosomes.

Meiosis

Two nuclear divisions resulting in 4 nuclei, partitioned into 4 new cells, never genetically identical, and contain one (haploid) chromosome set only.

Chromosome disorder categories

(1) abnormalities in chromosome number

(2) chromosome structural rearrangements

Why chromosomal disorders are often dramatic and fatal

Because even small segments of chromosomes can span many genes.

Nondisjunction

When chromosomes fail to separate during meiosis

Age of parents

What causes the risk of nondisjunction to increase

What happens to human zygotes missing an autosome

Fail to develop to birth

Genetic imbalance from an excess in gene dose

What people with an extra (3rd) copy of an autosome suffer from

Down Syndrome

Most common case of having an extra chromosome, the extra one is chromosome 21, individuals have characteristic physical features and developmental delays in growth and cognition

Increase in maternal age

What the incidence of Down Syndrome is correlated most with

Can function normally

Effect that having abnormal number of X chromosomes can have

Tortoiseshell cat

Female, has different fur colors due to an inactive X chromosome

XXX

Females with an extra (3rd) X chromosome and may have developmental delays and reduced fertility.

XXY

Klinefelter Syndrome - males who have an extra (2nd) X chromosome and have small testes, enlarged breasts, and reduced body hair.

X0

Turner Syndrome - females who have only one X chromosome and have short stature, webbed neck skin, hearing and cardiac impairments, and sterility.

Polyploid

An individual with more than the correct number of chromosome sets.

Plants

Kingdom of organisms in which polyploidy is very common

Cri-du-Chat

"Cry of the cat," syndrome associated with nervous system abnormalities and characteristic physical features resulting from a chromosomal deletion.

Chromosomal duplication effect

Often survivable, but with physical and mental abnormalities

Chromosomal deletion effect

Often survivable, but with physical and mental abnormalities

Chromosomal inversion effect

Typically mild or no effect, except infertility (due to the fact that a chromosome with an inversion isn't compatible to combine with the normal chromosome of another gamete)

Chromosomal translocation effect

May have no effect except for infertility (same reasons as for Inversion), although some specific translocations have been implicated in cancer and schizophrenia

Chromosome translocation picture

Chromosome inversion picture

Chromosome deletion picture

Chromosome duplication picture