Download Beyond mendelian genetics and human genetics

Freshman Biology
Semester Two
 RA Activity:
 Each
table partner reads one section and
takes notes p.296-298:


Recessive Genetic Disorders
Dominant Genetic Disorders
 Take
turns teaching each other about your
section while the other partner takes notes!
(you should have notes on Recessive and
Dominant disorders when finished!)
 Read and take notes on pg. 299-301


Pedigrees/Analyzing pedigrees
Complete Pedigree Quiz Problem on pg. 300
 Incomplete
dominance
 Codominance
 Multiple alleles
 Polygenic traits
 Multifactorial traits
 One
allele is not completely dominant over
the other; heterozygotes show a blending of
the trait
 Neither
allele is
dominant over the
other;
heterozygotes
express both alleles
at the same time
(not a blending)
 Ex: Both black and
white feathers in
chickens
 Ex: Both white and
red hairs in roan
cattle
 Sickle
Cell Anemia is an example of
Codominance in human red blood cells.
 What is the effect of the disorder?

 If
Sickle cells do not transport oxygen efficiently
a person has alleles for normal shaped
hemoglobin, they will have normal red
blood cells.
 A person who is homozygous for sickle cell
has all sickle shaped red blood cells.
 Heterozygous individuals have both types
of red blood cells.
 In
tulips, yellow
color is
incompletely
dominant to red.
Cross a homozygous
red (R) tulip with a
homozygous yellow
(Y) tulip. Determine
genotypic and
phenotypic ratios of
the offspring.
A
purple-feathered
penguin (P) mates
with a green
penguin (G).
What are the
genotypes and
phenotypes of their
offspring?
 If two of the above
offspring mate, what
is the phenotypic
ratio of their
offspring?

 Gene
has more than just two alleles possible
 Remember- each individual still just has 2
 Ex- rabbit fur color (4 possible alleles)
 Human
Blood Types have a gene that displays
multiple alleles and codominance
 ABO gene has three alleles
 IA


 IA
codes for a 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
and IB alleles are codominant
 Possible




Phenotypes and Genotypes
A blood type (IAIA or IAi)
B blood type (IBIB or IBi)
AB blood type (IAIB)
O blood type (ii)
 More
than one gene codes for a trait
 Wide range of phenotypes and genotypes
possible
 Ex- eye color
 Phenotype
is a blend between genetic
inheritance and environment
 Moms


Sons and Daughters one of their X
chromosomes (random choice)
Eggs have a single X chromosome
 Dads




give
give
Daughters their X chromosome
Sons their Y chromosome
Half of the sperm carry an X
Half carry a Y
A
Barr Body is an inactivated X chromosome
in a female body (somatic) cell.
 Why does this happen?


Males and Females only need one functioning X
chromosome in their body cells.
Since females have 2 X chromosomes in all of
their body cells, one is inactivated and unused.
 Can

we see this in organisms?
Calico colored cats have different colored
patches of hair, depending on which X
chromosome becomes an inactive Barr Body.
 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
 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
 Only
Males can have them
 Dads pass on the trait to all sons
 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
 Show

Females have two X’s


up more in males
Harder to inherit two “bad” X’s to show disorder
Males have only one X

They only have to inherit the one copy to show the
disorder
 Not
all genes independently assort
 Only happens with genes on different
chromosomes
 Genes on the same chromosome are
linked (where one goes the others go
too)

For example, if
 One homologous chromosome has alleles A, B,
and c for three genes
 The other homologous chromosome has alleles A,
b, and C
 Then the offspring cannot get A, B, and C or a, b,
and c or any other combinations
 Crossing-over
can change the
combinations of linked genes
 The further apart that two genes are on a
chromosome, the more likely that they
are to cross-over
 Gene maps are maps of chromosomes that
show the locations of genes and the
distances between them
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
A
karyotype is a picture of chromosomes
within a somatic cell
 Normal Karyotypes have 46 Chromosomes
 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
 Karyotypes


Sex of Individual
Presence of a Chromosomal Disorder


Extra or missing whole chromosomes
Missing piece or extra piece of chromosome
 Can’t

can tell:
tell:
Genetic Disorders from Small Mutations
 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 or sperm had the mistake
 Person
may be a mosaic (some normal,
some affected cells)

Mistake happened later in development
 Mistake
during Meiosis or Mitosis
 Non-disjunction: failure of the chromosomes
to separate properly

Often happens in Anaphase I when tetrads
separate
 Trisomy

3 copies of one type of chromosome
 Monosomy


1 copy of one type of chromosome
Only monosomy that is viable is XO
 Down’s
Syndrome (Trisomy 21)
 Edwards

Syndrome (Trisomy 18)
Characteristics
 Patau
Syndrome (Trisomy 13)
 Turners
Syndrome (XO)
 Kleinfelter
Syndrome (XXY)