Characteristics of Living Things

• Living things are made up of cells

• Unicellular – one celled organisms

• Multicellular – many celled organisms

Remember/Review

Characteristicsof Living Things

Living things reproduce to make offspring of the same species

Sexual reproductionAsexual reproduction

Living things grow and develop

Characteristicsof Living Things

1. What type of cell division is the diagram above?

Chromosome Numberin Body Cells vs. Gametes

• Body CellsDiploid (2n) - have 2 sets

• GametesHaploid (n) - have 1 set

Meiosis

Meiosis is

Reduction Division

Chromosome number is cut in half by separation of homologous chromosomes in diploid cells

Crossing Over

• Occurs in Prophase I

• Results in variations in daughter cells

Crossing-Over& Gene Mapping

• Farther apart 2 genes are, more likely they’ll be separated

• Frequency of crossing-over is equal to the distance between 2 genes

How close are 2 usually independently assorted genes?

Really far…

Summarize the Eventsof Meiosis

Events of Meiosis

Results of Meiosis

• 4 haploid (n) cells• Genetically different from each other

& the original cell

Differences BetweenMitosis & Meiosis

• MITOSIS produces 2 identical diploid (2n) cells

• MEIOSIS produces 4 different haploid (n) cells

Human Cells 2n=46.

• Sperm Cell– 23 chromosomes– Gamete is haploid (n)

• Egg Cell– 23 chromosomes– Gamete is haploid (n)

• White Blood Cell– 46 chromosomes– Body cell is diploid (2n)

Independent AssortmentApplied to Chromosomes

The “chromosomes” sort independently, not as individual “genes”

Introduction to Genetics

Genetics = the study of heredity

• Gregor Mendel–The Father of Genetics–carried out important studies of heredity

• Heredity—the passing on of traits from parents to offspring

• He studied pea plants

• Trait- a specific characteristic that is controlled by genes– Exp. Eye color, hair color, height

• Chromosomes–Tightly coiled DNA

where your genes are carried

• Genes–Sections of DNA that control your

traits

• Homologous Chromosomes–Chromosomes that are the same size and

shape and carry the same genes. You get one from your mother and one from your father that match up.

Short pea plant Tall pea plant

All tall pea plants

3 tall: 1 short

P1

F1

F2

–Alleles– The different forms a gene can take. (Letters)

• 2 Types of Alleles:–1. Dominant - Represented by a capital letter

»(Exp. A)

–2. Recessive - Represented by a lower-case letter (Exp. a)

–Genotype• The combination of two alleles (letters) that

represent the genetic make-up of an individual. (AA, Aa, aa)

–Phenotype• The observable physical characteristic of an

individual that are the result of its genotype. (Long eyelashes, Blue or Brown eyes)

3 Types of Genotypes:

• 1. Homozygous Dominant– 2 identical alleles that are capitalized (AA, TT)

• 2. Heterozygous– 2 different alleles (Aa, Tt)

• 3. Homozygous Recessive– 2 identical alleles that are lower-case (aa, tt)

Principle of Dominance

• An organism with a recessive allele for a particular trait will exhibit that form only when the dominant allele for the trait is not present.

• Organisms with a heterozygous genotype (Aa) will never exhibit the recessive trait because it is hidden (masked) by a dominant allele.

• You try this one:

A A

A

a

Dihybrid Cross:a cross that shows the possible offspring for two traits

16 squares

Fur Color:B: Black b: White

Coat Texture:R: Roughr: Smooth

In this example, we will cross a heterozygous individual with

another heterozygous individual. Their genotypes will be:

BbRr x BbRr

Dihybrid Cross

BbRr x BbRr

First, you must find ALL possible gametes that can be made from each parent.

Remember, each gamete must have one B and one R.

Dihybrid CrossBbRr x BbRr

Possible gametes:BRBrbRbr

Next, arrange all possible gametes for one parent along the top of your Punnett Square, and all possible gametes for the other parent down the side of your Punnett Square…

Dihybrid Crosses:a cross that shows the possible offspring for two traits

Fur Color:B: Black b: White

Coat Texture:R: Roughr:

Smooth

BbRr x BbRr

BR

bR

br

bR

Br

BR

br

Br

Then, find the possible genotypes and phenotypes of the offspring

Dihybrid Crosses:a cross that shows the possible offspring for two traits

Fur Color:B: Black b: White

Coat Texture:R: Roughr:

Smooth

BbRr x BbRr

BR

bR

br

bR

Br

BR

br

Br

BBRR

BbRR BbRr

BBRr BBrr BbRr Bbrr

BbRR BbRr bbRR bbRr

BbRr Bbrr bbRr bbrr

BBRr

BR bR

br

bR

Br

BR

br

Br

BBRR

BbRR

BbRr

BBRr BBrr BbRr Bbrr

BbRR

BbRr bbRR

bbRr

BbRr Bbrr bbRr bbrr

BBRr

How many of the offspring would have a black, rough coat?

How many of the offspring would have a black, smooth coat?

How many of the offspring would have a white, rough coat?

How many of the offspring would have a white, smooth coat?

Fur Color:B: Black b: White

Coat Texture:R: Roughr:

Smooth

BR bR

br

bR

Br

BR

br

Br

BBRR

BbRR

BbRr

BBRr BBrr BbRr Bbrr

BbRR

BbRr bbRR

bbRr

BbRr Bbrr bbRr bbrr

BBRr

How many of the offspring would have black, rough coat?

How many of the offspring would have a black, smooth coat?

How many of the offspring would have a white, rough coat?

How many of the offspring would have a white, smooth coat?

Fur Color:B: Black b: White

Coat Texture:R: Roughr:

Smooth

Phenotypic Ratio

9:3:3:1

More Practice…

• In the space provided in your notes work the following dihybrid problems

In pea plants, yellow seeds (Y) are dominant over green seeds (y), and rounded peas (R) are dominant over wrinkled peas (r).

Cross a plant that is heterozygous for both traits with a plant that is homozygous recessive for both traits. Draw a Punnett square to show all possible offspring, and determine the genotypic and phenotypic ratios.

YyRr X yyrr

YR yR

yr

yr

yr

yr

yrYr

YyRr yyRr yyrr

YyRr Yyrr yyRr yyrr

YyRr Yyrr yyRr yyrr

YyRr Yyrr yyRr yyrr

Yyrr

Question 1The passing on of characteristics from parents to offspring is __________.

D. allelic frequency

C. pollination

B. heredity

A. genetics

Question 2

What are traits?

Answer

A specific characteristic that is controlled by genes. Height, hair color and eye color are examples of traits in humans.

Question 3

Gametes are __________.

D. fertilized cells that develop into adult organisms

C. both male and female sex cells

B. female sex cells

A. male sex cells

Question 4

Which of the following genotypes represents a animal that is homozygous dominant for a trait?

a. KK

b. Kk

c. kk

Question 5Which of the following genotypes represents a plant that is homozygous recessive for height?

C. tt

B. Tt

A. TT

Mendelian Exceptions- Not all genes show simple patterns of dominant and recessive alleles

• Because the majority of traits are controlled by more than one gene/alleles

• There are some exceptions to Mendel’s Laws.

1. INCOMPLETE DOMINANCE

• Neither allele is completely dominant

• Both alleles combine equally to give a new trait.

• Called hybrids• EX: red flower (RR) crossed

with white flower (R’R’) produces pink flower (RR’)

• In snapdragons, the combined expression of both alleles for flower color produces a new phenotype that is pink. This illustrates incomplete dominance. The Punnett square above shows that both the white and red snapdragons are homozygous. Which of the following would be the correct product from a cross between two heterozygous pink snapdragons? [VA05 EOC]

– A 1 red, 2 pink, 1 white– B 2 red, 2 white– C 2 red, 1 pink, 1 white– D 1 red, 1 pink, 2 white

2. CODOMINANCE• Both alleles are

expressed• EX: cross a black

chicken with a white chicken, offspring will be black and white checkered. Roan cow (RW)

Red cow (RR) White cow (WW)

• In a certain cactus, prickly spines can be two pronged or one pronged. If a true breeding (homozygous) one-pronged cactus is crossed with a true breeding two-pronged cactus, the F1 generation has a mixture of spines, some are two-pronged, some are one-pronged.

• Is this an example of codominance or incomplete dominance?

codominance

Practice Problems

MULTIPLE ALLELES: more than two alleles control a phenotype

• Ex: blood type

Genotypes:AO- 2/4 or 50%OO- 2/4 or 50%

Phenotypes:Type A- 2/4 or 50%Type O- 2/4 or 50%

Blood type inheritance

• Blood type = presence or absence of proteins on red blood cells

• Usually have to do more than one punnett square to determine possibilities for kids.

PhenotypPhenotypeses

Blood Blood typestypes

GenotypeGenotypess

Alleles for Alleles for blood blood typetype

AA AA or AOAA or AO

BB BB or BOBB or BO

ABAB Only ABOnly AB

OO Only OOOnly OO

• Traits controlled by genes located on sex chromosomes are called sex-linked traits.

• The alleles for sex-linked traits are written as superscripts of the X or Y chromosomes.

Sex-linked inheritanceSex-linked inheritance

Sex DeterminationSex Determination• If you are female,

your 23rd pair of chromosomes are homologous, XX.

• If you are male, your 23rd pair of chromosomes XY, look different.

X XFemale

YXMale

XX Female

XY Male

X

X

X Y

XX Female

XY Male

XX Female

XY Male

Sex Linked Traits• When genes are located on the X chromosome,

females receive two alleles for these genes, but males only receive one.

• In males, the genotype is automatically known.– Colorblind male - XcY (recessive)– Normal male - XCY (dominate).

• A female can be:– XCXC - normal– XCXc - carrier– XcXc - colorblind

• Males can pass it to all of their daughters, none to sons

• Females have 50/50 chance of passing it to all of their children

• Ex: – Hemophilia- can’t clot blood– Colorblindness- can’t see

certain colors.

4. SEX-LINKED TRAITS: controlled by genes located on sex chromosomes

• Usually carried on X chromosome• Since females are XX, they are

usually carriers of the trait• Since males are Xy, they have one

big & one small, stumpy chromosome. • The small chromosome (y) does

not carry an allele so whatever allele is on the X (donated by mom) is what the boy will have.

• He is either completely dominant or completely recessive

• Boys cannot be a carriers of a sex linked trait.

5. Polygenic inheritance-2 or more genes affect the phenotype.

• Ex: height, weight, skin color, eye color

Heterochromia- uneven distribution of pigment resulting from disease or injury