chapter 5

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fundamental concept in biology is the cell theory.

it states:

all life is cellular

all cells arise from pre-existing cells

the cell is the smallest living thing

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cell division provides for:

growth

repair

reproduction

cell division can be used for sexual or asexual reproduction

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(sexual reproduction)

two parents produce genetically unique offspring.

gametes are formed through cell division from adult cells in the gonads

fertilized with 2 chromosome sets

(asexual reproduction)

one parent produces genetically identical offspring.

no sperm or egg involved

not fertilized and has 1 chromosome set

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DNA is the genetic material of every living thing.

long strands of DNA are called chromosomes which contain genetic information called genes

a gene is a length of DNA that codes for the proteins that make up our bodies

genes are the unit of inheritance

in the nucleus, chromosomal DNA is around protein and together form chromatin

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in cell division chromosomes:

become tightly packed

duplicate

pairs of duplicated chromosome are called sister chromatids which are formed when the cell is preparing to divide.

sister chromatids are joined at the centromere.

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the cell cycle is an ordered sequence of events in the "lifetime" of a cell.

two phases:

interphase - 90% of cell's lifetime, normal cell function

performs the normal functions, grows, prepares for cell division by duplicating its chromosomes

mitotic phase - active cell division

undergoes active division (mitosis)

splits two offspring cells - pinched in two leaving two independent offspring cells (cytokinesis)

cytokinesis is the division of the cytoplasm and is the final step. this process is different for plant & animal cells.

plant cells divide by forming a cell plate along the center line of the cell

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gametes are haploid: they contain only one copy of each chromosome.

male gametes: sperm

female gametes: eggs

the 46 chromosomes are organized in 23 homologous pairs, 22 pairs are autosomes. the remaining pair is the sex chromosome.

females are XX

males are XY

meiosis is the production of gametes, the cells produced are haploid.

meiosis starts with chromosome duplication before division.

has two rounds of cell division

the result is four haploid offspring cells that contain one half the number of chromosomes

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three major processes mean variation is normal for sexual reproduction:

independent assortment - chromosomes line up before cells divide

maternal and paternal chromosomes are shuffled randomly

8 M possible arrangements of chromosomes

random fertilization - randomized connected sex cells

crossing over - homologous chromosomes line up, cross over, and swap pieces during meiosis I

meiosis mishaps:

nondisjunction - when chromosomes fail to separate properly, resulting in too few or too many chromosomes

ex.

Trisomy 21 - a condition in which a person receives three copies of chromosomes 21 (results in down syndrome

sex chromosome nondisjunction - each combination of extra or missing sex chromosomes produce its own syndrome

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heredity - is the transmission of traits from one generation to the next

genetics - the study of heredity

character - an inherited feature that varies among individuals

trait - each possible variation of a character, derives from genes

alleles - alternate forms of a particular gene

phenotype - physical traits

genotype - underlying genetic makeup of the alleles it is carrying

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a carrier is a heterozygous individual that don't have the disease but can pass it onto their offspring.

for some genes, there is a pattern of incomplete dominance.

heterozygous individuals show an intermediate trait.

most genes have multiple alleles.

ex. human blood type, three alleles can be combined in six ways

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in some cases, one gene influences many characters in pleiotropy.

the sickle cell mutation can cause many physical changes.

polygenic inheritance - is the effect of many genes on a single character.

linked genes are located close together on the same chromosome and tend to be inherited together.

crossing over result in new hybrid recombinant chromosomes.