Gamete Formation & Genetic Variation

Gamete Formation The production of gametes is called __________________ and results in the formation of __________ and _________. The process of male gametogenesis is called _____________________ and the process of female gametogenesis is called __________________. gametogenesis spermegg spermatogenesis oogenesis

SPERMATOGENESIS Takes place in the ___________. It all starts with a diploid germ cell called a ____________________. This cell undergoes meiosis I and meiosis II and eventually becomes 4 haploid __________ cells Sperm can either be made throughout the year as in ___________ or only during breeding season as seen in ___________________. testes spermatogonium sperm humans migratory birds

OOGENISIS Takes place in the ___________. Starts with a diploid germ cell called an _____________. Undergoes meiosis I and meiosis II The cytoplasm does not equal divide and the larger of the 2 cells after meiosis I is called a _________________, the smaller cell is called a _______________ and is not a viable sex cell As the primary oocyte undergoes meiosis II, the cytoplasm unequally divides again and only ONE cell becomes an _______ (ovum) and the other cell is again a _____________ and is not a viable sex cell The unequal cytoplasmic division is to give the ovum enough nutrients to support the zygote in the first few days of fertilization Therefore after meiosis I and meiosis II, there is only ____ haploid ovum ovaries oogonium primary oocyte polar body egg polar body 1

SPERMATOGENESIS OOGENESIS

Meiosis & Genetic Variation Through crossing over and random segregation of the chromosomes during meiosis results in _______________________. When there are errors in meiosis these results in genetic errors throughout the entire organism. Why? genetic recombination This is because chromosomes are combined when the zygote is formed and then these chromosomes are copied during interphase before each mitosis. Therefore, all the cells that develop from this zygote will carry the mutation.

NONDISJUNCTION (Abnormal Meiosis) Occurs when homologous chromosome pairs move to the same pole during meiosis. The result is that one daughter cell is ____________ one chromosome and the other will have an _________ chromosome. When cells have too much information or too little information, the cells will not function properly. Since this most commonly occurs in the gametes, once the zygote is formed the entire organism will have this abnormal chromosomal count. In humans nondisjunction will produce gametes with _____ and _____ chromosomes. When a zygote is created from a cell that contains 23 and 24 chromosomes the individual will have a diploid count of ______. This condition is referred to as _____________ because there are 3 chromosomes instead of just 2 on one pair of the homologues. missing extra trisomy

If the zygote created from cells that contain 22 and 23 chromosomes, the individual will have a diploid number of _____. This condition is called _______________ because there is just one chromosome instead of the usual homologous pair. Once the cells of these zygotes begin to divide, each cell of the body will contain greater than or less than 46 chromosomes. 45monosomy

NONDISJUNCTION DISORDERS The most common type of trisomy is __________________. There was an unequal division of the 21st homologous pair and that is why this disorder is sometimes called _____________. Down Syndrome trisomy 21 - Three chromosomes # 21’s - 1 in 6000 babies - Mental retardation with wide range of mental abilities - risk of having child with DS increases with age of mother - woman in 40’s has 25x greater chance than woman in 20’s

Another nondisjunction order that occurs in the sex chromosomes is called _____________________. This occurs when both ____ chromosomes migrate to one pole and the other cell has ____ X chromosomes. When the egg with no X chromosomes is fertilized by a normal sperm cell with an X chromosome a female will be produced with ___________________. They never sexually mature and are unable to pass on this defect. Most are usually miscarried before the first 20 weeks of pregnancy. Turner Syndrome X no 45 chromosomes - Appear to be female - Do not develop sexually - Tend to have thick, wide necks - 1 in 3000 people have Turner Syndrome

_______________________ is caused by nondisjunction in either sperm or egg. The child inherits two X chromosomes and a single Y chromosome. The child appears to be a male at birth, but as he enters puberty, he produces high levels of female sex hormones. These males are sterile. Kleinfelter Syndrome 1 in every 500 males

KARYOTYPE CHARTS During genetic screening, a __________________ can be done which arranges all of the chromosomes in pairs. From here any chromosomal disorders and even the gender can be predicted from this chart. karyotype chart

KARYOTYPE CHARTS continued… Technicians take a small tissue sample and treat it with a solution that causes mitosis. They then treat the sample with another solution to stop mitotic division at metaphase seeing that the chromosomes are the most condensed and the centromeres is the most discernable. The cells are then placed on a slide and stained. A photograph is then taken and enlarged. The chromosomes are then cut out and matched up with their homologous pair. Finally the pairs are aligned at their centromeres in decreasing size. The sex chromosomes are always placed last.

Seatwork / Homework Read Section 5.2 (p. 167 – 174 only) Answer # 3, 4, 5, 7, 9, 11 (p. 174)