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Human Genetics. Chapter 27 pp 565-583. Chromosome Number. Human sperm or egg cell has 23 chromosomes Human body cell has 23 pairs of chromosomes, or 46 chromosomes total Different organisms have different numbers of chromosomes. Amniocentesis. Way of looking at the chromosomes of a fetus

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human genetics

Human Genetics

Chapter 27

pp 565-583

chromosome number
Chromosome Number
  • Human sperm or egg cell has 23 chromosomes
  • Human body cell has 23 pairs of chromosomes, or 46 chromosomes total
  • Different organisms have different numbers of chromosomes
  • Way of looking at the chromosomes of a fetus
  • Amniotic fluid is removed to extract fetal skin cells
  • Cells are grown for about 10 days to study chromosomes during cell division
sex chromosomes
Sex Chromosomes
  • Human females have two X chromosomes in each body cell
  • Human males have one X and one Y chromosome in each body cell
  • Chromosomes that do not determine the sex of the offspring
  • These are the same in males and females
human characteristics
Human Characteristics
  • Two different forms of the same gene – one on each chromosome
  • Dominant – keep other genes from showing their traits
  • Recessive – do not show their trait when a dominant gene is present
punnett square
Punnett Square
  • Way to show which genes can combine when egg and sperm combine
incomplete dominance
Incomplete Dominance
  • Neither gene is totally dominant over the other
  • New trait is expressed
  • Mixture of the dominant and recessive traits
  • Two genes are dominant over a third, but not dominant over each other
sex linked traits
Sex-linked Traits
  • Y chromosome does not have all of the gene located on the X chromosome
  • Genes on the X chromosome controls the traits
human blood types
Human Blood Types
  • Although three genes control blood type, a person only has two genes
  • A and B are dominant to O
  • They are not dominant to each other
blood types genes






AA or AO

BB or BO

Blood Types & Genes
sickle cell anemia
Sickle-cell Anemia
  • Genetic disorder in which some red blood cells are shaped like sickles
  • Sickle cells do not carry oxygen as well as round blood cells
  • RR = normal blood cells
  • RR’ = normal and sickle cells
  • R’R’ = sickle cell anemia
  • Rare recessive disorder in which a person’s blood does not clot
  • Small cuts may bleed for hours
  • Usually occurs in males
  • Dominant condition in which people see and write some letters or parts of words backwards
  • Also called word blindness
The dyslexic may reverse letters like b and d, or p and q, either when reading or writing.
  • He may invert letters, reading or writing n as u, m as w, d as q, p as b, f as t.
  • He may mirror write letters and perhaps numbers, ‘ε’ for ‘3’.
  • He may read or write words like no for on, rat for tar, won for now, saw for was.
  • He may read or write 17 for 71.
color blindness
Color Blindness
  • Condition in which reds and greens look like shades of gray or other colors
  • Males are more likely to be color blind
genetic counseling
Genetic Counseling
  • The use of genetics to predict and explain traits in children
  • Diagram that can show how a certain trait is passed along in a family