Mendel’s Laws Mendel’s Laws of Geneticsof Genetics

Turn to page 101 in Textbook Turn to page 101 in Textbook or 151 on Ebookor 151 on Ebook

Read the “Think About” Section with a partner at your table and make a list of characteristics about the girl in the photograph.

Which characteristics do you think were inherited? Which characteristics were acquired?

IntroductionIntroduction

Genetics- the study of heredity Heredity- the passing of traits

from parents to offspring– Trait = characteristic

• eye color, hair color, height, and weight

– Gene = sequence of DNA that determines a trait

Gregor MendelGregor Mendel Known as the “Father of Genetics” Began studying the patterns of

heredity through peas

Mendel’s ExperimentsMendel’s Experiments

Mendel’s ExperimentsMendel’s Experiments

Initial experiments were monohybrid crosses.– Involves one pair of contrasting traits

• Example: purple flower vs. white flower

3 Steps:– P generation (Parental)

– F1 generation (Filial)

– F2 generation

Mendel’s ConclusionsMendel’s Conclusions For each trait, an individual has two copies of the gene.

(One from each parent.)

Alleles - Alternative versions of genes

Law of Dominance: Alternative versions of genes account for variations in inherited characters.

– When 2 different alleles occur:

• One is expressed= DOMINANT

–Represented by a capital letter

• One is not expressed= RECESSIVE

–Represented by a lower case letter

Dominant vs. RecessiveDominant vs. Recessive

Trait: flower color Dominant- Purple flower– Written as “P”

Recessive- White flower– Written as “p”

Law of Segregation The

emergence of one trait will not affect the emergence of another

Law of

Independent Assortment Hereditary

factors do not combine, but are passed intact with certain factors dominant over others.

Punnett SquaresPunnett Squares

A diagram that predicts the expected outcome of a genetic cross

Used to predict some traits

– Ex. Breeders (dogs or horses)

Genotype= genetic makeup

Phenotype= physical traits

Heterozygous= 2 different alleles

– hybrids Homozygous= 2

identical alleles

Today is Sept 18thToday is Sept 18th List the following and tell if they

are homozygous, heterozygous, dominate or recessive.

TT, Tt, tt Draw a punnett square using Tt

x tt

A couple visits a geneticist to see what the odds are that A couple visits a geneticist to see what the odds are that they will have a child who has cystic fibrosis. The man is a they will have a child who has cystic fibrosis. The man is a known carrier of the recessive disease, while his wife is known carrier of the recessive disease, while his wife is not. What are the odds that their first child will have not. What are the odds that their first child will have cystic fibrosis?cystic fibrosis?

Dad- AaMom- AA

AAAA AAAA

AaAa AaAa

Mom

Dad

A A

A

a

The child will not havecystic fibrosis. However, there is a 50% chance thatthe child will be a carrier of the disease.

Genotype: ?

Phenotype: ?

Heterozygous: ?

Homozygous: ?

Genotype: ?

Phenotype: ?

Heterozygous: ?

Homozygous: ?

ProbablityProbablity

It is the likelihood that a specific event will occur.

Can be expressed as words, decimals, percentages, or fractions

Probability- Example 1Probability- Example 1

There are two sexes (male and female). What is the probability that a pregnant

woman will have a boy? A girl?

Overall there is a 100% chance that she will have a baby. Since there are two sexes, she has a 50% chance of having a boy and a 50% chance of having a girl.

Probability- Example 2Probability- Example 2 There are two sides to a quarter- heads and

tails. What is the probability that it will land on

heads? On tails?

There is a 100% chance that the quarter will land on either heads or tails. Therefore, 50% of the time, it may land on heads and the other 50% of the time, it may land on tails.

Probability- Example 3Probability- Example 3

If you flip a coin 3 times in row, what is the probability that it will land heads up every time?

With each flip, there is a 50% chance that it will land on heads.

Patterns of HeredityPatterns of Heredity

Polygenic traits Incomplete dominance Codominance Multiple alleles

Polygenic traitsPolygenic traits

Traits that occur due to several genes– Ex: eye color, hair color, skin color

Have varying degrees from one extreme to the other– Different shades of skin, hair, and eyes

Incomplete DominanceIncomplete Dominance

A trait that is intermediate between the two parents

Examples:– Snapdragons

• Red and white crossed together make pink

– Hair• One parent with straight hair, one parent has curly

hair to produce offspring that has wavy hair

CodominanceCodominance

Occurs when two dominant alleles are expressed at the same time causing both traits to be displayed

Ex. Colors of horses and cows

Multiple AllelesMultiple Alleles Traits brought on by

three or more alleles– Example: ABO blood

type There are three alleles

for the gene that determines blood type.– A type (IA) and B type

(IB) are codominant.

– O type (i) is recessive.

Child: O type

Parents: A, B, or O type Child: A type

Parents: A, AB, or O type Child: B type

Parents: B, AB, or O type Child: AB type

Parents: A, B, or AB type

IIAAIIBB IIAAii

IIBBii iiii

MOMIB i

i

IA

DA

D

Based on the Punnett square, the offspring will have either:AB type, A type, B type, or O type blood.

Dad has A type and Mom Dad has A type and Mom has B type.has B type.Dad has A type and Mom Dad has A type and Mom has B type.has B type.

PedigreesPedigrees A family history that shows

how a trait is inherited over several generations.

A circle represents a female. A square represents a male. If the square or circle is

shaded then, that person has a type of genetic disorder.

A line between a circle and square represents a marriage.

A line coming out from a circle and square represents offspring.

The Roman Numeral out to the side represents the generation.

KaryotypeKaryotype A picture of

chromosomes arranged

together in pairs– 2n=46, n=23

– 1st 22 pairs of chromosomes: autosomes

– Last pair of chromosomes: sex chromosomes

• XX- Female

• XY- Male

Genetic DisordersGenetic Disorders Caused by errors in genes that are passed from

parents to offspring. 4 Types:

– Chromosome Disorders – parts of or entire chromosomes are missing OR there are extra copies

– Autosomal Dominant Disorders – controlled by a dominant allele on a non-sex chromosome

– Autosomal Recessive Disorders - controlled by a recessive allele on a non-sex chromosome

– Sex-linked Disorders – controlled by alleles on the X chromosome

Trisomy 21 (Down’s Syndrome)Trisomy 21 (Down’s Syndrome) Have 3 copies3 of chromosome #21 Symptoms: short; heart and intestinal defects; poor

muscle tone; learns to walk and talk late Down Syndrome chances:

– Before age 35,

there is a 1/760 chance.– After age 35,

there is a 1/77 chance. 3

Klinefelter’s SyndromeKlinefelter’s Syndrome Due to disorder in sex chromosomes Male XXY; most are sterile have underdeveloped male secondary sex

characteristics

Turner’s SyndromeTurner’s Syndrome Due to disorder in sex chromosomes Female XO; sterile Poorly developed reproductive organs

Phenylketonuria (PKU)Phenylketonuria (PKU)

Can’t change phenylalanine into tyrosine. The build up of phenylalanine poisons brain cells.

Diet; treatment prevents damage but does not cure disease

Autosomal Recessive Disorder

Cystic FibrosisCystic Fibrosis

Autosomal Recessive Disorder

Abnormal amounts of mucus are produced in the respiratory tract; mucus clogs breathing apparatus

Tay Sachs DiseaseTay Sachs Disease

Autosomal Recessive Disorder Cannot produce a blood enzyme needed

to break down fats Fats accumulate in cells, and cells

rupture and die. Results in: blindness, deafness, mental

degeneration, death

Sickle Cell DiseaseSickle Cell Disease Abnormal hemoglobin molecules in red

blood cells cannot carry O2 effectively Sickled shape cells cannot travel through

small blood vessels Autosomal recessive disorder Most common in African Americans.

PolydactylyPolydactyly

Autosomal Dominant Disorder Having extra fingers or toes

Huntington’s DiseaseHuntington’s Disease

Autosomal Dominant Disorder Symptoms do not occur until after age 30 Progressive nervous system deterioration

until death occurs

Color BlindnessColor Blindness Sex-linked trait Inability to distinguish between certain

colors – Red-Green colorblindness is most common.

Occurs more frequently in males

HemophiliaHemophilia Sex-linked trait More common in males Blood lacks the protein necessary for

normal blood clotting. Treated by injections of normal clotting

proteins

DNA Techniques Restriction enzymes- cut DNA into small pieces

that can be sequenced Gel electrophoresis- technique used to separate

DNA strands of different lengths Polymerase Chain Reaction (PCR)- technique

used to make many copies of a particular gene Gene therapy- process of changing a gene to

treat a medical disease or disorder DNA microarray- technique used to screen for

genetic disorders DNA fingerprinting- technique used to

determine if 2 samples of genetic material are from the same person

Studying DNA

Genomics- the study of whole genomes, including genes and their functions

– Hybridization- crossing dissimilar individuals to bring together their best characteristics

– Inbreeding- crossing individuals with similar characteristics so that those characteristics will appear in their offspring