Chapter 14 The Human Genome

1. Chapter 14The Human Genome • Section 14-1 • Human Heredity • TEKS: 6F Identify and analyze karyotypes

2. Organisms that reproduce Sexually are made up of two different types of cells. • Somatic Cells are “body” cells and contain the normal number of chromosomes ….called the “Diploid” number (the symbol is 2n). Examples would be … skin cells, brain cells, etc. • Gametesare the “sex” cells and contain only ½ the normal number of chromosomes…. called the “Haploid” number (the symbol is n)….. Sperm cells and ova are gametes. n = number of chromosomes in the set… so….2n means 2 chromosomes in the set…. Polyploid cells have more than two chromosomes per set… example: 3n (3 chromosomes per set)

3. Gametes • The Male Gamete is the Sperm and is produced in the male gonad the Testes. • The Female Gamete is the Ovum (ova = pl.) and is produced in the female gonad the Ovaries.

4. sperm n=23 n=23 egg 2n=46 zygote Fertilization • The fusion of a sperm and egg to form a zygote. • A zygote is a fertilized egg

5. During Ovulation the ovum is released from the ovary and transported to an area where fertilization, the joining of the sperm and ovum, can occur…… fertilization, in Humans, occurs in the Fallopian tube. Fertilization results in the formation of the Zygote. (fertilized egg) Sperm + Ovum (egg) Zygote fertilization (n) + (n) (2n)

6. Why are chromosomes Important ? • Abnormal chromosome numbers, extra chromosomes or fewer chromosomes than normal, can seriously effect the survival chances of the offspring.

7. Chromosomes • If an organism has the Diploid number (2n) it has two matching homologues per set. One of the homologues comes from the mother (and has the mother’s DNA).… the other homologue comes from the father (and has the father’s DNA). • Most organisms are diploid. Humans have 23 sets of chromosomes… therefore humans have 46 total chromosomes….. The diploid number for humans is 46 (46 chromosomes per cell).

8. Homologous Chromosomes • Pair of chromosomes (maternal and paternal) that are similar in shape and size. • Homologous pairs (tetrads) carry genes controlling the same inherited traits. • Each locus(position of a gene) is in the same position on homologues. • Humans have 23 pairs of homologous chromosomes. 22 pairs of autosomes 1 pair of sex chromosomes

9. eye color locus eye color locus hair color locus hair color locus Paternal Maternal Homologous Chromosomes(because a homologous pair consists of 4 chromatids it is called a “Tetrad”) PaternalMaternalChromosomeChromosome

10. Humans have 23 Sets of Homologous ChromosomesEach Homologous set is made up of 2 Homologues. Homologue Homologous set #1 Homologue

11. Autosomes(The Autosomes code for most of the offspring’s traits) In Humans the “Autosomes” are sets 1 - 22

13. Karyotype • A picture of the chromosomes from a human cell arranged in pairs by size • First 22 pairs are called autosomes • Last pair are the sex chromosomes • XX female or XY male

15. Males and females are born in roughly a 50:50 ratio. All human egg cells carry a single X chromosome (23X). In sperm half carry an X chromosome (23X) and half carry a Y chromosome(23Y). BOYS OR GIRLS?

16. BOYS OR GIRLS? This insures that just about half of the zygotes will be 46XX (female) and the other half will be 46XY (male).

17. Boy or Girl? The Y Chromosome Decides Y - Chromosome X - Chromosome

18. Sex ChromosomesThe Sex Chromosomes code for the sex of the offspring.** If the offspring has two “X” chromosomes it will be a female. ** If the offspring has one “X” chromosome and one “Y” chromosome it will be a male. In Humans the “Sex Chromosomes” are the 23rd set XX chromosome - female XY chromosome - male

19. Sex Chromosomes “Sex Chromosomes” …….the 23rd set This person has 1 “X” chromosome and 1 “Y” chromosome… this is a male. 23

20. Sex Chromosomes “Sex Chromosomes” …….the 23rd set This person has 2 “X” chromosomes… and is a female. 23

21. WHERE DO THE CELLS COME FROM? • The liquid (amniotic fluid) around the unborn baby (fetus) in the womb contains skin cells shed by the fetus and waste products from the fetus. The fetal skin cells in the amniotic fluid - like every cell in our bodies - carry DNA. • A small amount of amniotic fluid (about 2 tablespoons; 20mls or so) is removed through a hollow needle inserted into the pregnant woman’s uterus (womb), through her abdomen. • Any fetal material in the fluid can then be tested - for example to determine whether the fetus has a genetic abnormality.

22. 2 WAYS TO GET CELLS FOR KARYOTYPES

23. PREPARING THE CELL SAMPLE

24. WHEN IS AN AMNIOCENTESIS PERFORMED? • An amniocentesis is generally performed during the fourth month of pregnancy.

25. CHROMOSOMAL ________________ Abnormalities • 1 infant in 200 newborns has a chromosomal abnormality • 28% of first trimester miscarriages have a chromosomal abnormality • Abnormalities in larger chromosomes don’t usually survive

26. CHROMOSOMAL MUTATIONS ____________________________: Change in the ______________ or ____________ of chromosomes STRUCTURE NUMBER

27. FAIL TO SEPARATE NONDISJUNCTION Homologous chromosomes ________________ during MEIOSIS = _________________________ One cell gets 2 copies of the chromosome the other cell gets none.

28. Normal Meiosis Nondisjunction http://web.udl.es/usuaris/e4650869/docencia/gen_etica/meioferti2.html http://www.tokyo-med.ac.jp/genet/anm/domov.gif

29. Nondisjunction Since it happens to a sperm or egg, the new baby can end up with _____________ of a chromosome =__________________ OR only ___________ of a chromosome = _________________ 3 COPIES TRISOMY ONE COPY MONOSOMY

32. Nondisjunction n+1 n n-1 n trisomy 2n+1 monosomy 2n-1

33. Some Non-disjunction Disorders • Down’s Syndrome – Trisomy 21 • Turner’s Syndrome – Monosomy 23 (X) • Kleinfelter’s Syndrome – Trisomy 23 (XXY) • Edward’s Syndrome – Trisomy 18 • Patau’s Syndrome – Trisomy 13

35. TRISOMY 21 Down syndrome (= ____________)

36. Down syndrome (Trisomy 21) • Most common chromosomal abnormality • 50% have heart defects that need surgery to repair • Mild to severe mental retardation • Increases susceptibility to many diseases • Risk of having a child with Down syndrome increases with age of mom

37. Down syndrome (Trisomy 21) • 1 IN 800 BIRTHS • SIMILAR FACIAL FEATURES • SLANTED EYES • PROTRUDING TONGUE

38. DOWN SYNDROME • SHORT, BROAD HANDS • STUBBY FINGERS • ROUGH SKIN • IMPOTENCY IN MALES • MENTALLY RETARDED • SHORTENED LIFESPAN

39. Down syndrome (Trisomy 21) Simian line on palm

40. Down syndrome (Trisomy 21) • Risk of having a child with Down syndrome related to age of mom • More common in women UNDER 16 or OVER 35 Cells that make eggs start meiosis in embryo Stop in PROPHASE I (synapsis)One egg restarts & finishes division each monthSo an egg released at age 40 has been in synapsis for 40 years . . . chromosomes more likely to “stick”

41. Down syndrome & age of mother Rate of miscarriage due to amniocentesis: • 1970s data0.5%, or 1 in 200 pregnancies • 2006 data<0.1%, or 1 in 1600 pregnancies

42. Edward’s Syndrome – Trisomy 18 • LOW BIRTH WEIGHT • ABNORMALLY SHAPED HEAD • HEART DEFECTS • MOST ORGAN SYSTEMS MALFORMED • ONLY 5-10% OF LIVE BORN WILL SURVIVE THEIR FIRST YEAR OF LIFE

43. Patau’s Syndrome – Trisomy 13 • USUALLY FATAL • 1 IN 14,OOO • BABIES BORN TYPICALLY LIVE ONLY A FEW DAYS • < 10% LIVE ONE YEAR

44. CAUTION THE NEXT SLIDE CONTAINS SOME GRAPHIC PICTURES LOOK AWAY IF YOU DON’T WANT TO SEE THEM

45. Patau’s Trisomy Syndrome

46. Turner’s Syndrome – Monosomy 23 (X) A congenital condition of females associated with a defect or absence of an X-chromosome, characterized by short stature, sexual underdevelopment, and other physical abnormalities.

47. Turner syndrome

48. XO Turner syndrome ____ • 1 in 2500 births • Females have only one X chromosome • Small size • Slightly decreased intelligence • 35% have heart abnormalities • Hearing loss common • Broad shoulders and neck webbed • Reproductive organs don’t develop at puberty • Can’t have children

50. Klinefelter syndrome XXy