Chapter 9
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Transcript of Chapter 9
Chapter 9Patterns of Inheritance
9.8 Pedigree analysis A pedigree can be used to analyze traits in
humans
9.9 Disorders determined by a single gene AUTOSOMAL RECESSIVE DISEASESAlbinismCystic fibrosis PKU (phenylketonuria)Sickle cell disease Tay- Sachs disease
Practice problemMary and Steve have a child with cystic
fibrosis but neither of them have the disease. What are the chances that their next child will have cystic fibrosis?
Ann is a carrier for sickle cell anemia. Her husband is not a carrier. Neither has any symptoms of the disease. What are the chances that their children will have sickle cell anemia?
Autosomal dominant disorders AchondroplasiaHuntingdon’s disease
Problems Peter’s father has Huntingdon’s disease. His
mother does not. Peter’s much older sister also does not have the disease. What are the chances that Peter has Huntingdon’s disease?
Problems Alicia and Phil are both achondroplasics.
What are the chances that they will have a normal stature child? What are the chances they will have a child with achondroplasia?
Mendel's assumptionsAll traits are determined by two alleles (or
one pair of genes)There are two possible genes or alleles for
that traitOne gene is completely dominant to the
other.One gene pair determines one traitGenes for different traits independently
assort (or one gene per chromosome)
Exceptions to Mendel’s assumptions Multiple alleles- traits may be determined by more
than two alleles- blood typeBlending and incomplete dominance- genes may not
be completely dominant – hair textureCo-dominance – both alleles contribute to phenotype
and do not interfere with each other –blood typeLinkage – genes on same chromosome are inherited
together (sex linkage)Epistasis/polygenic inheritance- one trait determined
by more than one gene pair – skin colorPleiotropy- one gene has multiple effects – sickle cell
9.12 Blending/Incomplete Dominance Heterozygous individuals are a blend of two
alleles. For example crossing a red and a white flower generates all pink flowers.
Cross two pink flowers.
Incomplete dominanceCross two snapdragon plants that are
heterozygous for pink flowers and tall height. Tall and red are dominant traits.
9.13 Blood type alleles Three alleles for blood type: A, B, oAlso written IA, IB, IoA and B are codominant, both are dominant
to oWhat are the possible combinations of the
two alleles for blood type?How many blood types exist?
Blood type problems A woman has blood type B and her husband
has blood type A. They have a baby with blood type O. What other blood types are possible in their future children?
Blood type and paternityA woman with Type O blood has a baby with
Type B blood. Two men claim responsibility for the child. Man #1 has blood type A. Man #2 has blood type AB. Who cannot be the child’s father?
9.14 Pleiotropy One allele can have many phenotypic effects
9.15 One trait controlled by multiple gene pairsPolygenic inheritance
Epistasis
Epistasis problemIn corn the dominant allele (I) creates colorless
kernels while the recessive allele (i) allows color to be deposited. At a different gene locus the domina t gene (P) creates purple kernels, while the recessive gene (p) creates red kernels.
What is the color of each kernel?IiPpIippiiPp
Problems Cross two corn plants heterozygous for both
genes
Sex linkage Sex linked genes are on X chromosome and
have nothing to do with genderFemales inherit two copies of the geneMales only inherit one – they only have one XSex linked recessive diseases are more
common in males
Sex – Linkage Problems Color blindness is a sex linked recessive
disease. A woman whose father was color blind marries a normal man. Find the phenotypic ratios in their children
A hemophiliac man and a normal woman marry and have children. What percentage of their children will also have hemophilia?
Sex- Linkage problems Fur color in cats is sex linked. Two co -
dominant alleles for fur color exist in tabby cats, orange and black. Tortoise shell cats have both alleles.
Cross a black female with an orange maleCross a tortoise shell female with a black
male
Are there ever any male tortoise shell cats?
HemophiliaLack a blood clotting proteinRoyal disease- Queen Victoria was a carrier.
Victoria’s daughters spread the disease to other European royal families through marriage. Alexis who was the son of the last czar of Russia was terribly afflicted. His parents preoccupation with his illness was a factor in the Russian revolution
Hemophilia Little to no treatment before the 1950s-
Crutches and wheelchairs for protection, risk of major tissue damage from bleeds
Doctors isolated the missing clotting protein and are able to collect it from donated blood.
All blood is tested for infectious disease because of a highly publicized hemophiliac named Ryan White who died of AIDS from a transfusion
Duchenne Muscular dystrophyUntreatable progressive muscle wasting
diseaseFatal usually in early 20s due to impairment
of heart and breathing muscles