35 Gametogenesis

Distinguish among somatic cells, germline cells, and gametes in terms of function and whether the cells are diploid or haploid.

Germ cell: diploid cells that are specified early in development, give rise to gametes by meiosis

somatic cells: diploid cells support sexual reproduction

gametes: haploid cells that propagate genetic information to progeny

Outline how rounds of DNA replication and division produce a haploid nucleus from the nucleus of a diploid germline cell.

only one round of DNA replication and 2 rounds of division

• meiosis I: separation of duplicated homologous chromosomes

• meiosis II: separation of sister chromatids

duplicated homologous chromosomes form what structure

bivalent/tetrad

• duplicated homologs pair during meiotic prophase

why is homologous pairing and cross over important during prophase of meiosis

it ensures genetic diversity and separation after first meiotic division so each haploid cell has a single sister chromatid / proper segregation of duplicated homologs

Differentiate how cohesins are degraded during anaphase in meiosis I from their degradation during anaphase in meiosis II.

Meiosis I: cohesins holding the arms of the non-sister chromatids together are suddenly degraded, cohesins at the centromere continue to hold the sister chromatids together

Meiosis II: cohesins holding the sister chromatids together at the centromere are degraded

how is the kinetochore different in meiosis I than in meiosis II

kinetochore of sister chromatids function as a single unit in meiosis I and function independently in meiosis II to allow separation of sister chromatids

Explain how nondisjunction gives rise to aneuploid gametes, and recall the consequences of this type of genetic error.

nondisjunction occurs due to errors in chromosome segregation which can give rise to disease

Understand how PGCs give rise to male and female gametes

PCG can form wither egg or sperm

• migrate to genital ridge, once they go to developing gonad they undergo mitotic division and eventually choose a path

• default path is to become ovary and develop female gametes

• some cells in genetical ridge express genes so males can develop male via the Y chromosome

  • somatic cells express Sry gene on Y chromosome to develop Sertoli cells

describe spermatogenesis

• how many haploid sperm are formed

• what is differentiation of sperm called

• when does spermatogenesis begin

spermatogenesis:

• A spermatocyte undergoing meiosis results in the formation of 4 haploid sperm

• Cellular differentiation of a sperm cells is called spermiogenesis

• Spermatogenesis begins at puberty and continues through most of the male's life

describe oogenesis

• describe the 1st arrest

• describe the second arrest

• how many nuclei form from primary oocyte

• when do oocytes undergo differentiation

• when does oogenesis begin

oogenesis

• Primary oocytes arrest at Prophase I until ovulation

• secondary oocyte arrest in metaphase II after ovulation and remains arrested until fertilization

• only 1 nuclei will from primary oocyte and will produce functional egg/ovum

• Oocytes undergo cellular differentiation prior to the completion of meiosis

• Oogenesis begins before a female fetus is born

describe oogenesis arrest in prophase I compared to ovulation in terms of cAMP levels, Wee 1, CDC 45, and M-CDK

prophase I

• cAMP high → active PKA

• inhibit CDC 25 and activate Wee 1 to inactivate MCDK complex

ovulation

• low cAMP → inactive PKA

• active CDC 25

• active MCDK

Describe where and how sperm and egg unite during fertilization

zona pellucida induces sperm to undergo acrosome reaction to allow penetration and fusion with egg

outline the mechanisms that prevent multiple sperm from entering the egg.

sperm fusion activate egg by increasing Ca2+ in cytosol, causing enzymes to be exocytosed changing the conformation of zona pellucid so no other sperm can enter

spermiogenesis

process of cell differentiation

• no cell division

• spermatid to mature spermatozoa

When are primary oocytes arrested

Diplotene at prophase I

which cells direct sexual differentiation along a male pathway

Sertoli cells

what helps direct PGCs to develop into sperm

the SRY gene of the Y chromosome on a somatic cell that eventually develops into a Sertoli cell

where does fertilization occur

ampulla region of the oviduct