Genetics• Study of inheritance, the
stability and variance of inheritance patterns
• Gregor Mendel, “The Father of Genetics”
• Worked with the garden pea plant using cross pollination
• What would happen if we all had the exact same DNA sequences? What if we had extremely divergent DNA sequences?
• What determines which genes we inherit from our mother and father?
Genetic TermsGene-basic unit of inheritance, arranged in a linear
sequences on a chromosomesAllele-alternative forms of a gene; alleles contain genetic
information that is expressed as traits. Examples of traits are flower color, seed shape, plant height
etc.Each trait can have a different version (allele); flower color
can be purple or white, we use one letter for the trait flower color, but change whether it is upper or lower case
Genetic Terms• Dominant- 1 copy of
allele results in expression of trait, always use a capital letter to show it is dominant, ex. A
• Recessive-requires 2 copies of same allele to get expression of trait, always use lower case letter to show it is recessive, ex. a
• If purple is dominant to white flowers, how would you write your alleles?
Genetic TermsHomozygous Dominant-2 same copies of
dominant allele, get expression of dominant trait, AA
Heterozygous Dominant-1 copy of dominant allele, 1 copy of recessive, still get dominant trait expression, Aa
Homozygous recessive-2 copies of recessive allele, get expression of recessive trait, aa
Genetic Terms• Genotype-genes of an organism• Phenotype-physical appearance of the
organism
True or False: The phenotype of an organism is dictated by the genotype of that organism
• True breed lineage vs. hybrid offspring • P, F1, F2 Generation
Genetic TermsMonohybrid cross-a cross that only predicts
the genotype and phenotype for one trait, ex. plant flower color
Dihybrid cross-a cross that predicts the genotype and phenotype of 2 traits, ex. plant flower color and height
Predicting Gametes If an organism has the genotype BB, how
many different gametes can it make? 1: BWhen predicting gametes, keep in
mind that each gamete must have 1 complete set of instructions
Cc DDEE GgHh2: C, c 1: DE 4: GH, Gh, gH, gh
KKLlMM TTUUVV AaBBCc2 1 4
Mendel’s Early Genetic Experiments: Monohybrid Cross
Crossed a true breed purple flower plant with a true breed white flower plant
P generation PP x pp P-purple p-white
PpF1 generation, all purple heterozygous
dominantCrossed the F1 generation with each other
Pp x Pp
F2 generation PP, Pp, Pp, pp
Genotypic Ratio 1 PP: 2 Pp :1 pp
Phenotypic Ratio 3 purple: 1 white
Mendel’s Law of SegregationMendel continued his monohybrid
crosses (1000s) for 7 different traits
Average ratio for all traits studied was always about 3:1
The Law of Segregation: Each individual has 2 of every
gene (alleles) for each trait These genes (alleles) will
separate from each other during meiosis into different gametes.
Fertilization gives each new individual 2 alleles for each trait
A
b B
a
A
BA
b a
Ba
b
Genetics ProblemIn parrots, alleles for blue feathers are
dominant to alleles for yellow.
Cross a heterozygous dominant blue feathered parrot with a yellow feathered parrot
BbBb bb bb
BbBb bbbb
Genotypic ratio 1 Bb : 1 bbPhenotypic ratio 1 Blue : 1 yellow
b
b
B b
Genetics ProblemRhinoceroses can be born without a horn, the
recessive condition.
Cross 2 heterozygous dominant rhinoceroses. Can they produce a baby rhino without a horn?
HHHH HhHh
HhHh hhhh
Genotypic Ratio 1 HH: 2 Hh : 1 hhPhenotypic Ratio 3 with horns : 1 no horn
H-horn presenth-no horn
H h
H
h
Mendel’s Early Genetic Experiments: Dihybrid Cross
• Mendel noticed that all purple flower plants were tall and all white flower plants were short
• Could you ever see a purple short plant or a white tall plant?
• Crossed a homozygous dominant tall purple flower plant with a homozygous recessive short white flower plant
P generation AABB x aabb
F1 AaBb
F2 AaBb x AaBb
4 by 4 punnett square
Phenotypic ratio 9 purple, tall: 3 purple, short: 3 white, tall: 1 white, short
Mendel’s Early Genetic Experiments: Principle of Independent Assortment
• The results from the many dihybrid crosses allowed him to develop the
• Principle of Independent Assortment-gene pairs (traits) are independent of each other and are sorted into different gametes
• Exception: Linked genes; they always sort together into same gamete
A
b B
a
A
BA
b a
Ba
b
Diploid (2N)
Haploid (1N)
In panthers, black fur is dominant to yellow fur. A recessive gene results in the absence of claws.Predict the offspring of a cross between a heterozygous black panther with no claws and a yellow panther that is heterozygous for claws
BbCcBbCc
BbccBbcc
bbCcbbCc
bbccbbcc
Genotypic Ratio 1:1:1:1Phenotypic Ratio 1:1:1:1
bC bc
Bc
bc
B-black fur b-yellow furC-claws c-no claws
Punnett Square and Probabilities• What is the
probability from the following cross that any offspring will have unattached earlobes or attached earlobes?
• The probability of inheriting a specific allele is like flipping a coin and occurs every time parents have an offspring
Mendel’s Early Genetic Experiments: Test Cross
If you have a purple flower, what are the possible genotypes?
PP or Pp
How do you decide? Do a Test Cross using a white flower plant
PP x pp = all offspring are Pp (purple)
Pp x pp = ½ offspring are Pp (purple) ½ offspring are pp (white)
Human GeneticsThe study of inheritance and prediction of
genes in humansVery difficult, many genes involvedSmall sample size, few offspringMate by chance, live in diverse
environmentsLong life span makes it difficult to track
genes in different generations
Human Genetics: Understanding a PedigreePedigree-a chart of genetic connections between
individuals; family tree that tracks genes/diseasesSingle genes can be followed by constructing pedigreesSquare=male circle=femaleShaded =affected non-shaded=not
affectedA line between a circle + square=matingLines from the mating=offspring
Human Inheritances Patterns• Autosomal Recessive
Inheritance-gene is located on autosome; 2 copies of gene required for expression of disease/trait; 1 copy=carrier, not affected
• Albinism, cystic fibrosis, sickle cell anemia, phenylketonuria, methemoglobinemia, Niemann-Pick disease
Effects of Autosomal Recessive Disorders
FFFF FfFf
Ff Ff ffff
25% (1 out of 4) will have cystic fibrosisWhat are the genotypic/phenotypic ratios?
What are the chances of offspring from 2 heterozygote parents for the cystic fibrosis gene having the disease?
F-normal, no cystic fibrosis f-cystic fibrosis
Parents are carriers
F f
F f
Human Inheritances Patterns• Autosomal
dominant inheritance- gene is located on autosome; 1 copy of gene results in expression of disease/trait
• Ex. Achondroplasia, Huntington’s, Osteogenesis Imperfecta, polydactyly, progeria, sperocytosis
PPPP Pp Pp
PpPp pppp
75% (3 out of 4) chance of having polydactylyWhat is the genotypic/phenotypic ratios?
What are the chances of offspring from a cross of 2 heterozygous parents for polydactyly also having the condition?
P-polydactyly (extra fingers/toes) p-normal
P p
P
p
Variations to Mendelian Inheritance Patterns: Multiple AllelesCodominance2 alleles are not dominant to each other, and
if both are present both are expressedEx. Blood Groups- ABO blood typingA dominant to O, but not to BB dominant to O, but not to AO recessive
Codominance: Blood TypingThere are 6 genotypes that express 4
different blood phenotypes
Phenotype GenotypeType A AA, AOType B BB, BOType AB ABType O OO
Codominance: Blood TypingWhat does a blood typing do? Why is blood
called A, B, AB, or O?Based on the different sugars found on red
blood cells ex. Type A blood has A sugars on RBCs
What type of sugars does AB or O have?Why do we need to type blood?
Codominance: Blood Typing ProblemsCross a person with type O blood with one
that has type AB blood
Give phenotypic and genotypic ratios
AOAO AOAO
BOBO BOBO
Genotypic Ratio 1 AO : 1 BOPhenotypic Ratio 1 Type A : 1 Type B
O O
A
B
Type B blood male and a Type O blood female never produce a Type O blood child.
Is this possible? Why or why not?
BOBO BOBO
BOBO BOBO
Type B blood can be BB or BO*
Genotypic Ratio All are BOPhenotypic Ratio All are Type B*this genotype would produce a Type O offspring
O O
B
B
BOBO
OOOO
BOBO
OOOO
Genotypic ratio: 1 BO: 1 OOPhenotypic ratio: 1 type B: 1 type O blood
If father’s genotype is BO, it would be possible to get an O blood type child
B O
O
O
Variations to Mendelian Inheritance Patterns
• Incomplete Dominance-one allele isn’t complete dominant to the other; heterozygotes are intermediate in phenotype
• Snap dragon flower color: R-red, r-white
• RR x rr = Rr all offspring are pink
• What happens when 2 pink flower plants are crossed? Give phenotypic and genotypic ratios
Rr Rr
RRRR RrRr
RrRr rrrr
R rR
r
R-red r-white Rr-pink
Pleiotropy• Expression of alleles (for 1 trait) has positive
or negative effects on other traits Ex. Sickle cell mutation
• Affects the protein hemoglobin which carries O2
• Insufficient O2 will cause RBCs to sickle and eventually burst anemia
• Secondary effectsheart/lung damage, kidney/heart failure, skull deformation, mental impairment
Pleiotropy: Marfan SyndromeSingle gene mutation affects 2 or more distinct and
unrelated traits mutation of fibrillin gene
Incomplete PenetrancePolydactyly extra fingers/toesAutosomal dominant disorder which exhibits
incomplete penetranceA dominant allele sometimes does not
determine the phenotypeSome who inherit polydactyly allele are
phenotypically normal
Pleiotropy: Sickle Cell Anemia• Homozygous for condition die in
early 40s, no cure, extremely debilitating
• Severe anemia, poor circulation, physical weakness, impaired mental function, spleen damage
• Why is this mutation maintained?• Protection/resistance against malariaS-no sickle cell s-sickle cell
(recessive)• SS-no sickle cell, no resistance• Ss-no sickle cell, resistance• ss-sickle cell, resistance
Heterozygote advantage
Cross 2 heterozygous dominant parents together.
How many children would have sickle cell?
How many children would not?
How many children are resistant to malaria? How many are not?
SSSS SsSs
SsSs ssss
3 children do not have sickle cell, 1 does3 children protected, 1 is not
Parents are Ss-do not have sickle cell
S s
S
s
Epistasis• When one gene pair masks/prevents another
gene pair’s expressionEx. Labrador fur color• B-black fur b-brown fur• E-melanin deposited e-no melanin
• The recessive genotype of “ee” will cause no melanin deposition, thus the resulting fur coat will be yellow, even when “B or b” alleles are present
Continuous Variation in Traits
• Multiple genes are responsible for the phenotype of an organism polygenic inheritance
• Skin and eye color, height• A great deal of variation
exists resembling a bell shaped curve
• Look at human height; a few genes regulate height, but there exists a normal amount of variation
• What factors contribute to height?
Environmental Effects on Phenotype: Multifactorial Traits
Fur color on Siamese cats or Himalayan rabbits-heat sensitive enzyme that produces melanin
Flower color on Hydrangea Plant-influenced by acidity of soil
Height of Yarrow plant cuttings-varies depending on elevation planted
Continuous Variation in TraitsGenetics allows us to predict genotypes of
organisms, but there are many external and internal factors that influence the actual phenotype of those organisms cleft lip/palate, clubfoot, hypertension, diabetes, schizophrenia, allergies, cancers
An individual’s phenotype is the outcome of the complex interaction among all its genes and environment in which it lives
G x E interaction
Sex Determination in HumansDetermined by the 23rd pair on chromosomesXX-female XY-maleA female only makes eggs that carry the X
chromosomeA male makes sperm that contain either the X
or Y chromosomeMales are haploid for the X chromosome,
females are diploid
Sex Determination in Humans• Sex is determined by the Y chromosome• Up until about 7 weeks, an embryo has a
uncommitted reproductive duct system• This duct system will develop into
testes/penis if a Y chromosome is present• This is due to the expression of the SRY gene
located on the Y chromosome• No Y chromosome duct system forms into
ovaries/uterus• Faulty SRY phenotypic female, sterile
Human Inheritance Patterns
• X-linked recessive-gene is located on the X chromosome; 2 copies of gene required for expression in females, 1 copy in males results in expression. XX vs XY
• Ex. Fragile X syndrome, hemophilia, color blindness, muscular dystrophy, Menkes syndrome, adrenoleukodystropy
X-linked Recessive Inheritance Problem
What type of offspring would a colorblind man and woman who is a carrier for CB have?
XXCCXXcc XXCCYY
XXccXXcc XXccYY
Female offspring ratio 1 CB: 1 no CBMale offspring ratio 1 CB: 1 no CB
Female-Cc not colorblind Colorblind male-c But CB is X-linked XCXc XcY
Xc Y
XC
Xc
X-linked Recessive Inheritance Problem
Can a female with muscular dystrophy ever have a son who does not have MS?
Can a male with hemophilia have a daughter who is not affected with the disease?
XXMMXXmm XXmmYY
XXmmXXMM XXmmYY
No, all male offspring would have MS
M-no MS m-has MS
XM Y
Xm
Xm
XXHHXXhh XXHHYY
XXHHXXhh XXhhYY
Yes, female offspring would not have hemophilia, but are carriers for the gene
H-no Hemophilia h-Hemophilia
Xh Y
XH
XH
Top Related