Chapter 11.4

OOGENESIS

MAKING a MATURE EGG, Produces: 1 "good" egg and 3 POLAR BODIES, CYTOPLASM DIVIDES UNEVENLY.

CROSSING OVER during PROPHASE I

process in which homologous chromosomes exchange portions of their chromatids during meiosis, Formation of Tetras allows exchange of DNA between homologous pairs, Allows shuffling of genetic material

TETRAD

structure containing 4 chromatids that forms during meiosis (group of FOUR (4) chromatids)

MEIOSIS is the way...

to make cells with ½ the number of chromosomes for sexual reproduction (23 each)

If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain?

46 + 46 = 92; a developing embryo would not survive if it contained 92 chromosomes.

How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?

46 chromosomes

Skips INTERPHASE II (No S)

CELL DIVIDES TWICE, BUT ...ONLY COPIES ITS DNA ONCE

Why do CROSSING OVER?

It makes rearranging of DNA occur. THIS IS CALLED GENETIC RECOMBINATION. This, in turn, results in genetic diversity which is important for species survival.

SPERMATOGENESIS

MAKING MATURE SPERM, After Meiosis they mature & grow flagella, Sperm provides DNA (23 chromosomes), All the starting nutrients, organelles, molecule building blocks, etc. have to come from the egg.

MITOSIS

Makes 2 cells genetically identical to parent cell & to each other Makes 2n cells Makes SOMATIC (body) Used by organisms to: increase size of organism, repair injuries, replace worn out cells

MEIOSIS

Makes 4 cells Each genetically different from parent cell & from each other Makes Haploid (n) cells Makes Germ-line cells AKA Gametes (sperm & eggs) Used for sexual reproduction

APOPTOSIS

POLAR BODIES DEGENERATE (DIE), They "Self digest" using LYSOSOMES, "cell suicide" for the good of organism

Homologous chromosomes pair up during

PROPHASE I = SYNAPSIS

HOMOLOGOUS CHROMOSOMES

SAME SIZE SAME SHAPE CARRY GENES for the SAME TRAITS BUT NOT IDENTICAL (They may contain different versions of the genes)

Separation of homologous involves

SEGREGATION & INDEPENDENT ASSORTMENT, Combined with crossing-over, there is maximum variation due to gene shuffling in the resulting gametes

In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?

Sperm and egg should each have 23 chromosomes.

If egg and sperm had the same number of chromosomes as other body cells (46 each).

The baby would have too many chromosomes

Is Prophase I of Meiosis the only time crossing over occurs?

Yes— because there is no other time when tetrads form which is the structure necessary for crossing over to occur.

Separation of homologous chromosomes occurs

during ANAPHASE I

DIPLOID 2n

term used to refer to a cell that contains both sets of homologous chromosomes (most cells have 2 copies of each chromosome), all body cells (somatic) are diploid

HAPLOID 1n or n

term used to refer to a cell that contains only a single set of chromosomes and therefore only a single set of genes (some cells have only one copy of each chromosome), All sperm and egg cells are haploid

Homologous

term used to refer to chromosomes that each have a corresponding chromosome from the opposite-sex parent