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-Construct / Interpret PEDIGREES

READING Q’s

1-IDENTIFY-Check 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-aa

READING Q’s

2-CATEGORIZE: The following genetic disorders as RECESSIVE or DOMINANT

a-albinism recessivedominant

b-Huntington's recessive dominantc-cystic fibrosisrecessive dominant

 

READING Q’s

3-EXPLAIN-For what purpose is a genetic pedigree used?

-study genetic relationships-trace inheritance of a trait generation to generation

READING Q’s

4-DRAWThe symbols that are used to represent a male AND female in a pedigree

MALE- FEMALE-

READING Q’s

5-EVALUATE-Circle the carriers in the second generation

READING Q’s

6-CALCULATE-What percentage of the children in this family inherited Tay-Sachs disease?

-1/4=25%

READING Q’s

7-IDENTIFY-Do any grandchildren in this family have polydactyly?

-NO

READING Q’s

8-EXPLAIN-Why are recessive traits difficult to study?

-Not all people who carry the recessive allele have the trait

GROUP WORK: APPLICATION NOTES

-As a group complete the areas below using your knowledge from the reading/discussion.MAIN IDEAREVIEW VOCABRECESSIVE / DOMINANT GENETIC DISORDERS

VOCAB-carrier-pedigree

MAIN IDEA

-PEDIGREESinheritance of traits over several generations

REVIEW VOCAB

DEFINE: gene-segment of DNA on chromosome

DEFINE: homozygous-2 identical alleles [TT / tt]

DEFINE: heterozygous-2 different alleles [Tt]

RECESSIVE/DOMINANT GENETIC DISORDERS

COMPARE/CONTRAST:recessive and dominant genetic disorders

RECESSIVE-expressed when indv HOMO recessive [tt]

DOMINANT-expressed when indv HOMO dominant [TT] or HETERO [Tt]

RECESSIVE/DOMINANT GENETIC DISORDERS

EXPLAIN why recessive disorders are more common than dominant disorders.

-DOMINANT: only one allele must be inherited to be affected

-if DOM trait interferes w/ survival- no pass on

-RECESSIVE: carriers do NOT display the disorder-many carriers are unaware they carry an

affected gene

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

-HUNINGTON’S-DOMINANT

-affects mucus-producing glands, digestive enzymes, sweat glands

-CYCTIC FIBROSIS-RECESSIVE

-affects height and body size-ACHONDROPLASIA-DOMINANT

RECESSIVE/DOMINANT GENETIC DISORDERS

PREDICT: what are the chances of 2 carriers of cystic fibrosis having a child with cystic fibrosis?

¼= 25%    F        f

   F                f

 FF  Ff

 Ff  ff

RECESSIVE/DOMINANT GENETIC DISORDERS

Positive Exposure

Positive exposure video clip Rick Guidotti - PART 2

Positive Exposure Inside Edition Part I - YouTube

PEDIGREE BASICS[the FAMILY TREE of genetics]WHAT is it:-diagram explaining genetic history

WHO uses it:-scientist-genetic counselors

WHY use it:-probability of child having disorder/condition-determine disorder/condition as autosomal/sex linked

PEDIGREES

SUMMARIZE: pedigree symbolsMALE

-sqaure-FEMALE

-circle-AFFECTED MALE

-shaded square-AFFECTED FEMALE

-shaded circle-

CARRIER-half shaded symbol- / PARENTS/OFFSPRING-line down from parent, circles/squares on second row

PARENTS-circle joined to square-GENERATIONS-I, II , III, IV, V

STEPS for INTERPRETING PEDIGREES1- DETERMINE if the pedigree chart is showing: AUTOSOMAL or X-LINKED disorder

-autosomal:-If it is a 50/50 ratio between men and women

-x-linked:-If most of the males in the pedigree are affected

2- DETERMINE if disorder is DOMINANT or RECESSIVE-dominant:

-one of the parents must have the disorder.-recessive

-neither parent has to have the disorder because they can be heterozygous.

Connecting Pedigree Symbols

Married Couple

Siblings

EX- PEDIGREE CHART

PRACTICE INTERPRETING

1. Determine if the pedigree chart shows an autosomal or X-linked disease.

-If most of the males in the pedigree are affected the disorder is X-linked

-If it is a 50/50 ratio between men and women the disorder is autosomal.

PRACTICE: Interpreting

Is it Autosomal or X-linked?

Answer

Autosomal

Interpreting a Pedigree Chart2. Determine whether the disorder is

dominant or recessive

-If the disorder is dominant, one of the parents must have the disorder.

-If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

Dominant or Recessive?

PRACTICE: Interpreting

Answer

Dominant

• Dominant or Recessive?

PRACTICE: Interpreting

Answer

• Recessive

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 PEDIGREESANALYZE and RESPOND:

 -RECALL if the trait is rec or dom based on the following information: -individuals I-1 and I-2 are unaffected but have affected childRECESSIVE DOMINANT-SPECIFIY if parents II-1 and II-2, who have an affected child, are carriers of that traitCARRIER NOT A CARRIER-TELL whether there is a dominant gene in the genotype of II-4NONE A LEAST ONE-Individual II-1is in generation 2 TRUE FALSE

X

X

X

X

ANALYZING PEDIGREES

THINK BACK and RESPOND: -A scientist uses a pedigree to study family historyTRUE FALSE-A pedigree traces the inheritance of a particular trait through only two generationsTRUE FALSE-In a pedigree, one who does not express the trait is represented by a darkened circle/squareTRUE FALSE-In a pedigree, a horizontal like between 2 symbols shows that these individuals are the parents of the offspringTRUE FALSE

X

X

X

X

MANY

ANALYZING PEDIGREES

DIAGRAM: Suppose both parents can roll their tongues but their son cannot.[TONGUE ROLLING = DOMINANT / T]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%

PEDIGREE CHART PRACTICE

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