Life Science

Most Eukaryotic organisms reproduce

sexually.

In sexual reproduction, two parents give

genetic material to produce offspring.

Each parent produces a reproductive cell called a gamete.

Gametes are produced by the process of MEIOSIS (not to be confused with mitosis)!

When the gametes of a male and a female fuse together (fertilization), a zygote is produced.

Because both parents give genetic material, the offspring has traits of both parents but is not exactly like either parent.

Most cells that divide produce new cells

that are exactly the same. • The process by which this occurs is called

Mitosis.

• Body Cells aka Somatic Cells

• Diploid, which is indicated by 2n

• Each diploid cell has pairs of chromosomes

called homologous chromosome

• For Humans, 2n = 46

Meiosis is a form of cell division that

produces daughter cells with HALF the

number of chromosomes that are in the

parent cell. • Sex Cells (Egg and Sperm) aka Germ Cells

• Haploid, which is indicated by n

• For humans, n = 23

In order to achieve the correct number of

chromosomes in the zygote.

To produce egg and sperm cells

Genetic Variation

Genetic Variation is a good thing for a

population.

Genetic variation is made possible by

sexual reproduction.

During meiosis, a process called CROSSING-OVER leads to genetic variation. • During prophase I of meiosis, homologous

chromosomes line up next to each other.

• Each homologous chromosome is made of two sister chromatids.

• Crossing-over occurs when a piece of one sister chromatid breaks off and combines with a different chromatid.

Gregor Mendel was a monk. It was in his monastery in Austria that he

tended a garden in which he observed the growth of many plants (specifcally garden peas)

His observations, experiments, and data collection led to area of biology known as genetics.

Heredity- the passing of genetic traits

from parent to offspring. • Everything that you are is a result of the

characteristics transmitted by your mother and

father.

The characteristics that you receive

produce the traits that you have.

In garden peas, Mendel examined flower

color, plant height, and seed texture.

Mendel started by growing pea plants

that were true breeding. • Plants that are TRUE BREEDING or PURE for a

trait produce offspring that have the exact same

traits.

Purple flowered plants produce purple flowered

plants.

Green seed colored plants produce green seed

colored plants.

True breeding plants are produced by

self-pollinating pea plants for several

generations.

This produced the parental generation,

or the p generation for Mendel.

Mendel then bred true breeding plants

with different traits. • For example, he crossed true breeding purple

flower pea plants with true breeding white

flower pea plants.

Mendel found some interesting results.

This produced the F1 generation.

Mendel found that crossing two different true breeding plants produced offspring that DID NOT show the trait of one of the true breeding parents.

Mendel concluded that one FACTOR in a pair may prevent the other from having an effect or appearing. • These FACTORS are alleles=> one is DOMINANT

over another!

Mendel observed that a TRAIT controlled by

a RECESSIVE factor had no observable

effect on an organism’s appearance.

The DOMINANT factor is the one that

appears.

A trait with a dominant and recessive allele

will always express the dominant trait. ◦ PP or Pp = ALWAYS PURPLE flowers

◦ pp = ALWAYS WHITE flowers

A. Tt

B. Pp

C. Gg

D. TT

A. P

B. C

C. F2

D. F1

A. F1 x F1

B. F2 x F2

C. P x P

D. P x F1

A. PP

B. pp

C. PP, Pp, pp

D. Purple flowers

A. PP

B. Purple, White

C. Pp

D. Lavender

A. Gamete

B. Sex cell

C. Somatic cell

D. gene

If a trait contains a dominant allele, then

that allele for that trait will be expressed.

This allele dominates over the recessive

allele

The set of alleles that an individual has for a characteristic is called the genotype.

Examples of genotypes • PP, Pp, pp

The genotype determines the phenotype. • Phenotype = what you or any organism looks

like.

• Purple colored flowers, white colored flowers

When both alleles are exactly the SAME,

the genotype is HOMOZYGOUS. • Ex: PP or pp

If an organism has two different alleles

for a single gene, the individual is

HETEROZYGOUS for that trait. • Ex: Pp

Mendel concluded that the paired factors (alleles) separate during the formation of sex cells.

Offspring receive one allele from each parent. ◦ Only chance decides which alleles will be passed on

to gametes. Segregation is random. The actual law states: when an organism

produces gametes, each pair of alleles is separated and each gamete has an equal chance of receiving either one of the alleles.

Inheritance of one character does not affect the

inheritance of any other.

◦ Ex: Just because a pea plant is dominant tall,

doesn’t mean it has to be dominant purple! The Law of Independent Assortment states: during

gamete formation (meiosis), the alleles of each gene

segregate independently.

◦ We know that many genes are linked to each

other on the same chromosome, so if they are

close together (avoid crossing over) then they

will be linked!

As said before, many traits are controlled

by more than one gene.

Examples of polygenic traits in humans

are height, skin color, hair color

Most characteristics are polygenic.

So far we have only discussed traits that

are controlled by pure dominance.

There are situations where there is

incomplete dominance.

An offspring has a phenotype that is

intermediate between the traits of its two

parents.

When a red SNAPDRAGON flower is

crossed with a white SNAPDRAGON,

neither the red allele nor the white allele

is completely dominant. • Produces pink colored flowered offspring

RR WW

RW

Work some Punnett Squares for

incomplete dominance: • RR X WW

• RW X RW

For some characteristics, two traits can

appear at the same time:

Codominance is when both alleles for the

same gene are FULLY expressed.

Work some Punnett Squares for

codominance: • RR X WW

• RW X RW

Human blood type is contolled by

codominance.

A. Two short-haired cats produce a liter of 4 kittens including 1 long-haired and 3 short haired.

B. A color blind man and a woman with normal vision produce a son with normal vision and a color blind daughter.

C. A tall purple colored pea plant and a short white flowered pea plant are crossed producing offspring including tall white flowered pea plants.

D. A red flowered snapdragon and a white flowered snapdragon are crossed producing pink flowered snapdragons.

A. Prophase II

B. Interphase

C. Metaphase I

D. Prophase I

A. Telophase I

B. Anaphase II

C. Telophase II

D. Metaphase I

A. 1:2:1

B. 2:1:1

C. 3:1

D. 1:1:2

A. 1:2:1

B. 2:1:1

C. 3:1

D. 1:1:2

A. Tt

B. tt

C. TT

A. White

B. Red

C. Purple

D. Pink

A. Pp

B. TT

C. Tt

D. Pt

A. TT

B. Rr

C. tt

D. TR

A. 0%

B. 25%

C. 50%

D. 75%

A. Red

B. White

C. Red and White

D. Pink

A. 0%

B. 25%

C. 50%

D. 75%

Some genes are located on the X and Y chromosome (sex genes) other than just those determining if the offspring will be male or female.

These genes are called sex-linked genes.

The human Y chromosome is much smaller than the X chromosome and appears to contain only a few genes.

What sex chromosomes does a male have? What about a female?

◦ Male = XY

◦ Female = XX Colorblindness

◦ Three genes associated with color vision are located on the X chromosome.

◦ In males, a defective version of one of these genes produces colorblindness.’

◦ Occurs in about 1 in 10 males and only 1 in 100 females.

Why are there so many more colorblind

males? • Because males only have one X chromosome, so

all X-linked alleles are expressed in males.

• In order for a recessive allele, such as the one for

colorblindness, to be expressed in females,

there must be two copies of the recessive allele,

not just one.

A. Male

B. Female

C. Can not tell

Pedigree charts are often constructed to

show the inheritance of genetic

conditions within a family.

Looks like a family-tree.

Traits for albinism, white forelock, and

PTC tasting can be tracked in a pedigree.

Female Male