Production of the Sperm and Egg Meiosis Introduction Production of the Sperm and Egg

Genetics and Heredity The transmission of traits from one generation to the next is called heredity or inheritance. However, offspring differ somewhat from parents and siblings, demonstrating variation. Genetics is the study of heredity and variation.

Genes Parents pass on genes to their offspring Genes program specific traits that emerge as we develop from fertilized eggs into adults. Example: Your may have a gene for blue eyes, which you inherited from your mother. Genes are segments of DNA. In plants and animals, sperm and ova (unfertilized eggs) transmit genes from one generation to the next.

Chromosomes Sex chromosomes: determine an individuals sex XX = Female XY = Male Autosomes: any chromosome that is not a sex chromosome

Types of cells Somatic cell: any cell other than the sperm or ovum Contains 46 chromosomes diploid: has two sets of chromosomes (2n) Gametes: reproductive cells – the sperm and ovum Contains 23 chromosomes haploid: only have one set of chromosomes (1n)

Homologous chromosomes Homologous chromosomes: The chromosomes that make up a pair Pairs are due to sexual reproduction: we inherit one chromosome of each pair from each parent. One from mommy one from daddy!   They carry the same genes controlling the same inherited characteristics They have the same length, centromere position, staining pattern Also known as “homologues”

Purpose of Meiosis The purpose of meiosis is to produce haploid cells: the sperm and ovum This way, when the sperm and ovum fuse the baby will have a full set of chromosomes Sperm (23) + ovum (23) = baby (46 chromosomes) The fertilized egg (zygote) now has two chromosomes bearing genes from the maternal and paternal family lines.

Life Cycle Fertilization and meiosis alternate in sexual life cycles.

Karyotype: a display of the 46 chromosomes (shows 23 pairs of chromosomes)

Normal Karyotype

Meiosis Gone Wrong What happens if meiosis does not work correctly?!

Down Syndrome characteristic facial features, short stature; heart defects susceptibility to respiratory disease, shorter lifespan prone to developing early Alzheimer's and leukemia often sexually underdeveloped and sterile, usually some degree of mental retardation.

Patau Syndrome Results in serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months.

Edward Syndrome Almost every organ system affected 1:10,000 live births. Children with full Trisomy 18 generally do not live more than a few months.

Klinefelter Syndrome Male sex organs; unusually small testes, sterile. Breast enlargement and other feminine body characteristics. Normal intelligence.

Turner’s Syndrome 1:5000 live births; the only viable monosomy in humans - women with Turner's have only 45 chromosomes!!! XO individuals are genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence. (98% of these fetuses die before birth)

Conclusion It is terribly important that meiosis works correctly! The homologous chromosomes need to be separated perfectly so the sperm and ovum have 23 different chromosomes. Let’s see how this takes place…