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7.4 Human Genetics & Pedigrees

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Melissa Panzer

on 19 April 2017

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Transcript of 7.4 Human Genetics & Pedigrees

Chapter 7: Extending Mendelian Genetics
Key Concept: A combination of methods is used to study human genetics
Main Idea #4: Several methods help map human chromosomes.
A chart that shows the phenotype of a particular genetic trait in a family from one generation to the next
When enough phenotypes are known, genotypes can often be inferred.
Main Idea #3: A pedigree is a chart for tracing genes in a family.
1. Define

Examine patterns of inheritance in humans (dominant & recessive interactions, sex-linked genes, polygenics, epistasis, etc).
3. Describe how a
is used. Interpret & build a
4. Explain how
are used
Learning Objectives
Main Idea #1: Human genetics follows the patterns seen in other sexually reproducing organisms--Let's review these!
How to read a pedigree
deletion of part of a chromosome or loss of a chromosome
Partial Monosomy 5 (Cri du chat Syndrome -- French for "cry of the cat" after the distinctive noise by affected persons' malformed larynx)
extra chromosomes or duplication of part of a chromosome
Trisomy 21 (Down’s Syndrome)
Karyotypes can show changes in chromosomes.
Main Idea #2: Females can carry sex-linked genetic disorders
You can use pedigrees to track autosomal or sex-linked genes
What leads to trisomy & monosomy?
Section 4: Human Genetics & Pedigrees
Patterns of inheritance
Karyotpes & chromosome mapping
Side note: genetic disorders can be caused by autosomal genes or by genes on sex chromosomes
Only females can be carriers for sex-linked disorders because males express all of their sex-linked genes
Multiple Alleles: Having three or more alternative alleles for a gene (example: I , I , i)
Boxes represent males; Circles represent females
A shaded shape means that a person shows a trait
A white shape means that the person does not show a trait
A shape that is half-shaded and half-white meant that a person is a carrier
Horiztonal = Marriage Lines
Vertical = Children Lines
Who are the parents of the carrier?
The spouse?
The siblings?
The children?
Numbering Your Pedigree
Each generation is given a Roman numeral
Each individual within a generation is given a number
Who is I-2?
Who is III-4?
Who is II-2?
Who is I-4?
What number is the affected female?
What number is the affected male?
Tay-Sachs is an autosomal recessive disorder
Step 1:
Write down the known genotypes we know for sure. Who do we know?
Step 2:
Solve for the genotypes we don't know for sure
What is the genotype of II-1? How do we know?
I-2? How do we know?
III-2? How do we know?
II-4? How do we know?
Main clue to infer whether the genes is on an autosome or on a sex chromosome?
If approximately the same number of males and females have the phenotype, then the gene is
most likely
on an autosome
If the phenotype is much more common in males, then the gene is
most likely
on the X-chromosome
Step 1:
Write down our X & Y chromosomes based on the sex of the individual
Step 2:
Write down the genotypes we know for sure. Who do we know?
Males are easiest to start with!
Step 3:
Solve for the genotypes we don't know for sure
Is the pedigree chart most likely for an autosomal or a sex-linked trait?
Hemophilia is a sex-linked recessive disorder
Step 1:
Write down the known genotypes we know for sure. Who do we know?
Step 2:
Solve for the genotypes we don't know for sure
Sickle Cell Anemia is an autosomal recessive disorder
Picture of all the chromosomes in a cell
When two chromosomes fail to separate during meiosis (
. This means that one cell ends up with both chromosomes, while the other cell has none.
Full transcript