Heredity
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Heredity. Chromosomes. We discussed earlier in this unit, the usage of karyotype charts Humans have 23 pairs of chromosomes 1 sex chromosome pair 22 autosome pairs Recall that males have one X and one Y, while females have two X’s

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Chromosomes
Chromosomes

  • We discussed earlier in this unit, the usage of karyotype charts

  • Humans have 23 pairs of chromosomes

    • 1 sex chromosome pair

    • 22 autosome pairs

  • Recall that males have one X and one Y, while females have two X’s

  • These split during meiosis, and we can use a Punnett square to determine the possible outcomes for sex of offspring



Human genetics
Human Genetics chromosome

  • Recall human blood type has multiple alleles

  • The traditional convention for expressing dominance and recessiveness no longer works

  • Alleles are often expressed as superscripts

  • Both A and B types are codominant, and O is recessive

  • A is IA, B is IB, and O is i

  • The following chart summarizes the genotypes and phenotypes



Example
Example not blend

  • A male heterozygous for blood type A plans to have children with a female who is heterozygous for B. What possible blood types could their offspring have?


I not blendBi

IB

i

IAIB

IAi

IA

IAi

i

IBi

ii



Pedigree charts
Pedigree Charts or O

  • After identifying the nature of a trait, geneticists often look at family history

  • By understanding the phenotypes of certain members of a family, they can gather more info about others

  • This is organized in a pedigree chart


Human traits
Human Traits or O

A square represents

a male.

A circle represents

a female.

A vertical line and a bracket connect the parents to their children.

A horizontal line connecting a male and a female represents a marriage.

A shaded circle or square indicates that a person expresses the trait.

A circle or square that is not shaded indicates that a person does not express the trait.



Genetic disorders
Genetic Disorders by genetics alone

  • Many conditions are due to recessive alleles

  • These will only manifest themselves if a dominant allele is present

  • An example is cystic fibrosis (CF)


Cystic fibrosis
Cystic Fibrosis by genetics alone

  • Caused by a recessive allele

  • Sufferers of cystic fibrosis produce a thick, heavy mucus that clogs their lungs and breathing passageways



From mutation to disease
From missing 3 DNA bases. Mutation to Disease

  • Normal CFTR is a chloride ion channel in cell membranes

  • Abnormal CFTR cannot be transported to the cell membrane

  • If it does, it will not transport Cl- as easily

  • Part 1

  • Part 2



  • Other conditions arise from codominant alleles missing 3 DNA bases.

  • In these cases, the heterozygotes have a different phenotype

  • You saw this with thalassemia in question 12

  • Sickle cell disease is another example

  • Individuals that are heterozygous for this usually have normal blood cells, but are resistant to malaria



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