Transcript recessive
11.1 BASIC PATTERNS OF HUMAN INHERITANCE WHAT YOU WILL LEARN -How to determine if an inherited trait is dom/rec -Examples of DOMINANT/RECESSIVE disorders -How a PEDIGREE shows a particular trait in families MAIN IDEA The inheritance of a trait is shown over several generations in a pedigree. READING Q’s REVIEW VOCAB: enzyme -PROTEIN that speeds up biological reactions READING Q’s IDENTIFY -CIRCLE the term that describes the genotype of a person who expresses a recessive trait -homozygous: organism with 2 of the same alleles for a particlular trait -DETERMINE the genotypes: recessive genetic disorder dominant genetic disorder DD Dd dd X X DD Dd dd X READING Q’s EXPLAIN -Why do ganglioslides build up in the brain of people with TaySachs disease? -ENZYME missing that breaks down ganglioslides—fatty acids READING Q’s EXPLAIN -How scientist determine if achondroplasia developed from a new mutation -achondroplasia is a dominant disorder: dwarfism -if BOTH parents are average height it dev from MUTATION Parents would be homozygous recessive so could only pass on a recessive allele—dominant allele would have to be a mutation READING Q’s EXPLAIN the purpose of a genetic pedigree -track a trait or disorder throughout several generations DRAW the symbols used in a pedigree for: MALE= FEMALE= READING Q’s EVALUATE -Circle the carriers in the second generation READING Q’s CALCULATE -What percentage of the children in this family inherited TaySachs disease? -1/4=25% READING Q’s IDENTIFY -Do any grandchildren in this family have polydactyly? -NO READING Q’s EXPLAIN -Why are recessive traits difficult to study? -Not all people who carry the recessive allele have the trait -Don’t know if you are a carrier unless___ -1 parent shows the trait = homozygous recessive -offspring shows trait = both parents carriers GROUP WORK: APPLICATION NOTES -As a group complete the guided note sheet using your knowledge from the reading. REVIEW VOCAB DEFINE: gene -segment of DNA on chromosome carrier -heterozygous for a recessive disorder--Aa RECESSIVE/DOMINANT GENETIC DISORDERS COMPARE: RECESSIVE GENETIC DISORDERS -only present if homozygous recessive -parents are carriers if don’t have disorder DOMINANT GENETIC DISORDERS -present if have at least 1 dominant allele -must have a parent with the disorder [mutations are exceptions] -don’t always appear until later in life RECESSIVE/DOMINANT GENETIC DISORDERS IDENTIFY: 1-four examples of recessive genetic disorders in humans 1-CYSTIC FIBROSIS 2-TAY-SACHS 3-ALBINISM 4-GALACTOSEMIA 5-ALKOPTONURIA 2-two examples of dominant genetic disorders in humans 1-HUNTINGTON’S 2-ACHONDROPLASIA RECESSIVE/DOMINANT GENETIC DISORDERS EXPLAIN why recessive disorders are more common than dominant disorders. -don’t always know there are carriers of disorder -parents may not know the disorder is in the family RECESSIVE/DOMINANT GENETIC DISORDERS IDENTIFY: the disease for each dominant/recessive disorders -caused by altered genes; results in lack of skin pigmentation -ALBINISM -recessive -characterized by body’s inability to tolerate galactose -GALATOSEMIA -recessive -gene found on chromosome 15;characterized by lack of enzyme that breaks down fatty acids -TAY SACHS -recessive RECESSIVE/DOMINANT GENETIC DISORDERS IDENTIFY: the disease for each dominant/recessive disorders -affects the nervous system; no treatment; breaks down part of brain -HUNTINGTON’S -dominant -affects mucus-producing glands, digestive enzymes, sweat glands -CYCTIC FIBROSIS -recessive -affects height and body size -ACHONDROPLASIA -dominant RECESSIVE/DOMINANT GENETIC DISORDERS -SHOW a cross between 2 carriers -what is the probability 2 carriers of cystic fibrosis will have a child w/CF? F f F FF Ff f Ff ff -25% RECESSIVE/DOMINANT GENETIC DISORDERS PREDICT: -can 2 normal height parents have a child w/achondroplasia? a a a aa aa a aa aa RECESSIVE/DOMINANT GENETIC DISORDERS PREDICT: -can 2 individuals w/achondroplasia have a child that is normal height? A a A AA Aa a Aa aa PEDIGREES SUMMARIZE: pedigree symbols MALE CARRIER -square - -half shaded symbol / FEMALE --circle joined to square -circle - PARENTS AFFECTED MALE PARENTS/OFFSPRING -shaded square - -line down from parent/ circles/squares on second row - AFFECTED FEMALE -shaded circle - PEDIGREE CHART PEDIGREE CHART GRANDPA X GRANDMA MOM X DAD GRAMPS X GRANNY ANALYZING PEDIGREES EVALUATE: the inheritance of achondroplasia shown in the pedigree -parent w/ disorder -father -#children with disorder -1 / 1st born son -genotype of younger son -homozygous recessive / aa ANALYZING PEDIGREES ANALYZE and RESPOND: -RECALL if the trait is rec or dom based on the following information: -In the pedigree, individuals I-1 and I-2 are unaffected -- have affected child RECESSIVE DOMINANT X -SPECIFIY if parents II-1 and II-2, who have an affected child, are carriers of that trait CARRIER NOT A CARRIER X -TELL whether there is a dominant gene in the genotype of II-4 NONE A X LEAST ONE -Individual II-1is in generation 2 X TRUE FALSE ANALYZING PEDIGREES THINK BACK and RESPOND: -A scientist uses a pedigree to study family history TRUE FALSE X -A pedigree traces the inheritance of a particular trait through only two generations MANY TRUE FALSE X -In a pedigree, one who does not express the trait is represented by a darkened circle/square TRUE FALSE X -In a pedigree, a horizontal line between 2 symbols shows that these individuals are the parents of the offspring X TRUE FALSE ANALYZING PEDIGREES DIAGRAM: Suppose both parents can roll their tongues but their son cannot. IDENTIFY this trait as: dominant recessive DRAW a pedigree showing this trait LABEL each symbol with the appropriate genotype What was the probability that they would have a non-tongue roller offspring? (hint: punnet square) -both parents carry recessive gene -parent genotype Tt -son genotype tt -probability of child tt= 25% Connecting Pedigree Symbols parents offspring EX- PEDIGREE CHART Interpreting a Pedigree Chart 1- Determine whether the trait/disorder is dominant or recessive -If the trait/disorder is dominant, one of the parents must have the disorder -If the trait/disorder is recessive, neither parent has to have the disorder because they can be heterozygous PRACTICE: Interpreting • Dominant or Recessive? Answer • Recessive PRACTICE: Interpreting Dominant or Recessive? Answer Dominant Interpreting a Pedigree Chart 2- Determine if the pedigree chart shows an autosomal or X-linked trait/disorder -If most of the males in the pedigree are affected the trait/disorder is X-linked -If it is a 50/50 ratio between men and women the trait/disorder is autosomal. PRACTICE: Interpreting Is it Autosomal or X-linked? Answer Autosomal Summary -Pedigrees are family trees that explain your genetic history. -Pedigrees are used to find out the probability of a child having a trait/disorder in a particular family. -To begin to interpret a pedigree -determine if the trait/disorder is: 1-dominant or recessive 2-condition is autosomal or X-linked PEDIGREE PRACTICE A PEDIGREE PRACTICE B PEDIGREE PRACTICE C PEDIGREE PRACTICE D INVESTIGATING HUMAN PEDIGREES -USE the information provided in the transcript to construct a pedigree showing hairy earlobes* in a family *HE -DETERMINE the oldest couple in the family -DRAW their pedigree symbols—include names -CONTINUE with other members in the family -DETERMINE genotypes as you gather enough information