Patterns of Heredity

Ch. 4 Genetics!!

Do Now!! True or False??• Color blindness is more common in

males than in females.• A person may transmit characteristics to

offspring which he/she does not show.• Certain inherited traits may be altered

by the stars, planets or moon early in development

• There is such a thing as “werewolf syndrome” that could be linked to genes.

Hypertrichosis (“werewolf syndrome”)

Stephen Bibrowski as “Lionel the Lion-faced Man”

Objectives

• To define heredity and inheritance• To determine how we inherit traits

from our parents• To take an inventory of our class’s

traits!

Genetics = the study of heredity by which traits are passed from parents to offspring

The passing of genes/traits from parents to offspring.

Heredity

• Many of your traits, including eye color, shape of your eyes, texture of your hair, height, and weight resemble those of your parents!

What is a gene?

• A unit of heredity that occupies a specific location on a chromosome and codes for a particular product.

• A specific segment of DNA found on the chromosome

Thanks Mom and Dad!

• We inherit genes from our parents

• Those genes code for the traits we express

• Most traits are coded by more than 1 gene:• Ex: Height

Homologous Chromosomes

• A pair of chromosomes are called homologs (homo meaning same)

• Homologous chromosomes have the same size, structure, and genetic information.

What are alleles?

• Versions of a gene that occupy corresponding positions on homologous chromosomes

• We inherit 2 alleles for each gene:• 1 from mom and

1 from dad!!

Sex Chromosomes• We have 23 pairs of chromosomes• 1 pair are known as the sex

chromosomes, which determines the sex of the offspring

• Males = XY• Females = XX

Do Now!!

• What is an allele?• What are homologous chromosomes?• Give an example of a trait that is

coded by more than one gene!

Objectives

• To discuss the importance of Gregor Mendel

• To identify the parts of Mendel’s pea plant experiments

• To differentiate between dominant and recessive alleles

The history of Gregor Mendel

• Father of genetics!

• Bred different varieties of garden pea.

• First to develop rules that accurately predict patterns of heredity.

• Discovered how traits were inherited

Pollination – transfer of pollen from anthers to stigma in flowers

1) self pollination occurs within the same flower or same plant

2) cross pollination occurs between different plants

Pea plants = great subject to study heredity

• Several traits exist in two clear different forms.

Ex: Flower color was either purple OR white

Pea plants = great subject to study heredity (cont.)

• The male and female reproductive parts are enclosed within the same flower.

• It is easy to control mating by allowing a flower to fertilize itself (self fertilization), or you can transfer pollen to another flower (cross pollination).

Pea plants = great subject to study heredity (cont.)

• The garden pea is small, grows easily, matures quickly, and produces many offspring.

• Results can be obtained quickly.

Steps in Mendel’s research…

1. Allowed each garden pea to self-pollinate for several generations to ensure “true-breeding” for that particular trait.

*P Generation = parental generation

Steps in Mendel’s research (cont.)2. Mendel then cross-pollinated two P

generation plants that had different forms of the trait (purple and white flower). The offspring from that were called the F1 generation.

*F 1 generation = Filial generation (of son or daughter)

Steps in Mendel’s Research (cont.)3. Allowed the F1 generation to self-pollinate and those offspring are called the F2 generation.

* F2 Generation = Filial generation 2

Ratio of Mendel’s Research• P Generation had a true-breeding purple

and white flower• F1 generation: ALL purple flowers• F2 generation: 705 purple flowers and 224

white flowers. • That is a ratio of about 3:1

Mendel’s Crosses with Pea Plants

Pure tallplants

X Pure shortplantsP1

parentalgeneration

Cross Pollination

All Tall plantsF1

first filialgeneration

Self Pollination

787 tall plants, 277 short plants F2

second filialgeneration

3 to 1 ratio

Mendel’s 3 Laws of Inheritance

1. Law of Dominance- Each trait is controlled by 2 factors:

• Dominant- what is expressed• Recessive- masked in presence of

dominant

• Alleles are alternative forms of a gene.

• Can be dominant or recessive!

*Reminder!!

Dominant capital letter (shields

recessive trait)

Recessive Lowercase letter (usually hidden)

T = tall t = short

Mendel’s 3 Laws of Inheritance

2. Law of Segregation-Each allele separates into different gametes

Ex. Ww – one W goes in one sperm and the other w goes into another sperm

Ww

w W

Mendel’s 3 Laws of Inheritance (cont.)

3. Law of Independent Assortment- Gene pairs (homologous) will separate randomly into gametes during meiosis

(Why? Random orientation of homologous pairs at the metaphase plate)

Do Now!! • What are Mendel’s 3 laws of inheritance?• What is the difference between dominant

and recessive traits?• Below is a chart of Mendel’s experiment.

Fill it in!:1 2 3

4 5

6 7

Objectives

• To differentiate between phenotype and genotype

• To define homozygous and heterozygous

• To practice monohybrid punnett squares

Phenotype vs. Genotype

Genotype: The set of alleles that an individual has (not always obvious)

Phenotype: the physical appearance of a trait

Homozygous – when both alleles of a pair are the same

homozygous dominant

homozygous recessive

TT

tt

Heterozygous – when both alleles of a pair are not the same

heterozygous (tall)

Tt

Heterozygous

• Different alleles present–Ex: Bb

Homozygous

• Two of the same alleles– Ex: BB or bb

• Can be homozygous recessive or homozygous dominant

Recessive vs. Dominant

Recessive: The trait not expressed when the dominant form of the trait is present

Dominant: The expressed form of the trait when present (even if it is just 1 allele)

In dogs, black fur is dominant over white fur color.

B = black furb = white

fur

BB or Bb

bb

WOOF WOOF!

Think - Pair - Share• If Jon Snow is heterozygous for black hair… (H=Black, h=blonde)

– 1. What is Jon Snow’s genotype?

– 2. What is Jon Snow’s phenotype?

• Beyonce is BB. (B= brown eyes, b=blue eyes)– 1. What is her genotype?

– 2. What is her phenotype?

– 3. Is she heterozygous or homozygous? Explain.

Probability

• Probability calculations can predict the results of genetic crosses. It is the likelihood that a specific event will occur.

= number of one kind of possible outcome Total number of all possible outcomes

Example: If you flip a coin, you will have 1 outcome, but two possible outcomes. Your answer would be ½.

How do you write a ratio?

• When flipping a coin and it lands on tails ½ or 1:2

• Genotypic ratio: What is genetically written

• Phenotypic ratio: what physical traits you would see Phenotypic Ratio

3:1

3 Black : 1 White

Punnett Square• A diagram that predicts the outcome

of a genetic cross by considering all possible combinations of gametes in the cross

Crossing only 1 trait is called a monohybrid

cross.

Crossing 2 traits is called a dihybrid cross.

Punnett Square Rules!

1. Assign symbols2. Determine parents genotype3. Draw punnett square4. Place gametes on left + top of

square5. Fill in punnett square6. Analyze + answer questions

Practice Punnett Squares:Monohybrid Cross

1.Phenotypic Ratio and %:2.Genotypic Ratio :

T: Tall plantst: Short plants

Practice Punnett Squares:Monohybrid Cross

1. Phenotypic Ratio and %:

2. Genotypic Ratio :

R: round seedsr: wrinkly seeds

Crosses that involve 2 traits

Practice Punnett Squares:Dihybrid Cross

1. Phenotypic Ratio:2. Genotypic Ratio :

Gene Linkage and Polyploidy

• There are several genes on a chromosome

• Gene Linkage:– When two genes are close to each other

on the same chromosome

Gene Linkage Linked genes on a chromosome

results in an exception to Mendel’s law of independent assortment

Linked genes usually do not segregate independently

Drosophila melanogaster (Fruit Flies)First organism

with linked genes

Linked genes typically travel together during crossing over

Chromosome Map

• A map of genes on a chromosomes• Crossing over occurs more frequently between

genes that are far apart

PolyploidyCells that contain more than 2

homologous sets of chromosomesEx. A triploid organism (3n) - means

that it has three complete sets of chromosomes.

Strawberries are octoploid!!

Matching

Pedigree• Shows history of a trait in a family• Allows researchers to analyze traits

within a family

In a pedigree…

• You can see how a genetic disorder runs in a family.

• Carriers are individuals who are heterozygous for an inherited disorder but do not show symptoms.

• Carriers can pass the allele for the disorder to their offspring

Figure out each genotype!

Figure out each genotype!

DO NOW!!

• Fill in genotypes!• B: Brown eyes• b: blue eyes

Multiple alleles – 3 or more alleles that control a trait

• Example: blood type!– Possible alleles: IA, IB, i– Which genotypes are heterozygous?

Homozygous?GENOTYPES RESULTING PHENOTYPES

IAIA

IAiType A

IBIB

IBiType B

IAIB Type AB

ii Type O

Antigens vs. Antibodies• Antigen: substance foreign to the body

that causes an immune response:– Can act as surface markers– EX: type A antigens on surface of type A

blood cells• Antibody: protein that reacts with specific

antigen:– EX: Type B blood contains anti-A

antibodies

Which is the universal donor? Universal acceptor?

Determine Blood Type

• Determine the possible offspring of the following crosses

• 1. AB and O• 2. Homozygous A and heterozygous

B• 3. AB and AB

Do Now!!

• Determine the possible blood types:

• Cross homozygous A and heterozygous B

• AB x AB

Polygenic Traits

Polygenic traits arise from the interaction of multiple pairs of genes.

Incomplete dominanceo Heterozygous phenotype is intermediate

between two homozygous phenotypes:o In between two extremes

o Heterozygous phenotype appears blended.o Ex: Four O’clock flowerso Red + White = Pink

Examples!

Codominance• Both traits are expressed (no blending)• Ex: Roan Cows

– white hair (HW) is codominant with red hair (HR)

– cows with genotype (HRHW) have coats with a mixture of red and white hairs (roan)

• Red + White = RED AND WHITE

Examples!

Sex Linked Traits• Traits located on the sex chromosomes (X

or Y)• X linked: gene is located on the X

chromosomes• Y linked: gene is located on the Y

chromosome

• Ex: color-blindness is X-linked!

Sex-Linked Traits

• A man who is color blind marries a woman that is heterozygous for color blindness. What is the chance of having a color blind boy?