chapter 12 objectives distinguish between sex chromosomes and autosomes. explain the role of sex...

Chapter 12

Objectives

• Distinguish between sex chromosomes and autosomes.

• Explain the role of sex chromosomes in sex determination.

• Describe how an X- or Y-linked gene affects the inheritance of traits.

• Explain the effect of crossing-over on the inheritance of genes in linkage groups.

• Distinguish between chromosome mutations and gene mutations.

Section 1 Chromosomes and Inheritance

Chapter 12

Chromosomes

• Genes reside on chromosomes.


Chapter 12

Chromosomes, continued

• Sex Chromosomes and Autosomes– Sex chromosomes contain genes that determine

an organism’s sex (gender). – The remaining chromosomes that are not directly

involved in determining the sex of an individual are called autosomes.


Chapter 12

Karyotypes: Male and Female


Chapter 12

Chromosomes, continued

• Sex Determination

– In mammals, an individual carrying two X chromosomes is female.

– An individual carrying an X and a Y chromosome is male.

• Sex of an offspring is determined by the male/father


Chapter 12

Genetic Research – Early Work

• Thomas Hunt Morgan – early 1900’s

– Compiled research by using small fruit fly Drosophila melanogaster

– While conducting his research he crossed a white-eyed (recessive) male with a normal red-eyed female.

• The F1 generation all had red eyes, but when the F1 generation were crossed together the ratio became 3 red-eyed to 1 white-eyed

– This shows evidence of crossing-over, but it doesn’t show until the F2 generation

– Exactly like Mendel’s pea plant diagram pg. 175


Chapter 12

Effects of Gene Location

• Sex-Linked Genes and Traits– Genes found on the X chromosome are X-linked

genes. – A sex-linked trait is a trait whose allele is located

on a sex chromosome.– Because males have only one X chromosome, a

male who carries a recessive allele on the X chromosome will exhibit the sex-linked trait.

• If a characteristic is sex-linked is occurs mostly in males


Chapter 12

Effects of Gene Location, continued

• Linked Genes

– Pairs of genes that tend to be inherited together are called linked genes.

• Colorblindness is sex-linked


Chapter 12


• Chromosome Mapping– The farther apart two genes are located on a

chromosome, the more likely a cross-over will occur.

– Researchers use recombinant percentages to construct chromosome maps showing relative gene positions.


Chapter 12


• Chromosome Maps:– Depict the linear sequence of genes on a

chromosome– Are constructed using crossing-over data from

mating experiments– Are practical with species having only a few

chromosomes


Chapter 12

Mutations

• Germ-cell mutations occur in gametes and can be

passed on to offspring.

• Somatic-cell mutations occur in body

cells and affect only the individual organism.

ex. Certain types of human skin cancers and leukemia result from somatic-cell

mutations, but can’t be passed

on to offspring to be inherited


Chapter 12

Mutations

• Lethal mutation cause death, often before birth

• Effects of a mutation can be helpful, harmful, and/or neutral


Chapter 12

Mutations, continued

• Chromosome Mutations– Chromosome mutations are changes in the

structure of a chromosome or the loss or gain of an entire chromosome.


Chapter 12Chromosomal Mutations


Deletion: loss of a piece of a chromosome due to breakage

Inversion: chromosomal segments break off, flips around backward, and reattaches

Translocation: piece of one chromosome breaks off and reattaches to a nonhomologous chromosome Fig 12-6 pg 239

Chapter 12


• Nondisjunction: a chromosome fails to separate from its homologue during meiosis. One gamete receives an extra copy of a chromosome and another gamete receives no copies.

• This occurs with Down syndrome, a person with it has 3 copies of chromosome #21, which gives them 47 chromosomes total instead of 46


http://img.dailymail.co.uk/i/pix/2007/07_02/gardinerDM1907_468x380.jpg

Chapter 12


• Gene Mutations– Gene mutations are changes in one or more of the

nucleotides in a gene.


Chapter 12

Gene Mutations


Homework

Section 12.1Review

Pg 240 #1-9

Section 2 Human GeneticsChapter 12

Objectives• Analyze pedigrees to determine how genetic traits and

genetic disorders are inherited.

• Summarize the different patterns of inheritance seen in genetic traits and genetic disorders.

• Explain the inheritance of ABO blood groups.

• Compare sex-linked traits with sex-influenced traits.

• Explain how geneticists can detect and treat genetic disorders.


Inheritance of Traits

• Pedigrees – Geneticists use pedigrees to trace diseases or

traits through families. – Pedigrees are diagrams that reveal inheritance

patterns of genes.

Chapter 12Section 2 Human Genetics

Pedigree for Cystic Fibrosis

Chapter 12

Some Important Genetic Disorders

Section 2 Human Genetics

Genetic Disorder: disease or disabling condition that have a genetic basis


Genetic Traits and Disorders

• Single genes having 2 or more alleles can determine traits, such as blood type or cystic fibrous

• Polygenic Inheritance– Geneticists have learned that most human

characteristics are polygenic characteristics (they are influenced by several genes)

– Ex. Skin color results from additive effect of 3-6 genes

– Other Ex. Eye color, height, and hair color


Genetic Traits and Disorders, continued

• Complex Characters– Complex characters, such as polygenic traits,

are influenced by both genes and environment.– Ex. Skin color is influenced by genes and if

person lives in area with a lot of sun, the skin will naturally be darker

– Ex. Height is influenced by genes and if the person has good nutrition and no diseases they should be taller than someone who has poor nutrition and diseases



• Multiple Alleles– Multiple-allele characters, such as ABO blood

groups, are controlled by three or more alleles of a gene.

» Look at top of page 244

Chapter 12

Click below to watch the Visual Concept.

Visual Concept

Comparing Single Allele, Multiple Allele, and Polygenic Traits


Chapter 12


Visual Concept

Comparing Complete, Incomplete,and Co-Dominance




• X-Linked Traits– The gene for colorblindness, an X-linked recessive

gene, is found on the X chromosome.



• Sex-influenced Trait– A sex-influenced trait, such as pattern baldness, is

expressed differently in men than in women even if it is on an autosome and both sexes have the same genotype.

• The difference is due to higher levels of testosterone in men, which interacts with genotype to produce pattern baldness

Chapter 12


Visual Concept

Comparing X-Linked and Sex-Influenced Traits



Detecting Genetic Disease

• Genetic screening examines a person’s genetic makeup and potential risks of passing disorders to offspring.

• Amniocentesis and chorionic villi sampling help physicians test a fetus for the presence of genetic disorders.


Detecting Genetic Disease, continued

• Genetic Counseling– Genetic counseling informs screened individuals

about problems that might affect their offspring.– Process uses family pedigree to look at family

history of disease and can assist parents in deciding whether or not to have children


Treating Genetic Disease

• Genetic disorders are treated in various ways.

• Among the treatments are symptom-relieving treatments and symptom-prevention measures, such as insulin injections for diabetes.

Chapter 12


Visual Concept

Genetic Disorder



Treating Genetic Disease, continued

• Gene Therapy– In gene therapy, a defective gene is replaced with

a copy of a healthy gene.– Somatic cell gene therapy alters only body cells. – Germ cell gene therapy attempts to alter eggs or

sperm.

Homework

Section 12.2 Review

Pg 248 #1-8

chapter 12 objectives distinguish between sex chromosomes and autosomes. explain the role of sex...

Documents

continuedsex chromosomes

autosomessex chromosomes

remaining chromosomes

role of sex chromosomes

chromosome mutations

gene mutations

y chromosome

inheritance of genes