Transcript Inheritance Honors pt. 2


Construct and interpret a pedigree.
Pedigree Analysis: Vocab
 Pedigree: family record or tree that shows
how a trait is inherited over several
generations.
 Carriers: have an allele for a phenotype,
but do not have that phenotype

What must their genotype be?
Studying Human Genetics
 Circle – female
 Square – male
 Shaded – afflicted with
trait
 Half shaded or Dot –
carrier
 X – deceased
 Horizontal line –


mating “marriage line”
“sibling line”
 Vertical line – children
 Diagonal lines – twins
 Order of birth is from
left to right
Autosomal Dominant
 Autosomal dominant – allele is dominant
and on an autosomal chromosome (1-22)
 Every person with the trait, also had a
parent with it.
Autosomal Recessive
 Autosomal Recessive - allele is recessive
and on an autosomal chromosome (1-22)
 Trait only appears when two alleles are
present so there can be carriers.
 Trait often skips several generations or
shows up seemingly out of nowhere.
What is the sex of person 7?
How many children does person 9 have?
What is the sex of person 9’s oldest child?
Does person 11 or person 9 have the trait?
How are person 1 and person 3 related?
How are person 8 and person 9 related?


Use a Punnett Square to determine phenotype
and genotype probabilities in a dihybrid cross.
Explain Mendel's three laws and how they can
be observed in a dihybrid cross.
Dihybrid Crosses
 More than one trait can be passed on at the same
time.
 Dihybrid Punnett Squares can determine the
outcome of two traits at once.
 STEP 1: Determine the possible gametes of the
parents
SsBb - will pass one “s” and
one “b” to offspring
Example:
SsBb 
SB, Sb, sB, sb
Predicting Dihybrid Crosses
Heterozygous x Heterozygous
 Round Yellow (RrYy) x Round Yellow (RrYy)
 Results:




9/16: round yellow
3/16: round green
3/16: wrinkled yellow
1/16: wrinkled green
 Ratio:

9:3:3:1
Dihybrid Crosses
9/16 = 56% yellow round
3/16 = 19% yellow wrinkled
3/16 = 19% green round
1/16 = 6% green wrinkled
 In a dihybrid cross, examples of all three laws can be
observed.
Law of Dominance = Rr zygotes have round seeds.
Law of Segregation = Each gamete has only one R allele.
Law of Independent Assortment = A gamete with R could then
have either Y or y .
Beyond Mendel’s Laws
of Inheritance


Identify inheritance patterns indicating
codominance, incomplete dominance, sexlinkage, multiallelic traits, and polygenic traits.
Construct monohybrid crosses for
codominance and incomplete dominance
scenarios.
Extending Mendelian genetics
 Mendel worked with a simple system
most traits are controlled by single gene
 each gene has only 2 version

 1 completely dominant (A)
 1 recessive (a)
 But it’s usually not that simple!
Incomplete dominance
 Incomplete dominance: Heterozygotes
have a new phenotype that is a blended
“in-between” appearance
 RR = red flowers RR
 rr = white flowers WW
 Rr = pink flowers RW
RR
Rr
rr
Incomplete dominance
P
X
true-breeding
red flowers
true-breeding
white flowers
100% pink flowers
1st
100%
generation
(hybrids)
self-pollinate
25%
red
2nd
generation
50%
pink
25%
white
1:2:1
Incomplete dominance
RW x RW
%
genotype
male / sperm
female / eggs
R
R
W
RR
W
RR
RW
RW
%
phenotype
25% 25%
50% 50%
RW
RW
WW
WW
25% 25%
1:2:1
1:2:1
Codominance
 Codominance


Heterozygotes express both
phenotypes simultaneously
Examples: Roan cows/horses,
speckled chickens, human ABO
blood groups
 A & B alleles are codominant
 both A & B alleles are dominant
over O allele
 the gene codes for different sugars
on the surface of red blood cells
Genetics of Blood type
phenogenotype
type
A
B
AB
O
antigen
on RBC
antibodies
in blood
donation
status
IAIA or IAi
type A antigens
on surface
of RBC
anti-B antibodies
__
IBIB or IBi
type B antigens
on surface
of RBC
anti-A antibodies
__
IAIB
both type A &
type B antigens
on surface
of RBC
no antibodies
universal
recipient
ii
no antigens
on surface
of RBC
anti-A & anti-B
antibodies
universal
donor
Blood donation
clotting clotting
clotting
clotting
clotting
clotting
clotting
One gene: many traits
 The genes that we have covered so far

affect only one trait
But most genes affect many traits
 dwarfism (achondroplasia)
 gigantism (acromegaly)
Many genes: one trait
 Polygenic inheritance
additive effects of many genes
 humans

 skin color
 height
 weight
 eye color
 intelligence
 behaviors
Human skin color
 AaBbCc x AaBbCc

can produce a wide
range of shades
Coat color in other animals
 Example: 2 genes: E,e and B,b


color (E) or no color (e)
how dark color will be: black (B) or brown (b)
eebb
eeB–
E–bb
E–B–
Environment effect on genes
 Phenotype is controlled by
both environment & genes
Human skin color is
influenced by both genetics
& environmental conditions
Color of Hydrangea flowers
is influenced by soil pH
Coat color in arctic
fox influenced by
heat sensitive alleles
Honors Biology
Chapter 12
HUMAN GENETICS
Genetics of sex
 Biological sex is determined by genetics
and hormonochemical environment during
development
 In mammals = 2 sex chromosomes

X&Y

2 X chromosomes = female: XX

X & Y chromosome = male: XY
X
X
X
Y
Sex chromosomes
Sex-linked traits
 Sex chromosomes have genes
on them
 These traits = sex-linked


Most sex-linked traits affect
men and women in different
frequencies
X
X
X
Y
Human examples:
 hemophilia
 Duchenne muscular dystrophy
 red-green color blindness
sex-linked recessive
Sex-linked traits
2 normal parents,
but mother is carrier
HY x XHh
H Xh
XHH
male / sperm
XH
XH
Y
XH
XH XH
XH Y
Xh
XH Xh
XhY
Y
XH
XH Xh
Xh
female / eggs
XH Y
X-linked Recessive
 X-linked Recessive – allele is recessive and is
located on the X chromosome
 Males are more likely to show trait
X-linked Dominant
 X-linked Dominant - allele is dominant and is
located on the X chromosome
 Only tiny pedigree clue: an afflicted father’s
daughters will all be afflicted but not his sons
Y-Linked Dominant or Recessive
 Y linked - allele is on the Y chromosome
 Affected fathers pass it onto every son, every
son has affected father
 Females never affected
Errors of Meiosis
Chromosomal Abnormalities


Explain how nondisjunction leads to
chromosomal abnormalities
Identify chromosomal abnormalities in a
karyotype.
Chromosomal abnormalities
 Breakage of chromosomes can occur
 Incorrect number of chromosomes

nondisjunction
 chromosomes don’t separate properly
during meiosis
Breakage of Chromsomes
 deletion

loss of a chromosomal segment
 duplication

repeat a segment
 inversion

reverses a segment
 translocation

move segment from one chromosome
to another
Nondisjunction
 Problems in meiosis that cause errors in
daughter cells

chromosome pairs do not separate properly
during anaphase I or anaphase II
 =too many or too few chromosomes
2n
n-1
n
n+1
n
Alteration of chromosome number
Nondisjunction
 Baby has wrong chromosome number

trisomy
 cells have 3 copies of a chromosome

n+1
monosomy
 cells have only 1 copy of a chromosome
n-1
n
n
trisomy
monosomy
2n+1
2n-1
Human chromosome disorders
 High frequency in humans
Estimated 2/3 of embryos miscarry
 alterations are too disastrous
 developmental problems result from
biochemical problems

Karyotyping
 The chromosomes are
photographed, cut out,
and arranged by size and
shape into pairs.
 Karyotype used to look
for abnormalities &
determine sex
How to Name a Karyotype
1. Look at X&Y chromosomes to
determine sex
2. Count the number of
chromosomes (more or less
than 46?)
3. Find the extra or missing
chromosome
4. To name:
# of chroms, sex chroms., +/disordered chroms
Example:
47, XX, +10 (a female with Trisomy
10)
Down syndrome
 Trisomy 21
Distinctive facial features, low
muscle tone, intellectual
impairment, heart or vision
defects
 1 in 800 children born in U.S.

 Chromosome 21 is the
smallest human chromosome

but still severe effects
 Age of the mother is the
highest risk factor
Sex chromosomes abnormalities
 Human development more tolerant of
wrong numbers in sex chromosome,
especially Y chromosome
 But produces a variety of distinct
syndromes in humans




XXY = Klinefelter’s syndrome
XXX = Trisomy X
XYY = Jacob’s syndrome
XO = Turner syndrome
Klinefelter’s syndrome
 XXY male
one in every 2000 live births
 Tall, usually infertile, lower
testosterone in puberty,
some health problems like
osteoporosis are more
common

Klinefelter’s syndrome
Jacob’s syndrome male
 XYY Males
1 in 1000 live male
births
 slightly taller than
average
 more active
 normal intelligence, slight learning disabilities
 delayed emotional immaturity
 normal sexual development

Trisomy X
 XXX


1 in every 2000 live births
produces asymptomatic, healthy females
 This is due to X chromosome inactivation
 Each female cell has one active X chromosome, and
one inactivated that turns into a Barr body
Turner syndrome
 Monosomy X or X0
1 in every 5000 births
 varied degree of effects
 Short stature, juvenile
features, webbed neck,
infertility

Genetic testing
 Amniocentesis in between month 3-6
used to detect chromosomal
abnormalities

sample of embryonic cells drawn from
amniotic fluid