Bell Work 2. Which cells are NOT formed during meiosis? Somatic cells Gametes Sex cells Sperm cells Bell Work Diploid (Body Cell) 2N Haploid (Sex Cell) 1N 46 50 10 8 20 14 31 28

DNA and Chromosomes Chromosomes are found in the nucleus Chromosomes are made of DNA Sections of chromosomes are called genes

DNA and Chromosomes Each organism has a distinct number of chromosomes, in humans, every cell contains 46 chromosomes. Other organisms have different numbers, for instance, a dog has 78 chromosomes per cell. Somatic Cells - body cells, such as muscle, skin, blood ...etc. These cells contain a complete set of chromosomes (46 in humans) and are called DIPLOID. Sex Cells - also known as gametes. These cells contain half the number of chromosomes as body cells and are called HAPLOID

DNA and Chromosomes Chromosomes come in pairs, called Homologous Pairs (or homologs). Imagine homologs as a matching set, but they are not exactly alike, like a pair of shoes. Diploid cells have 23 homologous pairs = total of 46 Haploid cells have 23 chromosomes (that are not paired) = total of 23

KARYOTYPE Human Chromosomes To examine human chromosomes, biologist photograph cells in mitosis when the chromosomes are fully condensed Cut out the chromosomes from the picture and group them together in pairs This type of picture is called a KARYOTYPE

Karyotypes A karyotype can tell you THREE things: Sex (male or female) Irregular numbers of chromosomes Any mutations in the chromosomes Basically: all the chromosomes in a cell are displayed and can be examined for any abnormalities

Remember… Humans have 46 chromosomes (23 pair) 2 of them are sex chromosomes  they determine what sex you are XX = female XY = male 44 of them are autosomes  they do not determine what sex you are

Who determines the sex of a child? The mother or the father? THE FATHER!!!!

Why does the father determine the sex of the offspring??? Mom is XX, she can donate either one X chromosome or the other X chromosome Dad is XY, he can donate either an X chromosome or a Y chromosomes. If the offspring receives the father’s X, it is female If the offspring receives the father’s Y, it is male

The Y chromosome If a Y chromosome is present, the person is male X chromosomes contain genes necessary for growth/development No cases of a person born with being 45,0Y Probably spontaneously aborted (miscarriage)

Human Genes The human genome is the complete set of genetic information Determines characteristics such as eye color and how proteins function within cells

Human Chromosomes Your chromosomes contain about 30,000 genes and 46 chromosomes Once thought to be over 100,000 genes That’s about 3 billion base pairs Remember: genes on the same chromosome are linked together They tend to be inherited together

Chromosomal Disorders Most of the time, the mechanisms that separate human chromosomes in meiosis work very well, but things can go wrong The most common error: NONDISJUNCTION The chromosomes fail to separate The result? Abnormal numbers of chromosomes Trisomy 21 (Down Syndrome) is a common example in human genetics

Disorders: Down Syndrome – three 21st chromosomes (trisomy 21) Turner Syndrome – single X chromosome Klinefelter’s Syndrome – XXY chromosomes Edwards Syndrome- trisomy 18

Edwards Syndrome (Trisomy 18) Frequency: 1 in 6000 births copyright cmassengale

Turner Syndrome single X chromosome Frequency: 1 in 2000 births copyright cmassengale

Klinefelter’s Syndrome XXY chromosome Frequency: 1 in 7000 males copyright cmassengale

Normal Female copyright cmassengale 2n = 46

Normal Male copyright cmassengale 2n = 46

Klinefelter’s Syndrome Karyotype Notation (total # chromosomes, sex chromosomes and extra or missing autosomal) copyright cmassengale

Male, Trisomy 21 (Down’s) copyright cmassengale 2n = 47

Female Down’s Syndrome (Trisomy 21) copyright cmassengale 2n = 47

Turner’s Syndrome (Single X) copyright cmassengale 2n = 45