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Genes in Action Chapter 14
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Sex Linked Traits Another way for traits to be passed on is by being sex linked Female Chromosomes: XX Male Chromosomes: Xy
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Female Parent Information A female will always pass on a X to her offspring The X chomosome is carried by the egg
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Male Parent Information A male will pass on either a X or a ‘y’ to his offspring. It depends on the sperm that unites with the egg There are X and y sperm
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Punnett Square for offspring
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In humans, the y chromosome carries very few genes…its too small The X chromosome is bigger and can hold more autosomal traits – Autosomal traits have to deal with the body
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If a gene is linked on the X chromosome (X-linked) Female offspring will inherit the gene as they do all other chromosomes (X from the father and X from the mother)
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If the trait is dominant, daughters will need one X to show the trait. They are then called “carriers” If the trait is recessive, daughters will need two XX to show the trait
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In males, regardless of whether the trait is dominant or recessive, if they inherit the X, they have it. Ex:
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Red Green Color Blindness Red Green Color blindness is an X linked recessive disorder Females need 2 XXs with the trait to have it Males just need 1 X with the trait to have it Female with just 1 X with the trait carry it
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Color Blindness Punnett Square It is X linked recessive
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Hemophilia Bleeding Disorder. People cannot clot their blood properly X linked recessive Mothers are potential carriers that give it to their sons
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Hemophilia Punnett Square
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Pedigrees chart constructed to show an inheritance pattern (trait, disease, disorder) within a family through multiple generations.
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Using a pedigree chart and key allows the genotype and phenotype of the family members and the genetic characteristics (dominant/recessive, sex-linked) of the trait to be tracked.
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Key for a pedigree
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Roman Numerals represent each generation
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Determining the type of Inheritance Autosomal (normal, not sex linked) dominant – Equal numbers of females and males affected – Many individuals will be affected because both homozygous and heterozygous dominant individuals are affected
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Determining the type of Inheritance Autosomal (normal, not sex linked) recessive – Equal numbers of males and females are affected – Fewer number of people are affected It’s all Guess and Check!!!
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12 3 45678910 1 2 I 123456 II III What kind is This?
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Mutations Mutations- change in the structure or amount of genetic material of an organism Genetic Mutant- individual with different DNA/chromosomes from the normal
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Causes of mutations Can occur naturally – Accidental changes to DNA during Cell cycle Mutagens cause mutations to occur more easily – Ex: radiation and some kinds of chemicals
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Effects of Mutations Mutations can effect the organism in 3 different ways – Help – Harm – No effect The effect depends on the where and when the mutation occurs
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Sickle Cell Anemia Caused by a mutation in the gene that produces hemoglobin Causes Sickle shaped red blood cells
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Sickle Cell Anemia It is a genetic recessive disorder Its believed the mutation came about as a defense against malaria
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Punnett Square for Sickle Cell
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Kinds of Mutations Different kinds of mutations are recognized as either changes in DNA or changes in the results of genes Each has different effects
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Mutations of Changes in DNA During DNA replication, the wrong nucleotide may be placed in a sequence 2 different types
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Mutations as Changes in DNA Point Mutation- change in a single nucleotide in a sequence from one base to another Insertion or Deletion- insertion or deletion of one or more nucleotides in a sequence – More rare
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Mutations as Changes in Results of Genes Changes in a DNA sequence may effect the results of genes 5 different types
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Mutations as Changes in Results of Genes Silent mutation- no effect on a gene’s function Missense Mutation- “replacement mutation” the DNA sequence has changed so different amino acid is used
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Mutations as Changes in Results of Genes Frameshift Mutation- An insertion or deletion in the DNA changes the starting point of reading for codons Nonsense Mutation- happens when a codon is changed to a “stop” codon. Amino acid chain is shorter than normal
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Mutations as Changes in Results of Genes More or Fewer Amino Acids- only occurs when an insertion or deletion is made in a multiple of 3. – Causes more or fewer amino acids to be made
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Mutations that occur in Chromosomes There are 5 of them They are deletion, duplication, inversion, translocation, and gene rearrangement They occur during “crossing over” of prophase 1 of meiosis
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Mutations that occur in Chromosomes Deletion- occurs when a piece of chromosome is lost Duplication- piece of a chromosome stays attached
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Mutations that occur in Chromosomes Inversion- piece of the chromosome reattaches in a different direction Translocation- chromosome piece ends up on a totally different chromosome
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Mutations that occur in Chromosomes Gene Rearrangement- Moving the actual gene from one chromosome to another
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