Transcript Human genetics * chapter 14

Mrs. Williams
Freshman Biology
Semester Two
HUMAN GENETICS
Human Genetics
 Humans have 23 paired chromosomes in
somatic cells
 Each chromosome has many genes located
on it
 Some genes have a simple Mendelian type
of inheritance
 Most traits have a complex inheritance
 Polygenic traits
 Multiple Alleles
 Influenced by Both Genetics and Environment
Karyotypes
 A karyotype is a diagram of chromosomes
within a cell
 Homologous chromosomes are paired
 Autosomes (non-sex chromosomes) are
arranged from largest to smallest
 Largest autosome is #1: smallest autosome is
#22
 Sex chromosomes are last (#23)
 XX in females
 XY in males
Karyotype Info
 Karyotypes can tell:
 Sex of Individual
 Presence of a Chromosomal Disorder
 Extra or missing whole chromosomes
 Large extra or missing piece of chromosome
 Can’t tell:
 Genetic Disorders from Small Mutations
Chromosomal Abnormalities
 Missing or extra whole chromosomes or pieces of
chromosomes
 The condition is determined by which
chromosome is affected
 This is because each chromosome has different
genes
 May affect all cells
 Fertilized egg had the mistake
 Person may be a mosaic (some normal, some bad)
 Mistake happened later in development
Nondisjunction
 Mistake during Meiosis or Mitosis
 Non-disjunction: failure of the chromosomes
to separate properly
 Often happens in Anaphase I when tetrads
separate
Terms for Chromosomal
Disorders
 Trisomy
 3 copies of one type of chromosome
 Monosomy
 1 copy of one type of chromosome
 Only monosomy that is viable is XO
Specific Disorders
 Down’s Syndrome (Trisomy 21)
 Edwards Syndrome (Trisomy 18)
 Patau Syndrome (Trisomy 13)
 Turners Syndrome (XO)
 Kleinfelter Syndrome (XXY)
Down Syndrome
(Characteristics)
Edwards Syndrome
(Characteristics)
Patau Syndrome
(Characteristics)
Turner Syndrome
(Characteristics)
Klinefelter Syndrome
(Characteristics)
Chromosomal Alterations
 Chromosomal Alterations Video
 Create a circle map describing chromosomal
alterations while you watch the video. Be sure
to include all important information!
Human Blood Types
 Human blood types have a gene that displays
multiple alleles and codominance
 ABO gene has three alleles:
 IA codes for an A-type ID tag on red blood cells
 IB codes for a B-type ID tag on red blood cells
 i codes for no ID tag on red blood cells
 IA and IB alleles are codominant
Human Blood Types
 Possible Phenotypes and Genotypes
 A blood type (IAIA or IAi)
 B blood type (IBIB or IBi)
 AB blood type (IAIB)
 O blood type (ii)
Inheritance of Sex
 Moms give
 Sons and Daughters one of their X chromosomes
(random choice)
 Eggs have a single X chromosome
 Dads give
 Daughters their X chromosome
 Sons their Y chromosome
 Half of the sperm carry an X
 Half carry a Y
Patterns of Inheritance
 Autosomal Dominant/Recessive
 Gene for Trait is found on a autosome
 Can be dominant or recessive
 Sex-linked
 Gene for Trait is found on a sex chromosome
 Most (almost all) are found on X (many more
genes than Y)
 Can be dominant or recessive
X-Linked Traits
 Moms
 No “bad” X’s- 0% chance of passing on
 One “bad” X- have a 50% of passing the “bad” X to
their offspring
 Two “bad” X’s- have a 100% chance of passing one
of them on
 Dads (can only have one copy)
 Only pass the “bad” X to daughters; sons get the Y
Y-Linked Traits
 Only Males can have them
 Dads pass on the trait to all sons
X-Linked Punnett Squares
 Genotypes of each parent are written as
superscripts on their sex chromosomes
 Ex: XHXh and XhY
 Remember males only have one copy
because they only have one X
 DO NOT CROSS TWO FEMALES
 When analyzing data
 If question asks about offspring, consider all 4
 If question narrows it down to one sex, only look
at the two of that sex
X-Linked Punnett Square
Recessive X-Linked Disorders
 Show up more in males
 Females have two X’s
 Harder to inherit two “bad” X’s to show disorder
 Males have only one
 Easier to inherit the one copy needed for them to
show the disorder
Exit Slip
 1. Name the two things that are unique about
the alleles for human blood types.
 2. What are the four possible genotypes and
phenotypes for human blood?
 3. Draw a Punnett Square showing a cross
between a female heterozygous for hemophilia
and a hemophiliac male and answer the
following:
 A. How many male offspring have hemophilia?
 B. How many female offspring have hemophilia?