HEREDITY

HEREDITY

Why we are the way we are?

REVIEW OF MITOSIS• Division of somatic

(body) cells• Phases

– Interphase – Prophase– Metaphase– Anaphase– Telephase– Cytokinesis

• Produces 2 identical diploid cells

MEIOSIS• Division of gametes

(reproductive) cells• Repeat all phases 2x’s,

EXCEPT for interphase• Crossing Over

– Chromosomes exchange parts during metaphase - creating different combinations of genes

• Produces 4 different haploid cells

GENDER DIFFERENCES• Males– Meiosis occurs in

testes– Starts @ puberty– Produces 4 mature

sperm cells each time

• Females– Meiosis occurs in

ovaries– Begins/ends prior to

birth– Produces 1 mature

egg & 3 polar bodies• Shriveled cells lost

their cytoplasm to single mature egg

CELL DIVISION T-CHARTmitosis meiosis

Type cells

Same/different

# of cells

# chromosomes

Term (# chrom)

MENDEL’S LAWS• Law of Dominance– Some traits show

up throughout many generations.• Dominant – hide

other traits• Recessive – can be

hidden– Symbols

• CAPITAL = dominant• lower = recessive

• Terms– Genotype

• Genetic make-up• TT, Tt = tall• tt = short

– Phenotype• Physical appearance• Tall or short

MENDEL’S LAWS• Law of Segregation– Traits have multiple

forms (dom & rec) – also called alleles

– Inherit one form from each parent

– Terms:• Homozygous

(purebred)– 2 identical alleles– TT or tt

• Heterozygous (hybrid)– 2 different alleles– Tt

MENDEL’S LAWS• Law of

Independent Assortment– Genes not tied

together– Allows for

differences between individuals of same species

– Example:• Not everyone who is

tall has to have brown hair

GENETIC PROBABILITY• Punnett square– Grid used to predict

genetic probability• Chance that

offspring will receive certain trait

• Monohybrid– Grid that looks at

only 1 trait

MONOHYBRID CROSSES1. Identify the

genotypes of the parents– This will determine the

size of the square2. Place 1 genotype on

the top of the square & the 2nd along left

3. Fill in the center squares

4. Determine the genotypic & phenotypic ratios of the offspring

MONOHYBRIDSExample #1A man who is homozygous for brown eyes and a women who is homozygous decide to have children.

If brown eyes are dominant, what color eyes will their children have?

MONOHYBRIDSExample #2

If both the mother and father are heterzygous for eye color, what color eyes will their children have?

MONOHYBRIDSExample #3

In monkeys, long tails are dominant over short tails. If a homozygous recessive female mates with a heterozygous male, what will their offspring look like?

DIHYBRID CROSS1. Identify the genotypes of

the parents2. Determine the possible

gametes each parent could provide.– This will determine the size of

the square3. Place the gametes of the

parents on the top & along left side – There will be 2 letters/block

4. Fill in the center squares– There will be 4 letters w/in

each block5. Determine the genotypic &

phenotypic ratios of the offspring

DIHYBRIDSExample #4

Assuming that spots are dominant over no spots & horns are dominant over no horns, what would the offspring of the following cows look like?

Male – homozygous spots & heterozygous for horns

Female – heterozygous spots with no horns

DIHYBRIDSExample #5

In pigs, pink is dominant to white and curly tails are dominant to straight tails.

Male –white w/ and purebred curly tailFemale – pure pink w/ straight tail

DIHYBRIDSExample #6Brown eyes dominant over blue & separate brows are dominant over unibrowsMom & Dad both heterozygous both traits

INCOMPLETE DOMINANCE• Dominant gene not

completely hide the recessive gene– Results in a blend or

mix of the two features

– Results in 3 possible phenotypes

– Heterozygous genotype now has its own physical appearance (phenotype)

• Often seen in shapes & colors– Example:

• TT tall• tt short• Tt medium

INCOMPLETE PROBLEMS• Example #7In carnations, Red is dominant over white & a mix of the two create pink.

What type of flowers would be produced by crossing a white carnation with a pink carnation?

INCOMPLETE PROBLEMSExample #8Straight hair is dominant over curly hair & a combination of genes results in wavy hair.

What would the children of two wavy haired parents look like?

CODOMINANCE• A condition where both

alleles of a gene are active (dominant)

• No recessive gene• A heterozygous

individual would have both physical features present

• Condition is most often seen in hair, feathers, fur & skin color

• Example: Cows– B Black– W white– BW Black & White

COMDOMINANT PROBLEMSExample #9

Tabby cats are the result of codominance, the genes for black and tan are both present.

What would be the result of a black cat & a tabby cat having kittens?

COMDOMINANT PROBLEMSExample #10

A roan cow is one that has both red & white hairs. What would the calves of two roan cows look like?

POLYGENIC INHERITANCE• Poly = many• Genic = genes• Many physical

features are controlled by more than 1 gene

• What makes us look so different

• Example:– Eyes

• Size• Shape• Slant• Distance• Color• Lash length

SEX DETERMINATION• 22 pairs autosomes– Same males &

females– Basic physical info

• 1 pair sex chromosomes– XX female– XY male

SEX-LINKED TRAITS• Genes carried on x

chromosome• Most are recessive and

so rarely seen in females – Males only need 1

recessive gene to show trait (XhY)

– Females need 2 recessive genes to show trait (XhXh)

– Females can be Carriers• Heterozygous, have 1

recessive gene but do NOT exhibit the trait

• XHXh

• Examples:– Red Green

colorblindness– Hemophilia– Muscular Dystrophy– Male Pattern

Baldness– Fragile X syndrome

SEX-LINKED PROBLEMSExample #11

If a colorblind woman is married to a man with normal vision, what are the chances that their children will be colorblind?


If a man with hemophilia and a completely normal female decide to have children, will they have to worry about their children having hemophilia?


If a bald man and a woman who carries the gene for baldness have children, will all of their children be bald?

PEDIGREE• Family tree shows

how a trait or genetic disorder is passed through the generations

• Symbols:– Male– Female– Marriage– Death/divorce– Relationship– Twins– Miscarriage

• Symbols:– Traits/diseases

• Person w/ trait• Person w/o trait• Carrier

• Format– Oldest youngest

(left) (right)– Generations

numbered along left side

– Arrow points to individual

PEDIGREE EXAMPLE

MULTIPLE ALLELES• Trait that requires

more than 1 gene to determine phenotype

• Blood types– Type A IAIA, IAIi– Type B IBIB, IBIi– Type AB IAIB– Type O ii

• Blood types are named by the types of antigens found in the red blood cells

– Antigen protein specific to individual

• AB universal receiver– (take all types since

their blood contains all possible antigens)

• O universal donor– (give blood anyone

since their blood contains no antigens)

BLOOD TYPE PROBLEMSExample #14

If the mother is homozygous for A and the father is heterozygous for B, what possible blood types could they provide to their children?


If both mom and dad have type AB blood, what possible blood types could they provide to their children?


Mr. & Mrs. Doe had a child named Jim at the same time Mr. & Mrs. Roe had their son Joe. The couples thought their children had been switched at birth and demanded blood tests to prove paternity. Use the test results to determine if there was a mix-up.

Mr. Roe – A

Mrs. Roe – A

Joe – O

Mr. Doe – O

Mrs. Doe – AB

Jim – A

HEREDITY

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