A Guide to the Natural World David Krogh © 2011 Pearson Education, Inc. Chapter 12 Lecture Outline Units of Heredity: Chromosomes and Inheritance Biology Fifth Edition

© 2011 Pearson Education, Inc X-linked Inheritance in Humans

© 2011 Pearson Education, Inc. X-linked Inheritance Certain human conditions, such as red- green color blindness and hemophilia, are called X-linked conditions. They stem from a variant form of gene (an allele) that is dysfunctional and that is located on the X chromosome.

© 2011 Pearson Education, Inc. X-linked Inheritance Figure 12.1

© 2011 Pearson Education, Inc. X-linked Inheritance Men are more likely than women to suffer from these conditions because men have only a single X chromosome.

© 2011 Pearson Education, Inc. X-linked Inheritance A woman with a dysfunctional blood- clotting allele on one of her X chromosomes usually will be protected from hemophilia by a functional allele on her second X chromosome.

© 2011 Pearson Education, Inc. X-linked Inheritance Hemophilia and red-green color blindness are examples of recessive genetic conditions, meaning conditions that will not exist in the presence of even a single functional allele.

© 2011 Pearson Education, Inc. X-linked Inheritance Given the nature of recessive genetic conditions, persons who do not themselves suffer from such conditions may still possess an allele for it, which they can pass on to their offspring.

© 2011 Pearson Education, Inc. mother not color-blind functional red- green allelles father not color-blind sperm egg nonfunctional red- green allelles daughters are not color-blind one son is color-blind XYXYXY XXX XX X Y X-linked Inheritance Figure 12.2

© 2011 Pearson Education, Inc. X-linked Inheritance Such persons, referred to as carriers, are heterozygous for the condition. The alleles they have for the trait differ: one is functional, the other is dysfunctional.

© 2011 Pearson Education, Inc. X-linked Inheritance Animation 12.1: X-linked Recessive Traits

© 2011 Pearson Education, Inc Autosomal Genetic Disorders

© 2011 Pearson Education, Inc. Autosomal Genetic Disorders Sickle-cell anemia is an example of an autosomal recessive disorder. It is autosomal because the genetic defect that brings it about involves neither the X nor Y chromosome.

© 2011 Pearson Education, Inc. Autosomal Genetic Disorders Figure 12.3

© 2011 Pearson Education, Inc. Autosomal Genetic Disorders It is recessive because persons must be homozygous for the sickle-cell allele to suffer from the condition—they must have two alleles that code for the same sickle-cell hemoglobin protein.

© 2011 Pearson Education, Inc. Autosomal Genetic Disorders Some genetic disorders are referred to as dominant disorders, meaning those in which a single allele can bring about the condition regardless of whether a person also has a normal allele.

© 2011 Pearson Education, Inc. Sickle-cell anemia is a recessive autosomal disorder; both the mother and father must carry at least one allele for the trait in order for a son or a daughter to be a sickle-cell victim. When both parents have one sickle-cell allele, there is a 25% chance that any given offspring will inherit the condition. 25% probability of inheriting the disorder (b) Huntington disease: transmission of a dominant disorder. (a) Sickle-cell anemia: transmission of a recessive disorder. mother not sick egg father not sick sperm mother not sick egg father sick sperm 50% probability of inheriting the disorder In Huntington disease, if only a single parent has a Huntington allele there is a 50% chance that a son or daughter will inherit the condition. S s SSSs ss hh H Hh hh h S s Figure 12.4

© 2011 Pearson Education, Inc. Some Human Genetic Disorders Animation 12.2: Some Human Genetic Disorders

© 2011 Pearson Education, Inc Tracking Traits with Pedigrees

© 2011 Pearson Education, Inc. Pedigrees In tracking inherited diseases, scientists often find it helpful to construct medical pedigrees, which are genetic familial histories that normally take the form of diagrams. Pedigrees allow experts to make deductions about the genetic makeup of several generations of family members.

© 2011 Pearson Education, Inc. Pedigrees Figure 12.5 Aa A? ?? ? Aa A?aa ? A? ? aaA? ? ? III II I femalemale normal carrier albino

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12.4 Aberrations in Chromosomal Sets: Polyploidy

© 2011 Pearson Education, Inc. Polyploidy Human beings and many other species have diploid or paired sets of chromosomes. In human beings, this means 46 chromosomes in all: 22 pairs of autosomes And either an XX chromosome pair (for females) or an XY pair (for males)

© 2011 Pearson Education, Inc. Polyploidy The state of having more than two sets of chromosomes is called polyploidy. Many plants are polyploid, but the condition is inevitably fatal for human beings.

© 2011 Pearson Education, Inc Incorrect Chromosome Number: Aneuploidy

© 2011 Pearson Education, Inc. Aneuploidy Aneuploidy is a condition in which an organism has either more or fewer chromosomes than normally exist in its species’ full set. Aneuploidy is responsible for a large proportion of the miscarriages that occur in human pregnancies.

© 2011 Pearson Education, Inc. Aneuploidy A small proportion of embryos survive aneuploidy, but the children who result from these embryos are born with such conditions as Down syndrome.

© 2011 Pearson Education, Inc. Nondisjunction The cause of aneuploidy usually is nondisjunction, in which homologous chromosomes or sister chromatids fail to separate correctly in meiosis This leads to eggs or sperm that have one too many or one too few chromosomes.

© 2011 Pearson Education, Inc. Nondisjunction Figure 12.7 NormalAbnormal Nondisjunction in meiosis I Nondisjunction in meiosis II % of gametes get normal number of chromosomes 100% of gametes get abnormal number of chromosomes 50% normal50% abnormal

© 2011 Pearson Education, Inc. Aneuploidy Aneuploidy can come about in regular cell division (mitosis) as well as in meiosis.

© 2011 Pearson Education, Inc. Aneuploidy and Cancer A number of cancer researchers believe that mitotic aneuploidy can be a cause of cancer rather than an effect of it, as previously believed. Recent evidence indicates that, at the least, such aneuploidy appears prior to the initiation of some forms of cancer.

© 2011 Pearson Education, Inc. Aneuploidy and Cancer Figure 12.9

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12.6 Structural Aberrations in Chromosomes

© 2011 Pearson Education, Inc. Chromosomal Aberrations Harmful aberrations can occur within chromosomes, with many of these aberrations coming about because of mistakes in chromosomal interactions.

© 2011 Pearson Education, Inc. Chromosomal Aberrations Chromosomal aberrations include: deletions inversions translocations duplications

© 2011 Pearson Education, Inc. Chromosomal Aberrations Figure Deletion Inversion Translocation Duplication

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