CHAPTER 12 INHERITANCE

PATTERNS AND HUMAN GENETICS

staff.tuhsd.k12.az.us

OBJECTIVES Tell the difference between sex

chromosomes and autosomes Define different types of mutations Evaluate and create pedigree charts

I. CHROMOSOMES In the early 1990’s a researchers

noticed that Drosophilia melanogaster (fruit flies) had 4 chromosomes3 were the same in both males and females

and 1 was different

house-flies.net exploratorium.edu

2 TYPES OF CHROMOSOMES Sex chromosomes contain genes

that determine the sex of an individual (“X” or “Y”)Males decide the gender

Autosomes-all the other chromosomes that are not involved in gender determinationCause about half of all genetic

diseases

II. LINKED TRAITS Pair of genes that are inherited together They are located in the same

chromosome and very close together.

graphicshunt.com

SEX-LINKED GENES AND TRAITS Refers to a trait that is coded for by an

allele on a sex chromosome (X or Y)More X-linked traits than Y-linked traits

because the of the size differenceMales who have an X chromosome that

carries a recessive allele will exhibit the sex-linked trait

Females have less of a chance expressing an X linked disease because they have 2 X-chromosomes

karakalpak.com

MUTATIONS Germ-cell – occur in the gametes

Effect the offspring Somatic-cell – occur in an organisms

body cellsCan not be inherited-results in things like

leukemia or skin cancer Lethal – cause death, often before birth Beneficial – help the organism survive

and reproduce

photography.nationalgeographic.com

CHROMOSOME MUTATIONS Change the structure of the

chromosome Deletion and Insertion

Loss of nucleotide bases or an addition of them

biology-online.org

INVERSION TRANSLOCATION

A piece of the chromosome breaks off and flips around backward

activars.com

• A piece of one chromosome breaks off and attaches to a nonhomologous chromosome

staff.jccc.net

http://www.youtube.com/watch?v=XAGxp9j5rtc&feature=related

NONDISJUNCTION The chromosomes don’t separate during

meiosis so one gamete receives 2 copies and the other receives none.

2 TYPES OF NONDISJUNCTION Trisomy – an extra chromosome in every

cellMost of these disorders make it very

difficult for the individual to survive Trisomy 21-down syndromeTrisomy 18 &13-normally die before age 1

Monosomy – absence of 1 chromosomeTypically lethal to embryonic

developmentTurner’s syndrome

cdadc.com

GENE MUTATIONS

Point mutation – change within a single gene

Substitution – one nucleotide replaces another

Frameshift mutation – if some nucleotides are deleted the entire segment of DNA moves down changing the codons for amino acids Detrimental to the proteins function

Insertion mutation – one or more nucleotides are added which can result in a frameshift mutation

EXAMPLE OF SUBSTITUTION Sickle Cell Anemia: only 1 amino acid is

substituted to produce the sickle shape Recessive trait that prohibits Hemoglobin from binding correctlyTo the red blood cell

unitedhealthdirectory.com

FRAMESHIFT MUTATION

Changing one letter completely alters the codon sequence

staff.um.edu.mt

EXAMPLES OF GENE MUTATIONS Substitution:

Original – the fat cat ate the wee rat.Mutation - The fat hat ate the wee rat.

Insertion:Original: The fat cat ate the wee rat.Mutation: The fat cat xlw ate the wee

rat. Frameshift:

Original: The fat cat ate the wee rat.Mutation: The fat caa tet hew eer at.

1. Below is the base sequece for the normal protein for normal hemoglobin and sickle cell:

Normal: GGG CTT CTT TTT Sickle: GGG CAT CTT TTTIs this a point or frameshift mutation? Explain.2. Delete the first H in the following sequence and

regroup the letters in groups of three. Does the sentence still make sense? What type of mutation is this

THE FAT CAT ATE THE RAT3. Name 2 chromosome mutations. How are they alike?

How are they different?4. Using the sequence ATT GCA AAG GGT. Give an

example of a deletion, insertion, and substitution. Circle the change you have made.

5. What is the difference between sex chromosomes and autosomes?

LIST OF GENETIC DISORDERS – PICK 1 FOR YOUR PROJECT Huntington’s Disease Down’s Syndrome Cystic Fibrosis Duchenne muscular

dystrophy Sickle Cell Anemia Trisomy 18 (Edwards) Tay-Sachs disease Color blindness PKU (Phenylketonuria)

Fragile X syndrome

• Thalassemia• Marfan syndrome• Breast Cancer• Hemophilia

• Cri du Chat• Polydactyly• Maple Syrup urine disease• Turner Syndrome• Klinefelter's syndrome, • (XXY syndrome)• Super males (XYY)• Patau syndrome• Albinism

II. PEDIGREES Diagram that shows how a trait is

inherited over several generations

http://www.uic.edu/classes/bms/bms655/gfx/pedigree1.gif

• A circle represents a female• A square

represents a male• If the circle or

square is filled in that means the individual has the trait• Horizontal

lines indicate marriage or having children• Vertical lines

show offspring

Reading Pedigrees

Is the mom or dad in generation I affected by a trait?

How many offspring are shown in generation II?

How many daughters & sons in generation II? How many have the trait? How many offspring does daughter #1 have? How many have the trait?

Practice Problems

PATTERNS OF INHERITANCE Autosomal Dominant Traits

Passed on to sons or daughters even if only one parent has the gene

Affected individuals who mate with an unaffected individual have a 50% chance of passing on the gene as long as they are not homozygous for the trait

Can appear in males and females equally

What must the genotype of the parents be to produce a child #7 who is unaffected?

What is the genotype of #9?

What are the genotypes of the 3 children in the third generation?

RECESSIVE PEDIGREES In order to be passed on both parents

must have the gene Traits can be passed on if both parents

are “carriers” of the traitHave the trait but it isn’t expressed because

they also have the dominant trait An individual who is infected may have

parents who are not If both parents are affected, all of their

children will be affected

CARRIERS FOR AUTOSOMAL RECESSIVE TRAITS

RECESSIVE PEDIGREE

• If individuals 2 + 3 in generation 3 have more children- will they be affected?• Can Individual #8 in gen. 3 have any unaffected children?• Can individual #9 in gen 3 have affected children?

SEX LINKED TRAITS Located only the sex chromosomes (X

and Y) More frequently expressed on males

than females Y-linked is male only X-linked –passed from mother to son

Mainly expressed in malesDaughters are carriers

X-LINKED TRAITS Traits that are on the X chromosome Males are affected more than females Color blindness is an X-linked recessive

disorder passed from mother to son

X-LINKED RECESSIVE

Evident in males because they only have 1 X chromosome

Women are rarely affected because they have 2 X chromosomes-better chance of not getting it

If the father has the mutated gene all of his daughters will have it

X-LINKED DOMINANT

No transmission from father to son All daughters of the affected male will

have it Only 1 dominant allele is needed for the

trait to be expressed What is the genotype of #2 in

generation II?

GENETIC DISORDERS Diseases that have a genetic basis Researchers have found that most traits

are Polygenic – influenced by several genesSkin color – combination of 3-6 genes which

control the amount of melanin in the skin

Complex characters – influenced by both genes and environmentHeight, certain diseases such as breast

cancer

cosbiology.pbworks.com

INCOMPLETE DOMINANCE

Displaying a trait that is intermediate of the two parentsWavy hair comes from one parent

having straight hair and one parent having curly hair

Red flower and a white flower produce a pink flower

doctortee.com

SEX INFLUENCED TRAIT Males and females can show different

phenotypes even when they share the same genotypeEx: Male pattern baldness – the allele is

dominant in males but recessive in females due to the higher testosterone levels in males

SINGLE-ALLELE TRAITS Trait controlled by 1 allele-dominant or

recessive

Dominant ExamplesHuntington’s Disease-

degradation of the brain

Polydactly- presence of a sixth digit

Achondroplastic dwarfism-dwarf size

Recessive ExamplesCystic Fibrosis-most

common lethal disease

Sickle-cell anemia-blood disorder

Albinism- lack of color pigment in skin, hair, and eyes

DETECTING GENETIC DISEASE

Amniocentesis – technique used to detect genetic disorders in a fetus

Chrionic villi sampling – takes some cells derived from the placenta

Treatments depend on the specific disease