Genes in Action Chapter 14

Sex Linked Traits Another way for traits to be passed on is by being sex linked Female Chromosomes: XX Male Chromosomes: Xy

Female Parent Information A female will always pass on a X to her offspring The X chomosome is carried by the egg

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

Punnett Square for offspring

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

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)

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

In males, regardless of whether the trait is dominant or recessive, if they inherit the X, they have it. Ex:

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

Color Blindness Punnett Square It is X linked recessive

Hemophilia Bleeding Disorder. People cannot clot their blood properly X linked recessive Mothers are potential carriers that give it to their sons

Hemophilia Punnett Square

Pedigrees chart constructed to show an inheritance pattern (trait, disease, disorder) within a family through multiple generations.

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.

Key for a pedigree

Roman Numerals represent each generation

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

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!!!

I II III What kind is This?

Mutations Mutations- change in the structure or amount of genetic material of an organism Genetic Mutant- individual with different DNA/chromosomes from the normal

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

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

Sickle Cell Anemia Caused by a mutation in the gene that produces hemoglobin Causes Sickle shaped red blood cells

Sickle Cell Anemia It is a genetic recessive disorder Its believed the mutation came about as a defense against malaria

Punnett Square for Sickle Cell

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

Mutations of Changes in DNA During DNA replication, the wrong nucleotide may be placed in a sequence 2 different types

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

Mutations as Changes in Results of Genes Changes in a DNA sequence may effect the results of genes 5 different types

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

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

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

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

Mutations that occur in Chromosomes Deletion- occurs when a piece of chromosome is lost Duplication- piece of a chromosome stays attached

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

Mutations that occur in Chromosomes Gene Rearrangement- Moving the actual gene from one chromosome to another