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?