Fundamentals of Genetics

Chapter 9

(Family Tree)KEY: females

males

Exhibit a trait

marriage

hildchildrendeath

Ex: shaded shapes – curly hairh d d t i ht h inon-shaded – straight hair

P1

FF1

F

Joseph Anna

F2

Sex-linked: trait usually seen in males

A t l t it i b th llAutosomal: trait appears in both sexes equally

D i t t it hild ill h tDominant trait: every child will have a parent with the trait

Recessive trait: child w/trait parents can appear normalpp

(B th t b h t )(Both parents may be heterozygous)

Cleopatra – Berenike IIIP diPedigree

Pedigree Problem

G ti 1 A h t f bGeneration 1: A man, heterozygous for brown eyes marries a woman with blue eyes.

Generation 2: They have 3 children The first and secondGeneration 2: They have 3 children. The first and second children are sons with brown eyes. The third is a daughter also with brown eyes. She marries a male with brown eyesbrown eyes.

Generation 3: They have 3 daughters. The first child has blue eyes. The second and third children have brown yeyes. The third daughter marries a man.

Generation 4: They have two sons, both with blue eyes.

Generation 1: A male with type A blood marries a female with type AB blood.

Generation 2: They have three children. The first is a daughter with type B blood. The second is a daughter

i h A bl d d h hi d i i h Bwith type A blood and the third is a son with type B blood. He marries a woman with type O blood.

Generation 3: They have three children. The first is a son with type B blood. The second and third children are daughters with type O blood. The third daughter marries

ith AB bl da man with AB blood.

Generation 4: They have two children. The first is a son ywith A blood and the second is a daughter with B blood.

KaryotypesKaryotypesChromosome preparation allowing theChromosome preparation allowing the

counting and identifying of chromosomes.Sex chromosomes: chromosomes that determineSex chromosomes: chromosomes that determine the sex of an organism.

females XXfemales –

males -

XXXY

Autosomes: the remaining prs. of chromosomes ft bt ti th hafter subtracting the sex chromosomes.

SRY geneSRY geneGene that codes for a protein that causesGene that codes for a protein that causes

the gonads of an embryo to develop as testestestes.

L t d i th Y hLocated in the Y chromosome.

SRY = Sex-determining Region Y.

What Sex Am I?What Sex Am I?

Abnormalities: Down SyndromeAbnormalities: Down Syndrome

• Persons have distinctive features of thePersons have distinctive features of the eyes, mouth, hands and sometimes internal organs.

• All have retarded development, degree is highly variable.

• Contain 47 instead of 46 chromosomes• Extra chromosome in the tiny 21• Results in trisomy-21; means 3 number 21

chromosomes.

Turner Syndromey

• Females have no functional ovaries; unable to produce ova

• Have short stature, webs of skin from the neck to the shoulders

• Cells of females have only 45 chromosomeschromosomes

• X chromosome is missing; persons are said to be XO in their karyotypesaid to be XO in their karyotype.

Klinefelter Syndrome

• Males are very tall and unable to reproduce• Cells of males have an extra X chromosome:• Cells of males have an extra X chromosome:

XXY

MutationsMutationsLasting changes in theLasting changes in the

hereditary material.

Mutagen: any agent that causes aMutagen: any agent that causes a mutation to occur.

3 types of mutations:

1. Germ- cell: occur in the organism’s1. Germ cell: occur in the organism s gametes. They do not affect the organism itself but can be passed onorganism itself but can be passed on to the offspring.

2. Somatic-cell: take place in an organism’s body cell. It can affect the organism.

Ex: certain types of human skin cancer and leukemia.

They cannot be inherited.

3 Lethal: cause death often before3. Lethal: cause death, often before birth.

DeletionDeletionA particular kind of mutation: loss of a piece of DNA from aloss of a piece of DNA from a chromosome. Deletion of a gene or part of a gene can lead t di b litto a disease or abnormality.

InsertionInsertionA type of chromosomal abnormality in which aabnormality in which a DNA sequence is inserted into a gene, disrupting th l t t dthe normal structure and function of that gene.

DuplicationDuplicationA particular kind of mutation: production of one or moreproduction of one or more copies of any piece of DNA, including a gene or even an entire chromosome.

InversionInversionChromosome segments that h b t d 180 dhave been turned 180 degrees. The gene sequence for the segment is reversed with grespect to the rest of the chromosome.

TranslocationTranslocationBreakage and removal of a l t f DNA flarge segment of DNA from one chromosome, followed by the segment's attachment y gto a different chromosome.

NondisjunctionNondisjunctionA special chromosome mutation in whicha pair of chromosomes fail to separate p pduring cell division.

X – linked TraitsX linked TraitsA trait determined by alleles that areA trait determined by alleles that are

carried by the X chromosomes but are absent from Y chromosomesabsent from Y chromosomes.

Recessive traits controlled by X-linked genes are expressed in males. There are no g palleles for the dominant trait to mask them.

I f l i X li k d t itIn females, a recessive X-linked trait does not appear unless there are 2 alleles for that trait, one in each of her X chromosomes.

HEMOPHILIAHEMOPHILIADisorder in which a person’s blood does notDisorder in which a person s blood does not

clot. Bleeding from a cut or bruise may take hours to stop. Almost always shows up in male children.

Detecting Genetic DiseaseDetecting Genetic DiseaseAmniocentesis: technique allowing aAmniocentesis: technique allowing a

physician to remove some amniotic fluid from the amnion between 14th and 16th

week of pregnancy.

Chorionic villi sampling: technique where the ph sician takes a sample of thethe physician takes a sample of the chorionic villi, cells derived from the zygote that grow between the mother’szygote that grow between the mother s uterus and placenta, between the 8th and 10th week10 week.

Genetic Counseling: the process of informing a person or couple about their genetic makeup.

Gene Therapy: technique that places a healthy copy of a gene into the cells of a y py gperson whose copy of the gene is defective.

G l t d i hGenes are located in chromosomes

G di t th th i fGenes direct the synthesis of enzymes.

Enzymes are proteinst d f t i th igenes must code for protein synthesis

• Proposed that a DNA molecule is a long, twisted double stranded structuretwisted, double-stranded structure.

• Each strand consists of a chain of smaller units called nucleotidesunits called nucleotides.

a) nucleotide consists of:1 sugar1. sugar2. phosphate group3 it t i i b3. nitrogen-containing base

b) 4 kinds of nucleotides in DNA:

Adenine AThymine T

Cytosine CCytosine C

Guanine G

• The sugar-phosphate parts join the nucleotides together & form the sides of a ladder.

• A base of one strand pairs with the base from the other strandfrom the other strand.

• Adenine (A) can only pair with Thymine (T)C t i (C) l i ith G i (G)• Cytosine (C) can only pair with Guanine (G)

• Properties of genes:li t ( tl d li t )a. genes replicate (exactly duplicate)

during cell division.b t t i llb. genes mutate occasionallyc. genetic instructions are passed from

generation to generation through meiosisgeneration to generation through meiosis and fertilization.

RNA Ribonucleic AcidRNA Ribonucleic Acid

The molecule that links the chromosomes in the nucleus to the ribosomes in the cytoplasm.

1. sugar in each RNA nucleotide is ribose instead of deoxyribose.

2. Thymine does not occur in RNA. It is replaced by Uracil (U).

3 different kinds of RNA:3 different kinds of RNA:1. Ribosomal RNA (rRNA) – makes up the1. Ribosomal RNA (rRNA) makes up the

ribosomes along w/a # of proteins.2. Messenger RNA (mRNA) – it carries the g ( )

DNA message to the ribosome.3. Transfer RNA (tRNA) – transfers amino ( )

acids from the cytoplasm to the ribosomes, where they are added to a growing chain of

i id b i b il i iamino acids being built into a protein molecule.

CodonCodon

A sequence of 3 nucleotides in mRNAA sequence of 3 nucleotides in mRNA that codes for a single amino acid.

ACA - Threonine

GCC - Alanine

UUU PhenylalineUUU - Phenylaline

Recombinant DNARecombinant DNABy using special enzymes, small pieces of DNABy using special enzymes, small pieces of DNA

from one organism can be spliced into the DNA of another organism.

benefits:1. Manufacturing of human insulin in large g g

amounts for those w/diabetes.2. Bacteria that prevents the formation of

frost on plants to temps. As low as -6o

Test CrossTest CrossThe crossing of an individual of unknownThe crossing of an individual of unknown

genotype with a homozygous recessive individual to determine the unknown genotype.

In dogs, there is an hereditary deafness caused by a recessive gene, “d.” A kennel owner has a male dog that she wants to use for breedingmale dog that she wants to use for breeding purposes if possible. The dog can hear, so the owner knows his genotype is either DD or Dd. If the dog’s genotype is Dd the owner does notthe dog’s genotype is Dd, the owner does not wish to use him for breeding so that the deafness gene will not be passed on. This can be tested by breeding the dog to a deaf femalebe tested by breeding the dog to a deaf female (dd). Draw the Punnett squares to illustrate these two possible crosses. In each case, what percentage/how many of the offspring would bepercentage/how many of the offspring would be expected to be hearing? deaf? How could you tell the genotype of this male dog? Also, using Punnett square(s) show how two hearing dogsPunnett square(s), show how two hearing dogs could produce deaf offspring.

A deaf female is genotype dd. What kind(s) of gametes (eggs) can she produce?(eggs) can she produce?

If the hearing male is DD, what kind(s) of gametes (sperm) can he produce?

If he is Dd, what kind(s) of gametes can he produce?

M k h P SMake the Punnett Square:If he is DD:

If he is Dd: