Chapter 11Rock for a Cause

Emily Schaller

• She has cystic fibrosis• A genetic disease she inherited from her

parents• Takes a cocktail of drugs and vitamins• Many symptoms of the disease:– Mucus that clogs airways in the lungs. Difficult to

breath– Don’t digest food well

Cystic Fibrosis

• 2,500 babies are born with the disease every year

• CF is the most common fatal genetic disorder in the US

• Mutations in a gene called CFTR• Encodes a protein known as cystic fibrosis

transmembrane regulator

Most genes have several alleles, each created by a genetic mutation

• A mutation is a change in the nucleotide sequence of DNA, which creates alternative alleles of a gene.

Most genes have several alleles, each created by a genetic mutation

• Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane regulator gene on chromosome 7.

Genes are the units of inheritance

• Genes are physically transmitted from parents to children.

• The particular alleles of genes you received from your parents are the reason you resemble your mother, father, and other family members.

Genes are the units of inheritance

• Not every child of a couple receives the exact same parental genes, so children differ from their parents and from each other.

• Emily’s parents didn’t have the disorder.• There two other children didn’t have the

disorder

Humans are diploid organisms

• Diploid organisms have two copies of every chromosome in their cells.

• One is inherited from the biological mother, and the other is inherited from the biological father.

Humans are diploid organisms

• These paired chromosomes are called homologous chromosomes.

Humans are diploid organisms

• Because chromosomes come in pairs, we have two copies of nearly every gene in our body cells.

• Genes located on the X and Y chromosome in males do not have a second copy.

Humans are diploid organisms

• The two members of the homologous pair have the same general function,

• The nucleotide sequence of each copy can differ – that is, a person can carry two different alleles of the same gene, one of which functions differently from the other.

Humans are diploid organisms

• A person’s phenotype includes the visible or measurable features of an individual.

• A person’s genotype is the particular genetic makeup of an individual.

Humans reproduce sexually

• Before parents pass their genes to their offspring, the copies of each gene are separated from each other.

• Not every child receives the same combination of alleles.

Humans reproduce sexually

• It is the unique combination of maternal and paternal alleles that come together during fertilization that determines a person’s genotype and contributes to his or her phenotype.

Humans reproduce sexually

• Gametes are specialized reproductive cells that carry one copy of each chromosome. They are haploid cells.

• Sperm are male gametes.

• Eggs are female gametes.

Humans reproduce sexually• To become haploid, the cells that form gametes go through a unique kind

of cell division, called meiosis. This process halves the chromosome number from 46 to 23.

• Meiosis results in genetically unique haploid gametes.

Humans reproduce sexually

• When a haploid sperm fertilizes a haploid egg, the result is a diploid zygote that now carries two copies of every gene on 46 chromosomes.

Humans reproduce sexually

• This zygote will divide by mitosis to become an embryo, which will eventually grow into a human child.

Meiosis• Meiosis contains two separate divisions. The first division,

Meiosis I, separates homologous chromosomes. Although each daughter cell is haploid, each chromosome is still in its replicated state.

Meiosis• Meiosis contains two separate divisions. The second division,

Meiosis II, separates sister chromatids, creating four haploid daughter cells.

Genetic diversity of offspring

• Sexual reproduction is the primary reason why children don’t look and behave exactly like one parent in particular.

• They inherit alleles from both parents and consequently are genetically a combination of the two.

Genetic diversity of offspring

• No two gametes produced by the same parent are identical due to two major events during meiosis: recombination and independent assortment.

Genetic diversity of offspring• Recombination occurs when maternal and paternal

chromosomes pair and physically exchange DNA segments.

Genetic diversity of offspring• As a result of recombination, maternal chromosomes actually

contain segments (and therefore alleles) from paternal chromosomes and vice versa.

Genetic diversity of offspring• Independent assortment means that alleles of

different genes are distributed independently of one another.

Genetic diversity of offspring

• Because the number of possible combinations of alleles is therefore huge, a unique combination of maternal and paternal chromosomes is distributed into each sperm and each egg cell.

Cystic fibrosis results from a recessive allele

• In people with cystic fibrosis, the CFTR protein is distorted. This results in production of abnormally thick mucus that builds up in the lungs.

Recessive and dominant alleles

• Cystic fibrosis is caused by a recessive allele – an allele that reveals itself in the phenotype only if the organism has two copies of that allele.

• Recessive alleles are designated by a lower-case letter, for example, a.

Treatment of Cystic Fibrosis

• Emily uses an inflatable vest that vibrates to loosen mucus in her lungs

• She inhales salt water to thin the mucus• Other medications to help with infections• Her parents do not have the disease.• Why does she have the disease?

Recessive and dominant alleles• Dominant alleles

can mask the presence of a recessive allele.

• Dominant alleles are designated by a capital letter, for example, A.

Recessive and dominant alleles

• Heterozygous individuals have two different alleles, for example, Aa.

• Homozygous individuals have two identical alleles, for example, AA or aa.

Recessive and dominant alleles

• To figure out the likelihood that parents will have a child with a particular trait, we can plot the possibilities on a Punnett square – a diagram used to determine the probabilities of offspring having particular genotypes, given the genotypes of the parents.

Recessive and dominant alleles• Carriers are

individuals who are heterozygous for a particular gene of interest, and therefore can pass on the recessive allele without showing any of its effects.

Recessive and dominant alleles• Diseases carried by dominant alleles have a high

probability of being passed to the next generation.

Inherited Genetic Conditions in humans-recessive

• Albinism– Lack of pigment in skin, hair, and eyes– http://images.search.yahoo.com/search/images?_

adv_prop=image&fr=yfp-t-701&sz=all&va=albinism

• Cystic Fibrosis– Excess mucus in lungs, digestive tract, and liver;

increased susceptibility to infections

Sickle cell disease

• Sickled red blood cells; damage to tissues

Tays-Sachs Disease

• Lipid accumulation in brain cells; mental deficiency, blindness, and death in childhood

Huntington disease-Dominant

• Mental deterioration and uncontrollable movements; onset at middle age

Polydactyly

• More than five digits on hands and feet• http://images.search.yahoo.com/search/imag

es?_adv_prop=image&fr=yfp-t-701&sz=all&va=polydactyly

Facial Features

• Chin Cleft– Indention in chin

• Tongue Rolling– Ability to curl tongue into a U shape

• Freckles– Pigmented spots on skin. Face and arms

• Dimples– Indentation in skin of cheeks