Chapter 18 and Chapter 20 Cell division and the Human Life Cycle + Chromosome Disorders

DNA l INFORMATION IS WRITTEN IN A CHEMICAL LANGUAGE= DNA l OUR CELLS READ THE DNA IN THE NUCLEUS AND FOLLOW THE INSTRUCTIONS WRITTEN ON IT l LONG STRANDS OF DNA ARE CALLED CHROMOSOMES

CHROMOSOMES l UNROLLED WHEN READ OR COPIED l WE HAVE 2 VERSIONS OF EACH TYPE OF CHROMOSOME (1 FROM MOTHER AND 1 FROM FATHER) l 23 TYPES x 2 VERSIONS= 46 TOTAL l THE 23RD PAIR (TYPE) ARE THE SEX CHROMOSOMES WHICH CONTAIN THE GENES THAT DETERMINE SEX

CHROMOSOME PROBLEMS l MISTAKES ARE SOMETIMES MADE AS THE EGG AND SPERM ARE BEING MADE l SOMETIMES THE CHROMOSOMES IN THE EGG OR SPERM ARE DAMAGED OR TOO MANY OR TOO FEW CHROMOSOMES END UP IN THE EGG OR SPERM l PROBABLY MOST OF THESE TYPES AF CHROMOSOME ERRORS ARE NOT SURVIVABLE AND END IN A MISCARRAIGE l SOME OF THE EMBRYOS WITH DAMAGED/MISING/EXTRA CHROMOSOMES DO SURVIVE AND DEVELOP BUT WITH PROBLEMS

CHROM. DISORDERS DOWN SYNDROME- SHORT STATURE, EYELID FOLD, ROUND HEAD, RETARDATION (VARYING LEVEL) ALSO CALLED TRISOMY 21- CAUSED BY AN EXTRA COPY OF CHROMOSOME #21 l MORE COMMON IN CHILDREN BORN TO OLDER MOTHERS

CRI DU CHAT l FRENCH FOR “CRY OF CAT” l SMALL HEAD, MALFORMED LARYNX l OLDER- MISSHAPEN EARS, RETARDATION l CAUSE= PART OF CHROMOSOME #5 IS MISSING

SEX CHROMOSOMES l X AND Y- THE 23RD PAIR l WOMEN- XX MEN- XY l EGG- X SPERM- X OR Y l 50/50 CHANCE OF PRODUCING A BOY VS. GIRL

SEX CHROM. DISORDERS FRAGILE X SYNDROME- DAMAGED X CHROMOSOME l CHILD- HYPERACTIVE, AUTISTIC l ADULT- PROMINENT JAW AND EYES l MALES- RETARDATION MORE COMMON

WRONG # OF SEX CHROM. XO- TURNER SYNDROME l FEMALE WITH NO SEXUAL CHARACTERISTICS- INFERTILE l SHORT, WEBBED NECK, BROAD CHEST l NORMAL INTELLIGENCE

XXY- KLINFELTER Male with an extra X chromosome l STERILE MALE WITH LARGE HANDS AND FEET, LONG ARMS AND LEGS, MAY HAVE BREASTS l SOME ARE SLOW LEARNERS

XXX- TRIPLO- X A female with an extra X chromosome l SOME HAVE MENSTRUAL IRREGULARITIES AND EARLY MENOPAUSE l OTHERS LIVE A NORMAL LIFE

XYY- JACOB SYNDROME MALE WITH AN EXTRA Y CHROMOSOME l TALL MALE WITH PERSISTENT ACNE l SOME HAVE SPEECH AND READING PROBLEMS

HUMAN LIFE CYCLE l GROWTH- MITOSIS- SIMPLE CELL DIVISION l SEXUAL REPRODUCTION- UNION OF GAMETES (SPERM AND EGG) l GAMETES HAVE ONLY ONE COPY OF EACH TYPE OF CHROMOSOME l ZYGOTE GETS TWO COPIES (VERSIONS) OF EACH CHROM.

MITOSIS l THE DIVISION OF ONE BODY CELL INTO 2 IDENTICAL BODY CELLS l NORMAL BODY CELLS ARE DIPLOID (2N) l 2N 2N + 2N l 5 STEPS

INTERPHASE l SOME CELLS STAY IN THIS PHASE FOREVER (example- brain and spinal cord cells- these are not replaced when they are damaged) l IF A CELL IS PREPARING TO DIVIDE, IT WILL COPY THE CHROMOSOMES l ID CHROMOSOMES ARE PRODUCED CALLED SISTER CHROMATIDS AND ARE JOINED AT THE CENTROMERE

PROPHASE l NUCLEAR MEMBRANE FRAGMENTS l DNA COILS UP INTO VISIBLE CHROMOSOMES l SPINDLE FIBERS FORM FROM CENTRIOLS AND ATTACH TO CHROMOSOMES

METAPHASE l CHROMOSOMES ARE ALIGNED ALONG THE CENTER OF THE CELL

ANAPHASE l SISTER CHROMATIDS ARE PULLED APART (CENTROMERE IS SEPARATED)

TELOPHASE l CHROMOSOMES ARRIVE AT THE POLES AND A LASSO-LIKE FIBER PINCHES THE CELLS APART l NUCLEAR MEMBRANE REFORMS l DNA UNCOILS INTO CHROMATIN AND IS READABLE AGAIN l RESULTS IN 2 ID DIPLOID DAUGHTER CELLS

GAMETE PRODUCTION l GAMETES ARE HAPLOID (N) l CONTAIN ONLY ONE COPY OF EACH TYPE OF CHROMOSOME MEIOSIS- PROCESS THAT PRODUCES GAMETES l 2N CELL IN OVARIES OR TESTES HAPLOID GAMETES

MEIOSIS l 2 SETS OF STAGES- MEIOSIS 1 AND 2 l PROPHASE 1 - RECOMBINATION (CROSSING OVER) OCCURS- HOMOLOGOUS CHROMOSOMES SWAP LEGS l RESULTS IN A NEW COMBINATION OF TRAITS IN 2 OF THE 4 GAMETES

PROBLEMS IN MEIOSIS l NON- DISJUNCTION - FAILURE OF THE CHROMOSOMES TO SEPARATE PROPERLY DURING MEIOSIS l RESULTS IN AN UNEQUAL DISTRIBUTION OF CHROMOSOMES IN THE GAMETES l CAUSE OF DOWNS SYNDROME AND SEX CHROMOSOME DISORDERS

Inheritance Patterns

GENETICS l THE STUDY OF HOW TRAITS ARE INHERITED ALLELES- ALTERNATIVE FORMS OF THE SAME TRAIT THAT HAVE THE SAME POSITION ON HOMOLOGOUS CHROMOSOMES

ALLELES DOMINANT ALLELE- WRITTEN AS A CAPITAL LETTER RECESSIVE ALLELE- WRITTEN AS A LOWERCASE LETTER l EVERYONE HAS 2 ALLELES, ONE ALLELE CAME FROM YOU MOTHER AND THE OTHER CAME FROM YOUR FATHER

COMBINATIONS l 2 DOMINANT ALLELES= THE DOMINANT APPEARANCE (HOMOZYGOUS) l 2 RECESSIVE ALLELES= THE RECESSIVE APPEARANCE (HOMOZYGOUS) l 1 DOMINANT AND 1 RECESSIVE ALLELE= USUALLY THE DOMINANT APPEARANCE (HETEROZYGOUS)

GENO AND PHENOTYPES GENOTYPE- THE ALLELES THAT ARE PRESENT PHENOTYPE- THE OUTWARD APPEARANCE OF AN ORGANISM

GAMETE FORMATION l A RESULT OF MEIOSIS l THE 2 ALLELES ARE SEPARATED FROM EACH OTHER SO THAT EACH GAMETE CONTAINS ONLY ONE OF THE 2 ALLELES

PUNNETT SQUARE l SHOWS THE POSSIBLE GENOTYPES OF THE OFFSPRING l ALL POSSIBLE PARENTAL GAMETES ARE WRITTEN ON THE EDGES l THE CENTER IS FILLED IN AND REPRESENTS THE POSSIBLE GENOTYPES OF THE CHILDREN

PUNNETT SQUARE S= smooth s= wrinkled l Male parent genotype= Ss l Female Parent genotype= Ss l Genotypes- 25% of offspring will be SS (homozygous dominant) 50% will be Ss (heterozygous) and 25% will be ss (homozyg. recessive) l Phenotypes- 75% of offspring will be smooth and 25% will be wrinkled

DOMINANT DISORDERS NEUROFIBROMATOSIS- l BIRTH- TAN SPOTS ON THE SKIN l SMALL BENIGN TUMORS GROW RANDOMLY THROUGHOUT THE BODY l CAN BE MILD OR SEVERE l CAUSE= A MUTATED GENE THAT CONTROLS CELL DIVISION

DOMINANT DISORDERS HUNTINGTONS DISEASE- l DEGENERATION OF BRAIN CELLS IN MIDDLE AGED PEOPLE l MUSCLE SPASMS AND PERSONALITY DISORDERS l YRS AFTER ONSET= DEATH l CAUSE= A DNA REPEAT ON CHROMOSOME #4

Polydactyly- DOMINANT

RECESSIVE DISORDERS l CYSTIC FIBROSIS- 1/20 CAUCASIANS IS A CARRIER- l THICK MUCUS IS PRODUCED IN THE LUNGS AND PANCREAS = DIFFICULTY BREATHING AND DIGESTING FOOD- AVERAGE LIFE SPAN= 28 YEARS l CAUSE= BAD GENE ON CHROMOSOME 7

RECESSIVE DISORDERS PHENYLKETONURIA (PKU) l PERSONS LACK AN ENZYME THAT BREAKS DOWN PHENYLALANINE l UNLESS CHILDREN ARE PUT ON A DIET LOW IN PHENYLALANINE THEY WILL BECOME RETARDED l CAUSE= DAMAGED GENE FOR THE IMPORTANT ENZYME

POLYGENIC TRAITS l ONE TRAIT IS DETERMINED BY 2 OR MORE SETS OF ALLELES l SKIN COLOR AND HEIGHT l SOME RESEARCH SUGGESTS THAT ALLERGIES AND CANCER MAY ALSO BE CONTROLLED BY POLYGENES

MULTIPLE ALLELIC TRAITS l HUMAN BLOOD TYPE l A, B, O, AB l USED IN PATERNITY SUITS TO DISPROVE FATHERHOOD

INCOMPLETE DOMINANCE l THE INDIVIDUALS WITH ONE OF EACH TYPE OF ALLELE HAVE A MIXTURE OF THE TWO TRAITS l Red x White = Pink

SICKLE CELL ANEMIA l N= NORMAL n= SICKLE CELLS l nn= SICKLE CELL ANEMIA= DIE WITHOUT TREATMENT l Nn= CELLS WILL SICKLE ONLY UNDER STRESS= MALARIA PROTECTION l IN AFRICA- 60% ARE CARRIERS l TREATED BY BONE MARROW TRANSPLANTS

SEX LINKED TRAITS l X- LINKED TRAIT= ONLY CARRIED ON THE X CHROMOSOME RED/GREEN COLOR BLINDNESS- 8% OF CAUCASIAN MALES MUSCULAR DYSTROPHY- MALE BABIES- POOR MUSCLE FUNCTION l SONS GET THESE X LINKED TRAITS FROM THEIR MOTHERS

MORE X-LINKED TRAITS HEMOPHILIA- 1/15,000 MALE BIRTHS l LACK A BLOOD CLOTTING FACTOR AND TEND TO BLEED/BRUISE MUCH MORE WHEN INJURED

SEX INFLUENCED TRAITS PATTERN BALDNESS l RECESSIVE IN FEMALES, BUT IN THE PRESENCE OF TESTOSTERONE IT WILL BE EXPRESSED l THIS MEANS THAT IT IS DOMINANT IN MALES l MALE- Nn OR nn = BALD l FEMALE- Nn= NORMAL because they don’t have enough testosterone for it to be expressed nn= BALD WOMAN